BCH2602 Exam Q&A
Question 1
Define the following terms. [28 x 1]
1.1. Gluconeogenesis
Synthesis of glucose from non-carbohydrate precursors.
1.2. Autotrophs
An organism that can synthesize all its cellular components from simple molecules using
the energy obtained from sunlight or oxidation of inorganic compounds.
1.3. Heterotrophs
Obtain energy from chemical fuels only.
1.4. Anabolism
The reactions by which biomolecules are synthesized from simpler components.
1.5. Uncoupling protein
A protein homodimer of 307-residue subunits that acts as a channel to control the
permeability of the inner mitochondrial membrane to protons.
1.6. F0F1 complex
A multi-subunit protein consisting of proton–translocating membrane-embedded
component (f0) linked to a soluble catalytic component (f1) that catalyses ATP
synthesis in the presence of a proton motive force.
1.7. Chylomicrons
Lipoprotein transport particles packaged from fatty acids and monoacylglycerol.
1.8. Metabolic pathway
The overall process through which living systems acquire and utilise the free energy they
need to carry out their various functions.
1.9. Triacylglycerol
A lipid in which three fatty acids are esterified to glycerol backbone.
1.10. Urea Cycle
Cycle where surplus amino acids are converted to urea.
1.11. Amphibolic
Describes a biochemical pathway that involves both catabolism and anabolism.
1.12. Steroid
An organic compound with four rings arranged in a specific configuration. E.g. the dietary
lipid cholesterol.
1.13. NADPH
(Nicotinamide adenine dinucleotide phosphate) is a reducing agent required in various
anabolic reactions. It is the reduced form of the coenzyme NADP+. NADPH is a similar
compound to NADH; however, it has an additional phosphate group attached.
1.14. L-Carnitine
L-Carnitine is an endogenous molecule involved in fatty acid
metabolism, biosynthesized within the human body using amino acids: L-lysine and L-
methionine, as substrates. Carnitine is involved in transporting fatty acids across the
mitochondrial membrane, by forming a long chain acetylcarnitine ester and being
transported by carnitine palmitoyltransferase I and carnitine palmitoyltransferase II.
1.15. Pentose phosphate pathway
The pentose phosphate pathway (also called the
phosphogluconate pathway and the hexose monophosphate shunt) is a metabolic
pathway parallel to glycolysis. It generates NADPH and pentoses (5-carbon sugars) as well
as ribose 5-phosphate, the last one a precursor for the synthesis of nucleotides.
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, BCH2602 Exam Q&A
1.16. Transpeptidation
A chemical reaction (as the reversible conversion of one peptide to another by a
protease) in which an amino acid residue or a peptide residue is transferred from one
amino compound to another.
1.17. Galactosaemia
Inherited disorder leading to disruption of galactose metabolism.
1.18. Metabolism
The sum total of all biochemical reactions that take place in an organism, through which
living systems acquire and utilise the free energy they need to carry out their various
functions.
1.19. Lipoprotein
Any of a group of soluble proteins that combine with and transport fat or other lipids in the
blood plasma.
1.20. Amphipathic
A molecule having both hydrophilic and hydrophobic parts.
1.21. Glyceraldehyde
A triose monosaccharide with chemical formula C₃H₆O₃. It is the simplest of all common
aldoses.
1.22. Peptidoglycan
A polymer consisting of sugars and amino acids that forms a mesh-like layer outside the
plasma membrane of most bacteria, forming the cell wall.
1.23. Reducing sugar
Any sugar that can act as a reducing agent because it has a free aldehyde group or a
free ketone group.
1.24. Catabolism
The breakdown of complex molecules in living organisms to form simpler ones, together
with the release of energy; destructive metabolism.
1.25. Metabolic pathway
A sequence of chemical reactions undergone by a compound or class of compounds in a
living organism.
1.26. Alcoholic fermentation
An anaerobic process in which glucose is converted into alcohol and carbon dioxide.
1.27. Glycosidic bond
A covalent bond that holds a carbohydrate (sugar) to another group that can or cannot
be another sugar.
1.28. Tautomer
Are isomers of a compound which differ only in the position of the protons and electrons.
They are constitutional isomers of organic compounds that readily interconvert.
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, BCH2602 Exam Q&A
Question 2
2.1. Why is Acetyl-CoA considered the central molecule of metabolism? [6]
It carries acetate, used in the build-up and breakdown of larger molecules. Acetyl CoA is
key in synthetic pathways leading to sesquiterpenes, precursors to cholesterol and other
sterols, flavenoids and other polyketides, polyenes and long-chain fatty acids. It is the
source of the acetyl group used in histone acetylation. The acetyl group is also
incorporated into a variety of other molecules such as acetylcholine, melatonin, heme
and TCA cycle intermediates. It also plays the role of an intermediary in: citric acid cycle,
fatty acid oxidation and synthesis, glyoxylate cycle.
2.2. What is the metabolic purpose of lactic acid production? [6]
To further metabolise pyruvate, a product of glycolysis. It also allows for the anaerobic
production of energy. The process also allows anaerobes to survive in environments such
deep water and soil. Many commercial dietary products have been available as a result
of lactic acid fermentation, e.g. cheese, yogurt.
Under normal circumstances, the muscle cells make use of oxygen to carry out normal
cellular respiration. But in the event where there is absence or lack of such (typically
occurring during extreme physical exertions), then it will undergo lactic acid fermentation.
Basically, the pyruvic acid becomes lactic acid in this type of fermentation.
2.3. Which reactions are the control points in glycolysis? [6]
Glucose → Glucose-6-P catalyzed by Hexokinase
Fructose-6-P → Fructose 1,6-BP catalyzed by Phosphofructokinase
PEP → Pyruvate catalyzed by Pyruvate Kinase
2.4. How does phosphorolysis differ from hydrolysis? [4]
Phosphorolysis is the cleavage of a bond by the addition of orthophosphate.
Hydrolysis is the cleavage of a bond by the removal of Pi.
2.5. Which reactions are the control points in the citric acid cycle? [6]
Isocitrate + NAD+ ↔ alphaketoglutarate + CO2 + NADH (isocitrate dehydrogenase
Alphaketoglutarate +NAD+ + CoA ↔ succinyl CoA + CO2 +NADH (alphaketoglutarate
dehydrogenase)
2.6. In contrast to water-soluble vitamins, which must be part of our daily diet, fat-soluble
vitamins can be stored in the body in amounts sufficient for many months. Suggest an
explanation for this difference. [4]
Water-soluble vitamins are rapidly excreted in the urine and not stored effectively. Fat-
soluble vitamins have much lower solubility and are excreted very slowly.
2.7. Although it is not the primary flux-control point for glycolysis, pyruvate kinase is subject to
allosteric regulation. What is the metabolic importance of regulating flux through the
pyruvate kinase reaction? What is the advantage of activating pyruvate kinase with
fructose-1,6-biphosphate? [6]
Pyruvate kinase regulation is important for controlling the flux of metabolites, such as
fructose (in liver), which enter glycolysis after the PFK step.
FB is generated by PFK in step 3 of glycolysis so it acts as a feed-forward activator of the
pyruvate kinase, which catalyzes step 10. This regulatory mechanism helps ensure that
once metabolites pass the PFK step of glycolysis, they will continue through the
pathway.
2.8. The citric acid cycle is not always a cycle, explain. [4]
The citric acid cycle serves as an important source of biosynthetic intermediates, and
there are important pathways involved. These pathways tend to draw carbon from the
cycle by utilizing intermediates in the cycle and hence lead to the impairment of the
cycle’s operation.
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