Category 1

Question 1

Which activated carrier carries acyl groups and is derived from pantothenate (vitamin B5)?

Answer 1

Coenzyme A.

Question 2

How do hormonal effects on glycogen metabolism occur?

Answer 2

Hormones regulate glycogen metabolism by altering the phosphorylation states of glycogen synthase and glycogen phosphorylase.

Question 3

What are storage polysaccharides in animals and plants and how do they differ?

Lecture 2

Answer 3

Starch (plants): Amylose (linear, alpha-1,4 linkages) + Amylopectin (branched, alpha-1,4 and alpha-1,6 linkages), Glycogen (animals): Highly branched, alpha-1,4 and alpha-1,6 linkages.

Question 4

What is the role of NAD+ in catabolic reactions?

Lecture 1

Answer 4

NAD+ is an activated carrier of electrons that, in its oxidized form, accepts 1 proton and 2 electrons via its reactive nicotinamide ring (derived from niacin).

Question 5

What distinguishes NADP+ from NAD+ in its role as an electron carrier?

Lecture 1

Answer 5

NADP+ contains an extra phosphoryl group compared to NAD+, allowing enzymes to distinguish it for use in anabolic reactions, such as fatty acid synthesis.

Question 6

What are proteoglycans, and why are they important?

Lecture 2

Answer 6

Proteins linked to glycosaminoglycans (GAGs) in the ECM; act as lubricants and shock absorbers. Their degradation is associated with arthritis.

Question 7

What are the defining characteristics of monosaccharides?

Lecture 2

Answer 7

3-7 carbons in length, aldehyde or ketone group with at least 2 alcohol groups, chiral carbons, and can form ring structures (pyranoses or furanoses).

Question 8

Would you expect glycolysis to be activated or inhibited in liver cells when blood glucose is low?

Answer 8

Inhibited: glycolysis is the breakdown of glucose. If glucose is low we don’t want to lower it further by breaking it down into pyruvate.

Question 9

What is the fate of pyruvate under anaerobic conditions in yeast?

Answer 9

Pyruvate is decarboxylated to form acetaldehyde, which is then reduced to ethanol using high-energy electrons from NADH. This regenerates NAD+ for glycolysis.

Question 10

What role do glycoproteins and glycolipids play in cells?

Lecture 2

Answer 10

Found in the extracellular matrix (ECM), they are involved in cell recognition and adhesion. They also determine blood group types on erythrocytes.

Question 11

How is malate converted back into oxaloacetate?

Answer 11

Malate is re-oxidised to oxaloacetate in the cytoplasm, converting NAD+ to NADH.

Question 12

What happens to oxaloacetate in the gluconeogenesis pathway after it is transported to the cytoplasm?

Answer 12

It is decarboxylated and phosphorylated to form phosphoenolpyruvate, using GTP as the phosphate donor.

Question 13

What are dextrans, and where are they found?

Lecture 2

Answer 13

Dextrans are bacterial and yeast-synthesised polysaccharides, commonly found in dental plaque.

Question 14

What is the advantage of glycogen being branched, as opposed to a linear polymer of glucose?

Answer 14

More free ends mean glycogen breakdown is faster.

Question 15

In gluconeogenesis, the first step involves conversion of pyruvate into phosphoenolpyruvate, via an oxaloacetate intermediate. Where in the cell does the conversion of pyruvate to oxaloacetate occur?

Answer 15

In the mitochondrial matrix.

Question 16

What is gluconeogenesis?

Answer 16

The process of synthesising glucose from non-carbohydrate sources such as lactate, amino acids, and glycerol.

Question 17

What are anomers, and how are they formed in monosaccharides?

Lecture 2

Answer 17

Anomers are stereoisomers formed when monosaccharides cyclise into ring structures via nucleophilic attack, producing two forms (e.g.,alpha and beta)

Question 18

What is the fate of pyruvate under anaerobic conditions?

Answer 18

Pyruvate undergoes fermentation: high-energy electrons from NADH are transferred back to pyruvate, converting it into lactate and regenerating NAD+ for glycolysis. Catalysed by lactate dehydrogenase.

Question 19

What enzyme introduces branch points in glycogen?

Answer 19

Branching enzyme, which creates α-1,6 glycosidic bonds.

Question 20

What is meant by an endergonic reaction?

Lecture 1

Answer 20

Energetically unfavourable reaction, CANNOT occur spontaneously and ?G is positive.

Question 21

What is the most abundant organic molecule in the biosphere?

Lecture 2

Answer 21

Cellulose

Question 22

How does insulin (a signal of high glucose levels) affect PFK2 and FBPase2 activity in the liver?

Answer 22

Insulin stimulates phosphoprotein phosphatase, which dephosphorylates the polypeptide containing both enzymes. This activates PFK2 and deactivates FBPase2, promoting glycolysis and inhibiting gluconeogenesis.

Question 23

Which enzyme cleaves α-1,4 glycosidic bonds during glycogen breakdown?

