TOPIC 10 PROTEIN METABOLISM OBJs

Question 1

basic structure of a protein

Answer 1

Question 2

• Protein degradation occurs in two places:

Answer 2

1. Stomach – starts in stomach and continues to the;
2. Small intestine

Question 3

_______ enzymes are responsible for degrading proteins

Answer 3

Proteolytic

Question 4

• Two main types of proteolytic enzymes:

Answer 4

1. Endopeptidases
2. Exopeptidases - Break terminal peptide bonds, either at amino terminal end (aminopeptidase) or carboxy (carboxypeptidase) terminal end

Question 5

1. Endopeptidases -

Answer 5

Break bonds from interior of chain

Question 6

Exopeptidases -

Answer 6

Break terminal peptide bonds, either at amino terminal end (aminopeptidase) or carboxy (carboxypeptidase) terminal end

Question 7

Stomach

Answer 7

• Digestion in the stomach is facilitated by gastric juice which contains pepsinogen and hydrochloric acid (HCl)
• Pepsinogen is a zymogen (or proenzyme) = an inactive form of an enzyme
• When activated it becomes pepsin, which is an endopeptidase which cleaves on the COOH side of aromatic or bulky aliphatic groups

Question 8

• Digestion in the stomach is limited by

Answer 8

1. Short contact time
2. Specificity of pepsin

Question 9

what passes into small intestine

Answer 9

chyme

Question 10

stomach digestion results in

Answer 10

polypeptide chains and digested mix (chyme)

Question 11

• Chyme stimulates the release of two polypeptide hormones from the small intestine:

Answer 11

1. Secretin – release stimulated by low pH
2. Cholecystokinin – release stimulated by polypeptides

Question 12

1. Secretin

Answer 12

– release stimulated by low pH

Question 13

2. Cholecystokinin

Answer 13

– release stimulated by polypeptides

Question 14

Both secretin and cholycystokin are

Answer 14

hormones

Question 15

Both secretin and cholycystokin cause the release of

Answer 15

enteropeptidase

Question 16

secretin also causes releases of

Answer 16

pancreatioc zygomens

Question 17

Pancreatic zymogens:

Answer 17

1. Trypsinogen
2. Chymotrypsinogen
3. Proelastase
4. Pro-carboxypeptidase
5. 5. Pro-carboxypeptidase B

Question 18

_____________ is the master switch that unleashes a cascade of proteolytic activity in the small intestine

Answer 18

Enteropeptidase

Question 19

end result of digestion in small intestine

Answer 19

polypeptide chains are broken down into much smaller (oligopeptide) chains and free amino acids

Question 20

• Mucosal cells also have two exopeptidases to further digest oligopeptides, which are:

Answer 20

1. Aminopeptidase: Cleaves amino acids from the amino terminus
2. Dipeptidase: Cleaves aromatic dipeptide pairs

Question 21

• Inside epithelial cells, dipeptides are hydrolysed into ________
• Free amino acids are then released into the blood stream, and transported to the ____ by the portal vein

Answer 21

amino acids

liver

Question 22

how many storage systems exist for amino acids

Answer 22

none

Question 23

excess amino are utilised in

Answer 23

metabolism

Question 24

3 roles of amino acids in metabolism:

Answer 24

1. Involved in synthesis of proteins
2. Metabolized to generate energy
3. Converted to small active molecules

Question 25

decarboxylation

Answer 25

amino acid is converted to small active molecules (active amine = become neurotrans or hormones)

Question 26

in deamination and transaminaiton

Answer 26

amino acids are metabolized to generate energy

Question 27

what are the two types of deamination

Answer 27

1. Oxidative deamination – (redox reaction)
   o Requires either NAD+ or FAD
2. Non-oxidative deamination
   o Does not require NAD+ nor FAD

Question 28

Explain the fate of active amines

Answer 28

hormone or neurotransmitter

Question 29

Describe the fate of the α-keto acid that is produced from either deamination or transamination of an amino acid

Answer 29

• The new a-keto acid is metabolized to generate energy

Question 30

Describe the two categories of transaminase (aminotransferase) enzyme

Answer 30

Non-specific transaminases
- Non-specific in their choice of amino acid
- e.g. glutamate transaminase
- the a-keto acid is metabolized to generate energy

Specific transaminases
- Specific in their choice of amino acid
- e.g. aspartate aminotransferase
- Oxaloacetate is metabolized to generate energy via the TCA cycle

Question 31

Distinguish between ketogenic and glucogenic amino acids

Answer 31

1. Acetyl CoA or acetoacetyl CoA
   o ketogenic amino acids – ketogenesis involved in lipid metabolism
2. Pyruvate or a TCA cycle intermediate
   o glucogenic amino acids – gluconeogenesis

Question 32

12. Explain the role of the Urea cycle and how it links to the TCA cycle

Answer 32

Fate of NH4 +
- Most cells cannot detoxify ammonia
- They produce alanine, glutamate or glutamine
- These amino acids can be transported to the liver or kidney, where the ammonia can be converted to non-toxic urea
- Via the urea cycle
- Urea is then excreted via the urine