Amino Acids, Peptides and Proteins

Question 1

amino acids components

Answer 1

amino group, carboxyl group, hydrogen and R group

Question 2

amphoteric species

Answer 2

can accept a proton or donate a proton; how they react depends on pH of environment

Question 3

At low pH, ionizable groups tend to be _____.

Answer 3

protonated

Question 4

At high pH, ionizable groups tend to be _____.

Answer 4

deprotonated

Question 5

If pH is less than pKa, a majority of species will be _____.

Answer 5

protonated

Question 6

If pH is higher than pKa, a majority of species will be _____.

Answer 6

deprotonated

Question 7

Amino Acids in Low pH (1)

Answer 7

Since there are plenty of protons in the solution, both the amino group and the carboxylic acid group will be fully protonated. Net positive charge.

Question 8

Zwitterions at intermediate pH (7.4)

Answer 8

At this point, the carboxyl group will become deprotonataed (COO-) while the amino group remains protonated (NH3+)

Question 9

Amino acids in basic conditions (10.5)

Answer 9

The carboxylate group stays deprotonated and the amino group also becomes deprotonated, becoming NH2-. Net negative charge.

Question 10

titration of amino acids

Answer 10

-presents as two curves (or three if side chain is charged)

Question 11

isoelectric point (pI)

Answer 11

• pH where all molecules are electrically neutral
• pI=average of the pKa values for the amino and carboxyl groups
• titration curve nearly vertical

Question 12

titration of amino acids with (-) side chains

Answer 12

pI=the average of the pKa values for the carboxyl group and the R group; relatively high isoelectric points

Question 13

titration of amino acids with (+) side chains

Answer 13

pI=average of the pKa values for the R group and the amino group; relatively low isoelectric points

Question 14

peptides

Answer 14

composed of amino acid subunits, called residues

Question 15

dipeptides+tripeptides

Answer 15

two AA residues; three AA residues

Question 16

oligopeptide v. polypeptide

Answer 16

oligo: relatively small peptide, up to about two AA residues
poly: longer peptide chains

Question 17

peptide bond

Answer 17

specialized form of amide bond that forms between the COO- group of one AA and the NH3+ group of another AA; forms functional group -C(O)NH-

Question 18

condensation/dehydration reaction

Answer 18

results in the removal of a water molecule

Question 19

N-terminus

Answer 19

free amino end when a peptide bond forms (left)

Question 20

C-terminus

Answer 20

free carboxyl end when a peptide bond forms (right)

Question 21

trypsin and chymotrypsin

Answer 21

hydrolytic enzymes that catalyze the hydrolysis of specific points in a peptide bond; break apart amide bond by adding a hydrogen to the amide nitrogen and OH group to the carbonyl carbon

Question 22

protein

Answer 22

polypeptides made of amino acids

Question 23

primary structure of protein

Answer 23

sequence of amino acids listed from N-terminus to C-terminus; stabilized by covalent peptide bonds

Question 24

secondary structure of protein

Answer 24

result of H bonding between nearby amino acids; alpha helix and beta sheet

Question 25

alpha helix

Answer 25

rodlike structure in which the peptide chain coils clockwise around a central axis; stabilized by intramolecular H bonds; important component in the structure of keratin

Question 26

beta-pleated sheets

Answer 26

peptide chains lie alongside one another, forming rows or strands held together by intramolecular H bonds

Question 27

proline in secondary structures

Answer 27

usually only found in the turns between the chains of beta sheets or at the start of an alpha helix because of its structure

Question 28

fibrous proteins

Answer 28

structures that resemble long sheets/strands; i.e. collagen

Question 29

globular proteins

Answer 29

structures that resemble spheres; i.e. myoglobin

Question 30

tertiary structure of proteins

Answer 30

3-D shape determined by hydrophilic/phobic interactions between R-groups

Question 31

disulfide bonds

Answer 31

bonds that form when two cysteine molecules become oxidized to form cystine; create loops in protein chain

Question 32

molten globules

Answer 32

intermediate states in protein folding

Question 33

denaturation

Answer 33

when a protein loses its tertiary structure and becomes nonfunctional; usually caused by heat and solutes

Question 34

solvation layer

Answer 34

when a solvent dissolves in a solvent, the nearby solvent molecules form this around the solute

Question 35

quaternary structure

Answer 35

not all proteins have this; only form when a protein contains more than one polypeptide chain; made up of smaller globular peptides called subunits; can induce allosteric effects

Question 36

conjugated proteins

Answer 36

derive part of their function from covalently attached molecules called prosthetic groups

Question 37

lipoproteins, glycoproteins and nucleoproteins

Answer 37

proteins with lipid, carbohydrate and nucleic acid prosthetic groups

Question 38

prosthetic group

Answer 38

play major roles in determine the function of the protein to which they are connected