Answer 23

Glycogen phosphorylase.

Question 24

Why are both carboxylation and decarboxylation required for forming phosphoenolpyruvate?

Answer 24

These steps reduce the energy required for the reaction, making it less endergonic and requiring only 1 molecule of ATP per pyruvate.

Question 25

Where is glucose finally synthesised during gluconeogenesis?

Answer 25

In the endoplasmic reticulum of liver cells by the enzyme glucose 6-phosphatase.

Question 26

Define the term metabolic pathway. What are the requirements of all metabolic pathways? ## Footnote Lecture 1

Answer 26

Series of enzyme-catalysed reactions where each reaction is specific and the overall set of reactions is energetically favourable.

Question 27

What is the reduced form of NAD+, and what does it carry? ## Footnote Lecture 1

Answer 27

NADH, which carries 1 proton and 2 electrons.

Question 28

What is the storage form of glucose in plants? ## Footnote Lecture 2

Answer 28

Starch

Question 29

Would you expect glycolysis to be activated or inhibited in muscle cells when energy charge is low?

Answer 29

Activated

Question 30

Where do the following reactions take place? Penotse Phosphate Pathway, Glycolysis, Citric Acid Cycle, Gluconeogenesis, Pyrruvate converted to acetyl CoA.

Answer 30

Glycolysis: Cytoplasm, Pentose Phosphate Pathway: Cytoplasm, Citric Acid Cycle: Mitochondrial Matrix, Pyruvate to Acetyl CoA: Mitochondrial Matrix, Gluconeogenesis: mainly in cytoplasm but some steps in mitochondrial matrix.

Question 31

Which enzymes regulate fructose 2,6-bisphosphate levels?

Answer 31

Phosphofructokinase 2 (PFK2) phosphorylates fructose 6-phosphate to form fructose 2,6-bisphosphate, while fructose bisphosphatase 2 (FBPase 2) reverses this reaction.

Question 32

What enzyme incorporates glucose into the growing glycogen chain?

Answer 32

Glycogen synthase (GS) adds glucose molecules via α-1,4 linkages but can only add to an existing glucose chain.

Question 33

How is gluconeogenesis regulated in muscles?

Answer 33

It is activated when energy levels (ATP) are high.

Question 34

Define homopolysaccharides and heteropolysaccharides. ## Footnote Lecture 2

Answer 34

Homopolysaccharides (same monomer units), Heteropolysaccharides (different monomer units).

Question 35

How is metabolism regulated in the short term and long term? ## Footnote Lecture 1

Answer 35

Short-term regulation: Allosteric control – small molecules activate or inhibit enzymes. Covalent modification – mainly reversible phosphorylation. Long-term regulation: Changes in enzyme levels via gene expression (transcription/translation) or protein degradation (proteolysis).

Question 36

What is the function of glycogenin in glycogen? ## Footnote Lecture 2

Answer 36

Glycogenin is a protein at the core of glycogen that serves as a primer for glycogen synthesis.

Question 37

What is the Cori cycle?

Answer 37

A process where lactate formed during anaerobic glycolysis in muscles is recycled into glucose in the liver.

Question 38

What is the role of coenzyme A (CoA) in metabolism? ## Footnote Lecture 1

Answer 38

Coenzyme A is an activated carrier of acyl groups, using its terminal sulfhydryl group to form thioester bonds with acyl groups.

Question 39

Describe the process of galactose entering the glycolysis pathway.

Answer 39

Galactose is phosphorylated to form galactose 1-phosphate. Galactose 1-phosphate reacts with UDP-glucose to form glucose 1-phosphate and UDP-galactose. Glucose 1-phosphate is converted into glucose 6-phosphate in an energetically neutral reaction by phosphoglucomutase. Glucose 6-phosphate is an intermediate of the glycolysis pathway.

Question 40

How does insulin regulate glycogen metabolism?

Answer 40

Insulin activates glycogen synthase and inhibits glycogen phosphorylase, promoting glycogen synthesis when glucose levels are high.

Question 41

What is the sequence of reactions leading to glucose incorporation into glycogen?

Answer 41

Glucose 6-phosphate → Glucose 1-phosphate → UDP-glucose → Glycogen chain (via glycogen synthase).

Question 42

Why is fermentation under anaerobic conditions important?

Answer 42

It allows respiration to continue when oxygen is scarce by regenerating NAD+, but it is a very inefficient process, conserving only 100kJmol-1 (approximately 3.5% of the available energy).

Question 43

What are examples of structural polysaccharides, and their functions? ## Footnote Lecture 2

Answer 43

Cellulose: Linear beta-1,4 glucose polymer (provides rigidity in plants; indigestible by humans), Chitin: N-acetylglucosamine polymer found in exoskeletons.

Question 44

What happens when glycogen phosphorylase encounters a branch point?

