Digestion: Proteins And Vitamins/minerals

Front 1

What do endopeptidases do?

Back 1

hydrolyze peptide bonds between specific aa's throughout the molecule.
-first enzymes to act, yielding a large number of smaller fragments.

Front 2

What is Pepsin, where is it secreted/where does it act, and what does it do?

Back 2

Pepsin- secreted by the chief cells in the stomach, Catalyzes the hydrolysis of peptide bonds adjacent to aa's with bulky side chains (aromatic and branched-chain aa's and methionine).

Front 3

What is Trypsin, where is it secreted/where does it act, and what does it do?

Back 3

Endopeptidase, Secreted into the SI by the pancreas.
-catalyzes hydrolysis of lysine and arginine esters

Front 4

What is chymotrypsin, where is it secreted/where does it act, and what does it do?

Back 4

Endopeptidase, Secreted into the SI by the pancreas.
-catalyzes hydrolysis of aromatic aa's

Front 5

What is elastase, where is it secreted/where does it act, and what does it do?

Back 5

Endopeptidase, Secreted into the SI by the pancreas.
-catalyzes hydrolysis of small neutral aliphatic aa's.

Front 6

What do exopeptidases do?

Back 6

catalyze the hydrolysis of peptide bonds, one at a time, from the ends of peptides.

Front 7

What do carboxypeptidases do?

Back 7

(secreted in the pancreatic juices) release aa's from the free carboxyl terminal

Front 8

What do aminopeptidases do?

Back 8

(secreted by the intestinal mucosal cells) release aa's from the amino terminal.

Front 9

What do dipeptidases and tripeptidases do?

Back 9

(located in the brush border of intestinal mucosal cells) catalyze the hydrolysis of di- and tripeptides, which are not substrates for amino- and carboxypeptidases.

Front 10

Proteases are secreted as ___________.

Back 10

Zymogens (inactive enzymes)

Front 11

What activates pepsinogen?

Back 11

gastric acid and activated pepsin.

Front 12

what activates trypsinogen?

Back 12

enteropeptidase (which is secreted by the duodenal epithelial cells.

Front 13

What activates cymotrypsinogen, proelastase, procarboxypeptidase, and proaminopeptidase?

Back 13

Trypsin!

Front 14

T/F: oligopeptides cannot be absorbed by the intestine.

Back 14

False,

Front 15

Which protein end products can be absorbed into the intestine?

Back 15

free amino acids, di and tripeptides, and oligopeptides

Front 16

What happens to dipeptides and tripeptides when the enter the brush boarder of the intestinal mucosal cells?

Back 16

they are hydrolyzed to free aa's, which are then transported into the hepatic portal vein.

Front 17

Can relatively large peptides be absorbed intact?

Back 17

yes, either by uptake into mucosal epithelial cells (transcellular) or by passing between epithelial cells (paracellular).

Front 18

T/F: small proteins are capable of producing an allergic reaction.

Back 18

False. They must be larger to stimulate antibody formation.

Front 19

How are water soluble vitamins and mineral salts absorbed into the small intestine?

Back 19

Either by active transport or by carrier-mediated diffusion followed by binding to intracellular proteins to achieve concentrative uptake.

Front 20

What is vit B12 absorption dependent on?

Back 20

glycoprotein: Intrinsic factor

Front 21

Vitamin D is essential in the absorption of which mineral?

Back 21

Calcium.

Front 22

T/F: Zinc probably requires a zinc-binding ligand secreted by the exocrine pancreas

Back 22

True

Front 23

Which intracellular calcium-binding protein required for Ca++ absorption is induced by vitamin D?

Back 23

Calbindin

Front 24

What is the name of the compound present in cereals that binds to Ca++ in the lumen and prevents its absorption?
What other mineral is chelated by it?

Back 24

phytic acid (inositol hexaphosphate)

zinc

Front 25

High concentrations of _____ ______ in the intestinal lumen, as a result of impaired fat absorption, can also reduce Ca++ absorption by forming insoluble calcium salts.

Back 25

Fatty acids

Front 26

What dephosphorylates phytic acid in the lumen, rendering it inactive?

Back 26

yeast

Front 27

What is hemochromatosis?

Back 27

iron overload

Front 28

How is Fe++ transported into duodenal mucosal cells?

Back 28

via a divalent metal transporter

Front 29

How does iron accumulate within the cell?

Back 29

Binds to ferritin

Front 30

How does iron leave the cell when it is needed in the blood?

Back 30

it binds to a transport protein, ferroportin, but only if there is free transferrin in plasma to bind to.

Front 31

What is hepcidin and what role does play?

Back 31

Downregulates expression of the feroportin gene (and possibly that for the divalent metal ion transporter).
It is a peptide that is secreted by the liver when body iron reserves are adequate.
In response to hypoxia, anemia, or hemorrhage, synthesis of hepcidin is reduced, increasing synthesis of ferroportin and increased Fe++ absorption.

Front 32

About how much dietary Fe++ is absorbed? How much from plant foods?

Back 32

about 10%; 1-5%

Front 33

Since inorganic iron is absorbed in the _______ state, the presence of ________ agents enhances absorption.

Back 33

Reduced; reducing

Iron is absorbed as Fe++ ferrous

Front 34

What is the most effective compound to enhance iron absorption and why?
(two other examples of iron absorption enhancers?)

Back 34

Vitamin C; it is a reducing agent

(alcohol and fructose)

Front 35

Absorption of both inorganic and heme iron is impaired by _______.

Back 35

Calcium. a glass of milk with a meal significantly reduces iron availability.

Front 36

What is a form of malnutrition thought previously to be caused by protein deficiency in the diet that typically affects young children in the tropics? (now it is thought to be preceded by infection and decreased energy intake)

Back 36

Kwashiorkor

Front 37

What is severe undernourishment causing an infant's or child's weight to be significantly low for their age (below ___ % of normal)?

Back 37

marasmus (below 60% of normal)

Front 38

What is the formula for calculating BMI?

Back 38

Weight(kg)/ [height (m) squared]

Front 39

What is the desirable range for BMI?

Back 39

20-25

Front 40

T/F: kwashiorkor affects only children and only those in developing countries.

Back 40

True

Front 41

What are two distinguishing features of kwashiorkor?

Back 41

fluid retention leading to edema; and fatty infiltration of the liver.

Front 42

Marasmus is an outcome of what?

Back 42

prolonged negative energy balance. Fat reserves have been exhausted, there is muscle wasting, and loss of protein from the heart, liver and kidneys. As a result of reduced synthesis of proteins, there is impaired immune response. There is also impairment in cell proliferation in the intestinal mucosa, decreasing SA of the SI and reduction in the absorption of nutrients.

Front 43

~10% of the energy yield of a meal is expended in what?

Back 43

Forming reserves (glycogen stores, triacylglycerol, and protein)