Polypeptides (Proteins)

Question 1

What are the elements in proteins?

Answer 1

C H O N S

Carbon Hydrogen Oxygen Nitrogen Sulfur

Question 2

What are functions of proteins?

Answer 2

• Transport
• Movement e.g. muscle contraction
• Cell & Tissue structure
• Regulation e.g. hormones
• Enzyme reactions

Question 3

What is a protein formed of?

Answer 3

Long chain of amino acids

Question 4

Describe the general formula of an amino acid

Answer 4

R group
I
(Amine group) H2N — - — - C ———- COOH (Carboxyl group)
I
H

Question 5

What type of reaction is the creation of dipeptide molecules?

Answer 5

Condensation reaction

Question 6

What type of bond is between amino acids

Answer 6

Peptide bond

Question 7

What does the Carbon from the carbonyx group bond with after the removal of water?

Answer 7

Nitrogen from the amine group

Question 8

What is the primary structure?

Answer 8

• A chain of amino acids

- A change at this level will have a profound change at higher levels

Question 9

What two types of secondary structures are there?

Answer 9

Alpha Helix and Beta Fold

Question 10

Describe the Alpha Helix

Answer 10

• coiled into a spring shape

- Hydrogen bonds between C=O and -NH groups to stabilise.

Question 11

Describe the beta fold

Answer 11

• Pleated sheets

- Hydrogen bonds between parallel chains

Question 12

What does the tertiary structure determine?

Answer 12

The bending of the 3 dimensional shape.

Question 13

Why does the secondary structure relate to the tertiary structure?

Answer 13

It brings the r groups from different amino acids closer, allowing them to interact using different types of bonding.

Question 14

What are the 4 types of bonds/interractions in tertiary structure?

Answer 14

• Ionic bonding
• Hydrogen bonding
• Disulphide bonds (disulfide bridges)
• Hydrophobic/hydrophilic interractions

Question 15

Describe the strength of hydrophobic/hydrophilic interactions

Answer 15

Weak interactions between polar and non-polar r-groups

Question 16

Describe the strength of hydrogen bonds

Answer 16

Weakest of all bonds

Question 17

Describe the strength of ionic bonds

Answer 17

Stronger than hydrogen, and forms between oppositely charged r-group

Question 18

Describe the strength of disulfide bonds

Answer 18

Covelant bonding - very strong.

Only between R-groups that contain sulfur atoms

Question 19

What is quaternary structure?

Answer 19

Association of two or more proteins (also called subunits)

- Interaction of different protein molecules, rather than within one molecule

Question 20

How many subunits does an enzyme contain?

Answer 20

2

Question 21

How many subunits does haemogloblin have? (Explain these)

Answer 21

4
2 pairs of identical subunits:
2 alpha and 2 beta

Question 22

Describe the properties of a globular protein (4 features)

Answer 22

Compact
Water Soluble
Usually spherical in shape
Hydrophobic r-groups kept away from aqueous environment

Question 23

Why is it an advantage that globular proteins are soluble?

Answer 23

• Essential for regulation
  • chemical reaction
  • immunity
  • muscle contraction

Question 24

What type of protein is insulin?

Answer 24

Globular protein

Question 25

What is the function of insulin?

Answer 25

Regulation of blood glucose concentration - transported in the bloodstream so needs to be soluble.

Question 26

What is a prosthetic group?

Answer 26

A non-protein component, usually within a globular protein

Question 27

Give an example of a prosthetic group

Answer 27

Lipoproteins
Glycoproteins
Haem groups (contain iron ion)

Question 28

What is haemoglobin?

Answer 28

A quaternary conjuncted protein that is the red,oxygen-binding pigment found in red blood cells.

Question 29

What does haemoglobin having 4 haem groups allow?

Answer 29

As haem groups contain iron ions, oxygen is able to bind creating oxyhaemoglobin

Question 30

What is Catalase?

Answer 30

An enzyme containing 4 haem groups.

The iron ions allow catalase to interact with hydrogen peroxide and speed up breakdown

Question 31

Why does catalase need to breakdown hydrogen peroxide?

Answer 31

Hydrogen peroxide is a byproduct of metabolism, but can be damaging to cells if allowed to accumulate.

Question 32

What are fibrous proteins?

Answer 32

Composed of long, insoluble molecule.

Amino acid sequence is quite repetative - leading to very organised structures

Question 33

3 examples of fibrous proteins:

Answer 33

• keratin
• collagen
• elastin

Question 34

Where can keratin be found?

Answer 34

Nails, hair, skin

Question 35

What element is keratin high in?

Answer 35

Sulfur:

Large population of the sulfur-containing amino acid, cysteine

Question 36

What types of bond is common in keratin?

Answer 36

Disulfide bonds, which are strong, inflexible and insoluble.

Question 37

How does disulfide bonds determine flexibility?

Answer 37

Proteins with high levels of disulfide bonds will have low levels of flexibility

Question 38

Where is elastin found?

Answer 38

In the walls of blood vessels and in the alveoli if the lungs.

Question 39

What stretchy molecules is elastin made of?

Answer 39

Tropoelastin

Question 40

What is collagen?

Answer 40

Fibrous protein, which is a connective tissue formed in skin, tendons, ligaments and the nervous system.

Question 41

How many polypeptides does collagen contain?

Answer 41

3