L18 - liver in metabolism - nitrogen

Question 1

what is AA pool

Answer 1

free AAs in low concs in cells/bloodstream

Question 2

what is protein turnover

Answer 2

proteins are continuously degraded to AA and resynthesized

they have differing half lives

Question 3

what is average protein turnover

Answer 3

300 - 400g a day

Question 4

can protein be stored?

Answer 4

no

Question 5

can plants and microorganisms synthesise all AAs?

Answer 5

yes

Question 6

what is nitrogen balance

Answer 6

N intake = N excretion

protein synthesis = protein degradation

Question 7

what is positive nitrogen balance

Answer 7

N intake > N excretion

protein synthesis exceeds rate of breakdown

Question 8

when can +ve nitrogen balance occur

Answer 8

normal growth
pregnancy
after serious illness (rebuilding proteins)

Question 9

what is -ve nitrogen balance

Answer 9

N intake < N excretion

Question 10

when can -ve nitrogen balance occur

Answer 10

starvation
during serious illness
late stage of some cancers

Question 11

what can happen if -ve nitrogen balance is prolonged?

Answer 11

irreversible muscle wastage - death

Question 12

what process degrades cellular proteins

Answer 12

ubiquitin

Question 13

what process degrades exogenous proteins

Answer 13

endocytosis / phagocytosis

then fused with lysosomes

Question 14

what hormone can increase rate of protein degradation in muscle

Answer 14

cortisol

Question 15

what is oxidative deamination

Answer 15

removal of amino group on amino acid

and removal of 2H

Question 16

where does oxidative deamination occur

Answer 16

liver

Question 17

what catalyses oxidative deamination

Answer 17

glutamate dehydrogenase

Question 18

what is transamination

Answer 18

combining an AA and a keto acid causes the amino group to swap

Question 19

where does transamination occur

Answer 19

liver / muscle

Question 20

what is the only AA that can undergo oxidative deamination

Answer 20

glutamate

Question 21

how is glutamate formed before undergoing oxidative transamination

Answer 21

transamination of any AA and 2-oxo-glutarate forms glutamate

Question 22

what enzyme catalyses transamination reactions

Answer 22

aminotransferases

Question 23

what is needed in an aminotransferase to carry out its function

Answer 23

pyridoxal phosphate prosthetic group (carries amino group)

Question 24

what is reduced during oxidative phosphorylation

Answer 24

NADP

Question 25

what happens to AAs after transamination

Answer 25

become oxo acids which can be: 1. metabolised by TCA cycle 2. converted back to glucose (starvation)

Question 26

what oxo acids can be converted back to glucose and where

Answer 26

13 glucogenic ones | in liver

Question 27

define glucogenic

Answer 27

AAs that can be converted into glucose after degradation

Question 28

define ketogenic

Answer 28

AAs that cannot be converted to glucose after degradation

Question 29

examples of ketogenic AAs

Answer 29

leucine | lysine

Question 30

what can leucine and lysine be degraded to

Answer 30

acetyl CoA

Question 31

name some AAs considered ketogenic and glucogenic

Answer 31

phenylalanine tyrosine tryptophan isoleucine

Question 32

what does it mean if an AA is considered glucogenic and ketogenic

Answer 32

part of its structure can be converted to glucose

Question 33

roles of liver in N metabolism

Answer 33

1. removal of AA etc from blood 2. synthesis of - haem - plasma proteins (albumin) - purines and pyrimidines 3. transdeamination 4. ornithine cycle (NH3 to urea)

Question 34

how is NH2 transported in blood and why

Answer 34

as glutamine/glutamate because its toxic

Question 35

where is urea produced

Answer 35

liver only

Question 36

how many NH2 groups can glutamine carry

Answer 36

2

Question 37

function of alanine in N excretion

Answer 37

provides NH4+ to urea cycle (after being transdeaminated to glutamate)

Question 38

function of aspartate in N excretion

Answer 38

provides 2nd NH4+ to urea

Question 39

what are the end products of N metabolism

Answer 39

urea creatinine uric acid NH4+

Question 40

where does uric acid come from

Answer 40

DNA & RNA breakdown

Question 41

what is hyperammonaemia

Answer 41

impaired conversion of NH3 to urea - liver failure