The Liver In Metabolism-Nitrogen

Front 1

What is meant by protein turnover?

Back 1

The balance between protein synthesis and protein degradation

Front 2

What is the amino acid pool?

Back 2

Free amino acids in the cells and in the blood

Front 3

What is nitrogen balance?

Back 3

Total intake of nitrogen = total excretion of nitrogen

Front 4

What is meant by a negative nitrogen balance?

What are some of the causes of this?

Back 4

Excretion > intake

Fasting, starvation, injury or trauma, patients with chronic infections or cancer

Front 5

What is a consequence of a negative nitrogen balance not being treated?

Back 5

There will be irreversible loss of essential body tissue, which will ultimately lead to death.

Front 6

What is meant by a positive nitrogen balance?

What are some causes of this?

Back 6

Intake > excretion

Normal growth in children, pregnancy, following serious injury, repair

Front 7

How are most cellular proteins degraded?

Back 7

They are recognised as 'old' or 'damaged', so removed by ubiquitin breakdown system

Front 8

How are foreign 'exogenous' proteins degraded?

Back 8

Taken into vesicles by endocytosis or autophagocytosis

Vesicles fuse with lysosomes and proteolytic enzymes degrade proteins into AA's

Front 9

What increases the rate of protein breakdown in muscle?

Back 9

Certain hormones e.g cortisol

Front 10

What is the equation for oxidative deamination?

Back 10

The co-enzyme is normally NAD+/NADP+ ---> NADH/NADPH

Front 11

What is transamination?

Back 11

Front 12

Which enzymes deaminates glutamate?

Back 12

Glutamate dehydrogenase

Front 13

What is a consequence of there being no corresponding dehydrogenases for other amino acids?

Back 13

They have to have their amino groups transferred enzymatically (by aminotransferases) to 2-oxoglutarate, forming glutamate.

Amino acid + 2-oxoglutarate <--> oxo acid + glutamate

Glutamate is then deaminated by glutamate dehydrogenase.

Front 14

In summary, glutamate has its amino group removed by an enzyme but other amino acids don't have specific dehydrogenase enzymes that can do this, so they are converted to glutamate by reacting them with a coenzyme. Deamination can then occur.

Back 14

False. The amino acids are converted to glutamate by reacting them with 2-oxoglutarate.

Front 15

What is an essential amino acid?

Back 15

One that when omitted from an otherwise complete diet, results in a negative nitogren balance or fails to support the growth of animals.

Front 16

What are the essential amino acids?

Back 16

Valine very

Methionine many

(Histidine) hairy

Lysine little

Phenylalanine pigs

Leucine live

Isoleucine in

Threonine the

Tryptophan torrid

(Arginine) argintine

Front 17

How many of the 20 amino acids can humans synthesise? How do we get the other amino acids?

Back 17

10

We rely on dietary sources for the other 10 amino acids

Front 18

What is the role of aminotransferases in the metabolism of amino acids?

Back 18

Aminotransferases catalyse the reaction with an L amino acid (that isn't glutamate) with 2-oxoglutarate to form L glutamate and an oxo acid.

Front 19

What are glucogenic amino acids?

Back 19

They are converted into glucose.

In starvation, the carbon skeletons of 13 of the amino acids can be converted back to glucose by the liver

E.g glutamate is converted to 2-oxoglutarate which is then converted to oxaloacetate in the TCA cycle. Under appropriate condition, the 2-oxoloacetate can be converted into glucose.

e.g F and Y

Front 20

What are ketogenic amino acids?

Back 20

Ketogenic amino acids can be degraded directly into acetyl CoA ( and hence ketone bodies with can be metabolised by the TCA cycle to CO2 and H20 and provide a source of ATP.

Ketogenic amino acids cannot be converted to pyruvate or glucose. e.g leucine and lysine

After losing their amino groups, most of the 20 amino acids become keto acids.

Front 21

What is the role of the liver in nitrogen metabolism?

Back 21

Removal of amino acids, glucose and fats from the portal blood supply.

Front 22

What are absorbed amino acids used for the synthesis of?

Back 22

Haem, cellular proteins (carnitine), purines and pyrimidines, plasma proteins, DNA & RNA

Front 23

How are excess amino acids degraded?

Back 23

By transdeamination. (transamination followed by oxidative deamination)

The ammonia is converted to urea for excretion.

Front 24

Skeletal muscle continuously degrades proteins to amino acids but the liver is the only organ which can convert the amino groups of these amino acids to urea for excretion from the body. True or false.

