Biochemistry 37: Protein Digestion And Amino Acid Absorption

Front 1

How does trypsinogen become trypsin?

Back 1

enteropeptidase activity

Front 2

HCL is created in the gut lumen by what cells?

Back 2

parietal

Front 3

How does pepsinogen become pepsin?

Back 3

autocatalytic (cleaves itself) in the acidic gut lumen

Front 4

Where does pepsin cleave proteins?

Back 4

endopeptidase (cleaves in the AA chain, not on the ends), tends to find aromatic or acidic amino acids

Front 5

Why does the pancreas secrete bicarbonate into the small intestine?

Back 5

to raise the pH after coming out of the stomach, allows intestinal/pancreatic enzymes to function

Front 6

Why is it important that the active pancreatic enzymes are all activated within a short time span?

Back 6

they have the ability to digest each other if given enough time

Front 7

Why is trypsin said to have a central role in digestion?

Back 7

it can directly cleave peptides, as well as activate many other digestive enzymes

Front 8

How does chymotrypsinogen become chymotrypsin?

Back 8

activated by trypsin

Front 9

How does proelastase become elastase?

Back 9

activated by trypsin

Front 10

How does procarboxypeptidase become carboxypeptidase?

Back 10

activated by trypsin

Front 11

What type of protease are trypsin, chymotrypsin and elastase?

Back 11

serine proteases

Front 12

Where does trypsin cleave peptides?

Back 12

where carbonyl group is attached to lysine or arginine

Front 13

Where does chymotrypsin cleave peptides?

Back 13

hydrophobic amino acids

Front 14

Where does elastase cleave peptides?

Back 14

amino acids with small side chains (alanine, glycine, serine), and elastin

Front 15

What causes Kwashiorkor?

Back 15

protein deficit in 3rd world countries due to malnutrition.

Front 16

What occurs in children with Kwashiorkor?

Back 16

muscle wasting due to lack of protein intake, drop of albumin = edema

Front 17

Why do children with Kwashiorkor have muscle wasting?

Back 17

they are malnourished and cannot create albumin due to protein deficit. also canot create digestive enzymes and cannot digest proteins that they make intake

Front 18

What is α-1-antitrypsin?

Back 18

a protease inhibitor made by liver

Front 19

What occurs in patients with α-1-antitrypsin deficits?

Back 19

since there is less inhibition of proteases, elastases can cleave elastin with little regulation. in the lungs, they lose their recoil ability = emphysema

Front 20

What is nephelometry?

Back 20

measuring α-1-antitrypsin levels in blood sample. use light scattering techniques

Front 21

Once peptides have been broken down by pancreatic enzymes (trypsin, chymotrypsin, elastase), what are these smaller peptides attacked by?

Back 21

exopeptidases, cleave AAs off the ends of the peptide

Front 22

Where does carboxypeptidase cleave peptides?

Back 22

it is an exopeptidase so it cleaves the AAs on the end of the peptide

Front 23

Carboxypeptidase A works to cleave which Amino acids?

Back 23

hydrophobic ones

Front 24

Carboxypeptidase B works to cleave which Amino acids?

Back 24

lysine, arginine (basic amino acids)

Front 25

Where do Trypsin, chymotrypsin, elastase, and carboxypeptidase come from?

Back 25

pancreas

Front 26

Where do aminopeptidase enzymes come from?

Back 26

the brush border cells of the intestines

Front 27

Where do aminopeptidases cleave peptides?

Back 27

exopeptidases, cleave one AA at a time from the end of the peptide

Front 28

Once a peptide is broken into AAs, how does it enter the cells of the intestines?

Back 28

passive co-transport with Na+ (gradient in the cell is created by Na/K pump)

Front 29

How does an amino acid get from the intestine cell into the blood stream?

Back 29

facilitated transport down gradient into portal vein

Front 30

What is inspissation in the pancreatic duct?

Back 30

drying and thickening of the pancreatic secretions (seen in cystic fibrosis). leads to duct obstruction

Front 31

Why is it important that the pancreas also create and store a trypsin inhibitory protein?

Back 31

to prevent accidental trypsin activation. that would lead to all the digestive enzymes accidentally activating and can lead to pancreatitis

Front 32

Why/when would amino acid transport on the serosal side of the intestines (into the blood) reverse direction?

