Study "Bio paper 1", a flashcard deck on FORKSAI.
A pharmaceutical company is developing a new drug that needs to be transported efficiently throughout the bloodstream. Explain why a protein similar in structure to haemoglobin would be a better choice for this drug's transport mechanism compared to one resembling collagen, detailing the specific structural features that support your reasoning.
A protein similar to haemoglobin would be superior for drug transport because haemoglobin is a globular protein, meaning it is roughly spherical and soluble in water. This solubility is crucial for efficient movement within the aqueous environment of blood plasma. In contrast, collagen is a fibrous, rope-like protein that is insoluble, making it unsuitable for transport. Furthermore, haemoglobin's quaternary structure, comprising four polypeptide chains, provides multiple potential binding sites, which could be engineered to carry drug molecules effectively, unlike collagen's purely structural role.
Define the key structural differences between amylose and amylopectin, and explain how these differences contribute to starch's efficiency as an energy storage molecule.
Amylose is a long, unbranched chain of alpha-glucose units linked by 1-4 glycosidic bonds, which coils into a helix. Amylopectin, on the other hand, is a branched chain with both 1-4 and 1-6 glycosidic bonds. These structural features make starch an efficient storage molecule because the coiled nature of amylose allows it to be compact, fitting a large amount of energy into a small space. The branched ends of amylopectin provide numerous sites for rapid enzymatic hydrolysis, enabling quick glucose release when energy is needed, while its insolubility prevents it from affecting the cell's water potential.
A biologist observes a plant cell wall under an electron microscope and identifies numerous hydrogen bonds between adjacent polysaccharide chains. Based on this observation, identify the specific polysaccharide forming these chains and explain how its unique monomer arrangement facilitates this extensive hydrogen bonding and contributes to the cell wall's structural integrity.
The polysaccharide observed is cellulose. Cellulose is composed of beta-glucose monomers, which are arranged in a unique way where every other glucose molecule is rotated 180 degrees. This 'flipped' orientation results in straight, unbranched chains. These straight chains can then align side-by-side, allowing extensive hydrogen bonds to form between hydroxyl groups on adjacent chains. This dense network of hydrogen bonds between parallel chains forms microfibrils, which are incredibly strong and provide the robust structural support characteristic of plant cell walls.
A novel enzyme is discovered that functions optimally at a pH of 1.5. Describe the expected shape of a graph plotting its reaction rate against pH, and explain the biological reasons for the sharp decline in activity observed when the pH deviates significantly from this optimum.
The graph of reaction rate against pH for this enzyme would exhibit a bell-curve shape, peaking sharply at pH 1.5. As the pH deviates significantly from 1.5, either higher or lower, the reaction rate would drop sharply. This decline is due to denaturation. Extreme pH values cause changes in the charges of the R groups within the enzyme's polypeptide chains. These altered charges disrupt the ionic and hydrogen bonds that maintain the enzyme's specific tertiary structure, leading to a permanent change in the active site's shape. Consequently, the substrate can no longer bind effectively, and the enzyme loses its catalytic activity.
During a medical procedure, a patient experiences a sudden drop in blood pressure. A medical student suggests that the issue might be related to the total cross-sectional area of the patient's circulatory system. Explain how a significant increase in the total cross-sectional area of blood vessels, particularly in the capillaries, contributes to the natural drop in blood pressure as blood moves away from the heart.
The significant drop in blood pressure as blood moves from arteries to capillaries is largely due to the massive increase in the total cross-sectional area. Although individual capillaries are tiny, their sheer number means that the combined area through which blood flows increases dramatically. This increased area reduces the resistance to flow for any single blood cell, but more importantly, it means the same volume of blood is spread out over a much larger space. This spreading out, combined with friction between the blood and the vessel walls, causes the pressure to dissipate, resulting in the very low pressure observed in the capillaries, which is essential for efficient exchange of substances.
