Metabolism I

Question 1

What are catabolic processes, give an example.

Answer 1

Catabolic processes break down proteins, carbs and fats into smaller, less complex molecules to yield ATP. DG is negative. Energy yielding process. Examples include Glycolysis (6C–>3C), amino acid degradation and fatty acid degradation.

Question 2

What are anabolic processes, give an example.

Answer 2

Anabolic processes form more complex molecules from smaller building blocks, requiring ATP (energy-requiring). DG is positive. Examples include Gluconeogenesis (3C–>6C), amino acid synthesis and fatty acid synthesis.

Question 3

What is Biological Oxidation?

Answer 3

Loss of hydrogen atoms/ electrons, increasing potential energy of molecule.

Question 4

What do coenzymes do?

Answer 4

Small no-protein substance acting to initiate or aid the function of an enzyme, acting as a transfer site for a enzyme. Coenzymes are chemically different to cofactors.

Question 5

Name 3 cellular coenzymes that transport H+

Answer 5

NAD (nicotinamide adenine dinucleotide)
NADP (nicotinamide adenine dinucleotide phosphate)
FAD (flavin adenine dinucleotide)

Question 6

What is Biological reduction?

Answer 6

Addition of hydrogen atoms/electrons, increasing potential energy of molecule.

Question 7

What is the Fischer Projection?

Answer 7

2D representation of 3D organic molecules proposed for the depiction of carbohydrates, created by Emil Fischer in 1891.
Key;
1. Chiral carbon is vertical
2. Horizontal bonds project towards viewer, Vertical project away.
3. C1 is always at the top.
4. Cannot be rotated, an enantiomer is produced.
5. D-notation, right side
6. L-notation, left side

Question 8

What is a ‘Pyran’?

Answer 8

A 6 membered (5C + 1O) cyclic sugar.

Question 9

What is a ‘Furan’?

Answer 9

A 5 membered (4C + 1O) cyclic sugar.

Question 10

Describe catabolism of glucose.

Answer 10

1. Glucose stored as a polysaccharide, Glycogen, through the processes of Glycogenesis. (occurs in muscle).
2. Glycogen converted back to Glucose by Glycogenolysis.
3. Intermediated of glucose catabolism are used in amino acid synthesis
4. Catabolised amino acids are used in glucose synthesis when supply is low.

Question 11

Describe the three anabolic processes forming glucose.

Answer 11

1. Gluconeogenesis, pyruvate to glucose.
2. Cori cycle, during low O2, lactate released from skeletal muscle after exercise, travels to liver, converted to pyruvate by lactate dehydrogenase, pyruvate converted to glucose by gluconeogenesis.
3. Glucose-alanine cycle, in large amounts of lactate, lactate converted to alanine through transamination reaction with glutamate, alanine travels to liver, converted to pyruvate, back to glucose. (processes lactate, transports amino nitrogen and a-keto acids for amino acid synthesis)

Question 12

Name a non-essential amino acid.

Answer 12

Alanine, aspartate, asparagine, glutamate, glutamine, glycine, proline, serine, cysteine, tyrosine.

Question 13

Name an essential amino acid.

Answer 13

Histidine, isoleucine, leucine, lysine, methionine, phenylalanine.

Question 14

How are amino acids used for protein synthesis obtained?

Answer 14

Degradation of other proteins.

Question 15

What are proteins destined for catabolism labelled with?

Answer 15

Ubiquitin

Question 16

What are polyubiquitinated proteins and what are they degraded by?

Answer 16

Polyubiquitin proteins are short-lived proteins marked with ubiquitin, destined for degradation, or often cell cycle regulatory proteins who’s degradation is necessary for controlled cell division. Misfolded proteins in the ER also become polyubiquitinated proteins. These are broken down by proteasome.

Question 17

What are proteasomes?

Answer 17

Located in the cytoplasm and nucleus, proteasomes depredate polyubiquitinated proteins by proteolysis (breaks peptide bonds). Proteases aid the reaction.

Question 18

Name the two anabolistic processes of amino acids.

Answer 18

Protein synthesis and Biosynthesis of nitrogen compounds (Porphyrins, Creatine, Hormones, Nucleotides)

Question 19

What non-essential and essential amino acids does Oxaloacetate produce?

Answer 19

Oxaloacetate produces aspartate (NE) forming= Asparagine (NE), Methionine (E) , Threonine (E) = isoleucine (S), Lysine (E).

Question 20

What non-essential and essential amino acids does Pyruvate produce?

Answer 20

Alanine (NE), Valine (E), Leucine (E)

Question 21

What essential amino acids does Ribose 5-phosphate produce?

Answer 21

Histidine (E)

Question 22

What non-essential amino acids does 3-phosphoglycerate produce?

Answer 22

Serine (NE), Cystenine (NE), Glycine (NE)

Question 23

What non-essential and essential amino acids does a-Ketoglutarate produce?

Answer 23

Glutamate (NE), Glutamine (NE), Proline (NE), Arginine (E)

Question 24

What non-essential and essential amino acids does phosphoenolpyruvate and Erthyrose 4-phosphate produce?

Answer 24

Phenylalanine (E)= Tryrosine (NE), Tyrosine (NE), Tryptophan (E)

Question 25

How are dietary lipids transported in blood?

Answer 25

Lipoprotein spheres.

Question 26

What are triglycerides catabolised to and by what enzyme?

Answer 26

1 Glycerol and 3 fatty acids molecules by lipoprotein lipase.

Question 27

How do fatty acids form Acetyl CoA?

Answer 27

Fatty acids undergo B-oxidation to form Acetyl CoA in peripheral tissues, where it will enter the Krebs cycle to release ATP.

