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Question 1
Incorrect
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A 40-year-old male complains of a painful and swollen right calf. The possibility of deep vein thrombosis (DVT) is being considered. What tests should be conducted to confirm the diagnosis?
Your Answer: CT of the leg veins
Correct Answer: Dopplers of the leg veins
Explanation:Diagnostic Methods for Deep Vein Thrombosis
When it comes to diagnosing deep vein thrombosis (DVT), there are several methods available. The most common ones are Doppler studies and venography. Doppler studies use B mode ultrasonography to examine the venous system, while venography involves injecting a contrast dye into the veins and taking X-rays. CT scans are not typically used for DVT diagnosis because they require contrast and expose the patient to radiation. D-Dimer concentrations can help rule out DVT if they are negative, but they cannot diagnose it. MRI scans are useful for examining soft tissues and bones, but they are not the best option for visualizing the vasculature. Finally, oxygen saturation of the limbs is not a reliable diagnostic method because tissue perfusion can be the same even if there is arterial disease. Overall, Doppler studies and venography are the most effective methods for diagnosing DVT.
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This question is part of the following fields:
- Basic Sciences
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Question 2
Correct
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A 50-year-old female patient presents to the vascular clinic for evaluation of varicose veins. During the assessment, a test is conducted to determine the site of incompetence. The patient is instructed to lie down, and her legs are raised to empty the veins. A constricting band is then placed below the sapheno-femoral junction, and the patient is asked to stand up to observe for varicose vein filling. What is the name of this test?
Your Answer: Tourniquet test
Explanation:Tests for Varicose Veins and Arterial Insufficiency
The Trendelenburg and tourniquet tests are both used to evaluate the site of incompetence in varicose veins at the sapheno-femoral junction. During the Trendelenburg test, the examiner applies pressure with their fingers over the junction, while in the tourniquet test, a tourniquet is placed just below the junction. If the veins fill rapidly upon standing, it suggests that the sapheno-femoral junction is not the source of the incompetence.
Buerger’s test is used to assess the arterial circulation of the lower limb. The lower the angle at which blanching occurs, the more likely there is arterial insufficiency. This test is important in diagnosing peripheral artery disease.
The ankle-brachial pressure index (ABPI) is another test used to assess arterial insufficiency. Blood pressure cuffs are used to measure the systolic blood pressure in the ankle and arm. The ratio of the two pressures is calculated, and a lower ratio indicates a higher degree of claudication.
Finally, Perthe’s test is used to assess the patency of the deep femoral vein before varicose vein surgery. This test involves compressing the vein and observing the filling of the superficial veins. If the superficial veins fill quickly, it suggests that the deep femoral vein is patent and can be used for surgery.
In summary, these tests are important in diagnosing and evaluating varicose veins and arterial insufficiency. They help healthcare professionals determine the best course of treatment for their patients.
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This question is part of the following fields:
- Basic Sciences
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Question 3
Incorrect
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What is the composition of enzymes found in lysosomes?
Your Answer: Alcohol dehydrogenases
Correct Answer: Acid hydrolases
Explanation:Lysosomes: The Digestive System of the Cell
Lysosomes are organelles that come from the Golgi apparatus and are enclosed by a membrane. They are responsible for breaking down various biological macromolecules such as proteins, nucleic acids, carbohydrates, and lipids. Lysosomes contain acid hydrolases, which are enzymes that cleave chemical bonds by adding water and function at an acidic pH of around 5. They are involved in digesting foreign agents that are internalized by the cell and breaking down other cellular organelles like mitochondria, allowing for their components to be recycled.
The acidic pH within lysosomes is maintained by a proton pump in the lysosomal membrane, which imports protons from the cytosol coupled to ATP hydrolysis. This acidic environment is necessary for the activity of the acid hydrolases. D-amino acid oxidases and peroxidases are not found in lysosomes but in peroxisomes. Alcohol dehydrogenases and ATPases are not involved in digestion but in other cellular functions. Alcohol dehydrogenases catalyze the interconversion between alcohols and aldehydes or ketones with the reduction of NAD+ to NADH, while ATPases catalyze the breakdown of ATP into ADP and a phosphate ion, releasing energy for the cell’s functions.
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This question is part of the following fields:
- Basic Sciences
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Question 4
Incorrect
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A premature baby is born and the anaesthetists are struggling to ventilate the lungs because of insufficient surfactant. How does Laplace's law explain the force pushing inwards on the walls of the alveolus caused by surface tension between two static fluids, such as air and water in the alveolus?