Back 32

during starvation, when proteins are not entering the cell on the apical side (from the intestine), they must take AA from the blood

Front 33

How would a polypeptide end up in the blood?

Back 33

by passing through the intestinal epithelium (via pinocytosis) or by slipping between the intestinal cells. normally peptides need to be broken down into AAs then the AAs are absorbed through the intestinal cells into the blood

Front 34

Why might is be a problem if peptides are present in the blood of an infant?

Back 34

immune system can react to them and lead to allergies to the food they eat. normally peptides need to be broken down into AAs then the AAs are absorbed through the intestinal cells into the blood

Front 35

What is Hartnup disease's pattern of inheritance?

Back 35

autosomal recessive

Front 36

What causes Hartnup disease?

Back 36

defect in transport of AA across intestinal and renal cells

Front 37

What causes the symptoms of Hartnup's disease?

Back 37

lack of essential AA in the blood, since they cannot be reabsorbed into the blood from intestines or kidneys

Front 38

What is cystinuria?

Back 38

high levels of cystine in the urine; can lead to kidney stones

Front 39

What levels of amino acids would we expect to see in a Hartnup's patient's blood?

Back 39

low levels, AA cannot enter the blood form intestines or kidneys

Front 40

Why might a patient with Hartnup's disease be at high risk for kidney stones?

Back 40

Since they cannot reabsorb AA from the urine into the blood, the Amino acids can collect in the ducts. they can form stones over time, specifically cystine

Front 41

Why are muscles degraded during period of starvation?

Back 41

the amino acids can be used for gluconeogenesis

Front 42

What happens to excess dietary protein in the body?

Back 42

it is stored as glycogen and triacylglycerol for storage

Front 43

Life span of an RBC

Back 43

120 days

Front 44

In patients with cystinuria, why is there not usually hypoaminoacidemia (low AA in the blood)?

Back 44

cystinuria mean cystine is not re-entering the blood from urine, so we expect low levels in the blood. but cystine is made by the body. Cystine levels in the blood can remain normal

Front 45

What is a nonessential amino acid?

Back 45

one that can be made by the body

Front 46

Why does cystinuria increase the risk of kidney stones?

Back 46

cystine is insoluble and if here are high levels in the urine it precipitates and can collect

Front 47

What is renal colic?

Back 47

genitourinary bleeding and pain, e.g. kidney stones

Front 48

2 mechanisms for enzyme degradation

Back 48

lysosomal protein turnover and ubiquitin-proteosome pathway

Front 49

What happens to the AAs after the lysosomal degradation of peptides?

Back 49

they enter the cell's cytoplasm from the lysosome

Front 50

What family of proteases degrade the proteins in the lysosome during lysosomal protein turnover?

Back 50

cathepsin family of proteases

Front 51

What is the primary process of degradation in the lysosomal protein turnover pathway of protein degradation?

Back 51

autophagy within a cell

Front 52

Describe the process of autophagy within a cell.

Back 52

cytoplasm is sequestered in the cells and the new vesicles (with protein in them) fuse with the lysosome. the lysosome uses cathepsin proteases to degrade the protein into AAs. the AAs leave the lysosome and enter the cytosol

Front 53

What triggers the lysomal protein turnover pathway?

Back 53

starvation. we want more AA monomers in the cell cytosol so it can enter the blood

Front 54

Ubiquitin binds to which AA?

Back 54

lysine (amino group)

Front 55

What is polyubiquitinylation?

Back 55

the process of marking the proteins for degradation by adding a chain of ubiquitin on the target protein

Front 56

Why is ATP needed for the ubiquitin-proteosome pathway?

Back 56

to unfold the target protein and bring it into the proteosome active site

Front 57

What is the function of cap proteins in the ubiquitin-proteosome pathway?

Back 57

cap protein complexes bind the target protein and bring it to the proteosome; needs ATP

Front 58

What happens to ubiquitin after the target protein is destroyed?

Back 58

it is released and recycled

Front 59

What is a PEST sequence?

Back 59

region of a protein rich in Proline, Glutamine, Serine, Threonine; typically hydrolyzed by ubiquitin pathway

Front 60

What causes pellagra?

Back 60

lack of niacin or tryptophan, leads to less NAD/NADP.

Front 61

Glutathione serves what purpose in cells?

Back 61

prevent against oxidative damage

Front 62

How is glutathione syntehsized?

Back 62

from glutamate, via the γ-glutamyl cycle