Lecture 9 and 10

Question 1

What percentage of the western diet is protein?

Answer 1

30%

Question 2

How many proteinogenic amino acids are there?

Answer 2

20- these are the ones encoded by DNA.

Question 3

How many of the 20 amino acids are essential in diet?

Answer 3

9

Question 4

What are the other 4 amino acids found in proteins produced from post-translational modification?

Answer 4

y-carboxyglutamate, hydroxylysine, 4-hydroxyproline and 3-hydroxyproline.

Question 5

What percentage of the body is made of protein?

Answer 5

14%

Question 6

What are some structural proteins?

Answer 6

Collagen, ligaments, tendons

Question 7

What are some functional proteins?

Answer 7

hormones, enzymes, membrane proteins like transporters, muscle filaments

Question 8

What are some amino acid neurotransmitters?

Answer 8

GABA, glutamate, glycine

Question 9

What receptor does glutamate activate?

Answer 9

TIR1/TIR2.

Question 10

What is orthenine used in?

Answer 10

Urea cycle

Question 11

What are taurine and betaine used as?

Answer 11

osmolytes

Question 12

what is beta-alanine found in?

Answer 12

The naturally occurring dipeptide carnosine

Question 13

What is in high concentrations in breast milk?

Answer 13

Taurine

Question 14

What is the average daily intake of protein in diet?

Answer 14

70-100g. This makes up 50% of the protein entering the GI tract. This is the exogenous source.

Question 15

What are the endogenous sources of protein entering the GI tract?

Answer 15

enzymes, hormones, immunoglobulins, desquamated epithelial cells.

Question 16

What are the three stages of protein digestion?

Answer 16

Intraluminal, membrane and cytoplasmic.

Question 17

What digests protein in the lumen?

Answer 17

Pepsin and pancreatic enzymes

Question 18

Name three examples of pancreatic proteases

Answer 18

trypsin, chymotrypsin, carboxypeptidases A and B.

Question 19

What are the products of intralumenal digestion?

Answer 19

Oligopeptides or single amino acids.

Question 20

Approximately how many surface proteases and peptidases are there at the SI membrane?

Answer 20

10

Question 21

What are the products of membrane digetsion?

Answer 21

di and tri peptides

Question 22

What is the apical transporter of di and tri peptides?

Answer 22

PepT1

Question 23

How many amino acid transporters are there at the BBM?

Answer 23

7

Question 24

How many amino acid transporters are there at the BLM?

Answer 24

9

Question 25

What was the classical hypothesis?

Answer 25

Stated that all proteins were broken down to single amino acids at the surface and could only be absorbed this way.

Question 26

What was the dual hypothesis?

Answer 26

Both amino acids and di/tri peptides could be absorbed.

Question 27

What is Hartnup disorder a problem with?

Answer 27

Absorption of neutral amino acids

Question 28

How does the study on Hartnup patient prove there to be different amino acid transporters?

Answer 28

Because the patients cannot absorb alanine, a neutral amino acid, but can absorb arginine, a cationic amino acid. They can also absorb di-peptides.

Question 29

What is cystinuria a problem with?

Answer 29

Absorption of cationic amino acids.

Question 30

Which form would the classical hypothesis suggest is absorbed more readily? Glycine monomer, dimer, trimer or tetramer?

Answer 30

A monomer.

Question 31

What is the kinetic advantage of absorbing di or tri peptides?

Answer 31

Every time the transport protein goes through its transport cycle, 2 or 3 amino acids are moved across rather than 1.

Question 32

What is the acid microclimate and where is it?

Answer 32

pH of 5.5-6.8 at the top 1/3 of the villi.

Question 33

Why did they use Gly-Sar?

Answer 33

It is a hydrolysis resistant dipeptide.

Question 34

What is valinomycin?

Answer 34

A ionophore which inserts K+ channels into the membrane to make the inside more negative.

Question 35

Describe dipeptide transport.

Answer 35

Na+ independent, pH dependent and enhanced by a negative inside membrane potential. Driven by the proton electrochemical gradient.

Question 36

What is BCECF?

Answer 36

A pH dependent fluorescent dye.

Question 37

When the dipeptide is added outside, what is seen inside the BBMV?

Answer 37

acidification

Question 38

Where is PepT1 predominantly expressed?

Answer 38

In the small intestine

Question 39

Is there any other dipeptide transporter?

Answer 39

No- we know this because fluid absorption is abolished when PepT1 is knocked out.

Question 40

How is the acid microclimate maintained during absorption?

Answer 40

NHE3

Question 41

Does Na+ uptake increase with dipeptide uptake?

Answer 41

Yes

Question 42

What is S1611?

Answer 42

A selective inhibitor of NHE3