Your Answer: Directly proportional to the radius of the alveolus
Correct Answer: Inversely proportional to the radius of the alveolus
Explanation:The Relationship between Alveolar Size and Surface Tension in Respiratory Physiology
In respiratory physiology, the alveolus is often represented as a perfect sphere to apply Laplace’s law. According to this law, there is an inverse relationship between the size of the alveolus and the surface tension. This means that smaller alveoli experience greater force than larger alveoli for a given surface tension, causing them to collapse first. This phenomenon is similar to what happens when two balloons of different sizes are attached together, with the smaller balloon emptying into the larger one.
In the lungs, this collapse of smaller alveoli can lead to atelectasis and collapse if surfactant is not present. Surfactant is a substance that reduces surface tension, making it easier to expand the alveoli and preventing smaller alveoli from collapsing. this relationship between alveolar size and surface tension is crucial in respiratory physiology, as it helps explain the importance of surfactant in maintaining proper lung function.
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This question is part of the following fields:
- Basic Sciences
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Question 5
Incorrect
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What occurs in eukaryotic prometaphase?
Your Answer: The chromosomes align across a plane
Correct Answer: The nuclear membrane and the nucleoli disintegrate and kinetochores appear
Explanation:The Significance of Prometaphase in Cell Division
Prometaphase is a crucial phase in cell division that marks the transition from prophase to metaphase. Although it is often considered as a part of these two phases, it has distinct events that make it an individual phase. During prometaphase, the nuclear membrane disintegrates, and the nucleoli are no longer visible. Additionally, each chromosome forms two kinetochores near the centromere, which serve as attachment points for spindle fibers. These fibers connect to the opposite poles of the cell, forming travelling lines that will separate the sister chromatids during anaphase.
Prophase is characterized by chromatin condensation, while DNA and centrosome duplication occur during interphase. Chromosome alignment takes place during metaphase, and the sister chromatids separate during anaphase. Prometaphase, therefore, plays a crucial role in preparing the chromosomes for separation during anaphase. Its distinct events make it an essential phase in cell division, and its proper execution is necessary for successful cell division.
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This question is part of the following fields:
- Basic Sciences
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Question 6
Incorrect
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Over the last five years, the total number of patients admitted and deaths in the East and North Hertfordshire NHS Trust have been recorded. In the year 2010/2011, there were 95,071 patients admitted and 1,912 deaths. What is the crude mortality ratio for this group in that year (per 100 admissions)?
Your Answer: 2.3
Correct Answer: 2
Explanation:In this scenario, the crude mortality ratio is established by comparing the number of deaths occurring within the hospital in a given year to the total number of admissions, disregarding age or gender-specific mortality rates. For instance, with 1,912 deaths out of 95,071 admissions, the ratio computes to 0.02, or 2.0% when calculated per 100 admissions (1,912/95,071 = 0.02/100= 2.0%. When recalculated per 1,000 admissions, the crude admission rate would be 20 per 1,000.
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This question is part of the following fields:
- Basic Sciences
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Question 7
Incorrect
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What is a good dietary source of vitamin A?
Your Answer: White cabbage
Correct Answer: Liver
Explanation:The Importance of Vitamin A in Our Body
Vitamin A is an essential nutrient that can be found in various sources such as liver, fish liver oils, dark green leafy vegetables, carrots, and mangoes. It can also be added to certain foods like cereals and margarines. This nutrient plays a crucial role in our body as it is required for vision, growth and development of tissues, regulation of gene transcription, and synthesis of hydrophobic glycoproteins and parts of the protein kinase enzyme pathways.
One of the primary functions of vitamin A is to support our vision. It is a component of rhodopsin, a pigment that is necessary for the rod cells of the retina. Without vitamin A, our eyesight can be compromised, leading to various eye problems. Additionally, vitamin A is also essential for the growth and development of many types of tissues in our body. It helps in maintaining healthy skin, teeth, and bones.
Moreover, vitamin A is involved in regulating gene transcription, which is the process of converting DNA into RNA. This nutrient also plays a role in the synthesis of hydrophobic glycoproteins and parts of the protein kinase enzyme pathways. These processes are essential for the proper functioning of our body.
