1.6 Proteins

Question 1

What is an amino acid?

Answer 1

The basic monomer units which combine to make up a polymer called a polypeptide which can be combined to form proteins

Question 2

Draw the structure of an amino acid

Question 3

What are the different groups in an amino acid?

Answer 3

Amine group
Carboxyl group

Question 4

How many universal amino acids are there?

Question 5

What gives amino acids different properties?

Answer 5

Different R groups

Question 6

What do amino acid monomers combine to form?

Answer 6

A dipeptide

Question 7

What type of reaction forms dipeptides?

Answer 7

Condensation reaction

Question 8

What process breaks the peptide bond?

Answer 8

Hydrolysis

Question 9

Draw the reaction for the formation of a dipeptide

Question 10

How does a polypeptide form?

Answer 10

Many amino acid monomers can be joined together in a process called polymerisation
The resulting chain of many hundreds of amino acids is called a polypeptide

Question 11

Describe the primary structure of a protein and the function of it

Answer 11

• Determine shape and function
• Simple protein may consist of a single polypeptide chain, more commentary however, a protein is made up of a number of polypeptide chains

Question 12

How does the secondary structure form?

Answer 12

The chain of amino acids folds itself into an alpha helix or a beta-pleated sheet

Question 13

How is the secondary structure
shape maintained?

Answer 13

Hydrogen bonds between the -NH group and the C=O groups (not the R groups)
The hydrogen of the NH group is slightly positive, and the oxygen of the C=O group is slightly negative

Question 14

What is the tertiary structure maintained by?

Answer 14

Disulfide bridges
- strong covalent bonds that form between the R groups of some amino acids
Ionic bonds
- form between any carboxyl and amine groups that are not involved in the peptide bond, these are stronger than hydrogen bonds, but can be broken by changes in pH
Hydrogen bonds
- individually weak, collectively strong and can be broken by increasing the temperature above optimum

Question 15

Describe the quaternary structure

Answer 15

Large proteins are often formed from a number of polypeptide chains that are linked in various ways
There may also be non-protein groups (e.g. haem groups)

Question 16

What is the most well known quaternary protein?

Answer 16

Haemoglobin
Made up of four polypeptide chains and has a non-protein iron-containing ham groups associated with it

Question 17

What is the specific shape and function of a protein determined by?

Answer 17

The sequence of amino acids

Question 18

What is the order of bases on a chromosome a code for?

Answer 18

The order of the amino acids (primary structure)

Question 19

What does the order of amino acids determine?

Answer 19

Whether the alpha helix or beta pleated sheet can form (secondary structure)

Question 20

What is the positioning of the R group determined by?

Answer 20

The order of amino acids
This determines the formation of the stronger bonds (tertiary structure)

Question 21

What are the two major categories of proteins?

Answer 21

Fibrous proteins and globular proteins

Question 22

Describe the characteristics of fibrous proteins

Answer 22

• Usually secondary proteins
• Length, strength and flexibility
• Form straight chains, running parallel to one another
• Chains are linked by cross bridges (hydrogen bonds) and thus are very stable molecules
• Secondary level of folding is often a key part of these structures
• Often have repeating amino acids sequences in their chains
• Do not hydrolyse as easily as globular proteins

Question 23

Describe the characteristics of globular proteins

Answer 23

• Tertiary structure that resembles a globule or a sphere, and fold into a compact shape
• Involved in controlling cellular activities
• Shape is very specific
• Soluble in water, making colloidal solutions
• Can be altered easily, so not stable and hydrolyses more easily than fibrous proteins