Back 24

True

Front 25

What is the urea cycle?

Back 25

Aspartate is a source of nitrogen

Front 26

What is the role of glutamine in nitrogen metabolism?

Back 26

The amino groups are transported as glutamine in the bloodstream

Safe carrier of ammonia in the blood-ammonia is toxic to the brain

Gln can carry 2 ammonia equivalents to the liver for urea excretion

Gln can deliver ammonium ions to the kidney for pH regulation

Front 27

What is the role of alanine in nitrogen metabolism?

Back 27

Forms part of aminotransferase enzyme

Front 28

What is the role of aspartate in nitrogen metabolism?

Back 28

A source of nitrogen in the urea cycle

Front 29

Ammonia is neurotoxic. What can it cause?

Back 29

Cerebral oedema (accumulation of fluid in the brain)

Coma

Death

Front 30

Why is hyperammonaemia?

Back 30

XS of ammonia in blood

Causes liver failure and genetic defects due to a reduction in catalytic activity of an enzyme in the urea cycle

Front 31

What are the end products of nitrogen metabolism?

Back 31

Urea

Creatinine

Uric acid

Ammonia

Front 32

Why is transamination alone not a way to metabolise a protein?

Back 32

We are not removing an amino group from the body

Front 33

What is the reaction catalysed by glutamate dehydrogenase?

Back 33

Front 34

What are some fates of the amino acids?

Back 34

Front 35

What is the equivalent oxo-acid for alanine?

Back 35

Pyruvate

Front 36

What is a keto acid?

Back 36

An amino acid which has had its amino group removed so it contains a carboxylic acid group and a ketone group.

Also called oxo-acids

Front 37

Of the ammonium ions produced in oxidative deamination, what may happen to them?

Back 37

They may be fed into the urea cycle, or used by the liver.

Front 38

Can essential amino acids be formed from other amino acids?

Back 38

No. Essential amino acids cannot be formed from other amino acids but must be supplied in the diet.

Front 39

What do transaminases have as a cofactor that is bound to their active site?

Back 39

Transaminases have pyridoxal phosphate as a cofactor tightly bound to their active site

Front 40

The main source of glucose carbons for gluconeogenesis is .....

Back 40

alanine derived from breakdown of muscle proteins.

Front 41

Give an example of a protein with a long half life

Back 41

Structural protein e.g collagen (years)

Front 42

A high protein intake in a well-fed individual is wasted. What happens to the excess amino acids>

Back 42

They are rapidly catabolised and the nitrogen is excreted as urea in the urine

Front 43

What are 4 ways that nitrogen can be excreted?

Back 43

Urea

Uric acid

Creatinine

NH4+

Front 44

Which hormone increases the rate of protein breakdown in muscle?

Back 44

Cortisol

Front 45

Is oxidative deamination reversible?

Back 45

No

Front 46

Is transamination reversible?

Back 46

Yes

Front 47

All aminotransferases contain a tightly bound prosthetic group which is derived from vitamin B6 and acts as a carrier of the ______ _______.

This is present as pyridoxal phosphate or ___________ _____________ and during transamination there is a reversible interconversion of the two forms.

Back 47

amino group

pyridoxamine phosphate

Front 48

Can plants and microorganisms synthesis all 20 amino acids?

Back 48

Yes (from NH3 and CO2)

Front 49

Draw urea

Back 49

Front 50

Draw carbamoyl phosphate

Back 50

Front 51

There is no polymeric form of amino acids who function is simply to be called upon when needed. What are the reserves in the form of?

Back 51

Amino acids in the amino acid pool

Front 52

What is the significance of alanine, glutamate, aspartate and glutamine in nitrogen metabolism?

Back 52

They are the main amino acids used to transport excess ammonia safely in the blood to the liver, for disposal via the urea cycle.

Front 53

Give 5 examples of amino acids which are both glycogenic and ketogenic

Back 53

Phenylalanine

Tyrosine

Tryptophan

Threonine

Isoleucine

Front 54

How is glutamine metabolised?

Back 54

Front 55

What is this?

Back 55

Arginosuccinic acid

Front 56

Uric acid is produced from the breakdown of what?

Back 56

DNA and RNA

Front 57

Ketone bodies can be used for energy by most (but not all) tissue. In most cell types , they can be converted into TCA cycle intermediates.

Give two examples of these intermediates.

Back 57

Acetyl CoA

Succinate