In conclusion, vitamin A is a vital nutrient that our body needs to function correctly. It is essential for our vision, growth and development of tissues, regulation of gene transcription, and synthesis of hydrophobic glycoproteins and parts of the protein kinase enzyme pathways. Therefore, it is crucial to include vitamin A-rich foods in our diet or take supplements if necessary.
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This question is part of the following fields:
- Basic Sciences
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Question 8
Incorrect
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What is the primary reason for malnutrition?
Your Answer:
Correct Answer: Inadequate intake of calories in any form
Explanation:Malnutrition
Malnutrition refers to a state where the dietary intake is insufficient to maintain a healthy state and stable weight. It can be caused by over- or under-nutrition, but it is commonly used to describe under-nutrition. Malnutrition can be defined as a state of nutrition where a deficiency, excess, or imbalance of energy, protein, and other nutrients causes measurable adverse effects on tissue, function, and clinical outcome. Protein malnutrition is the most severe form of malnutrition, causing significant mortality and clinical effects such as kwashiorkor. Carbohydrate malnutrition is less common as carbohydrate sources are widely grown and cheap. Fat malnutrition rarely results in problems if there is adequate dietary protein and carbohydrate. Deficiencies of fat-soluble vitamins can result in various clinical effects. Body size can give some indication of nutritional status, but many obese patients may have nutritional deficiencies due to their faddy diets.
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This question is part of the following fields:
- Basic Sciences
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Question 9
Incorrect
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What factor causes a shift of the oxygen dissociation curve to the left?
Your Answer:
Correct Answer: Increased pH
Explanation:The Oxygen Dissociation Curve and its Effects on Oxygen Saturation
The oxygen dissociation curve is a graph that compares the oxygen saturation of hemoglobin (Hb) at different partial pressures of oxygen. When more oxygen is needed by the tissues, the curve shifts to the right. This means that at the same partial pressure of oxygen, less oxygen is bound to Hb, allowing it to be released to the tissues. This effect is caused by increased levels of CO2 and temperature, which assist in the transfer of oxygen to more metabolically active tissues. Additionally, increased levels of 2,3-DPG also aid in this process.
On the other hand, a left shift in the curve reflects conditions where there is less need for oxygen in the tissues, such as in the lungs. This allows for increased binding of oxygen to Hb, allowing it to be taken up before transport to the tissues that require it. Overall, the oxygen dissociation curve plays a crucial role in regulating oxygen saturation in the body and ensuring that oxygen is delivered to the tissues that need it most.
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This question is part of the following fields:
- Basic Sciences
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Question 10
Incorrect
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During which phase of aerobic respiration is FADH2 generated?
Your Answer:
Correct Answer: Krebs cycle
Explanation:The Krebs Cycle and the Role of FADH2
The Krebs cycle is a crucial part of aerobic respiration in cells. It involves a series of reactions that convert acetate, derived from carbohydrates, fats, and proteins, into carbon dioxide and energy in the form of ATP. Additionally, the Krebs cycle produces precursors for some amino acids and reducing agents like NADH and FADH2 that are involved in other metabolic pathways.
FAD is a redox cofactor that plays a vital role in the Krebs cycle. It receives two electrons from the sixth reaction of the cycle, where succinate dehydrogenase converts succinate into fumarate by removing two hydrogen atoms and attaching them onto FAD. This process results in FAD gaining two electrons and reducing into FADH2.
FADH2 then donates the electrons to the electron transport chain, which is another part of cellular respiration. This mechanism helps compensate for the relatively low amount of ATP produced by the Krebs cycle (2.5 molecules of ATP per turn) compared to the electron transport chain (26-28 molecules of ATP). Overall, the Krebs cycle and the role of FADH2 are essential for generating energy in cells.
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This question is part of the following fields:
- Basic Sciences
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Question 11
Incorrect
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What is a primary function of vitamin A?
Your Answer:
Correct Answer: Vision
Explanation:Vitamin A: Forms, Sources, and Functions
Vitamin A is a crucial nutrient that exists in various forms in nature. The primary dietary form of vitamin A is retinol, also known as pre-formed vitamin A, which is stored in animal liver tissue as retinyl esters. The body can also produce its own vitamin A from carotenoids, with beta-carotene being the most common precursor molecule.
The richest sources of vitamin A include liver and fish liver oils, dark green leafy vegetables, carrots, and mangoes. Vitamin A can also be added to certain foods like cereals and margarines.
