Protein breakdown and urea formation

Question 1

What is positive nitrogen balance?

Answer 1

Too much nitrogen input

Question 2

What is negative nitrogen balance?

Answer 2

To little nitrogen input

Question 3

What are the two parts of the metabolism of amino acids?

Answer 3

The carbon skeleton

Nitrogen

Question 4

What happens to amino acids?

Answer 4

They aren’t stored, they’re used or broken down

Question 5

what is the carbon skeleton from the metabolism from amino acids used for?

Answer 5

Used for:
Energy metabolism
Biosynthetic pathways

Question 6

Why has nitrogen got to be removed?

Answer 6

Nitrogen is so toxic so has to be removed safely

Question 7

How is nitrogen removed in mammals?

Answer 7

In mammals, nitrogen converted to the non-toxic neutral compound urea and excreted in the urine

Question 8

What is the enzyme involved in the first step in the transfer of amino acid nitrogen to urea (transamination)?

Answer 8

Enzyme involved in transaminase

Question 9

What happens in transamination?

Answer 9

Nitrogen group of amino acid A transferred to keto acid B give to second amino acid B and Keto acid A

Question 10

Why are keto acid important in transamination?

Answer 10

Keto acids are important metabolic intermediates

Question 11

Examples of transaminase

Answer 11

Alanine and Aspartate

Question 12

What does alanine form when catalysed with alpha ketoglutarate?

Answer 12

Alanine catalyses α-ketoglutarate to give pyruvate and glutamate

Question 13

What does aspartate form when catalysed with alpha ketoglutarate?

Answer 13

Aspartate catalyses α-ketoglutarate to give oxaloacetate and glutamate

Question 14

What are high levels of alanine and aspartate indicative of?

Answer 14

High levels of alanine and aspartate in the blood are indicative of liver damage

Question 15

What does transamination reaction require?

Answer 15

Whole reaction requires pyridoxal phosphate derived from vitamin B6

Question 16

In the second step of transfer of amino acid nitrogen to urea(oxidative deamintation), what is glutamate converted into and by what?

Answer 16

Glutamate can be converted to α-ketoglutarate by glutamate dehydrogenase

Question 17

What type of reaction is the conversion of glutamate to alpha ketoglutarate and what is used?

Answer 17

Fully reversible and can either use NAD or NADP

Question 18

What else is formed in oxidative deamination, other than alpha ketoglutarate?

Answer 18

Ammonia is also formed and is the substrate to the urea cycle

Question 19

How is glutamine synthesised and why is it needed?

Answer 19

○ Elimination of free ammonia:
§ Glutamate gains nitrogen from ammonia
§ ATP and glutamine synthase involved
Glutamine main transporter of nitrogen as it is readily soluble

Question 20

In step 3 of the transfer of amino acid nitrogen to urea(urea formation), what is the means of this step?

Answer 20

Means of excreting nitrogen

Question 21

Where are the enzymes present for urea formation and where are they not?

Answer 21

Present in liver but not muscle

Question 22

Where does urea formation occur?

Answer 22

Takes place in mitochondria and cytoplasm

Question 23

What are the substrates involved in urea formation?

Answer 23

Substrates are bicarbonate, aspartate and ammonium ions(released from either glutamine or glutamate)

Question 24

How many amnio groups are used in the formation of urea and where do they come from?

Answer 24

○ Formation of urea uses two amino groups

One from glutamate and one from aspartate

Question 25

How does the urea cycle interact with the tricarboxylic acid cycle?

Answer 25

* Ammonia first reacts to form carbamoyl phosphate * Combines with ornithine to give citrulline * Citrulline breaks down to give arginine which under the influence of arginase gives urea * Fumarate converted to malate and then oxaloacetate

Question 26

What is formed when oxaloacetate further reacts with an amino acid?

Answer 26

Oxaloacetate Can be used to react with further amino acid to give a keto acid and asparate

Question 27

What is used for energy in muscles during prolonged exercise or starvation?

Answer 27

In prolonged exercise or starvation, branched amino acids are used for energy

Question 28

What enzymes are not present in muscles?

Answer 28

Enzyme of the urea cycle not present

Question 29

What are the two routes of transport to transport nitrogen to liver from muscle?

Answer 29

○ Alanine § Nitrogen transferred to alanine via glutamate and pyruvate ○ Glutamine Glutamate is made into glutamine

Question 30

What are the steps involved in the glucose alanine cycle?

Answer 30

• Break down of protein • Transamination to form alanine • Alanine reacts to form glutamate and pyruvate Glutamate synthesises urea

Question 31

What happens to the carbon skeleton formed in the glucose alanine cycle?

Answer 31

• Carbon skeleton that is formed is converted to pyruvate

Question 32

What is the fate of the carbon skeleton

Answer 32

Will form α-keto acids. Some of the backbone of other amino acids can also feed into different components of the TCA cycle

Question 33

What amino acids are the only ones which cannot inter-convert into alpha keto acids?

Answer 33

lysine and threonine

Question 34

What is normal metabolism after a meal for a healthy individual in terms of insulin and glucagon levels?

Answer 34

High insulin | Low glucagon

Question 35

In normal metabolism after a meal, what happens to most amino acids?

Answer 35

Most amino acids from a protein meal used for protein synthesis in peripheral tissues such as skeletal muscle

Question 36

In normal metabolism after a meal, what happens to excess amino acids?

Answer 36

Excess amino acids used as sources of energy and nitrogen derived from their oxidation is incorporated into urea in the liver and excreted

Question 37

In normal metabolism during starvation, what are the insulun a glucagon levels like?

Answer 37

Insulin is low | Glucagon is high

Question 38

In normal individual during short term starvation, where is the net flow of amino acids and production of what is increased?

Answer 38

§ Net flow of amino acids from muscle to liver Increased production of glucose and urea

Question 39

In normal individual during long term starvation, what happens to tissue proteins?

Answer 39

Tissue protein is spared because ketone bodies replace glucose as major energy fuel for the brain

Question 40

What is the nitrogen balance in untreated diabetes and why?

Answer 40

Negative nitrogen balance due to decreased protein synthesis or increased protein breakdown

Question 41

When is negative nitrogen balance seen?

Answer 41

Seen in conditions like chronic infections, late stage cancer or trauma

Question 42

What are some of the effects in negative nitrogen balance mediated by?

Answer 42

Some of these effects are mediated by cytokines