An athlete is preparing for a marathon and needs to store a readily accessible energy reserve. Compare and contrast starch and cellulose in terms of their glucose type, bonding, and functional roles, explaining why starch is the preferred molecule for energy storage over cellulose.
Starch and cellulose are both polymers of glucose but differ fundamentally in their glucose type, bonding, and function. Starch is made of alpha-glucose units with 1-4 and 1-6 glycosidic bonds, forming coiled and branched structures, serving as an energy storage molecule. Cellulose, conversely, is made of beta-glucose units with only 1-4 glycosidic bonds, resulting in straight, unbranched chains that provide structural support. Starch is preferred for energy storage because its coiled and branched structure makes it compact for efficient storage and provides numerous ends for rapid enzymatic breakdown into glucose when energy is needed. Cellulose's rigid, unbranched structure, stabilized by extensive hydrogen bonding, is designed for strength and is not easily digestible by most organisms for energy.
A patient is diagnosed with a genetic disorder that impairs the formation of strong connective tissues, leading to fragile skin and tendons. Explain how a defect in the synthesis of collagen, specifically affecting the incorporation of glycine or the formation of hydrogen bonds, could account for these symptoms.
Collagen is a crucial structural protein, forming a triple helix from three polypeptide chains held together by hydrogen bonds. A defect in collagen synthesis, particularly affecting glycine incorporation, would severely compromise its structure. Glycine, being the smallest amino acid, is uniquely required at every third position to allow the three polypeptide chains to wind tightly into the triple helix. Without proper glycine placement, the helix cannot form correctly, weakening the overall structure. Similarly, if the hydrogen bonds that stabilize the triple helix are impaired, the chains would not be held together strongly, leading to a loose, fragile structure. Both scenarios would result in a compromised, less robust collagen, explaining the fragile skin and tendons observed in the patient.
Describe the key events and pressure changes that occur during ventricular systole in the left side of the heart, including the roles of the bicuspid and semilunar valves and the sounds produced.
During ventricular systole, the left ventricle contracts, causing its internal pressure to rise rapidly. Initially, as ventricular pressure exceeds atrial pressure, the bicuspid (mitral) valve snaps shut, producing the 'lub' sound and preventing backflow into the atrium. As the ventricle continues to contract, its pressure quickly surpasses the pressure in the aorta. This pressure difference forces the aortic semilunar valve open, allowing a surge of oxygenated blood to be ejected into the aorta. The ventricle continues to contract until its pressure begins to drop as blood is expelled.
An experiment is designed to investigate the effect of increasing substrate concentration on enzyme activity. Describe the expected trend in reaction rate and explain the biological reason for the eventual plateau observed, identifying the limiting factor at that point.
As substrate concentration increases, the rate of enzyme activity will initially rise proportionally, as more substrate molecules are available to bind with active sites, leading to more enzyme-substrate complexes. However, the rate will eventually plateau, reaching a maximum velocity (Vmax). This plateau occurs because all available enzyme active sites become saturated with substrate molecules. At this point, the enzyme concentration becomes the limiting factor, as there are no longer enough active sites to process additional substrate molecules, even if more are present. Increasing substrate concentration further will not increase the reaction rate.
Explain the 'cohesion-tension theory' as it applies to water movement in plants, detailing how transpiration from the leaves initiates the upward pull of water from the roots.
The cohesion-tension theory describes how water moves from the roots to the leaves in plants. It begins with transpiration, the evaporation of water from the leaves through stomata, which creates a negative pressure or 'tension' in the xylem vessels. Because water molecules are cohesive (they stick to each other due to hydrogen bonds) and adhesive (they stick to the xylem walls), this tension pulls the entire column of water upwards, much like sucking through a straw. As water molecules evaporate from the leaves, they pull on the adjacent water molecules, which in turn pull on the ones below them, creating an unbroken chain of water stretching from the roots to the leaves, effectively drawing water up against gravity.