Vitamin A plays several essential roles in the body, including supporting vision by being a component of rhodopsin, a pigment required by the rod cells of the retina. It also contributes to the growth and development of various types of tissue, regulates gene transcription, and aids in the synthesis of hydrophobic glycoproteins and parts of the protein kinase enzyme pathways.
In summary, the different forms and sources of vitamin A and its vital functions in the body is crucial for maintaining optimal health.
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This question is part of the following fields:
- Basic Sciences
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Question 12
Incorrect
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Which of the following would not increase the rate of diffusion of a substance across a lipid membrane such as the cell wall?
Your Answer:
Correct Answer: Thickness of the membrane
Explanation:Diffusion and Fick’s Law
Diffusion is a natural process that occurs when molecules move from an area of high concentration to an area of low concentration. This process is passive and random, meaning that it does not require any external energy input. Fick’s Law states that diffusion occurs more quickly across a large, permeable, and thin membrane. For example, in lung disease, the thickening of the alveolar epithelial barrier can lead to a poor carbon monoxide transfer coefficient because the thicker membrane slows down the diffusion process. the principles of diffusion and Fick’s Law can help us better understand how molecules move and interact in various biological and chemical processes. By optimizing the conditions for diffusion, we can improve the efficiency of many natural and artificial systems.
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This question is part of the following fields:
- Basic Sciences
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Question 13
Incorrect
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A man in his forties comes in with chest pain resembling a heart attack and is diagnosed with a myocardial infarction. During his hospitalization, it is discovered that he has familial hypercholesterolemia but his triglyceride levels are normal. What is the underlying biochemical abnormality?
Your Answer:
Correct Answer: Defective LDL receptors
Explanation:Lipid Metabolism and Transport in the Body
The breakdown of triglycerides in the small intestine is facilitated by pancreatic lipase. These triglycerides are then transported to the liver and other parts of the body through chylomicrons.
Very low-density lipoprotein (VLDL) is responsible for carrying triglycerides from the liver to peripheral tissues. When there is an overproduction of VLDL in the liver, it can lead to high levels of triglycerides in the body.
Pure hypercholesterolaemia is a condition that arises due to a defect in the process of cholesterol uptake into cells. This process relies on apolipoprotein B-100 binding to LDL receptors and facilitating endocytosis. When this process is disrupted, it can lead to high levels of cholesterol in the body.
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This question is part of the following fields:
- Basic Sciences
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Question 14
Incorrect
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The arrangement of amphipathic phospholipids in the mammalian cell membrane, what is it like?
Your Answer:
Correct Answer: A lipid bilayer with hydrophilic heads facing out and hydrophobic tails facing in
Explanation:The Function and Structure of the Mammalian Cell Membrane
The mammalian cell membrane serves as a protective barrier that separates the cytoplasm from the extracellular environment. It also acts as a filter for molecules that move across it. Unlike plant and prokaryotic cells, mammalian cells do not have a cell wall. The main component of the cell membrane is a bilayer of amphipathic lipids, which have a hydrophilic head and a hydrophobic tail. The phospholipids in the bilayer are oriented with their hydrophilic heads facing outward and their hydrophobic tails facing inward. This arrangement allows for the separation of the watery extracellular environment from the watery intracellular compartment.
It is important to note that the cell membrane is not a monolayer and the phospholipids are not linked head-to-tail. This is in contrast to DNA, which has a helical chain formation. Overall, the structure and function of the mammalian cell membrane are crucial for maintaining the integrity and proper functioning of the cell.
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This question is part of the following fields:
- Basic Sciences
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Question 15
Incorrect
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In which part of the cell are the electron transport chain carriers situated?
Your Answer:
Correct Answer: Mitochondrial cristae
Explanation:The Electron Transport Chain in Mitochondria
The electron transport chain (ETC) is a crucial process in cellular aerobic respiration that occurs in the mitochondrial cristae. These are folded membranes inside the organelle. During respiration, NADH and FADH produced from other parts of the process, such as glycolysis, transfer electrons from electron donors to electron acceptors through redox reactions. This electron transfer is coupled with proton transfer across the mitochondrial membrane, creating an electrochemical proton gradient. This gradient induces the production of ATP, which is used as an energy currency by the cell.
ATP is produced through a mechanism called chemiosmotic phosphorylation. The structure of the mitochondrion is essential for this process to occur. The cristae provide a large surface area for the ETC to take place, and the mitochondrial membrane is impermeable to protons, allowing for the creation of the proton gradient. The inner membrane also contains ATP synthase, the enzyme responsible for producing ATP through chemiosmotic phosphorylation.
