Lecture 28 - Amino acids as fuel molecules

Question 1

Amino acids as a fuel molecule process

Answer 1

• Protein
• Amino acids as a fuel molecule

Question 2

Protein digestion

Answer 2

• Involves hydrolysis of peptide bonds
• Performed by several different proteases/peptidases

Question 3

Endopeptidases

Answer 3

• Attack peptide bonds within the protein polymer
• each round produces smaller peptides
  Pepsin, trypsin, chymotrypsin

Question 4

Exopeptidases

Answer 4

• Attack the last peptide bond near the end of protein polymer
• Releases amino acids, di- and tri-

Question 5

What are zymogens, and why are they important in protein digestion

Answer 5

Zymogens are inactive forms of proteases, preventing premature activation. They are activated in the G.I by the cleavage of peptides from their structure

Question 6

What is role of pepsinogen in protein digestion

Answer 6

Pepsinogen is a zymogen activated by low pH in the stomach to become pepsin, which begins in the breakdown of proteins by hydrolysing peptide bonds

Question 7

How is trypsinogen activated, and what is its function

Answer 7

Trypsinogen is activated by membrane - bound enterokinase to become trypsin. Trypsin activates other proteases and cleaves peptide bonds near the carboxyl terminal of amino acids.

Question 8

Describe the role of carboxypeptidases and amino peptidases in protein digestion

Answer 8

Carboxypeptidases and aminopeptidases are exopeptidases that release individual amino acids by cleaving near the carboy-terminal and amino-terminal ends of peptides, respectively

Question 9

How are peptides absorbed in the S.I

Answer 9

Absorption of tri and di peptides in the S.I by co-transport with H+ ion via a membrane transporter. Absorbed di- and tri peptides are further digested into individual amino acids by cytoplasmic peptidases.

Question 10

What are the two types of reactions that deaminate amino acids

Answer 10

Amino acids can be deaminated by:
1. Oxidative deamination where amino groups are released as free ammonia
2. Transamination: where amino groups are trasnferred to keto acids

Question 11

How are amino acids absorbed in the S.I

Answer 11

Amino acids pass through a facilitative transporter into the interstitial fluid and then into the blood. Uptake into epithelial cells by a transporter, Na+ dependent and animo acid moving to a high concentration linked with Na+ moving to a lower concentration.

Question 12

What is the role of aminotransferases in metabolism

Answer 12

Aminotransferases transfer amino groups from amino acids to keto acid, producing new amino acids and keto acids, which can enter metabolic pathway

Question 13

How is excess nitrogen removed from body

Answer 13

Excess nitrogen is removed by converting it into ammonia via deamination, which is then processed into urea in the liver and excreted by the kidneys

Question 14

what is the significance of pyridoxal phosphate (PLP) in transamination

Answer 14

PLP derived from Vitamin B6 is a coenzyme that carries the amino group during transamination reactions, facilitating the transfer between amino acids and keto acids.

Question 15

Two forms of PLP

Answer 15

• Pyridoxal phosphate (no amino group)
• Pyridoxamine phosphate (with amino group)

Question 16

Transamination reactions involve two steps

Answer 16

First step:
Amino group is transferred from the amino acid to the pyridoxal phosphate (become pyridoxamine phosphate)
Second step:
Amino group is transferred pyridoxamine phosphate (becomes pyridoxal phosphate) to the keto acid

Question 17

What happens to keto acids generated from amino acid deamination

Answer 17

Keto acids can enter metabolic pathways like the citric acid cycle, where they are further oxidised for energy or used to synthesise glucose or fatty acids, depending on the bodys need. They directly enter pathways, some keto acids require modification first.

Question 18

Why is ammonia toxic and how is it safely removed

Answer 18

Ammonia is toxic because it disrupts cellular processes. It is converted into urea in the liver via the urea cycle, which is less toxic and easily excreted by the kidneys

Question 19

What are some common amino acid/keto acid pairs in metabolism

Answer 19

• Glutamate and a-ketoglutarate
• Aspartate and oxaloacetate
• Alanin and pyruvate