Lecture #22 - Proteins

Question 1

Dietary protein:

1. Supplies what to make body proteins?
2. Supplies essential what? Why would we need to eat them?
3. Source of what for purines, pyrimidines and haem?
4. What can be used for fuel (since N is excess, what is it converted to?)

Answer 1

2. Bc we can’t synthesise them

Question 2

What is Kwashiokhor disease?

Answer 2

Children in parts of Africa and South America are prone to a disease called Kwashiorkhor. This is a result of insufficient protein in the diet despite the fact there is ample energy available.

• Not enough protein in meals even if enough calories
• can’t produce albumin so have oedema. Low plasma albumin conc but high plasma FA conc leads to enlarged liver (fatty liver) and water moves into tissues because osmotic thing messed up etc

Question 3

What are the 8 essential aa’?

Answer 3

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Question 4

The regulation of digestion is done by what kind of hormones?
What stimulates the release of these hormones?
Why is digestion of (I think she’s talking about proteins) so tightly controlled?

Answer 4

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Question 5

Have a look at the tables on the first page of lecture and probably memorise them

Answer 5

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Question 6

Protein digestion:

1. Involves hydrolyses of what?
2. Performed by what? Why so many?
3. All proteases are secreted in what form? What is this form called?
4. How are the proteases activated?

Answer 6

2. If not specific then we’d digest ourselves

Question 7

What are the three main proteases and what is their specificity determined by? What are their respective side chains that they clean next to?

Where do each of the three proteases do their job (end of second page is ans)

Answer 7

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Question 8

Protein digestion occurs in two stages - what are they? Why enzymes are involved at each stage?

Answer 8

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Question 9

Pepsinogen activation:

1. Where does this occur?
2. What is the pepsinogen originally like? What are the domains etc doing
3. What happens when pepsinogen meets up with stomach’s highly acid environment?
4. What does the active pepsin now start doing?

Answer 9

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Question 10

The activation of the other pancreatic enzymes - where does it occur, how does it occur and why are they in their zymogen form until the enter the duodenum?

Answer 10

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Question 11

What is pancreatitis? Explain all the details

Answer 11

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Question 12

After the three endopeptidase do they job, what acts now? Where?

What are the end products?

How are the end products digested into single aa’ and what are they released by?

Answer 12

Carboxy and amino peptidase in small intestine

Question 13

Okay so this isn’t really a question but me just trying to explain ish:

After the five proteases (trypsin, chymotripsin, pepsin, carboxypeptidase and amino peptidase) have done their job, the end products are di and tri peptides with some aa’

Then the di and tri peptidases (which are secreted by the intestinal mucosa) break down most of the di and tri peptides.

Across the luminal membrane (which is from lumen into cells), you have 5 aa’ transporters that take up the aa’ but the di and tri peptides are taken up by the cotransporter with H+ ions via PepT1. But even then, the absorbed di and tri peptides are digested into aa’ by cytoplasm peptidase and exported from cell into blood

Answer 13

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Question 14

• What are the five main aa’ transporters from the lumen into the cells? How do they work?
• What about the transport of aa’ from cell to capillaries?
• How about the absorption of peptides - very little absorption of peptides longer than ____ aa’?
• How are the di and tri peptides absorbed?
• What happens to the absorbed di and tri peptides?

Answer 14

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Question 15

When does absorption of intact proteins happen? Why?

Answer 15

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Question 16

1. Secretion of the enzymes as zymogens - why?
2. Inappropriate activation of zymogens is associated with what disease?
3. How are the stomach and SI protected against the action of the activated proteases?
4. What leads to ulcers?

Answer 16

1. Protect against self digestion

Question 17

What is a peptic ulcer caused by?

Answer 17

Pepsin has started eating (formed a hole) in gastric epithelium

Question 18

Cystic fibrosis:

1. What is it normally?
2. What happens to the patient’s mucous secretions? What problem could that cause?
3. So what do patients need to do?

Answer 18

2. Block the secretion of enzymes

3. Consume digestive enzymes

Question 19

What is the process for the digestion of nucleic acids?

1. DNA and RNA are subject to _____ hydrolysis in the stomach
2. Intestinal ____ hydrolyse the _____ bond between nucleotides
3. Individual nucleosides absorbed via what?

Answer 19

Our food also contains nucleic acids (DNA and RNA) which, just like carbohydrates and protein, are degraded by hydrolytic enzymes in the gastrointestinal tract. The sugar phosphate backbone of the DNA molecule is initially cleaved by acid hydrolysis in the stomach. The fragmented DNA is hydrolysed into nucleotides in the intestine by pancreatic nucleases. The nucleotides are further broken down into the nucleosides by phosphatase enzymes. The nucleosides are absorbed across the intestinal epithelia via a Na+-dependent transport system.