Nitrogen

Question 1

what is the glucose-alanine cycle for

Answer 1

a process by which amino acids are transported to the liver from muscle

Question 2

what is going on at the same time as the glucose-alanine cycle? and therefore what all is being formed?

Answer 2

glycolysis

amino acids and pyruvate

Question 3

what happens in the muscles with amino acids during exercise?

Answer 3

Proteins are broken down into amino acids due to muscle damage

Question 4

what is pyruvate converted into in muscles

Answer 4

alanine

Question 5

how is N2 carried safely around the body

Answer 5

mainly glutamine but alanine if coming from muscle

Question 6

where is alanine (or glutamine) transported in the blood to?

Answer 6

the liver

Question 7

once in the liver what is Alanine converted to?

Answer 7

back to pyruvate and then in turn glutamate is produced as alpha ketoglutarate donates amino group to alanine
N2 from glutamate feeds into urea cycle as ammonia and binds with carbomoyl phosphate

Question 8

once glutamate is produced in liver what happens to it

Answer 8

it can be excreted and feed into the urea cycle
it is excreted as NH4+ ammonia (N2 within it)
this later forms urea in the urea cycle
carbon skeleton is left- pyruvate

Question 9

what 3 places can N2 come from in the body that feed centrally back to glutamante

Answer 9

alanine from muscles
amino acids from diet
other tissues in the body in form of glutamine

Question 10

what molecule re-captures ammonia in the urea cycle? what does this produce? and what does the recapturing of ammonia prevent in the body?

Answer 10

carbamoyl phosphate and it produces citrulline

build of ammonia in the blood which can cause toxicity and result in brain damage

Question 11

what is the second nitrogen acquiring reaction in the urea cycle? ie the second entry of N2

Answer 11

aspartate entering the urea cycle

Question 12

what is the first nitrogen acquiring reaction in the urea cycle?

Answer 12

nitrogen coming from glucose alanine cycle as ammonia. Binds with carbomyl phosphate and it produces citrulline.

Question 13

what happens to carbon skeletons (ie left over molecule once nitrogen has been removed)

Answer 13

they become major metabolic intermediates

can be glucogenic (gluconeogenesis) or ketogenic (C.A.C)

Question 14

glucogenic intermediates

Answer 14

amino acids that feed into gluconeogenesis

ie produce glucose or glycogen in the liver (C.A.C)

Question 15

ketogenic intermediates

Answer 15

amino acids that feed into acetoacetate (a principle ketone body) or acetyl CoA
ie they produce ketone bodies, acetyl CoA doesn’t enter the C.A.C as no NET synthesis of oxaloacetate

Question 16

can amino acid carbon skeletons be ketogenic and glucogenic? if so examples

Answer 16

yes

isoleucine, tyrosine and phenylaline

Question 17

Nitrogen in the atmosphere

Answer 17

N2- ammonia- nitrite- nitrate which can then be taken up by plants and microbes
Humans cannot fix nitrogen

Question 18

how do humans conserve the N2 they have as they cannot fix nitrogen?

Answer 18

a process called transamination

the movement of amino groups between molecules (recycle it)

Question 19

transamination principles

Answer 19

no loss or gain of N2 just movement
if you put an amino group on a ketone you get an amino acid
readily reversible

Question 20

what is needed to enable transamination to be readily reversible?

Answer 20

enzymes- transaminases

these participate in synthesis and degradation of amino acids

Question 21

what do transaminases rely on

Answer 21

Pyridoxal phosphate cofactor (PLP)

need this bound to them to assist catalysis

Question 22

which vitamin is PLP made from

Answer 22

Vitamin B6

Question 23

what is L-glutamine’s purpose

Answer 23

temporary storage of nitrogen

can donate an amino group when needed for biosynthesis

Question 24

diagnosis: how does the presence of aminotransferases in the plasma help?

Answer 24

indicates cell damage - breakdown of proteins/amino acids

Question 25

which enzymes are particularly useful in diagnosis

Answer 25

AST and ALT- especially liver disease

Question 26

when does Amino acid oxidation occur- in which 3 circumstances?

Answer 26

to degrade leftover amino acids from normal protein turnover

to degrade dietry amino acids that exceed body’s protein synthesis needs

to break down and supply precursors for carb production during period of starvation etc

Question 27

what are inherited metabolic disorders?

Answer 27

Group of genetic diseases involving metabolic defects

typically result in deficiencies of key enzymes

Question 28

what is an example of a urea cycle disorder

Answer 28

OTC- sex linked inheritence

characterised by hyperammonaemia

Question 29

what are examples of amino acid disorders

Answer 29

PKU
MSUD
cystinuria

Question 30

what are examples of carbohydrate disorders

Answer 30

galactosemia

Question 31

what are 3 effects of enzyme defects

Answer 31

Decreased formation of the product

Accumulation of the substrate

Increased formation of other metabolites

Question 32

Metabolic disorders and inheritence

Answer 32

most IEMs show autosomal recessive inheritance

Question 33

what are some common clinical features of inherited metabolic disorders presenting in childhood

Answer 33

Acidosis
Failure to thrive
Vomiting, refusal of feeds, irritability
Central nervous system dysfunction
Hypoglycaemia

Question 34

Phenylketonuria (PKU)

Answer 34

increased Phenylalanine levels due to lacking a key enzyme- this gets converted into toxic side product which can pass through bbb

treatable
build up of metabolite before enzyme

Question 35

diagnosis of PKU

Answer 35

screening
quantitative amino acid analysis
blood tests