In summary, the electron transport chain in mitochondria is a complex process that involves the transfer of electrons and protons across the mitochondrial membrane to create a proton gradient. This gradient is then used to produce ATP through chemiosmotic phosphorylation. The structure of the mitochondrion is crucial for this process to occur efficiently.
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This question is part of the following fields:
- Basic Sciences
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Question 16
Incorrect
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You are evaluating a geriatric patient in the emergency department who has fallen and needs a venous cannula for fluid resuscitation. To ensure maximum flow into the vein, you plan to apply the Hagen-Poiseuille equation to select an appropriate cannula size. Which of the following statements is true according to this law?
Your Answer:
Correct Answer: Flow will be faster through a shorter cannula
Explanation:Poiseuille’s Equation and Fluid Flow in Cylinders
Poiseuille’s equation is used to describe the flow of non-pulsatile laminar fluids through a cylinder. The equation states that the flow rate is directly proportional to the pressure driving the fluid and the fourth power of the radius. Additionally, it is inversely proportional to the viscosity of the fluid and the length of the tube. This means that a short, wide cannula with pressure on the bag will deliver fluids more rapidly than a long, narrow one.
It is important to note that even small changes in the radius of a tube can greatly affect the flow rate. This is because the fourth power of the radius is used in the equation. Therefore, any changes in the radius will have a significant impact on the flow rate. Poiseuille’s equation is crucial in determining the optimal conditions for fluid delivery in medical settings.
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This question is part of the following fields:
- Basic Sciences
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Question 17
Incorrect
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What is the main role of the Golgi apparatus in eukaryotic cells?
Your Answer:
Correct Answer: Process of proteins
Explanation:The Golgi Apparatus, Cell Division, and Homeostasis
The Golgi apparatus is a structure found in eukaryotic cells that consists of flattened membrane stacks. Its primary function is to modify proteins that have been synthesized in the rough endoplasmic reticulum, preparing them for secretion or transport within the cell. However, the Golgi apparatus is not directly involved in cell division, which is controlled by the nucleus.
Cell homeostasis, on the other hand, is primarily maintained by membrane-embedded channels or proteins such as the sodium-potassium pump. This mechanism ensures that the cell’s internal environment remains stable. The sodium-potassium pump is an active transport mechanism that involves the binding of three intracellular sodium ions to the protein. Adenosine triphosphate (ATP) donates a phosphate group to the protein, which causes it to change shape and release the sodium ions out of the cell.
The protein then accepts two extracellular potassium ions, and the donated phosphate group detaches, causing the protein to revert to its original shape. This allows the potassium ions to enter the cell, increasing the intracellular potassium concentration and decreasing the intracellular sodium concentration. This process is in contrast to the extracellular conditions.
In summary, the Golgi apparatus modifies proteins for secretion or transport, while cell division is controlled by the nucleus. Cell homeostasis is maintained by membrane-embedded channels or proteins such as the sodium-potassium pump, which actively transports ions to stabilize the cell’s internal environment.
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This question is part of the following fields:
- Basic Sciences
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Question 18
Incorrect
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Which food is a rich source of vitamin D in the diet?
Your Answer:
Correct Answer: Oily fish
Explanation:Sources of Vitamin D
Vitamin D is a type of fat-soluble vitamin that can be found in certain foods such as cheese, butter, eggs, and oily fish. However, vegetable sources of vitamin D are limited, although some foods are fortified with this vitamin. For instance, 100 grams of sundried shiitake mushrooms contain 1600 IU of vitamin D, while one egg contains 20 IU. Wild salmon is also a good source of vitamin D, with 100 grams containing 800 IU, while farmed salmon contains 200 IU.
Aside from food sources, sunlight is also a good source of vitamin D. Exposure of arms and legs to sunlight for 10-15 minutes can provide 3000 IU of vitamin D. However, it is difficult to obtain the daily requirement of 25-50 IU of vitamin D through sunlight alone, especially for people living in temperate climates. As a result, many people may have insufficient vitamin D levels. It is important to ensure that we get enough vitamin D through a combination of food sources and sunlight exposure.
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This question is part of the following fields:
- Basic Sciences
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Question 19
Incorrect
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What is the term for the process described below in laboratory testing?
