Proteins

Question 1

State the general structure of an amino acid

Answer 1

1. Has an alpha carbon in the middle
2. Elements are connected through covalent bonds
3. Has an amine group, which is basic because it receives a proton from the carboxyl group
4. Has a carboxyl group, which is acidic because it donates a proton to the amine group
5. Amino acids are amphiprotic (have both acidic and basic structures
6. R-group, which determines the properties of assembled polypeptides (hydrophilic R-groups are polar or charged, acidic or basic)

Question 2

How are dipeptides or polypeptides formed?

Answer 2

Through the condensation reaction, where a peptide bond joins the two amino acids

Question 3

What is the condensation reaction with amino acids?

Answer 3

It forms polypeptides between one amino acid’s amine group and another amino acid’s carboxyl group, catalyzed by ribosomes.

Question 4

What are the dietary requirements for amino acids?

Answer 4

1. Essential Amino Acid - Cannot be produced by the body and must be present in the diet
2. Non-essential Amino Acid - Can be produced by the body and not required in the diet
3. Conditional Amino Acid - Can be produced by the bacteria in the body, but only essential at certain times (e.g. infancy, pregnancy, illness, etc.)

Question 5

What is protein folding?

Answer 5

It determines its eventual function and level of biological activity

Question 6

What is denaturation?

Answer 6

Structural change in protein results in permanent loss of biological properties because the way proteins fold determines their function

Question 7

What causes denaturation?

Answer 7

1. Heat - It disrupts hydrogen bonds that hold the proteins together (protein can unfold)
2. pH - The change in the pH (charge) of the proteins will change the solubility and shape

Question 8

What are the functions of proteins?

Answer 8

Structure
Hormones
Insulation
Transport
Sensation
Movement
Enzymes

Question 9

What is the primary structure? (HL)

Answer 9

A linear sequence of amino acids in a polypeptide bond determines how the chain will fold. Different amino acids will fold into different configurations because of the chemical properties of the R-group

Question 10

What is the secondary structure? (HL)

Answer 10

Polypeptides fold into alpha helixes or beta-pleated sheets stabilized by hydrogen bonding due to polarity
1. alpha helix - Structure when amino acid sequence folds into a coil arrangement
2. beta-pleated sheets - Structure when two or more sections of a polypeptide are arranged into parallel with hydrogen bonds in between

Question 11

What is the tertiary structure? (HL)

Answer 11

The interactions between the R-groups can determine it. R-groups can become negatively or positively charged by binding or dissociation of H+.
Ionic bonding - Between negatively or positively charged R-groups (sensitive to pH changes)
Hydrogen bonding - Between polar R-groups
Disulfide bonds - pairs of cysteines forming covalent bonds
Hydrophobic interactions - between hydrophobic R-groups

Question 12

What is the quaternary structure? (HL)

Answer 12

It is the structure when there is more than one polypeptide.
1. Conjugated - When it has nonpolypeptide subunits (e.g., Haemoglobin has iron)
2. Non-conjugated - When it has only polypeptide subunits (e.g. insulin and collagen)

Question 13

What are globular proteins?

Answer 13

Shape - More compact and rounded
Purpose - Functional role
Acid Sequence - Repetitive amino acid sequence
Durability - more sensitive to pH and temperature
Examples - enzymes, haemoglobin, insulin
Solubility - soluble in water

Question 14

What are fibrous proteins?

Answer 14

Shape - Composed of long and narrow strands
Purpose - Structural role
Acid sequence - Irregular amino structure
Durability - Less sensitive to pH and temperature
Example - Collagen, Keratin, and Elastin
Solubility - Insoluble in water