NUT2001 > Protein > Flashcards

Protein Flashcards

(47 cards)

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1
Q

Protein digestion - general principles

A

Multi-step process
Digestion in stomach, mechanical mixing and further hydrolysis in small intestine

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2
Q

Proteins must be hydrolysed to … and … for absorption

A

Amino acids and small peptides

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3
Q

Proteins must be hydrolysed to amino acids and small peptides for absorption - except…

A

Young animals absorb intact proteins e.g. colostrum and immunoglobulins

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4
Q

Protein digestion involves … and … processes in the … and …

A

Chemical and enzymatic
Stomach and small intestine

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5
Q

Summary of protein digestion

A

HCl in stomach
Pepsin in stomach
Pancreatic enzymes
Proteolytic enzymes in brush border

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6
Q

Protein digestion - oral cavity

A

Ingested food undergoes mechanical digestion:
Mastication - chewing: involves teeth, tongue, cheeks and lips
Mixed with saliva - moistens and lubricates, aids bolus formation and swallowing
Tongue - mixes food with saliva, forms bolus, moves bolus towards pharynx for deglutition
No chemical digestion of proteins in mouth
Food bolus enters oesophagus
Entry controlled via oesophageal sphincter
Bolus is propelled via peristaltic waves towards stomach
Enters stomach via lower oesophageal sphincter

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7
Q

Protein digestion - stomach

A

Gastric acid secretion
Disinfection (pressure) of stomach and upper small intestine stimulates gastric secretions
Nervous stimulation can act directly or indirectly e.g. by stimulating gastrin secretion

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8
Q

Regulated by nervous excitation via vagus nerve in three phases:

A

Cephalic phase - sight and smell of food will initiate response
Gastric phase - some chemicals and food components can stimulate gastric secretion
Intestinal phase - food and chemicals in lower small intestine stimulated gastric secretion

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9
Q

What do goblet cells secrete

A

Mucus

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10
Q

What to parietal cells secrete

A

Gastric acid

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11
Q

What do chief cells secrete

A

Pepsinogen

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12
Q

What do D cells secrete

A

Somatostatin

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13
Q

What do G cells secrete

A

Gastrin

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14
Q

What 5 types of cells can be found in the gastric pit?

A

Goblet cells
Parietal cells
Chief cells
D cells
G cells

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15
Q

Gastric acid secretion is stimulated by 3 principal … which are found in the blood stream supplying the gut tissues

A

Secretogogues

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16
Q

Each secretogogue has a specific … on the basolateral membrane of parietal cell

A

Receptor

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17
Q

Secretogogues act…

A

Synergistically

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18
Q

3 principle secretogogues

A

Histamine - acts on H2 receptors which require an intact imidazole ring structure
Acetylcholine - stimulates gastrin release
Gastrin - hormone secreted by G-cells of pyloric glands

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19
Q

In the resting state parietal cells have short … which extend from the surface of the cell

20
Q

Canaliculi are surrounded by vesicles called …

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A

Tubulovesicles

21
Q

Tubulovesicles have … in their membranes

22
Q

When stimulated by secretogues, tubulovesicles fuse together with canaliculi at the apical membrane causing canaliculi to expand their …

23
Q

H+/K+/ATPase releases … and … into lumen

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A

H+ and water (by osmosis) - produces HCl

24
Q

Chief cells

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A

Secrete pepsinogen (zymgoen)
HCl released from parietal cells
Changes shape of pepsinogen
Pepsinogen activates itself to pepsin by cleavage of peptide bond
Pepsin also activates pepsinogen by proteolysis
Pepsin is a digestive enzyme

25
Protein digestion - stomach
HCl secreted by parietal cells reduces pH to 2-3 Disrupts hydrogen, electrostatic bonds and denatures protein - coagulation and precipitation of soluble proteins Pepsinogen - secreted by chief cells in gastric mucosa as inactive pre-cursor of pepsin Active pepsin breaks down denatured protein ‘exposed’ through action of acid Cleavage of protein at specific sites next to amino acids by hydrolysis of peptide bonds Only active at high H+ concentrations
26
Protein digestion - small intestine
No digestive enzymes secreted by SI Digestion due to enzymes secreted into SI by pancreas and enzymes embedded within enterocyte brush border membrane
27
Pancreatic proteolytic enzymes
Trypsin Chymotrypsin Carboxypeptidase A Carboxypeptidase B Elastase
28
Pancreatic proteolytic enzymes are secreted as zymogens which have to be activated by…
Proteolytic cleavage
29
All protetolytic enzymes act by cleaving … at specific sites in the polypeptide chain
Peptide bonds
30
Cleaving of peptide bonds can occur within the molecule structure (…) or by nibbling from the ends of the molecule (…)
Endopeptidase or exopeptidase
31
Endopeptidases
Trypsin - carboxy side of Lys and Arg residues Chymotrypsin - carboxy side of aromatic residues: Phe, Tyr, Trp Elastase - broad spectrum, especially neutral amino acids
32
Exopeptidases
Carboxypeptidase A - COOH terminal especially when this is an amino acid with an aromatic or branched chain aliphatic side chain Carboxypeptidase B - COOH terminal specific to Lys and Arg
33
Products of luminal phase of protein digestion in SI
Free amino acid and short peptides
34
Endopeptidases cleave where?
Centre of molecule
35
Exopeptidases cleave where?
At end of molecule
36
Peptide digestion by enterocytes occurs in two stages
Degradation of oligopeptides in SI lumen by brush border enzymes Degradation of absorbed tri and di peptides by intracellular peptidases
37
Peptidases embedded in the apical membrane of enterocytes act on oligopeptides at the …
SI lumen / enterocyte interface
38
Peptidases hydrolyse oligopeptides to … and …
Small peptides and free amino acids
39
Absorption of amino acids into enterocytes
Unique as absorption prior to final digestion in some cases Absorbed using transport proteins Specific classes of carriers for different amino acids - depends on chemical nature of side chain Mostly active transport using energy Indirect energy requirement where transport linked to Na+ or H+ symport with energy requiring transport of Na+ or H+ back out of enterocyte
40
Intracellular peptidases hydrolyse some but not all absorbed peptides to … or …
Amino acids or shorter peptides
41
Transport across basolateral membrane to interstitial fluid out of enterocyte is down a … so requires specific transport proteins but not …
Concentration gradient and energy
42
Proteins may be from … or from …
Diet or within digestive tract
43
Amount is dependant on …
Dietary protein intake Dietary anti-nutritional factors Dietary fibre
44
Proteins are digested extracellularly by bacterial proteases and peptidases to give … and …
Peptides and amino acids
45
Peptides and amino acids are absorbed into microbial cells where they are further metabolised to … and …
C-skeletons and NH3
46
If there is sufficient … available microns re-synthesise amino acids form C-skeletons and NH3 to make new microbial proteins
ATP
47
In humans colonic protein metabolism has …
Little nutritional value
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