Amino acid catabolism

Question 1

What additional transport proteins are needed for mitochondrial uptake of L-ornithine?

Answer 1

NH4+, HCO3-, L-citrulline

These transport proteins facilitate the transport of these substances into and out of the mitochondria.

Question 2

What happens to proteins tagged for degradation?

Answer 2

They are recognised by specific proteases and degraded, releasing ubiquitin for reuse.

Question 3

What is the role of E3 in the ubiquitin pathway?

Answer 3

Catalyses the transfer of ubiquitin from E2-ubiquitin to the target protein.

Question 4

What are destabilising residues in proteins?

Answer 4

Phenylalanine, tryptophan, aspartate, arginine, lysine.

Question 5

What are stabilising residues in proteins?

Answer 5

Methionine, glycine, alanine, serine.

Question 6

What is the substrate for E3 in the ubiquitin pathway?

Answer 6

E2-ubiquitin combination.

Question 7

What is the function of the PEST region in proteins?

Answer 7

Recognised by proteolytic enzymes for degradation.

Question 8

What is the primary process for protein breakdown?

Answer 8

Proteolysis.

Question 9

What are the two types of peptidases found in the gut?

Answer 9

Endopeptidases, exopeptidases.

Question 10

What are the key ‘thematic reactions’ in amino acid metabolism?

Answer 10

Transamination, oxidative deamination.

Question 11

What is the main goal of catabolic transamination?

Answer 11

To channel amino nitrogen into a small number of amino acids.

Question 12

How many essential amino acids are there?

Answer 12

Nine.

Question 13

What is the fate of pyruvate during amino acid breakdown?

Answer 13

It can form glucose via gluconeogenesis.

Question 14

What are glucogenic amino acids?

Answer 14

Amino acids that can supply gluconeogenesis.

Question 15

What are ketogenic amino acids?

Answer 15

Amino acids that can contribute to fatty acid or ketone body synthesis.

Question 16

What is the role of the Urea Cycle?

Answer 16

Converts toxic ammonia to urea in the liver.

Question 17

What are the two processes involved in protein degradation?

Answer 17

Endocytosis, autophagy.

Question 18

What is the energy cost to form one molecule of urea?

Answer 18

4 high energy phosphates (3 ATP + 1 PPi).

Question 19

What types of proteins are degraded by the lysosomal pathway?

Answer 19

Long-lived proteins.

Question 20

What is oxidative deamination?

Answer 20

The release of the amino group from glutamate as ammonia.

Question 21

What is the significance of alanine in amino acid transport?

Answer 21

It transports ammonia from muscle to liver.

Question 22

What is the function of glutamine synthase?

Answer 22

Traps ammonia by forming glutamine.

Question 23

What are the five enzymes involved in the Urea Cycle?

Answer 23

Argininosuccinate synthase, arginase, argininosuccinate lyase, ornithine transcarbamoylase, carbamoylphosphate synthase.

Question 24

What is the main source of amino acids for catabolism?

Answer 24

Dietary proteins, storage proteins, metabolic turnover of endogenous proteins.

Question 25

What are aminotransferases also known as?

Answer 25

Transaminases.

Question 26

What is the primary function of aminotransferases?

Answer 26

Catalyse the transfer of the amino group from an amino acid to a keto acid.

Question 27

What is the relationship between α-oxoglutarate and glutamate?

Answer 27

α-oxoglutarate is converted to glutamate via transamination.

Question 28

What is the breakdown product of dietary proteins?

Answer 28

Amino acids and small peptides.

Question 29

What happens to ammonia in terrestrial animals?

Answer 29

It is converted to urea, a non-toxic form.

Question 30

What is the difference between essential and non-essential amino acids?

Answer 30

Essential cannot be synthesized by the body; non-essential can.

Question 31

What is the significance of histidine and arginine during cell growth?

Answer 31

They are essential during periods of rapid cell growth, such as childhood and illness.

Question 32

What is the role of the inner mitochondrial membrane?

Answer 32

It is an effective barrier to charged, polar, and large molecules.

Question 33

What are ammonotelic organisms?

Answer 33

Aquatic organisms that excrete ammonia as the major end-product of nitrogen metabolism.

Question 34

Fill in the blank: The Urea Cycle is a unique function of the _____ in mammals.

Answer 34

liver.

Question 35

What is the main aim of catabolic transamination?

Answer 35

To channel the amino nitrogen into a small number of amino acids, including glutamate

Question 36

Where is urea produced in mammals?

Answer 36

In the liver through the action of the Urea Cycle

Question 37

Who originally described the Urea Cycle?

Answer 37

Krebs and Henseleit

Question 38

What are the two major routes of deamination?

Answer 38

* Transamination * Oxidative deamination

Question 39

What do endopeptidases do?

Answer 39

Hydrolyse internal peptide bonds

Question 40

What do exopeptidases do?

Answer 40

Remove successive amino acids from the end of the peptides

Question 41

What are the two types of exopeptidases?

Answer 41

* Carboxypeptidases * Aminopeptidases

Question 42

Does transamination result in net deamination?

Answer 42

No

Question 43

What is the reason transamination does not result in net deamination?

Answer 43

One amino acid is replaced by another amino acid

Question 44

What must be considered in human metabolism regarding amino acids?

Answer 44

The breakdown of all amino acids, not just the non-essential ones

Question 45

What begins the degradation of most amino acids?

Answer 45

The removal of the α-amino nitrogen (–NH2 or –NH3+)

Question 46

Each amino acid is broken down by a specific pathway that converges to give common metabolic intermediates. Name some of these intermediates.

Answer 46

* Pyruvate * Oxaloacetate * α-Oxoglutarate * Acetyl CoA * Succinyl CoA