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NUTR 3210 > Lecture 11 - Proteins part 3 > Flashcards

Lecture 11 - Proteins part 3 Flashcards

1
Q

Is there a constant turnover between protein synthesis and breakdown?

A

Yes

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2
Q

What happens to AA during protein breakdown?

A

Body is very efficient at recycling AA during protein breakdown. Most AA derived from protein breakdown are reused to make new protein, while a little bit is catabolized

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3
Q

What are the reactions of protein catabolism?

A

AA -> NH3 (ammonia), NH4 (ammonium) -> urea cycle or urine -> urine
AA-> carbon skeleton (alpha ketoacid) -> acetyle coA -> either energy or triglyceride
AA-> carbon skeleton (alpha ketoacid) -> glucose -> either energy or glycogen

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4
Q

What is the fate of NH3 (NH4 +) from AA catabolism?

A

NH4+ is toxic and needs to be converted to something safe for transport between organs

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5
Q

How is protein breakdown occurring with the amino group steps?

A

Muscle or other non-hepatic tissue is using glutamine and alanine (interorgan transporters) which transport the amino group broken down from the protein
Fed state:
only glutamine transports the amino group to the liver where it gets converted to urea which is then secreted in the kidney to the urine and expelled
Fasted state:
both glutamine and alanine are transporting the amino group however they bypass the liver and take the ammonium group straight through to the kidneys and is getting passed out directly as ammonium to the urine

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6
Q

What are the 3 differences between fed and fasted states in the fate of urea?

A
  1. fasted state involves the formation of both glutamine and alanine, while the fed state is primarily glutamine
  2. fed state involves both the liver and kidneys
  3. fed state mainly involves the excretion of the amino group as urea, whereas the fasted state mainly involves the excretion of the amino group as ammonium directly
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7
Q

Why is there a difference in the mechanisms between the fed and the fasted state?

A

because catabolizing an alpha ketoacid leads to the production of bicarbonate (HCO3-). Bicarbonate is a weak base that reacts with H+ (if this happens, no change in pH)
in the fed state: high dietary protein intake increases amino acid catabolism, which leads to an increase in HCO3- (because H+ is being used up) this can increase the pH a bit to 7.8
in the fasted state: minor amounts of protein are catabolized to release glucogenic AA (for gluconeogenesis), primary source of energy is TAG from adipose tissue and the breakdown of TAG leads to the production of acidic ketone bodies which results in slight acidosis pH can drop to 7 (nutritional ketosis)

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8
Q

What is the bodies response to high protein diet intake (fed)?

A
  1. the liver converts the amino group to urea in a process that consumes HCO3-
  2. catabolism of sulfur-containing AA produces a bit of sulphuric acid to neutralize alkaline pH
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9
Q

How does HCO3- react with H+?

A

alpha keto acids enter krebs cycle in all cells, resulting in HCO3- production which creates CO2 and H2O, the CO2 is exhaled by the lungs

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10
Q

How does the breakdown of TAG during the fasted state lead to acidic ketone bodies?

A

products of TAg breakdown (long hydrocarbon chains) are not very water-soluble. The liver converts these long hydrocarbons into small soluble ketone bodies (which the brain can use for energy during starvation)

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11
Q

What is the bodies response during the fasted state?

A

when AAs are catabolized in a fasted state, the amino group is brought directly to the kidney (thus bypassing the urea cycle where HCO3- is used up) this means that HCO3- produced by the krebs cycle can be used to neutralize the weak acidosis state caused by the ketone bodies

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12
Q

What are the four AA important in nitrogen catabolism?

A

Glutamate
Aspartate
Alanine
Glutamine

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13
Q

How is glutamate important for nitrogen catabolism?

A

common end product of transamination rxns

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14
Q

How is aspartate important for nitrogen catabolism?

A

donates an amino group in the urea cycle

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15
Q

How is alanine important for nitrogen catabolism?

A

inter-organ nitrogen carrier, muscle to liver

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16
Q

How is glutamine important for nitrogen catabolism?

A

most abundant AA in the body, inter-organ nitrogen carrier (goes to liver and kidney), can donate an amino group to other reactions

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17
Q

What is the alpha keto acid for glutamate?

A

alpha ketoglutarate

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18
Q

What is the alpha keto acid for aspartate?

A

oxaloacetate

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19
Q

What is the alpha keto acid for alanine?

A

pyruvate

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20
Q

What are the four reactions that move nitrogen from a catabolized protein between organs for excretion?

A
  1. transamination
  2. oxidative deamination
  3. a) glutamine production
    b) glutamate regeneration
  4. urea cycle
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21
Q

What is transamination?

