Protein Metabolism

Question 1

What are the three main functions of proteins

Answer 1

Enzymes, hormones and structural

Question 2

How many essential AA are there

Answer 2

9

Question 3

How many amino acids are not essential (can be made from other AA in the diet)

Answer 3

11

Question 4

What are complete proteins

Answer 4

Proteins that contain 9 essential AA e.g. whey

Question 5

What are the 9 essential AA

Answer 5

Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine

Question 6

What is the basic structure of an AA

Answer 6

Central carbon atom (alpha carbon [Cα]) linked to:
Amino group (positive charge)
Carboxylic acid group (negative charge)
Hydrogen
Distinctive side chain (R)

Question 8

Where does Branched Chain AA metabolism occur

Answer 8

skeletal muscle

Question 9

What are the three Branched Chain Amino Acids (BCAA)

Answer 9

Leucine, isoleucine, valine

Question 10

Which amino acid can stimulate synthesis of new muscle proteins

Answer 10

Leucine

Question 11

Which organ lacks the first two enzymes in the pathway that breaks down BCAAs and hence cannot metabolise BCAAs

Answer 11

Liver

Question 12

Where are amino acids primarily metabolised

Answer 12

Liver and skeletal muscle

Question 13

Can amino acids be stored in the body

Answer 13

No, freely circulate in the amino acid pool in the blood, can be incorporated into tissue/ used in the body or excreted

Question 14

What is the rate of amino acid turnover

Answer 14

300g/day

Question 15

What is the free amino acid pool

Answer 15

The free amino acid pool represents the AAs in the circulation and extracellular fluids

Question 16

What is the free amino acids pool composed of

Answer 16

Comprised of: AA from food, AA degraded in tissues (all – not just muscle), AA metabolized in liver in a constant flux throughout the day

Question 17

How much of protein turnover is directed towards muscle (muscle protein turnover)

Answer 17

20-30% towards muscle (1-2% per day)

Question 18

What is transanimation

Answer 18

The process by which other AAs are formed by transferring an α-amino group (NH3) to a keto acid (an amino acid without its amino group) to form a new AA

Question 19

What are the enzymes that catalyse transanimation reactions

Answer 19

transaminases and aminotranferases

Question 20

Are the transanimation reactions irreversible or reversible

Answer 20

Reversible

Question 21

What happens to the amino acid that loses its amino group in transanimation

Answer 21

frees up the keto acids (carbon backbones) to have roles in other metabolic systems, as the nitrogen in the amino group cannot be used for energy production

Question 22

Describe the transanimation process

Answer 22

An amino acid transfers is NH3 group (α amino group) to an alpha-keto acid.
This reaction is catalysed by an amino transferase enzyme.
This leads to the formation of a new amino acid.
When the amino group is transferred, a carbon skeleton is left and this forms a new keto acid that can be used in the TCA cycle.

Question 23

Where does transanimation occur

Answer 23

Both cytosol and mitochondria

Question 24

Describe the specificity of enzymes involved in transanimation

Answer 24

These enzymes are specific to each group – e.g., alanine aminotranferase

Question 25

What else can transamination be used for apart from energy production

Answer 25

Produce ketone bodies

Question 26

Which two amino acids are ketogenic

Answer 26

Leucine and lysine

Question 27

What products can be formed in the process of transanimation

Answer 27

Pyruvate, acetyl-CoA, fumarate, succincyl CoA, alpha ketoglutarate, Oxaloacetate, acetoacetyl CoA

Question 28

What is the glucose alanine cycle

Answer 28

Converting alanine into glucose for energy

Question 29

Why is the glucose alanine cycle useful

Answer 29

The glucose-alanine cycle allows us to form glucose from proteins in the muscle. So when we are starving, fasting or during very long duration exercise and when energy stores are running low we can use this cycle to form glucose for energy.

Question 30

Describe the glucose alanine cycle

Answer 30

Glutamate and pyruvate can react together and form the AA, alanine (transamination) and ketone acid alphaketogluterate in muscle This is catalysed by the enzyme alanine transferase Alanine can then be shuttled via the blood stream to the liver In the liver it can be converted back to pyruvate in the same reaction, just in the reverse manner. Pyruvate can then be used to produce glucose in the liver (gluconeogenesis) This glucose can be shunted back across to the muscles to be used to fuel energy production

Question 31

What is oxidative deaminatiom

Answer 31

Oxidative deamination is when the amino group is taken from the newly formed AA e.g., glutamate This leaves a keto acid e.g., alpha keto-glutarate that can be used in the TCA cycle (or for further transamination)

Question 32

What enzyme catalyses oxidative deamination

Answer 32

The enzyme that catalyses this is known as glutamate dehydrogenase (specific to glutamate)

Question 33

When is ketogluterate production upregulated (oxidative deamination)

Answer 33

When ADP is high (low energy status)

Question 34

What are the products of oxidative deamination

Answer 34

Ketogluterate and ammonia

Question 35

When does oxidative deamination occur and why

Answer 35

This occurs when energy is low – so very hard long exercise or when starved. We are essentially oxidizing our proteins to produce energy.

Question 36

What is ketogluterate

Answer 36

carbon skeleton, which can go on to be used in the TCA cycle – or be used for more transanimation

Question 38

What is the urea cycle

Answer 38

Ammonia is quickly converted to urea in the liver and the excreted via the kidneys- the removal of urea

Question 39

How many steps is the urea cycle

Answer 39

5 steps

Question 40

What is the starting product of the urea cycle

Answer 40

Ammonia

Question 41

Why do we need the urea cycle

Answer 41

Any AAs that the body does not use are removed via the urea cycle in the liver Degrading AAs leads to an accumulation of a highly toxic product, ammonia.

Question 42

How many g of urea will a normal individual excrete per day

Answer 42

35-55g