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1BDS Biochemistry > Digestion 2 > Flashcards

Digestion 2 Flashcards

1
Q

By what enzyme are proteins hydrolysed?

A

Pepsidases

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2
Q

What are the 2 different types of pepsidase?

A

Endopepsidase and Exopepsidase

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3
Q

What is the function of endopepsidase?

A

They cleave internal peptide bonds and breakdown large polypeptides into smaller oligopeptides

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4
Q

What is the function of exopepsidase?

A

They cleave from the ends of the protein/peptide and breakdown these oligopeptides into di- and tri- peptides and amino acids

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5
Q

What are the 3 products of protein digestion?

A

Tri-peptides
Di-peptides
Amino Acids

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6
Q

What does the low pH of stomach acid do for protein digestion?

A

Denatures the protein and causes unravelling of the peptide chain to make the protein more accessible to digestive enzymes

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7
Q

What do chief cells in the gastric mucosa secrete?

A

Pepsinogen

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8
Q

What is pepsinogen?

A

The inactive precursor of pepsin

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9
Q

What initially activates pepsinogen?

A

Low pH of stomach acid

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10
Q

What are the functions of pepsin?

A
  • Autocatalyses further conversion of pepsinogen to pepsin
  • Digests target protein into large peptide fragments and amino acids
  • This then stimulates CCK hormone release in duodenum
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11
Q

What are the 2 hormones issued in the duodenum that are secreted?

A

Secretin and CCK

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12
Q

What stimulates the release of SECRETIN and what is its action?

A

Stimulated by: acidity of stomach acid into duodenum

Action: stimulates secretion of bicarbonate rich pancreatic fluid to neutralise acid

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13
Q

What stimulates the release of CCK and what is its action?

A

Stimulated by: breakdown of protein into large peptide chain and amino acids by pepsin

Action: causes contraction of gall bladder and relaxation of sphincter of Oddi and so promotes entry of bile and pancreatic juices into duodenum

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14
Q

What are zymogens?

A

pancreatic enzymes that are released as inactive precursors

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15
Q

What do duodenal enteropeptidases do?

A

Convert trypsinogen to trypsin

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16
Q

List 5 pancreatic zymogens and their active postcursors, N.B. trypsin activates the last 4 pathways

A 
Trypsinogen --> trypsin
Chymotrypsinogen --> chymotrypsin
Proelastase --> elastase
Procarboxypeptidase --> carboxypeptidase
Prophospholipase A2 --> phospholipase A2
17
Q

Where on the polypeptide chain does trypsin hydrolyse polypeptides?

A

On the carboxyl side or arginine and lysine residues

18
Q

How do hydrophobic amino acids pass through the brush border of the small intestine?

A

Through passive diffusion

19
Q

How do the rest of the amino acids pass through the brush border/basolateral border of the small intestine?

A

Against a concentration gradient so relies on active carrier mechanisms on the brush border AND the basolateral border of enterocytes

20
Q

How many amino acid specific transporter are there on the bush border and how many are sodium dependent?

A

7 in total, 5 Na+ dependent

21
Q

How many amino acid specific transporter are there on the basolateral border and are they sodium dependent or independent?

A

3, all 3 are Na+ independent

22
Q

How are di- and tri-peptides transported into the enterocyte?

A

through secondary active transport by on H+ dependent co-porter

23
Q

What are the fat soluble vitamins?

A

A, D, E, K

24
Q 
Answer these with regards to FAT SOLUBLE vitamins:
Chemical Property?
Excess is? 
Deficiency?
Toxicity?
Deficiency related to Malabsorption
A 
hydrophobic
stored in body
slower onset
more common
yes
25
Q 
Answer these with regards to WATER SOLUBLE vitamins:
Chemical Property?
Excess is? 
Deficiency?
Toxicity?
Deficiency related to Malabsorption
A 
hydrophilic
excreted in urine
faster onset
less common
no
26
Q

How do FAT SOLUBLE vitamins get transported?

A

carried in micelles

27
Q

How do WATER SOLUBLE vitamins get transported?

A

simple passive diffusion

28
Q

What are cobalamins?

A

The 4 metabolically important forms of B12

29
Q

What is the name for the active metabolite of Vitamin D?

A

Calcitriol

30
Q

Where is calcium predominantly absorbed?

A

in the proximal small intestine

31
Q

What are the two cellular calcium transport processes?

A
  • Paracellular absorption - through the intracellular space

- Transcellular absorption - through the cell

32
Q

What is iron important for?

A

the transfer of molecular oxygen

33
Q

Where is 75% of the body’s iron found?

A

In haemoglobin and myoglobin

34
Q

Where the other 25% of the body’s iron found?

A

tissues: bone marrow, liver and reticuloendothelial system

35
Q

What type of iron is dietary iron?

A

The FERRIC form - Fe3+

36
Q

What enzyme reduced the ferric form of iron to its ferrous form and where is this enzyme located?

A

Ferrireductase, found on the brush border of enterocytes

1BDS Biochemistry (5 decks)

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