Answer 44

Transferase moves monomers from the branch to the linear chain, and then α-1,6 glucosidase hydrolyses the α-1,6 bond to complete debranching.

Question 45

Why is oxaloacetate converted to malate in the first step of gluconeogenesis that forms oxaloacetate?

Answer 45

To be transported into the cytoplasm via the malate shuttle, there is no oxaloacetate transporter in the inner mitochondrial membrane.

Question 46

Describe the process of frutose from the liver entering the glycolysis pathway.

Answer 46

Fructose is phosphorylated to form fructose 1-phosphate. Fructose 1-phosphate is broken down into glyceraldehyde and dihydroxyacetone phosphate. Glyceraldehyde is phosphorylated to form glyceraldehyde 3-phosphate. Both glyceraldehyde 3-phosphate and dihydroxyacetone phosphate are intermediates in the glycolysis pathway.

Question 47

How do high levels of ATP inhibit the glycolysis pathway?

Answer 47

ATP binds to an allosteric site on phosphofructokinase, preventing it from catalysing the phosphorylation of Fructose 6-Phosphate to Fructose 1,6-Phosphate.

Question 48

How do adrenaline and glucagon regulate glycogen metabolism?

Answer 48

Adrenaline and glucagon inhibit glycogen synthase and activate glycogen phosphorylase, promoting glycogen breakdown in response to low glucose or stress.

Question 49

Which step in glycolysis is the main regulatory step?

Answer 49

Step 3: Phosphorylation of Fructose 6-Phosphate to Fructose 1,6-Phosphate by the enzyme Phosphofructokinase.

Question 50

When the equilbrium constant (Keq) > 1, is the reaction favourable or unfavourable for the products? ## Footnote Lecture 1

Answer 50

Favourable - at equilibrium there is a higher [products].

Question 51

Are carbohydrates more commonly found in the D-isomer or L-isomer? ## Footnote Lecture 2

Answer 51

D-isomer

Question 52

How much glucose does the adult body require daily?

Answer 52

Roughly 160g per day, with approximately 120g used by the brain.

Question 53

How is glycogen metabolism regulated in the liver by allosteric control?

Answer 53

Glucose and glucose 6-phosphate activate glycogen synthase and inhibit glycogen phosphorylase, promoting glycogen synthesis when glucose levels are high.

Question 54

What are biosynthetic precursors, and how do they regulate gluconeogenesis?

Answer 54

Citrate, acetyl CoA, and adenine are biosynthetic precursors. High levels of these molecules activate gluconeogenesis and inhibit glycolysis.

Question 55

What is the energy cost of gluconeogenesis per molecule of glucose?

Answer 55

6 NTP molecules (4 ATP and 2 GTP) are required per molecule of glucose formed.

Question 56

What enzyme breaks down lactose, and into which components?

Answer 56

Lactase breaks down lactose into galactose and glucose.

Question 57

What is the role of glycogenin in glycogen synthesis?

Answer 57

Glycogenin is a self-glycosylating protein that acts as a primer for glycogen synthase to initiate glycogen synthesis. It is important because Glycogen Synthase can only add to an existing glucose chain.

Question 58

What is UDP-glucose, and why is it significant? ## Footnote Lecture 2

Answer 58

UDP-glucose is an activated glucose carrier involved in glycogen synthesis and galactose metabolism.

Question 59

What is the activated form of glucose used in glycogen synthesis and how is it formed?

Answer 59

UDP-glucose, formed from glucose 1-phosphate and UTP.

Question 60

How is glycogen metabolism regulated in muscle by allosteric control?

Answer 60

Glycogen phosphorylase is activated by Ca²⁺ (muscle contraction) and AMP (low energy) and inhibited by ATP.

Question 61

The enzyme phosphoglucomutase can shuffle phosphate groups between the first and sixth carbon in glucose. Which pathways of carbohydrate metabolism from the following list require this action? Glycolysis, Gluconeogenesis, Pentose phosphate pathway, Glycogen synthesis, Glycogen breakdown, Catabolism of fructose, Catabolism of galactose, Catabolism of lactose.

Answer 61

Glycogen synthesis: G6P is converted to G1P by phosphoglucomutase, which is then used to synthesise glycogen. Glycogen breakdown: glycogen is converted to G1P, which is then converted to G6P by phosphoglucomutase. Catabolism of galactose: Galactose is converted to G1P as an intermediate, which is then converted to G6P by phosphoglucomutase for entry into glycolysis or other pathways. Catabolism of lactose: Lactose is broken down into glucose and galactose. The galactose enters the same pathway as above, requiring phosphoglucomutase to convert G1P to G6P.

Question 62

Give examples of disaccharides and their component sugars. ## Footnote Lecture 2: Carbohydrate Structure

Answer 62

Sucrose: a-Glucose + a-Fructose (a-1,2 linkage), Lactose: a-Galactose + a-Glucose (a-1,4 linkage), Maltose: a-Glucose + a-Glucose (a-1,4 linkage).