A

the bidirectional process of the transfer of an amino group to an AA carbon skeleton (alpha keto acid)

22
Q

What are transaminations catalyzed by?

A

aminotransferases

23
Q

What are the three AA that do not undergo transamination?

A

lysine, proline and threonine

24
Q

Draw a general transamination reaction?

A
25
Q

What is pyridoxal phosphate?

A

active form of B6, coenzyme that holds amino group during transfer

26
Q

What are some characteristics of transamination reactions?

A
  • bidirectional
  • active in all tissues
  • always produce an AA usually glutamate and an alpha keto acid
  • at least 1 transaminase exists for each AA, with each using glutamate/alpha ketoglutarate as one of the pairings
27
Q

What are the most abundant amino transferases in the liver?

A

glutamate pyruvate transaminase (GPT) also known as ALT

glutamate oxaloacetate transaminase (GOT) also known as AST

28
Q

What is bad about ALT and AST?

A

if you see a lot of this in the blood, something is wrong

29
Q

Draw the transaminations for GPT and GOT enzymes

A
30
Q

What is oxidative deamination?

A
  • one of the four reactions that moves nitrogen from a catabolized protein between organs
  • glutamate is the main AA to undergo it - because glutamate is the main product of transamination
  • Amino group is released from the glutamate backbone
  • reaction favours the formation of alpha ketoglutarate
31
Q

How is the free NH4+ produced in oxidative deamination used in different tissues?

A
  1. in extrahepatic tissue the NH4+ is used in the synthesis of glutamine
  2. in the liver, NH4+ is used for urea synthesis
  3. in the kidneys, NH4+ is excreted directly as is into urine
32
Q

What is the reaction from glutamate in oxidative deamination?

A

glutamate <——> (NAD+ -> NADH) (glutamate dehydrogenase) alpha ketoglutarate + NH4+

33
Q

What is glutamine production

A
  • one of four rxns to move nitrogen from catabolized protein between organs
  • formation of glutamine (primary inter-organ nitrogen carrier)
  • muscle produces 90% of glutamine found in the body
34
Q

What is the reaction for glutamine production?

A

glutamate ——-> glutamine
(ATP->ADP+Pi) (H2O out) (NH4+ in)
glutamine synthetase

35
Q

Where does glutamine go after glutamine production takes place?

A

fed: liver and drop amino to make urea
fasted: kidney

36
Q

What is glutamate regeneration?

A
  • one of four reactions to move nitrogen from catabolized protein between organs
  • opposite to glutamine production
  • releases amino group from the glutamine s.c.
  • active in liver in fed state
  • active in kidney during fasting
37
Q

What is the reaction for glutamate regeneration?

A

Glutamine ————-> glutamate
(H2O in) (NH4+ out)
glutaminase

38
Q

What is a characteristic of glutamine production and glutamate regeneration?

A

it is a bidirectional reaction but there are different enzymes for forward and reverse reactions

39
Q

What is the process of glutamine and glutamate in the body?

A

make glutamine in muscle -> travel in blood to deliver amino group to liver/kidney -> regenerate glutamate

40
Q

What is the urea cycle?

A
  • one of the four reactions to move nitrogen from catabolized protein between organs for excretion
  • toxic NH4+ gets converted to less toxic urea in the liver
  • urea transported to kidney for excretion
41
Q

What is the basic reaction of the urea cycle?

A
  • HCO3- and NH4+ (coming from glutamine production) becomes urea
  • aspartate condenses with citrulline and donates an amino group
  • requires energy
42
Q

What is the forms of urinary N in the fed vs fasted state?

A

fed: 80-90% will be NH4+
fasted: 80-90% will be urea

43
Q

does the urea cycle require ATP?

A

yes

44
Q

What happens if there are defects in any of the enzymes in the urea cycle?

A

leads to developmental neurotoxicity due to a build-up of NH4+ in the body

45
Q

Draw the glucose-alanine cycle

A
46
Q

What does the glucose-alanine cycle do?

A
  • usually active during fasting
  • converts AA
  • can be compared to the cori cycle
47
Q

How can alpha ketoacids be formed?

A

deamination - removal of amino group from AA. the carbon skeleton that remains is the alpha keto acid

transamination - transfer of an amino group from an AA to an alpha keto acid, in the process, the donating AA becomes an alpha keto acid and the receiving alpha keto acid becomes an AA

48
Q

What do alpha keto acids contain?

A

ketone and carboxylic acid functional groups

49
Q

what is ketogenic?

A

a degraded AA that can be converted into acetyl CoA

50
Q

what is glucogenic?

A

a degraded AA that can be converted into glucose

51
Q

Glucogenic vs ketogenic?

A

glucogenic - go towards glucose
ketogenic - go towards lipids

NUTR 3210 (17 decks)

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