Describe the biosynthetic pathway for sucrose from the triose phosphates showing the main steps, including intermediates, enzymes and cofactors. Indicate where this process takes place.


Attempt all questions.
Each question is worth ONE mark.
Marks are awarded for the correct response.
1. The reference compound for naming D and L isomers of sugars is:

a. glucose
b. glyceraldehyde
c. ribose
d. D-glucose
e. A hexose.

2. When two carbohydrates are epimers:

a. They rotate in plane-polarised light in the same direction
b. They differ in length by one carbon
c. One is an aldose, the other a ketose
d. One is a pyranose, the other is a furanose
e. They differ only in the configuration around one carbon atom.

3. D-Glucose is called a reducing sugar because it undergoes an oxidation-reduction reaction at the anomeric carbon. One of the products of this reaction is :

a. D-Galactose
b. D-Gluconate
c. D-Glucuronate
d. D-Ribose
e. Muramic acid.

4. Which of these enzymes is not part of the Calvin cycle:

a. Aldolase
b. Glyceraldehyde 3-Phosphate dehydrogenase
c. Phosphofructokinase-1
d. Ribulose-5-phosphate kinase
e. Rubisco.
5. The assimilation of CO2 into organic compounds (triose phosphates) in green plants:

a. Involves the condensation of the two carbon acetate with CO2 to form 3-Phosphoglycerate
b. Requires NADPH
c. Results in the production of ATP
d. Takes place at equal rates in light and darkness
e. Takes place in the cytosol.

6. In the carbon assimilation reactions of photosynthesis, the biosynthesis of 1 mol of hexose from 6 mol of carbon dioxide requires:

a. 12 mol of NADPH and 12 mol of ATP.
b. 18 mol of NADPH and 12 mol of ATP.
c. 18 mol of NADPH and 18 mol of ATP.
d. 12 mol of NADPH and 18 mol of ATP.
e. No NADPH and 12 mol of ATP.

7. The synthesis of sucrose and starch in plants uses ______ and _____as the substrates:

a. ADP-Fructose; UDP-Glucose
b. UDP-Glucose; ADP-Glucose
c. Fructose 1-phosphate; Glucose 1-phosphate
d. Glucose 1-phosphate; Glucose 6-phosphate
e. UTP-Glucose; AMP-Glucose

8. The enzyme Sucrose phosphatase has the role of:

a. Catalysing the conversion of sucrose to sucrose-6-phosphate
b. Catalysing the conversion of fructose-6-phosphate to sucrose
c. Catalysing the conversion of fructose-6-phosphate to sucrose-6-phosphate
d. Catalysing the conversion of sucrose-6-phosphate to sucrose
e. Catalysing the conversion sucrose to glucose and fructose

9. Which one of the following cellular organelles is not unique to plant cells in carrying out the indicated pathway or function of carbohydrate metabolism:
a. Amyloplasts (starch storage)
b. Chloroplasts (Calvin cycle)
c. Glyoxysomes (glyoxylate cycle)
d. Mitochondria (Citric acid cycle)
e. Vacuoles (organic acid storage).

10. The conversion of 1 mol of Fructose 1,6-Bisphosphate to 2 mol of Pyruvate by glycolysis results in the net formation of:

a. 1 mol NAD+ and 2 mol ATP
b. 1 mol NADH and 1 mol ATP
c. 2 mol NAD+ and 4 mol ATP
d. 2 mol NADH and 2 mol ATP
e. 2 mol NADH and 4 mol ATP

11. The ultimate electron acceptor in the fermentation of glucose to ethanol is:

a. Acetaldehyde
b. Acetate
c. Ethanol
d. NAD+
e. Pyruvate

12. Conversion of 1 mol of Acetyl-CoA to 2 mol CO2 and CoA via the citric acid cycle results in the net production of:

a. 1 mol Citrate
b. 1 mol FADH2
c. 1 mol NADH
d. 1 mol Oxaloacetate
e. 7 mol ATP

13. Which of these statements about the composition of membranes is true?

a. All biological membranes contain cholesterol.
b. Free fatty acids are major components of all membranes.
c. The inner and outer membranes of mitochondria have different protein compositions.
d. The lipid composition of all membranes of eukaryotic cells is essentially the same.
e. All biological membranes contain predominantly carbohydrates