Question 28

What is glycerol used for in Glycolysis?

Answer 28

Glycerol is modified (phosphorylated) in the liver to form glycerol 3-phosphate, used to produce DHAP (dihydroxyacetone phosphate) through a process called Glyceroneogenesis, therefore enters glycolysis.

Question 29

Where is anabolism of triglycerides facillitated?

Answer 29

Small intestine, Liver and Adipocytes (where DHAP is used).

Question 30

What is the name given to a pathway that is anabolic and catabolic?

Answer 30

Amphibolic.

Question 31

When only can a spontaneous reaction occur?

Answer 31

When DG is negative.

Question 32

Describe each step of stage 1 of Glycolysis.

Answer 32

1. Glucose is actively converted to glucose 6-phosphate via the enzyme hexokinase, requiring 1 ATP molecule (producing ADP)
2. Glucose 6-phosphate is reversibly converted to Fructose 6-phosphate by the enzyme phosphoglucose isomerase.
3. Fructose 6-phosphate is actively converted to Fructose 1,6-bisphosphate by the enzyme phosphofructokinase, requiring 1 ATP molecule (producing ADP)

Question 33

Describe stage 2 of Glycolysis.

Answer 33

1. Fructose 1,6-bisphosphate (6C) is split to Dihydroxyacetone phosphate and Glyceraldehyde 3-phosphate by the enzyme Aldolase.
   * *key feature- DHAP can isomerase into GAP, giving 2 GAP from every Fructose 1,6-bisphosphate

Question 34

Describe each step of stage 3 of Glycolysis.

Answer 34

1. Glyceraldehyde 3-phosphate is reversibly converted to 1,3-Bisphosphoglycerate by the enzyme glyceraldehyde 3-phosphate dehydrogenase, requiring the cofacter NAD being reduced to NADH (gain of hydrogen).
2. 1,3-Bisphosphoglycerate is reversibly coverted to 3-Phosphoglycerate by the enzyme phosphoglycerate kinase, producing ATP.
3. 3-Phosphoglycerate is reversibly converted to 2-Phosphiglycerate by the enzyme phosphoglycerate mutase.
4. 2-Phosphoglycerate is reversibly converted to phosphoenolpyruvate by the enzyme Enolase, producing H2O.
5. Phosphoenolpyrivate is converted to pyruvate by the enzyme pyruvate kinase producing ATP.

Question 35

Name key points of Glycolysis.

Answer 35

1. Glucose is converted to pyruvate
2. For every molecule of Glucose, 2 Pyruvate molecules are yeilded.
3. Net yeild: 2 Pyruvate, 2 ATP, 2NADH, 2H+, 2H2O.

Question 36

What is Gluconeogensis and what steps prevent it being a direct reverse of Glycolysis?

Answer 36

Gluconeogenesis occurs in the liver and is the formation of glucose from non-glucose precursors when glycogen is not avaliable

1. first step irreversible (glucose –> glucose 6-phosphate)
2. third step irreversible (fructose 6-phosphate –> fructose 1,6-bisphosphate)
3. last step irreversible (phosphoenolpyruvate –> pyruvate)

Question 37

How is the first step of Gluconeogenesis facilitated? (how is irreversible step overcome?)

Answer 37

Pyruvate is converted to oxaloacetate by the enzyme pyruvate carboxylase (found in mitochondria), requiring ATP to be hydrolyzed to ADP and CO2. Oxaloacetate is then converted to the required phosphoenolpyrivate by the enzyme phosphoenolpyrivate carbocykinase (PEPCK located in cytosol) requiring GTP expelling CO2 to produce the 3C molecule.

Question 38

How is the 6th step of Gluconeogensis facilitated? (how is the irreversible step overcome?)

Answer 38

Fructose 1,6-bisphosphate is converted to fructose 6-phosphate by the enzyme fructose bisphosphatase releasing a phosphate group.

Question 39

How is the 9th step of Gluconeogensis facilitated? (how is the irreversible step overcome?)

Answer 39

Glucose 6-phosphate is converted to glucose by the enzyme glucose 6-phosphatase releasing a phosphate group.

Question 40

Name the four glycogen synthesis enzymes.

Answer 40

1. UDP
2. Tyrosine glucosyltransferase
3. Glycogen synthase
4. Amylo-(1,4–>1,6)-transglycosylase.

Question 41

What is the first step of Glycogen synthesis?

Answer 41

Glucose is irreversibly converted to glucose 6-phosphate by hexokinase/ glucokinase (liver), and thenn glucose 6-phosphate is converted to glucose 1-phosphate by the enzyme phosphoglucomutase.

Question 42

What is the second step of Glycogen synthesis?

Answer 42

Glucose 1-phosphate attaches onto UDP forming UDP-glucose releasing PPi (2Pi) by the enzyme UDP-glucose pyrophosphorylase.

Question 43

What is the third final step of Glycogen synthesis?

Answer 43

UDP-glucose attaches onto glycogen chain by the enzyme glycogen synthase and releases UDP back, and extending thr glycogen chain (Glc)n+1

Question 44

Name the three glycogen degrading enzymes.

Answer 44

1. Glycogen phosphorylase
2. Glycogen debranching enzyme (transferase)
3. Phosphoglucomutase

Question 45

How is glycogen metabolism regulated?

Answer 45

Glycogen phosphorylase and glycogen synthase are regulated by enzyme phosphorylation and the hormones insulin, glucagon or adrenaline. activation of protein kinases A in the liver is the signal to stop glycogen synthesis and trigger degradation.