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Biochemistry > Dai 1 > Flashcards

Dai 1 Flashcards

0
Q

What are the acidic AA?

A

Asp, glu (negative charge at pH 7)

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1
Q

What are the basic AA?

A

His-Lys-Arg Base (positive charge at pH 7)

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2
Q

What are the ones with hydroxyl groups + uncharged polar?

A

Ser, Thr, Tyr

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3
Q

Uncharged polar AA?

A

Asparagine, glutamine

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4
Q

Non-polar (neutral)

A

Glycine, alanine

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5
Q

Non-polar, hydrophobic

A

Greasy MILV, met-iso-leu-val

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6
Q

Non-polar side ring

A

Phe, Trp

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7
Q

What is essential vs non essential amino acids?

A

Essential AA must be consumed from diet, non essential can be synthesized by the body

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8
Q

How many nonessential AA are there? What are they and what are they made from?

A

11 nonessentials.
Glucose: serine, glycine, alanine, aspartate, glutamate, asparagine, glutamine, proline, arginine*

Essential AA: tyrosine (from phenylalanine), cysteine (from methionine)

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9
Q

How many essential AAs? What are they?

A

10 essentials: phenylalanine, trp, met, ile, leu, val, his, lys, arg*, thr

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10
Q

How is arginine both essential and nonessential?

A

Body can make it, but can’t make enough in children so it must be supplemented

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11
Q

What is biological value (BV) of food? What has high value?

A

Extent of essential amino acids present in particular food.

-Food of animal origin have high BV. (ie. eggs have all essential AA; BV = 100)

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12
Q

Where is most AA synthesized?

A

liver

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13
Q

When do nonessential AA become essential?

A

When there is loss of biosynthetic precursors and/or enzymes

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14
Q

What are the important precursors for nonessential AA from glucose?

A

phosphoglycerate, pyruvate, oxaloacetate, alpha-ketoglutarate, methionine (not from glucose though?)

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15
Q

Where is most N in AA obtained? How is it used? How is it excreted?

A

Obtained from atmospheric N fixed by bacteria. Used to make protein and other compounds such as heme, creatine.

90% of N excreted is urea, some as NH4+

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16
Q

What is the carbon skeleton of AA used for?

A

7 metabolic intermediates for other pathways.

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17
Q

Where is protein broken down?

A

muscle and liver

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18
Q

What is the amino acid pool?

A

Normally 90-100g of free AA in steady state, our body does not store large quantities of nitrogen

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19
Q

What are some sources of AA? products of AA?

A

sources: diet, body protein breakdown, synthesis of nonessentials
products: body protein syn, glucose, ketone bodies, metabolized to CO2 for energy production

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20
Q

When might AA be heavily used for energy production?

A

during conditions like starvation

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21
Q

what is body protein turnover?

A

process of synthesizing new protein to replace degraded protein (simultaneous process). amount of protein in healthy adult kept constant

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22
Q

What is nitrogen balance?

A

nitrogen consumed = nitrogen excreted (healthy state: no net change in body nitrogen)

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23
Q

what is positive N balance?

A

nitrogen consumed from diet > nitrogen excreted.

  • net increase in protein stores
  • common in growth, pregnancy, tissue growth
24
Q

What is negative N balance? How many scenarios are there?

A

nitrogen consumed in diet < nitrogen excreted

-3 scenarios

25
Q

What are the scenarios for negative N balance?

A

1) body protein breakdown - aa used for energy production
- starvation (C skeleton for gluconeogenesis, N excreted)
2) inadequate dietary protein
- “kwashiorkor”
- normal caloric intake but inadequate proteins causes edema, lost of muscle mass
3) Low quality protein: lack of essential AA
- vegetarians susceptible
- enough protein but can’t use

26
Q

What are the phases of protein digestion?

A

gastric, pancreatic, intestinal phases

27
Q

Describe the product of gastric phase and enzyme involved

A

Dietary protein -> polypeptides and AA by pepsin

28
Q

Describe the pancreatic phase products and enzymes

A

Polypeptides and AA -> oligopeptides and AA

enzymes: trypsin, chymotrypsin, elastase, carboxypeptidase

29
Q

Describe the intestinal phase products and enzymes involved

A

oligopeptides and AA -> AA

enzymes: amino peptidase, di- tri- peptidases
- enzymes produced by intestinal epithelial cells

30
Q

Protein digestion is efficient/inefficient, highly/lowly regulated process

A

Efficient, highly regulated process (hormones, multiple enzymes, inactive zymogens)

31
Q

Digestive tract has high/low reserve

A

High - proteins can be very efficiently digested

32
Q

What does pepsin cleave?

A

after aromatic and acidic aa (phe, tyr, glu, asp)

33
Q

what does trypsin cleave?

A

after basic aa

34
Q

what does chymotrypsin cleave?

A

after aromatic and hydrophobic aa

35
Q

what does elastase cleave?

A

small aa

36
Q

What are examples of exopeptidases?

A

amino, carboxy peptidases

37
Q

What are zymogens (proenzymes)? Why are they important?

A

Inactive enzyme precursor that need biochemical changed to cleave sequence for change in conformation and become active

  • prevents self digestion
  • happens in cascade (one activated zymogen can activate other zymogens downstream)
38
Q

How is AA absorbed?

A

Using brush border (rich in microvilli) system (at least 7 of them in liver+kidney with varying specificity)

  • Absorbed by enterocytes and then enter bloodstream
  • Low concentration of AA in lumen, high in cell, low in blood
  • use of Na+/AA symport system (requires ATP), followed by facilitated diffusion through basolateral membrane down concentration gradient
39
Q

What is cystinuria?