14. Which of the following is untrue (false) about fatty acids?

a. Long chain carboxylic acids
b. Maybe branched or unbranched
c. Maybe saturated or unsaturated
d. The chain length is generally between 4 and 36 Carbons
e. Some are steroids

15. The rate limiting step in the synthesis of fatty acids is:

a. Condensation of Acetyl-CoA and Malonyl-CoA
b. Formation of Acetyl-CoA from acetate
c. Formation of Malonyl-CoA from malonate and CoA
d. The reduction of the acetoacetyl group to a β-hydroxybutyryl group
e. The reaction catalysed by Acetyl-CoA carboxylase.

16. Enzymes that catalyse the synthesis of long chain fatty acids in plant cells:

a. Act as separate freely associated proteins
b. Are encoded by mitochondrial DNA
c. Are localised in the mitochondrial matrix
d. Act as part of a single polypeptide containing distinct enzyme activities
e. Have none of these characteristics

17. During β-oxidation of fatty acids, _________ is produced in the peroxisomes but not in the mitochondria?

a. Acetyl-CoA
b. FADH2
c. H2O
d. H2O2

18. The order in which amino acids are linked in peptides is given:

a. From the C-terminal to the N-terminal end
b. In alphabetical order
c. From the N-terminal to the C-terminal end
d. In order of increasing molecular weight of the amino acid residues
e. In order of decreasing molecular weight of the amino acid residues
19. Which group consists only of amino acids with polar side chains?

a. Serine, threonine and leucine
b. Serine, threonine and cysteine
c. Serine, threonine and valine
d. Serine, threonine and isoleucine
e. Serine, threonine and glycine
20. Which of the following statements about the fixation of atmospheric nitrogen (N2) into NH3 by living cells is false?

a. It involves the transfer of 8 electrons per mol of N2.
b. It occurs in certain microorganisms, but not in humans.
c. It requires a source of electrons, normally ferredoxin.
d. It requires one ATP per mol of N2 fixed.
e. It requires two key protein components, each containing iron.

21. Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule?

a. Arginase
b. Glutamate dehydrogenase
c. Glutamate synthase
d. Glutamine synthetase
e. Nitrogenase

22. In amino acid catabolism, the first reaction for many amino acids is a(n):

a. Decarboxylation requiring thiamine pyrophosphate (TPP).
b. Hydroxylation requiring NADPH and O2.
c. Oxidative deamination requiring NAD+.
d. Reduction requiring pyridoxal phosphate (PLP).
e. Transamination requiring pyridoxal phosphate (PLP).

23. Transamination from alanine to –ketoglutarate requires the coenzyme:

a. Thiamine pyrophosphate (TPP).
b. NADH.
c. Biotin.

d. Pyridoxal phosphate (PLP).
e. no coenzyme is involved.

24. Phenylpropanoids are synthesised from the shikimic acid pathway from:

a. Phosphoenolpyruvate
b. Phenylalanine
c. Malonyl CoA
d. Serine
e. Alanine

25. The simple phenolics have a basic structure of:

a. A six carbon glucose skeleton
b. A linear 3-carbon skeleton
c. A six carbon phenyl ring with a side chain
d. A five carbon furan ring with a side chain
e. A six carbon phenyl ring but no side chain

26. Hydrolysable tannins are polymers of phenolic acids and a carbohydrate which include:

a. Gallic acid and starch
b. Flavan-3-ols and sucrose
c. Benzoic acid and glucose
d. Gallic acid and glucose
e. Chorismic acid and glucose

