08 Protien Digestion

Question 1

What are proteins ?

Answer 1

twenty amino acids of which nine are essential and eleven are non-essential.

Four amino acids are considered conditionally essential

Question 2

What is conditionally essential amino acids ?

Answer 2

Basicly non essintial, but becomes essential under certen conditions

Four amino acids are considered conditionally essential including arginine, tyrosine, glutamine, and cysteine.

Question 3

………. Are Amino acids that can not be synthesized in the body

Answer 3

Essintial amino acids

Question 4

An example for conditionally essential AA ?

Answer 4

An example is phenylketonuria (PKU). Individuals with PKU cannot synthesize tyrosine from phenylalanine, so tyrosine becomes essential in the diet of PKU patients

Question 5

Because whole proteins are not absorbed they must be digested into …………………………….. prior to absorption.

Answer 5

digested into AAs or di- and tri- peptides

Question 6

Proteins are more diverse than carbohydrates and thus require a broader spectrum of peptidases and transporters than carbohydrates. True or false?

Answer 6

True

Question 7

Where does protein digestion begins?

Answer 7

In stomach

Question 8

Where does protein digestion happen?

Answer 8

Digestion begins in the stomach and is accomplished by both gastric and pancreatic proteases, with the vast majority (70%) accomplished by pancreatic proteases.

So this major 70% happens in small intastin intastine

Question 9

What happens in gastric digestion phase?

Answer 9

gastric phase of digestion begins with the secretion of pepsinogen from chief cells and HCl from parietal cells. HCl works to denature proteins and more importantly converts inactive pepsinogen to active pepsin

Question 10

What digests protiens in stomach ?

Answer 10

HCL and pepsin

Question 11

Pepsin targets which type of protein ?

Answer 11

Pepsin cleaves proteins at large aliphatic or large aromatic side chains

Question 12

When chyme enters the small intestine after coming of out the stomach, how does pepsin get inactivated?
If it is still active it will auto-digestion the intastine

Answer 12

As the chyme enters the intestine, pepsin is inactivated (at pH >4.5)

Clinical Correlation- The requirement for acidic pH to activate pepsinogen has implications for using proton pump inhibitors.

Question 13

What happens in the intastinal phase ?

Answer 13

The intestinal phase is responsible for the bulk of proteolysis and is mainly due to the actions of the pancreatic proteases.

Question 14

There are two main forms of pancreatic enzymes

Answer 14

endopeptidase – cleaves internal bonds exopeptidase – cleaves external bonds

Question 15

What pancreatic enzymes target terminal parts?

Answer 15

Exopeptidase targets external parts / terminal parts examples → aminopeptidase and carboxypeptidase

Question 16

What pancreatic enzymes target inner parts?

Answer 16

Endopeptidase including trypsin, chymotrypsin and elastase.

Question 17

Exopeptidases include ……….

Answer 17

Exopeptidases include carboxypeptidase A and B and aminopeptidase. Carboxypeptidase A acts on neutral AA and carboxypeptidase B acts on basic AA

Question 18

Where are pancreatic enzymes stored ?

Answer 18

Pancreatic enzymes are stored in acinar cells as pro-enzymes (zymogens) and are activated by trypsin, which itself is self-activated (and by enterokinase)

Question 19

Whaen …………… is activated to Trypsin, it causes activates of all the other enzymes ( Chymotrypsinogen > Chymotrypsin.
Procarboxypeptidase A and B > Carboxypeptidase A and B.

Proelastase > Elastase)

Answer 19

Trypsin

Question 20

What inhibits trypsin ?

Answer 20

Trypsin inhibitors are small proteins or peptides that are present in plants (Soybeans, peas, beans, wheat), organs (pancreas), and fluids (colostrum). They decrease the activity of trypsin and therefore all proteases. The trypsin inhibitors are inactivated by heat.

Question 21

How to deactivate/inactivate trypsin inhibitors

Answer 21

The trypsin inhibitors are inactivated by heat.

Question 22

Additional protein digestion occurs at the brush border, increasing the amount of protein suited for intracellular transport. True or false

Answer 22

True

Question 23

Brush border peptidases produce …………………..

Answer 23

produce single amino acids and smaller peptides (di and tri-peptides) from tetrapeptides and larger peptides.

Question 24

What breaks down dipeptides and tripeptides into single amino acids inside the cell?

Answer 24

Intracellular cytoplasmic peptidases

Question 25

Greater than 99% of protein enters the bloodstream as single amino acids, but some remain in the enterocytes and are used to support the cell. True or false

Answer 25

True

Question 26

Remember, absorption has 2 steps

1. …………
2. …………

Answer 26

1. intastinal lumen to cell

2. Cell to blood

Question 27

Most protein absorption takes place in …………….

Answer 27

duodenum and jejunum where oligopeptides (3 to 4 AA and shorter) and AA transported.

Question 28

Does Oligopeptides have more rapid absorption than free amino acids?

Answer 28

Yes

Question 29

Some amino acids share the same transport system, so if a large amount of one particular amino acid is consumed, the absorption of others may be inhibited. True or false?

Answer 29

True

Question 30

There are several different transporters of AA that work by different mechanisms. One active transporter is PEPT1. How does PEPT1 work?

Answer 30

PEPT1 is coupled to sodium-hydrogen exchanger (NHE3).
It is in the apical side near lumen.
Gets 3 Na+ inside the cell and 1 H+ outside the cell

PEPT1 is an active transporter

Question 31

FREE AA are transported out of the lumen by several different mechanisms including …………….

Answer 31

facilitated diffusion
Na+ independent carriers
Na+ dependent carriers
proton co-transport

Question 32

The basolateral membrane of the enterocyte contains additional transporters which export amino acids from the cell into the blood by both ………………. and ……….. …………..

Answer 32

Facilitated Diffusion

Na+ dependent and independent carriers.

Question 33

What is Hartnup Disease ?

Answer 33

Hartnup Disease is due to abnormal transport of neutral AA (i.e. tryptophan) caused by a mutation in SCL6A19 transporter. There is significant clinical variability in the presentation from no symptoms to rash or neurologic symptoms (developmental delays).
It affects central nervous system

Question 34

An abnormal transport of a neutral aa called …………………. Causes hartnup disease

Answer 34

Tryptophan

Question 35

Symptoms pf hartnup disease are due to lack of……………… which is a tryptophan metabolite

Answer 35

nicotinamide

Question 36

Deficiency of the amino acid tryptophan is believed to account for the symptoms associated with Hartnup disease. Tryptophan is essential for the creation (synthesis) of………….., which is also supplemented through nutrition as a vitamin (also known as vitamin B3).

Answer 36

nicotinamide

Question 37

How is hartnup diagnosed?

Answer 37

Diagnosis is made by presence of high levels of neutral AA in the urine.

Question 38

How is hartnup treated?

Answer 38

supplementation with nicotinamide.

Question 39

What is Cystinuria?

Answer 39

Cystinuria is decreased intestinal absorption of dibasic AAs (lysine, arginine, cystine) due to a defect in SLC3A1 transporter.

So cystenie is not absorped

Question 40

How to diagnose Cystinuria?

Answer 40

Diagnosis is made by elevated urine cysteine.

Question 41

Traetment of Cystinuria?

Answer 41

hydration and dietary limitation of methionine.

Question 42

One of Cystinuria symptoms is ………

Answer 42

Patients present with kidney stones. Cystinuria accounts for 10% of kidney stones.