chapter 5 section 1

Question 1

What are the three basic classes of proteins based on shape and solubility?

Answer 1

Fibrous, globular, and membrane proteins.

Question 2

What are the characteristics of fibrous proteins?

Answer 2

Linear, serve structural roles; insoluble in water or dilute salt solutions.

Question 3

What are the characteristics of globular proteins?

Answer 3

Roughly spherical; hydrophobic interior, hydrophilic exterior; usually soluble in water;

Question 4

What are the characteristics of membrane proteins?

Answer 4

hydrophobic residues on outside in membrane regions; insoluble in water but soluble in detergents

Question 5

Give examples of each protein class.

Answer 5

Fibrous – Collagen; Globular – Myoglobin; Membrane – Bacteriorhodopsin.

Question 6

What defines the tertiary structure of a protein?

Answer 6

the folding of a polypeptide chain into a compact, roughly spherical 3D conformation.

Question 7

Name three ways tertiary structure can be represented

Answer 7

1) Cα tracing (backbone positions), 2) Ribbon diagram (helices and sheets), 3) Space-filling model (atoms as spheres).

Question 8

What is quaternary structure?

Answer 8

the way multiple polypeptide chains fit together and interact to form a functional protei.

Question 9

What information does quaternary structure include?

Answer 9

The types of subunits, the number of each, and how they interact.

Question 10

Give an example of a protein with quaternary structure.

Answer 10

Hemoglobin – a tetramer with 2 α and 2 β chains

Question 11

What are the two principal secondary structures in proteins?

Answer 11

α-helix and β-pleated strand (sheet).

Question 12

How is an α-helix commonly represented?

Answer 12

As a flat helical ribbon, a cylinder, or a backbone coil around a helical axis.

Question 13

How is a β-strand commonly represented?

Answer 13

As a flat, wide arrow with the backbone and side-chain orientations indicated.

Question 14

What defines the tertiary structure of a protein?

Answer 14

The three-dimensional folding of a polypeptide chain into a compact, globular shape.

Question 15

Why do proteins adopt a globular tertiary structure?

Answer 15

to minimize surface-to-volume ratio and reduce unfavorable interactions with the environment.

Question 16

What is the primary structure of a protein?

Answer 16

The specific sequence of amino acids in a polypeptide chain.

Question 17

Why is primary structure important?

Answer 17

It defines the protein’s identity, and all other structural features and functions follow from it.

Question 18

What is secondary structure?

Answer 18

regions of amino acid chains that are stabilized by hydrogen bonds from the polypeptide backbone

Question 19

How are secondary structures stabilized?

Answer 19

Through hydrogen bonds between the backbone amide and carbonyl groups of the polypeptide.

Question 20

What is the primary structure of a protein?

Answer 20

The amino acid sequence of a protein

Question 21

How are disulfide bridges related to primary structure?

Answer 21

Disulfide bridges form covalent crosslinks between cysteine residues, stabilizing the protein’s folded structure.

Question 22

What defines secondary structure in proteins?

Answer 22

Regular structural patterns like alpha helices and beta sheets formed by hydrogen bonds between backbone atoms.

Question 23

What role do hydrogen bonds play in secondary structure?

Answer 23

They stabilize alpha helices and beta sheets along the polypeptide backbone.

Question 24

What is the difference between primary and secondary structure?

Answer 24

Primary is the linear sequence of amino acids; secondary is the local folding pattern formed by hydrogen bonding.

Question 25

Why are secondary structures important?

Answer 25

They contribute to the protein’s overall 3D shape and are building blocks for higher levels of structure.

Question 26

What is a protein’s conformation?

Answer 26

The overall three-dimensional shape of a protein.

Question 27

How is conformation different from configuration?

Answer 27

Conformation can change by rotation around single bonds without breaking covalent bonds; configuration requires breaking and remaking bonds.

Question 28

What allows proteins to adopt different conformations?

Answer 28

Rotation around single bonds along the peptide backbone.

Question 29

Are all theoretical protein conformations equally likely?

Answer 29

No, only a few conformations are energetically favored under physiological conditions.

Question 30

Why is protein conformation important?

Answer 30

It determines the protein’s functional 3D shape and interactions.

Question 31

What is meant by "conformational possibilities"?

Answer 31

The range of 3D shapes a protein chain can adopt due to rotations around its single bonds.