A

Defect in Lys/Arg/Cys- and Cys/Ornithine transporter

  • COAL
  • excretion of cystine and basic AA in urine (cannot reabsorb in kidney)
  • forms cystine stones
  • recessive, treatment - drink lots of water
40
Q

What is neutral amino aciduria (Hartnup disease)?

A

defect in neutral aa transport (SLC6A19 transporter)

  • renal/epithelial cells can’t absorb neutral AA ->excretion in urine (e.g. Trp)
  • can cause pellegra like rash and headache
  • treated with healthy, high protein diet; dietary supplement of tryptophan and niacin (nicotinamide)
  • tryptophan is a precursor of niacin
41
Q

What is -uria vs -emia?

A
  • uria : elevated levels in urine

- emia: elevated levels in the blood

42
Q

How is nitrogen disposed of?

A

alpha-amino groups are collected in glutamate by 1) TRANSAMINATION, then are released as NH4+ by 2) OXIDATIVE DEAMINATION, and finally converted to urea by 3) UREA CYCLE DEAMINATION

liver->blood->kidney, where urea is excreted
-glutamate is like the garbage collector

43
Q

What is transamination?

A

Transfer of amino group from AA to alpha-keto acid (has C=O group on AA instead of the amino group

  • in muscle and liver
  • enzyme: aminotransferase (transaminases)
  • ex: alanine -> pyruvate, aspartate -> OAA, glutamate -> alpha-ketoglutarate
44
Q

What is the cofactor for transamination? What is the mechanism like?

A

Cofactor: pyridoxal phosphate (PLP, derivative of vitamin B6)

  • “ping-pong” mechanism
  • amino group moves around
  • alpha-keto -> glutamate very common in the transamination process
45
Q

How can we detect liver or muscle damage?

A

alanine aminotransferase (ALT), or aspartate aminotransferase (AST)

we expect elevated levels in blood

46
Q

Transamination rxn is reversible/irreversible

A

Reversible

47
Q

How can transamination rxn be used in medicine?

A

In hyperammonemia: replace AA with alpha-keto acid. Forces formation of AA.

Thr, Lys, and Pro (imino acid) cannot participate in transamination

48
Q

What is oxidative deamination of glutamate? Where does it occur?

A

Amino group released as free ammonia from glutamate
Glutamate -> alpha-ketoglutarate (glutamate dehydrogenase)
-occurs in mito of liver (and kidney)
-glutamate -> alpha-keto (oxidative deamination prefers NAD+)
-reverse (reductive deamination prefers NADPH)

49
Q

How is oxidative deamination regulated? (2 levels)

A

1) fully reversible
-depends on concentration of substrates and NADPH
2) allosteric regulation of glutamate dehydrogenase
GTP-allosteric inhibitor (higher GTP -> forward rxn inhibited)
ADP-allosteric activator (higher ADP -> forward rxn activated) low energy, make more alpha-keto, produce more energy

50
Q

Why is elevated ammonia toxic? What might it effect?

A

Causes reversal of glutamate oxidative deamination rxn, results in depletion of energy sources (alpha-keto, ATP, NADH, NADPH). Lots of glutamate = excitatory neurotransmitter.
-CNS defects.

51
Q

How is urea transferred?

A

NH3->Urea->blood->kidney->urine

-some happen in mito and some in cytosol

52
Q

What is BUN?

A

Blood urea nitrogen

  • high BUN -> kidney problems
  • low BUN -> genetic defect in urea cycle
53
Q

What are the first two steps of the urea cycle? Where?

A

In mito: (this is site of ammonia production from oxidative deamination)
1) carbamoyl phosphate synthetase I (CPS I)
CO2+ammonia -> carbamoyl phosphate
2) Ornithine transcarbamoylase (OTC)
ornithine + carbamoyl phosphate -> L-citrulline

54
Q

Step 3 and 4 of urea cycle? Where?

A

3) arginiosuccinate synthetase
citrulline -> arginosuccinate (produces aspartate, which has N for urea)
4) arginosuccinate lyase (arginosuccinase)
arginosuccinate -> L-arginine (produces fumarate)
5) arginase
L-arginine -> urea + ornithine (hydrolysis, only in liver cells)

55
Q

What is the net rxn of urea cycle?

A

Aspartate + Nh3 + Co2 + 3ATP + H2O -> Urea + Fumarate + 2ADP + AMP + 2Pi + PPi

  • 3 atp used
  • co2 provides carbon of urea, free ammonia provides one of the nitrogens
  • amino group of aspartate provides the other nitrogen atom (importance of aspartate aminotransferase)
  • both N ultimately from glutamate
56
Q

How is urea cycle regulated?

A

1) amount of enzymes (increase in response to high-protein diet)
2) CPS I activity (rate-limiting step in urea cycle)
- acetylglutamate is allosteric activator
- acetyl CoA + glutamate -> N-acetyle-glutamate (N-acetylglutamate synthase; allosteric activator is arginine)
- high lvls of acetyl CoA imply energy rich state
- high lvls of glutamate and arginine (substrates of urea cycle) suggest abundance of AA

57
Q

What are some indication of urea cycle enzyme deficiencies?

A
  • lethargic, vomiting
  • high plasma ammonia (hyperammonemia)
  • decreased BUN
  • elevated glutamine, even glycine

Biochemistry (12 decks)

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