27. Lycopene is a

a. protein
b. polysaccharide
c. terpenoid
d. fatty acid
e. sterol

28. Which of the following most accurately describes rubber?

a. triterpene formed from isopentyl diphosphate
b. polyterpene
c. poly phenol
Session 2, 2015 – PSC208 Page 8 of 19
d. structural polysaccharide
e. sesquiterpene formed from 3-hydroxy-3-methyl glutaryl CoA

29. Which of the following is / are a common precursor(s) for plant sterols and terpenoids?

a. 3-hydroxy-3-methyl glutaryl CoA
b. Isopentyl diphosphate
c. Squalene
d. 3-hydroxy-3-methyl glutaryl CoA and Isopentyl diphosphate
e. 3-hydroxy-3-methyl glutaryl CoA, Isopentyl diphosphate and squalene
30. Rotundone is a terpenoid compound found in some Vitis vinifera grape varieties that contributes to wine quality. Which of the following best describes the olfactory properties of rotundone?

a. Peppery
b. Citrus
c. Berry fruit such as raspberry
d. Mushroom, earthy
e. Dried fruit, tropical flower

Attempt ALL questions
1. Explain why all mono and disaccharides are soluble in water (1 mark)

2. In the following structure:

a. How many of the monosaccharide units are furanoses and how may are pyranoses? (2 marks)
b. What is the linkage between the two monosaccharide units? (1 mark)
c. Is this a reducing sugar? Explain (2 marks)
3. Draw the structure of the repeating basic unit of cellulose. (2 marks)

4. Describe the steps in the Calvin cycle from the fixation of CO2 to the synthesis of Glyceraldehyde 3-phosphate (Triose phosphates) showing substrates, intermediates, cofactors and enzymes. (3 marks)

5. Briefly describe the possible metabolic fates of pyruvate produced by glycolysis in plants and explain the circumstances in which each is favoured. (3 marks)

6. With the aid of a diagram, show the path of electron flow from donor to acceptor in the mitochondria showing the complexes involved, carriers and demonstrate the purpose of this electron flow. (3 marks)

7. Draw the structure of a Glycerophospholipid (2 marks).

a. Comment on how variation in the glycerophospholipids can arise. (2 marks)
b. Where would expect to find these glycerophospholipids in plants? (1 mark)


8. Describe the four steps that are required in plants to oxidise a two carbon unit from a fatty acid molecule by the process of β oxidation. Include the enzymes and intermediates that are required (no structures). Indicate which organelle is involved. (4 marks)

9. An important biological reaction of amino acids is the formation of a peptide. Provide a description of the general structure of a peptide showing how they are conventionally arranged. (3 marks)

10. Uptake of nitrogen is vital for plant growth. Describe the metabolic steps required when inorganic nitrate is taken up for incorporation into amino acids (3 marks)


11. Describe the steps required in the catabolism of an amino acid, including the intermediates, enzymes and cofactors. Comment how yeast manage cellular levels of nitrogen. (4 marks)

12. Describe the three groups of the simple phenolics and give the structures to show the essential differences. Give an example of each group. (3 marks)
13. Compare and contrast the two groups of phenolic polymers known as the tannins, indicating the constituent phenolics, size of polymer and general characteristics. Which of these are found in grapes and where? (3 marks)

14. Using named examples, discuss the difference between monoterpenes, sesquiterpenes and triterpenes. (3 marks)

Attempt THREE Questions
All questions are worth 10 marks each.
Sucrose synthesis is important for plants as it is the main transport sugar. Describe the biosynthetic pathway for sucrose from the triose phosphates showing the main steps, including intermediates, enzymes and cofactors. Indicate where this process takes place.
With the aid of a diagram, describe the process of glycolysis showing the key intermediates and enzymes starting with sucrose and indicate all the products of this reaction.

Starch and cellulose are both homopolysaccharides of glucose, yet they differ considerably in their physical properties. Why is this so? Use diagrams and/or structures to explain your answer.

Describe the general aspects of the biosynthesis of the phenolics. Structures are not required.

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