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Nutr 301 > Protein digestion > Flashcards

Protein digestion Flashcards

1
Q

what are some functions of protein

A

movement, structure, regulate metabolism, transport, communication, infection protection

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2
Q

what determines a protein’s function

A

structure

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3
Q

why is protein needed from the diet?

A

maintain protein balance + essential amino acid supply

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3
Q

what determines a protein’s structure

A

side chains

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4
Q

how does obligatory protein loss occur

A

through epithelia, through urine/feces, synthesis of non-protein substances

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5
Q

give brief explanation of 1’, 2’, 3’, and 4’ structure

A

primary = linear number and order of amino acids
secondary = folding of proteins into patterns (globular or fibrous peptide bonds) > b-sheets/a-helices
tertiary = additional folding due to r-group interactions (polypeptide chains)
quaternary = interaction between polypeptide chains

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6
Q

what are the essential amino acids

A

Histidine, Isoleucine, Leucine, Threonine, Lysine, Methionine, Phenylalanine, Tryptophan, Valine

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7
Q

what is a conditionally essential AA

A

an AA that only becomes essential in certain states or conditions

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8
Q

what is/are the conditionally essential AA when underdeveloped/insufficient synthesis in neonates

A

Cysteine, Glutamine, Glycine, Tyrosine, Arginine

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9
Q

what is/are the conditionally essential AA when there’s an increased requirement such as stress/injury/surgery

A

Glutamine

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10
Q

what is the function of glutamine

A
  • amide N donor for DNA biosynthesis
  • precursor for glucose formation
  • oxidative fuel for intestinal/immune cells
  • inter-organ transport of N + C, rids tissues of excess NH4
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11
Q

what is/are the conditionally essential AA when decreased synthesis occurs

A

Arginine, mainly from si/kidney

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12
Q

what is/are the conditionally essential AA when defective synthesis occurs

A

lacking enzymes that convert AAs to others (eg lacking PAH = can’t convert phenylalanine to tyrosine = build up to toxicity level)

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13
Q

what are the 4 major phases of protein digestion

A
  1. mechanical digestion in mouth
  2. gastric hydrolysis (opens up structures)
  3. pancreatic proteases (smaller peptides in si)
  4. hydrolysis of peptide linkages at brush border (final breakdown into tri/di/oligopeptides + free AA)
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14
Q

how does protein digestion happen in the mouth?

A

mechanical break down from chewing + moistening with saliva

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15
Q

how does protein digestion happen in the stomach

A

star of chemical breakdown by
- HCl: denatures protein + activates pepsinogen to pepsin
- Pepsin: breaks protein down into smaller peptides + free AA & inhibits pepsinogen synthesis

16
Q

how does protein digestion happen in the si and pancreas

A
  • polypeptides + AA stimulate release of CCK from duodenum of si
  • CCK stimulates pancreatic juice release = neutralizes acid and enzymes from stomach are denatured
  • pancreas releases inactive zymogens which must be converted to active enzymes
17
Q

what enzymes hydrolyze shorter peptide chains? longer protein chains?

A

shorter = peptidases
longer = proteases

18
Q

what is the first acting enzyme in protein digestion in the si?

A

trypsinogen to trypsin via enteropeptidase

19
Q

what do active zymogens do?

A

break down whole proteins into di/tri/oligo peptides

20
Q

what are incretins? most important ones?

A

hormone that stimulates insulin secretion in response to meals, released in anticipation of glycemic spike
- glucagon-like peptide-1 (GLP1) & glucose-dependent insulinotropic (GIP)

21
Q

what is the role of DPP4

A

inactivates incretins/GLP1 in plasma
- DPP4 inhibitors = allows the incretins to last longer in the blood for beneficial effects

22
Q

are all proteins completely broken down by pancreatic enzymes?

A

no, brush border peptidases get last ones but we can absorb free AA + small amounts of di/tri peptides

23
Q

what is the flow of protein digestion

A

luminal digestion > membrane digestion > cytoplasmic digestion > into blood via portal vein

24
Q

what is the pathway of general protein transport/absorption

A
  1. proteins into large peptides/di or tripeptides/AA (large peptides into AA/di or tripeptides via brush border peptidases)
  2. AA through brush border via AA transport systems + di/tripep through brush border via Na dependent peptide transport system
  3. some di/tri into AA via cytoplasmic peptidases
  4. AA (90%) via AA transport systems + di/tripep (10%) via peptide transport system through basolateral into blood
25
Q

what is the transport process of di/tri peptides

A

large proteins are broken down into di/tri, pass through the brush border membrane in the lumen via a H+/peptide cotransporter (PEPT1) where in the cytosol they are then further broken down into free AA or pass through basolateral membrane via peptide transport system
- H+ that came in with it is balanced out with a Na+/H+ exchanger (NHE3) on the brush border membrane

26
Q

what is the competition between amino acid transporters on the brush-border membrane

A

relying on ion gradients (sodium/calcium/proton gradients) to function. This competition occurs at the membrane’s surface (mainly apical) affecting uptake into the enterocyte based on transporter location and ion gradient availability

27
Q

how does a Na-dependent AA transporter work

A
  • Na binds = increased affinity for AA = AA binds
  • Na + AA cotransporter forms = conformational change = Na + AA transported into cell cytosol
  • intracellular AA metabolism + Na/K pump removes Na
28
Q

what impacts the rate of protein digestion

5 points

A
  • structure (simple = faster)
  • food matrix (fibre = slower)
  • chain length (free AA = faster)
  • pH (neutral before basic or acidic)
  • essential before non-essential
29
Q

how does the small intestine regulate in capacity of AA absorption

A
  • change in absorptive surface area
  • change in individual enterocytes (gene expression of amino-peptidases/membrane transporters)
30
Q

what is a negative impact of TPN administration? what can help with it

A

intestinal atrophy + reduced absorptive capacity of the intestine
- glutamine can help

31
Q

why are intact proteins not absorbed? what is an exception?

A
  • brush border proteases break them down
  • no transporters for them on basolateral membrane
  • cannot permeates through enterocyte tight junctions = excess stored/absorbed as fat

exception: newborn babies’ passive immunity via immunoglobulins/antibodies (colostrum)

32
Q

describe celiac disease

A
  • gluten in only partially digested = disruption of epithelial tight junctions = protease resistant gliadin peptide absorbed
  • peptides trigger immune response and release of T-cells due to genes that bind more tightly to antigens (HLA DQ2)
  • inflammation and damage to intestinal surface occurs as a result = can lead to villous atrophy = nutrient malabsorption/secondary intolerance
33
Q

what is the role of enterocytes in AA absorption/availability

A
  • AA pass through them unmetabolized
  • AA are used for protein synthesis in them
  • partially/completely oxidized AA are used for energy
  • intermediary metabolic conversion of AA/metabolites + transporting them out
34
Q

amino acids are major fuel for small intestine mucosa, what are the implications of this for protein utilization efficiency

A

reduces the amount available for synthesis = not all dietary protein consumed is fully utilized for muscle or tissue building, as some is “used up” by the gut for its own energy and function = why the portal concentration of some AA are lower than dietary intake

35
Q

what are some results of protein malabsorption

A
  • severe pancreatic dysfunction
  • extensive intestinal resection
  • severe chronic malnutrition (bc loss of gut function to absorb)

Nutr 301 (8 decks)

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