Ch. 3 Proteins

Question 1

The “first in rank” macromolecules.

Answer 1

Proteins

Question 2

-in ending reflects the presence of _______.

Answer 2

Amino groups

Question 3

_____ from amino groups contributes significantly to protein mass (16% on average).

Answer 3

Nitrogen

Question 4

Two key aspects of proteins

Answer 4

1. structure: from building blocks to three-dimensional shape
2. function: diverse roles in biological systems

Question 5

Proteins are composed of a limited set of ____ fundamental amino acids.

Answer 5

20

Question 6

Modified amino acids exist but arise from the 20 fundamental ones after __________.

Answer 6

Protein synthesis

Question 7

How many amino acids are essential?

Answer 7

8

Question 8

How are essential amino acids obtained in the body?

Answer 8

Through the diet, because they cannot be synthesized through the body.

Question 9

How many amino acids are “non-essential”?

Answer 9

12

Question 10

How does the body synthesize the 12 non-essential amino acids?

Answer 10

Through compounds already present in our cells.

Question 11

The general formula of amino acids includes:

Answer 11

central (alpha) carbon atom with 4 attached groups: carboxyl group COO-, amino group +H3N, hydrogen H, variable group (side chain) R.

Question 12

Amino acids are ionized in _______ solutions.

Answer 12

Aqueous

Question 13

What is an amino acid’s predominant form at physiological pH?

Answer 13

Neutral (zwitterionic)

Question 14

Side chains vary in ______

Answer 14

Size, charge, polarity, and chemical reactivity

Question 15

Amino acids link ____ to form proteins.

Answer 15

Covalently

Question 16

Short stretches of amino acids are known as ________.

Answer 16

Peptides

Question 17

Peptides are _______.

Answer 17

Proteins digested to produce shorter chains.

Question 18

What indicates the number of amino acids in a peptide chain? Give 3 examples.

Answer 18

Prefixes - di, tri, tetra

Question 19

What term describes 10-20 amino acids in a chain?

Answer 19

Oligopeptide

Question 20

What term describes more than 20 amino acids in a chain?

Answer 20

Polypeptide

Question 21

Proteins are often referred to as ________.

Answer 21

Polypeptide chains

Question 22

How do peptide bonds form?

Answer 22

Via a synthesis condensation reaction, producing water.

Question 23

How do peptide bonds break?

Answer 23

A hydrolysis reaction, requires the addition of water.

Question 24

The left side of a Lewis structure is known as _______.

Answer 24

N-terminus

Question 25

The right side of a Lewis Structure is known as _______.

Answer 25

C-terminus

Question 26

What is a residue?

Answer 26

The part of the amino acid involved in peptide formation (what is left over after linking with others to become a larger polymer).

Question 27

A free carboxyl group deriving from aspartate and a free amino group belonging to phenylalanine.

Answer 27

Dipeptide Asp-Phe (isomer of Phe-Asp)

Question 28

What are the four levels of protein structures?

Answer 28

Primary, secondary, tertiary, and quaternary

Question 29

The most basic level of protein structures.

Answer 29

Primary

Question 30

Humans can have around ______ to ______ proteins.

Answer 30

100,000 to 200,000

Question 31

Primary structure is determined by ________.

Answer 31

Genetic information in genes encodes the amino acid sequences.

Question 32

3D arrangements within proteins, polypeptide chain folding in specific patterns.

Answer 32

Secondary structure

Question 33

*Key Players* - Noncovalent with some covalent character; Forms between δ+(H) and δ-(O or N) atoms, because O and N have a higher electronegativity than H; Stabilizes the secondary structure.

Answer 33

Hydrogen Bonds

Question 34

The two common types of secondary structures

Answer 34

Alpha (α) helix, Beta (β) sheet

Question 35

Resembles a right-handed spiral staircase, backbone forms a spiral, side chains point outward, stabilized by hydrogen bonds between adjacent turns.

Answer 35

Alpha (α) Helix

Question 36

Resembles a crinkled bedsheet, strands are segments of stretched polypeptide chain, strands undulate with parallel peptide unit planes, adjacent residue side chains point in opposite directions.

Answer 36

Beta (β) Sheet

Question 37

Conformation of the entire polypeptide chain, flexible and can fold to bring distant residues together, stabilized by various (four) interactions.

Answer 37

Tertiary structure

Question 38

4 different types of tertiary interactions

Answer 38

Electrostatic Bond, Van Der Waals Interaction, Disulfide Bond, Hydrophobic Interaction

Question 39

Formed between oppositely charged groups; weaker than hydrogen bonds.

Answer 39

Electrostatic Bonds

Question 40

Positively charged groups of electrostatic bonds

Answer 40

Terminal amino group, lysine, arginine, and possibly histidine

Question 41

Negatively charged groups of electrostatic bonds

Answer 41

Terminal carboxyl group, aspartate, and glutamate

Question 42

Noncovalent attraction due to electron movements, momentary asymmetries induce electrostatic forces, weaker than electrostatic bonds

Answer 42

Van Der Waals Interaction

Question 43

Covalent bond between cysteine residues (sulfur atoms from two cysteine residues), forms through shedding of H atoms, stronger than peptide bonds, remains united as cystine after protein breakdown.

Answer 43

Disulfide bonds

Question 44

Side chains (alanine, valine, leucine) cluster together, driven by repulsion by surrounding water, more stable than exposure to water, **weakest interaction discussed**

Answer 44

Hydrophobic Interaction

Question 45

The process of altering a protein's structure, causing it to unfold or break up.

Answer 45

Denaturation

Question 46

Two main factors of leading to denaturation, provide 2 examples of this process.

Answer 46

High temperature and extreme pH values - cooking eggs, yogurt formation.

Question 47

Why does high temperature lead to denaturation? Is it reversible or irreversible?

Answer 47

Thermal movement disrupts protein structure , alteration of the polypeptide chain - often irreversible.

Question 48

Why do extreme pH values lead to denaturation? Is it reversible or irreversible?

Answer 48

Addition or removal of protons (H+) from chemical groups, affects hydrogen and electrostatic bonding - typically irreversible.

Question 49

Consists of multiple polypeptide chains (known as subunits/simply chains), stabilized by the same bonds as tertiary structures.

Answer 49

Quaternary Structure