Pathways and Enzymes
What is the fundamental difference between an anabolic pathway and a catabolic pathway in terms of energy and molecular complexity?
An anabolic pathway requires energy to build up simple molecules into complex ones, whereas a catabolic pathway releases energy by breaking down complex molecules into simple ones.
What specific role do dehydrogenase enzymes play in both glycolysis and the citric acid cycle?
They remove hydrogen ions and electrons from substrates and pass them to coenzymes / NAD (forming NADH).
Explain why birds and mammals require a complete double circulatory system to support their high metabolic rates.
They have 2 atria and 2 ventricles with no mixing of oxygenated and deoxygenated blood, allowing blood to be pumped out at higher pressure for efficient oxygen delivery to body cells.
Give the exact reason why cell division does not occur during the lag phase of microbial growth.
Enzymes are induced to metabolise substrates (or DNA replication occurs) (Note: SQA strictly rejects "cells are acclimatising / getting used to the environment").
State the dual role of restriction endonucleases in recombinant DNA technology.
They cut specific target genes out of donor chromosomes AND cut open the vector/plasmid.
Explain how a non-competitive inhibitor alters enzyme activity differently than a competitive inhibitor, and state why increasing substrate concentration does not reverse its effect.
A non-competitive inhibitor binds away from the active site (at an allosteric site), changing the shape of the active site so the substrate can no longer bind. Increasing substrate concentration cannot reverse this because the substrate and inhibitor do not compete for the same site.
State the exact intracellular locations of the Citric Acid Cycle and the Electron Transport Chain.
The Citric Acid Cycle occurs in the matrix of the mitochondrion; the Electron Transport Chain occurs on the inner mitochondrial membrane.
Describe the physical change that occurs in skin blood vessels during vasoconstriction, and state its effect on heat loss.
Arterioles/blood vessels constrict/narrow, reducing blood flow to the skin surface, which reduces heat loss (Note: SQA strictly rejects "prevents/stops heat loss" or "blood vessels move").
Name the phase of microbial growth in which secondary metabolites like antibiotics are produced, and explain their ecological advantage in the wild.
Produced in the stationary phase; antibiotics kill competing microorganisms to reduce competition for limited resources/nutrients (Note: SQA rejects "kills bacteria" alone without mentioning reducing competition).
Why MUST the exact same restriction endonuclease be used to cut both the target gene and the vector plasmid?
To produce complementary sticky ends (Note: SQA strictly rejects "so it cuts in the same place" or "same base sequence").
Describe the mechanism of feedback inhibition in a metabolic pathway.
End-product reaches a critical concentration and binds to/inhibits the first enzyme in the pathway, stopping further production of the end-product.
Explain the essential role of oxygen at the very end of the Electron Transport Chain.
Oxygen acts as the final hydrogen ion and electron acceptor, combining with hydrogen ions and electrons to form water
Compare conformers and regulators in terms of their metabolic costs and the width of their ecological niches.
Conformers have low metabolic costs but a narrow range of ecological niches; regulators have high metabolic costs (due to homeostasis) but a wide range of ecological niches.
Explain the difference between a viable and a total cell count, and state which phase of growth can only be identified using a viable cell count.
A viable cell count counts only living cells, while a total cell count counts both living and dead cells. Only a viable count shows the death phase (where cell numbers decrease).
State the essential function of the origin of replication region on a recombinant plasmid vector.
It allows self-replication of the plasmid (so it can make multiple copies inside the host cell) (Note: SQA rejects "replication site").
Describe the exact mechanism of induced fit when a substrate approaches an enzyme.
The active site of the enzyme changes shape to fit the substrate more closely after the substrate binds.
In the first reaction of the Citric Acid Cycle, an acetyl group combines with oxaloacetate. Name the 6-carbon compound formed, and state the fate of the carbon removed during this cycle.
The 6-carbon compound is citrate; the removed carbons are released as carbon dioxide
Describe how the hypothalamus coordinates a response when thermoreceptors detect a drop in core body temperature.
The hypothalamus acts as the temperature monitoring centre and sends nerve impulses along neurons to skin/muscle effectors to trigger physiological responses (like shivering or vasoconstriction).
Explain why sterile conditions must be maintained inside an industrial fermenter.
To reduce or eliminate competition between wild microorganisms and the desired strain for nutrients, and to prevent product spoilage (Note: SQA strictly negates "to prevent contamination" or "patient safety").
Explain how a selectable marker (such as an antibiotic resistance gene) allows scientists to identify successfully modified host cells.
Only transformed cells (cells that have taken up the recombinant plasmid) can survive/grow in the presence of the antibiotic.
Define activation energy in terms of the chemical state of the reactants.
The energy required to break the bonds in the reactants to reach their unstable transition state.
Describe how ATP synthase generates ATP during oxidative phosphorylation.
The flow of hydrogen ions down their concentration gradient back across the inner membrane rotates ATP synthase, generating ATP from ADP and inorganic phosphate ($\text{P}_i$).
Explain how a respirometer or calorimeter measures metabolic rate, noting the specific measurement taken in a calorimeter.
A respirometer measures oxygen consumption per unit time (or $\text{CO}_2$ output); a calorimeter measures the temperature increase of water to calculate heat generated by the organism (Note: SQA rejects "calorimeter measures heat directly").
On a semi-logarithmic graph of bacterial growth, why does the exponential (log) phase appear as a straight line with a constant positive slope?
On a semi-logarithmic graph of bacterial growth, why does the exponential (log) phase appear as a straight line with a constant positive slope?
Explain why recombinant human proteins produced in bacterial cells are often inactive, and how using recombinant yeast cells overcomes this problem.
Bacteria lack eukaryotic organelles so their expressed proteins fold incorrectly (lack post-translational modifications). Yeast cells are eukaryotic, so they carry out correct protein folding and post-translational modification.