Proteins

Question 1

What are the functions of proteins?

Answer 1

Antibodies, transport and structure

Question 2

What are the 2 secondary structures of proteins?

Answer 2

Alpha helix and beta pleated sheets (and some irregular coils)

Question 3

What is the structure of alpha helix?

Answer 3

Folded backbone strand in a tight coil around a central axis with side chains directed outwards

Question 4

How is alpha helix stabilised?

Answer 4

Hydrogen bonds

Question 5

How do beta pleated sheets run?

Answer 5

Anti-Parallel

Question 6

How many adjacent segments are in Beta pleated sheets?

Answer 6

2 or more to form a sheet-like structure

Question 7

What makes up a tertiary protein structure?

Answer 7

More than 50 amino acids in secondary structures

Question 8

What shapes can tertiary proteins have?

Answer 8

Spherical or globular

Question 9

Why do enzymes have tertiary structures?

Answer 9

To form active sites

Question 10

What bonds are involved in tertiary structures?

Answer 10

Disulphide crosslinks (Covalent bonds), Hydrophobic attraction and Hydrogen bonds

Question 11

Is Keratin Globular or Fibrous?

Answer 11

Fibrous

Question 12

Where is keratin found?

Answer 12

Hair, nails and skin

Question 13

What is the structure of protein?

Answer 13

Rope like

Question 14

What makes Keratin extensible?

Answer 14

Crosslinks resist stretch to restore fibres to original length. The less S-S links, the lower the flexibility

Question 15

What is the structure of collagen?

Answer 15

Triple helix

Question 16

How does the triple helix of collagen affect the extensibility?

Answer 16

The triple helix tightens under tension and resists stretch so makes it inextensible

Question 17

What bonds stabilise collagen?

Answer 17

Extensive H bonds and S-S crosslinks

Question 18

What are examples of globular proteins?

Answer 18

Enzymes, hormones and for storage

Question 19

What is the structure of an enzyme?

Answer 19

Spherical and folded so that the hydrophobic side chains are tucked away

Question 20

What is the make up of myoglobin?

Answer 20

1 poly-peptide unit with 75% α-helix

Question 21

What does myoglobin have to hold oxygen?

Answer 21

a Haem group (prosthetic group)

Question 22

Why does a protein denature?

Answer 22

Beyond “normal” pH and at high temperatures, weak bonds such as H bonds break. This alters the shape and therefore function of a protein

Question 23

Which bonds stay in place during protein denaturing?

Answer 23

Peptide bonds

Question 24

How are proteins hydrolysed?

Answer 24

Heating proteins in acid breaks down the proteins to simpler peptides and amino acids

Question 25

What is the isoelectric point?

Answer 25

The pH at which the charge on the protein is 0

Question 26

What is the charge if the pH is above isoelectric point?

Answer 26

-ve

Question 27

When is the overall charge on a protein +ve?

Answer 27

When the pH is below the isoelectric point

Question 28

When are proteins at their least soluble undenatured form?

Answer 28

At the isoelectric point

Question 29

What prevents aggregation?

Answer 29

When charged proteins repulse each other

Question 30

How are proteins separated using electrophoresis?

Answer 30

Proteins are loaded on a gel and given a negative charge using a buffer. A potential difference is applied and the larger proteins move slower than smaller proteins