Chapter 7: Proteins and Amino Acids (Oct 15 lec)

Question 1

Why is it that herbivores can digest animal protein and carnivores can digest animal protein?

Answer 1

both plant and animal proteins are made up of the same 20 amino acids
- same bonds and structural themes, different amino acid profiles

Question 2

peptides=

Answer 2

chains of amino acids joined by peptide bonds

Question 3

proteins and polypeptides

Answer 3

both are chains of amino acids joined by peptide bonds

• polypeptides= a long chain
• proteins= an even longer chain

Question 4

Water is ___ when a peptide bond is formed. Is this process reversible?

Answer 4

lost

Yes! water molecule required to break down peptide bonds

Question 5

primary protein structure

Answer 5

a sequence of a chain of amino acids

Question 6

secondary protein structure

Answer 6

h-bonding of the peptide backbone causes the amino acids to fold in a repeating pattern
- alpha helix or pleated beta sheet

Question 7

tertiary protein structure

Answer 7

3D folding pattern of a protein due to side chain interactions

• lowest energy configuration spontaneously forms
• this tertiary structure can be the fully functional protein

Question 8

quaternary protein structure

Answer 8

protein consisting of more than 1 amino acid (polypeptide) chain

• tertiary not always fully functional by themselves, but when put together it’s functional
• compact structure limits where enzymes can be active (hard to get peptide bonds to break them)

Question 9

How does cooking denature protein?

Answer 9

disrupts the tertiary structure- protein folding

Question 10

T/F

cooking is necessary for the digestion of protein

Answer 10

false- it’s possible to digest protein that’s not denatured

Question 11

a denatured protein is

Answer 11

more stretched out, more susceptible to enzyme degradation

- allows access to peptide bonds by pepsin in stomach

Question 12

If ingested protein is not denatured, it is denatured in the ___ by ____

Answer 12

stomach
HCl (does not break down the protein itself, just denatures it)

Question 13

zymogen=

Answer 13

an inactive precursor of an enzyme

Question 14

peptidase/ protease=

Answer 14

an enzyme that catalyzes the breakdown of proteins

Question 15

In the small intestine and pancreas, pH is near ____ and peptidases are secreted by _____

Answer 15

neutral

zymogens

Question 16

Trypsin is an enzyme that aids with ____. _____is the precursor of trypsin and is stored in the ___.

Answer 16

digestion

Trypsinogen
pancreas

Question 17

How does trypsinogen get activated into trypsin?

Answer 17

Enterokinase (an enzyme secreted by mucus in the intestine) cleaves trypsinogen to trypsin.
Once active, trypsin can go back and activate trypsinogen and other zymogens

Question 18

match the terms

• Enterokinase, trypsin, trypsinogen
• active enzyme, cleaving enzyme, zymogen

Answer 18

cleaving enzyme= enterokinase

zymogen= trypsinogen

active enzyme= trypsin

Question 19

why are proteins secreted as proteins?

Answer 19

To prevent the enzymes from digesting proteins in the cells in which they’re synthesized (b/c it’s an inactive precursor)

Question 20

What do endopeptidases do?

Where do they work?

Answer 20

takes a long chain and chops it up into shorter chains (not yet amino acids)
more chains= more carboxy ends for exopeptidases to work

small intestine

Question 21

What do exopeptidases do?

Answer 21

hydrolyze the ends of a chain (either carboxy or amino end)

• carboxypeptidase
• aminopeptidase

Question 22

T/F
active enzymes cleave specific peptide bonds.

Give ex

Answer 22

true

ex. Chymotrypsin –> basic amino acids

Question 23

Why does the intestine block absorption of intact protein?

Answer 23

the immune system would go crazy… reacting to foreign protein (lots of things that can hurt us are proteins, so the body attacks it)

Question 24

exceptions: when can the body absorb intact proteins?

Answer 24

1. newborns: first 24hrs after birth (gut closes to intact proteins after this)
   - purpose= passive immunity
2. Adults:
   - paracellular routes- tight junctions b/w cells (leaky gut)