Enzymes are immobilised on a solid surface, such as a bead or well, and allowed to come into contact with the sample. After washing, another enzyme is added with a label allowing quantitation of the analyte.Your Answer:
Correct Answer: Enzyme-linked immunosorbent assay
Explanation:ELISA: A Common Immunoassay in Medical Diagnostic Testing
An enzyme-linked immunosorbent assay (ELISA) is a type of immunoassay that is widely used in medical diagnostic testing. This method uses antibodies to identify and/or quantify the analyte being tested. The ELISA process involves several steps, including coating a plate with the antigen, adding the patient’s sample, washing the plate to remove any unbound material, adding an enzyme-linked antibody, washing the plate again, and adding a substrate to produce a measurable signal.
Over time, many modifications have been made to the ELISA, making it a versatile tool in the laboratory for measuring various analytes. Some of the substances that can be measured using immunoassays include thyroid hormone, testosterone, oestrogen, troponin, and vitamin D. The ELISA has been around for a long time and is still widely used today due to its accuracy, sensitivity, and specificity.
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This question is part of the following fields:
- Basic Sciences
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Question 20
Incorrect
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What is the conversion of pyruvate before it enters the Krebs cycle?
Your Answer:
Correct Answer: Acetyl-CoA
Explanation:The Krebs cycle occurs in the mitochondrion and involves the conversion of acetyl-CoA to oxaloacetate. This cycle produces six NADH, two FADH, and two ATP for each molecule of glucose. Pyruvate is converted to acetyl-CoA before entering the Krebs cycle, and water and carbon dioxide are end products. Acetic acid itself has no role in the cycle, but its acetyl group is used to form acetyl-CoA. Some anaerobic bacteria can convert sugars to acetic acid directly.
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This question is part of the following fields:
- Basic Sciences
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Question 21
Incorrect
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What is the cause of the symptoms of weakness, dermatitis, diarrhoea and dementia in pellagra?
Your Answer:
Correct Answer: Deficiency of the vitamin niacin
Explanation:Niacin Deficiency and Other Genetic Diseases
Niacin, a vitamin present in two forms – nicotinamide and nicotinic acid, is found in a variety of plant and animal foodstuffs. However, in some cases, the form of the vitamin is not easily absorbed by the human body, leading to deficiency. This deficiency is common in areas where maize is the primary dietary carbohydrate. Additionally, niacin can be produced by the body from the amino acid tryptophan. Diseases that affect the availability of tryptophan, such as Hartnup disease and carcinoid syndrome, can also result in niacin deficiency.
Pellagra is a condition that arises from niacin deficiency. It initially presents with non-specific symptoms such as nausea, fatigue, and reduced appetite, followed by pigmented dermatitis in sun-exposed areas, gastrointestinal disturbance, mood disturbance, and dementia in severe cases.
Apart from niacin deficiency, genetic diseases affecting collagen synthesis, such as Ehlers Danlos, present with symptoms of fragile stretchy skin and joint hypermobility. Genetic diseases affecting haemoglobin, such as sickle cell anaemia, present with symptoms of pain, hepatosplenomegaly, shortness of breath, and anaemia. Deficiencies in B12 and folate can also lead to macrocytic anaemia, paresthesia, and lethargy.
In conclusion, the causes and symptoms of niacin deficiency and other genetic diseases is crucial for early diagnosis and effective treatment. A balanced diet and regular medical check-ups can help prevent and manage these conditions.
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This question is part of the following fields:
- Basic Sciences
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Question 22
Incorrect
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At what stage of meiosis does the process of homologous recombination occur?
Your Answer:
Correct Answer: Prophase I
Explanation:Homologous Recombination: A Mechanism for DNA Repair and Genetic Variation
Homologous recombination is a process that allows for the exchange of nucleotide sequences between two similar or identical DNA molecules. This occurs during meiosis, specifically during the second phase of prophase I, where sister chromatids swap sequences. The primary purpose of homologous recombination is to accurately repair harmful double-strand DNA breaks. This process results in new combinations of DNA sequences that provide genetic variation in daughter cells and, ultimately, the organism’s offspring.
In prokaryotic organisms such as bacteria and viruses, homologous recombination occurs during horizontal gene transfer. This process involves the exchange of genetic material between different strains and species. Homologous recombination plays a crucial role in the evolution of these organisms by allowing for the acquisition of new traits and adaptations.
Overall, homologous recombination is a vital mechanism for DNA repair and genetic variation. It ensures the accuracy of DNA replication and contributes to the diversity of life on Earth.
