Biochemically Small PeptidesㅡQuarternary Structure Of Proteins

Question 1

The two best-known peptide hormones, both produced by the pituitary gland, are
___________ and __________. Each hormone is a nonapeptide (nine amino acid residues) with six of the residues held in the form of a loop by a disulfi de bond formed from the interaction of two cysteine residues.

Answer 1

oxytocin
vasopressin

Question 2

Another name for vasopressin is _____________.

Answer 2

antidiuretic hormone (ADH)

Question 3

____________ are pentapeptide neurotransmitters produced by the brain itself that bind at receptor sites in the brain to reduce pain.
The pain-reducing effects of ____________ action play a role in the “high” reported by long-distance runners, in the competitive athlete’s managing to finish the game despite being injured, and in the pain-relieving effects of acupuncture.

Answer 3

Enkephalins

Question 4

The two best-known enkephalins are ___________ and ____________, whose structures differ only in the amino acid residue present at the C-terminal end of the peptide.

Answer 4

Met-enkephalin: Tyr–Gly–Gly–Phe–Met
Leu-enkephalin: Tyr–Gly–Gly–Phe–Leu

Question 5

The tripeptide __________ is present in signifi cant concentrations in most cells and is of considerable physiological importance as a regulator of oxidation–reduction reactions. Specifically, ____ functions as an antioxidant, protecting cellular contents from oxidizing agents such as peroxides and superoxides (highly reactive forms of oxygen often generated within the cell in response to bacterial invasion).

Answer 5

glutathione (Glu–Cys–Gly)

Question 6

A __________ is a protein in which only one peptide chain is present.

Answer 6

monomeric protein

Question 7

A _____________ is a protein in which more than one peptide chain is present.

Answer 7

multimeric protein

Question 8

The peptide chains present in multimeric proteins are called __________.

Answer 8

protein subunits

Question 9

A ____________ is a protein in which only amino acid residues are present.
More than one protein subunit may be present in a _________, but all subunits contain only amino acids.

Answer 9

simple protein

Question 10

A _____________ is a protein that has one or more non-amino acid entities present in its structure in addition to one or more peptide chains. These non-amino acid components, which may be organic or inorganic, are called prosthetic groups.

Answer 10

conjugated protein

Question 11

A __________ is a non-amino acid group present in a conjugated protein.

Answer 11

prosthetic group

Question 12

___________ is the order in which amino acids are linked together in a protein.

Answer 12

Primary protein structure

Question 13

The British biochemist _______________ (1918– )
determined the primary structure of the protein hormone insulin in 1953.

Answer 13

Frederick Sanger

Question 14

____________ is the arrangement in space adopted by the backbone
portion of a protein.

Answer 14

Secondary protein structure

Question 15

The two most common types of secondary structure are the
_____________ and the ______________.

Answer 15

a. alpha helix (a helix)
b. beta pleated sheet (b pleated sheet)

Question 16

An _____________ is a protein secondary structure in which a single protein
chain adopts a shape that resembles a coiled spring (helix), with the coil configuration
maintained by hydrogen bond.

Answer 16

alpha helix structure

Question 17

A ___________ is a protein secondary structure in which two fully
extended protein chain segments in the same or different molecules are held together
by hydrogen bonds.

Answer 17

beta pleated sheet structure

Question 18

This “_____________” is the most frequently encountered type of b pleated sheet
structure.

Answer 18

U-turn structure

Question 19

An _________________ is a protein secondary structure that is neither an
a helix nor a b pleated sheet.

Answer 19

unstructured protein segment

Question 20

_____________ is the overall three-dimensional shape of a protein that results from the interactions between amino acid side chains (R groups) that are
widely separated from each other within a peptide chain.

Answer 20

Tertiary protein structure

Question 21

Four types of stabilizing interactions contribute to the tertiary structure of a protein:

Answer 21

(1) covalent disulfide bonds
(2) electrostatic attractions (salt bridges)
(3) hydrogen
bonds and
(4) hydrophobic attractions

Question 22

__________, the strongest of the tertiary-structure interactions, result from
the ㅡSH groups of two cysteine residues reacting with each other to form a covalent disulfide bond. This type of interaction is the only one of the four
tertiary-structure interactions that involves a covalent bond.

Answer 22

Disulfide bonds

Question 23

___________, also called salt bridges, always involve the interaction
between an acidic side chain (R group) and a basic side chain (R group). The side
chains of acidic and basic amino acids, at the appropriate pH, carry charges, with
the acidic side chain being negatively charged and the basic side chain being positively charged.

Answer 23

Electrostatic interactions

Question 24

___________ can occur between amino acids with polar R groups. They are relatively weak and are easily disrupted by changes in pH and temperature.

Answer 24

Hydrogen bonds

Question 25

_____________ result when two nonpolar side chains are close to
each other.

Answer 25

Hydrophobic interactions

Question 26

Hydrophobic interactions are common between __________ and
______________.

Answer 26

phenyl rings
alkyl side chains

Question 27

In 1959, a protein tertiary structure was determined for the first time. The determination involved __________, a conjugated protein whose function is oxygen storage in muscle tissue.

Answer 27

myoglobin

Question 28

______________ is the highest level of protein organization. It is found only in
multimeric proteins. Such proteins have structures involving two or more peptide chains that are independent of each other—that is, are not covalently bonded to each other.

Answer 28

Quaternary structure

Question 29

An example of a protein with quaternary structure is __________, the oxygen-
carrying protein in blood. It is a tetramer in which there are two
identical a chains and two identical b chains.

Answer 29

hemoglobin