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This question is part of the following fields:
- Basic Sciences
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Question 23
Incorrect
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What is the primary factor that increases the risk of thiamine (vitamin B1) deficiency?
Your Answer:
Correct Answer: Chronic alcohol excess
Explanation:Thiamine: Its Roles, Sources, Deficiency States, and Manifestations
Thiamine is a vital nutrient that plays several roles in the body. It acts as a cofactor to enzymes involved in energy production, metabolism of branched chain amino acids, and regulation of nerve and muscle action potentials. It is found in many foods, including wheat, oats, and yeast-containing products. However, deficiency states can occur in chronic alcohol dependence, renal dialysis, and cultures that mainly consume white rice. The deficiency can manifest as ‘dry’ beriberi, which causes peripheral neuropathy, muscle weakness, fatigue, and reduced concentration, or ‘wet’ beriberi, which also involves heart failure and edema. In severe cases, Wernicke-Korsakoff syndrome can develop, which is an emergency requiring urgent IV replacement of thiamine. If left untreated, it can lead to irreversible amnesia, confabulation, and dementia. Therefore, all patients with alcohol-related admissions should be considered for Pabrinex, a B vitamin infusion.
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This question is part of the following fields:
- Basic Sciences
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Question 24
Incorrect
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During which stage of the cell cycle does the replication of DNA occur?
Your Answer:
Correct Answer: S phase
Explanation:The Five Phases of the Cell Cycle
The cell cycle is a complex process that is divided into five main phases, each with its unique cellular events. The first phase is the G0 phase, which is a resting phase where the cell has stopped dividing and is out of the cell cycle. The second phase is the G1 phase, also known as interphase Gap 1, where cells increase in size, and a checkpoint control mechanism prepares the cell for DNA synthesis.
The third phase is the S phase, where DNA replication occurs. The fourth phase is the G2 phase, also known as Gap 2, which is a gap between DNA synthesis and the onset of mitosis. During this phase, the cell continues to grow until it is ready to enter mitosis. Finally, the fifth phase is the M phase, also known as mitosis, where cell growth stops, and the cell focuses its energy to divide into two daughter cells.
A checkpoint in the middle of mitosis, known as the metaphase checkpoint, ensures that the cell is prepared to complete division. the five phases of the cell cycle is crucial in how cells divide and grow.
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This question is part of the following fields:
- Basic Sciences
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Question 25
Incorrect
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What is the estimated percentage of oxygen in the blood that is attached to haemoglobin?
Your Answer:
Correct Answer: 100%
Explanation:Calculation of Oxygen in Blood
The majority of oxygen in the blood is bound to haemoglobin, with the exact amount varying based on the oxygen saturation and haemoglobin level. To calculate the amount of oxygen per litre of blood, the formula (13.9 × Hb × sats/100) + (PaO2 × 0.03) can be used. For example, an average man with an Hb of 14, saturations of 98% on room air, and a PaO2 of 12 would have 191 ml of oxygen per litre of blood. It is important to note that only 0.36 ml of this oxygen is dissolved in the blood.
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This question is part of the following fields:
- Basic Sciences
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Question 26
Incorrect
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What is the primary means of transportation for vitamin D in the human body?
Your Answer:
Correct Answer: In blood, bound to the group specific component
Explanation:The Role of UV Light and Vitamin D in Calcium and Phosphate Regulation
In order for the body to produce Vitamin D3, UV light at a specific wavelength is required to convert cholesterol in the skin. Vitamin D2 and D3 are then transported in the bloodstream bound to the Vitamin-D Binding Protein and undergo further modifications in the liver and kidney to become the active form, 1,25 (OH)2Vitamin D. This active form plays a crucial role in regulating calcium and phosphate concentrations in the body.
1,25 (OH)2Vitamin D increases calcium absorption in the duodenum and inhibits the secretion and synthesis of PTH, which helps to maintain calcium concentrations. It also increases phosphate absorption in the jejunum and ileum, which is important for maintaining phosphate concentrations. Additionally, 1,25 (OH)2Vitamin D promotes bone turnover by stimulating both osteoblast and osteoclast activity.
Overall, the production and activation of Vitamin D through UV light and dietary sources is essential for proper calcium and phosphate regulation in the body.
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This question is part of the following fields:
- Basic Sciences
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Question 27
Incorrect
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A couple in their late 30s come to the clinic seeking information about the risk of their three children inheriting Huntington's disease. The husband has recently been diagnosed with the disease, while the wife is not affected. What is the likelihood, expressed as a percentage, that their children will inherit the disease?
Your Answer:
Correct Answer: 50%
Explanation:Huntington’s Disease
Huntington’s disease is a genetic disorder that typically appears later in life and is characterized by symptoms such as chorea, cognitive decline, and personality changes. It is an autosomal dominant disease, meaning that there is a 50% chance of passing it on to offspring. If the gene is inherited from an unaffected parent, the child will not be affected. This is different from autosomal recessive inheritance, where both parents must pass on the gene for it to affect their children.
The disease is caused by an increase in the length of a repeating trinucleotide sequence (CAG) in the Huntington protein. This sequence can change in length through generations, and longer sequences are associated with earlier onset of symptoms (genetic anticipation). Since Huntington’s disease usually presents itself after people have already started their families, there are many issues associated with genetic testing.
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This question is part of the following fields:
- Basic Sciences
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Question 28
Incorrect
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At what stage of eukaryotic mitosis do the centromeres of chromosomes separate?
Your Answer:
Correct Answer: Anaphase
Explanation:Chromosome Division during Anaphase
Chromosomes are joined together in an X shape at the centromere. During anaphase, the centromeres break down and the chromosomes divide into two identical pairs called sister chromatids. These sister chromatids then move to opposite sides of the cell along a network of spindle fibres. When the cell divides during telophase, each daughter cell receives one sister chromatid from the parent cell. This ensures the accurate copying and propagation of genes. The process of chromosome division during anaphase is crucial for the proper distribution of genetic material in cells.
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This question is part of the following fields:
- Basic Sciences
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Question 29
Incorrect
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What are the primary constituents of the cytoskeleton in eukaryotic cells?
Your Answer:
Correct Answer: Microfilaments, intermediate filaments and microtubules
Explanation:The Eukaryotic Cytoskeleton: A Structural Support System
The eukaryotic cytoskeleton is a network of structures that provide structural support to the cell. It helps the cell maintain its shape, protects it from external pressure, and performs intracellular transport. The cytoskeleton is made up of three major structures: microfilaments, intermediate filaments, and microtubules. Microfilaments are thin double helices made up of actin and are involved in pressure resistance and cell motility. Intermediate filaments have a more complex structure and maintain cell shape while bearing tension. Microtubules are hollow cylinders made up of alpha and beta tubulin proteins and are involved in intracellular transport, cell movement, and form the mitotic spindle during cytokinesis.
Cilia, flagella, and lamellipodia are structures that are not part of the cell’s cytoskeleton but are made up of components of it and perform unique functions such as cell movement and extracellular sensing. Kinesin and dynein are motor proteins that support microtubule function. Microfilaments and alpha/beta microtubules are incorrect because they leave out intermediate filaments. Tubulin and actin are proteins of microtubules and microfilaments, respectively, but myosin is a motility protein involved in muscle contraction. The eukaryotic cytoskeleton is an essential component of the cell that provides structural support and enables various cellular functions.
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This question is part of the following fields:
- Basic Sciences
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Question 30
Incorrect
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What is the apoptotic event that occurs just before the formation of an apoptosome?
Your Answer:
Correct Answer: Release of cytochrome c from mitochondria
Explanation:Apoptosis and the Role of the Apoptosome
Apoptosis, also known as programmed cell death, is a natural process that occurs in all multicellular organisms. It involves a series of changes in cell morphology, including membrane blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation. The formation of the apoptosome is a crucial part of the apoptosis cascade. It is a large protein structure that is triggered by the release of cytochrome c from the mitochondria in response to various stimuli, such as DNA damage, infections, or developmental signals.
The apoptosome is formed when cytochrome c binds to Apaf-1, a cytosolic protein, in a 1:1 ratio. This triggers the recruitment and activation of the initiator pro-caspase-9, which then activates effector caspases, a family of apoptotic proteases, to initiate the apoptotic cascade. It is important to note that the activation of caspase-9 occurs only after the formation of the apoptosome.
In summary, apoptosis is a natural process that occurs in multicellular organisms, and the apoptosome plays a crucial role in triggering the apoptotic cascade. the mechanisms behind apoptosis and the formation of the apoptosome can provide insights into various diseases and developmental processes.
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This question is part of the following fields:
- Basic Sciences
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