Proteins

Question 1

What are Amino Acids?

Answer 1

The basic monomer units which combine to make up a polymer called a polypeptide, which are then combined to form proteins.

Question 2

How many amino acids occur in all living organisms and what does this provide?

Answer 2

20 amino acids that provide indirect evidence for evolution.

Question 3

What is the amino group of an amino acid?

Answer 3

NH2 - a basic group form which the amino part of the name amino acid is derived.

Question 4

What is the carboxyl group?

Answer 4

COOH - an acidic group which gives the amino acid the acid part of the name.

Question 5

What is the third component of an amino acid?

Answer 5

H - hydrogen atom.

Question 6

What is the R group of an amino acid and why is it important?

Answer 6

The R group can be a variety of different chemical groups. Each amino acid has a different R group, and amino acids only differ on their R group.

Question 7

General Structure of an Amino Acid

Answer 7

H      
H                                O ---- H
       N ----  C  ---- C
H                                O
                  R

Question 8

How is a peptide bond formed between amino acids?

Answer 8

Amino Acid monomers can combine to form a dipeptide, through the removal of water in a condensation reaction.

Question 9

Where does the water come from in formation of a peptide bond?

Answer 9

Combining an - OH form the carboxyl group of one amino acid, with an - H from the amino group of another amino acid.

Question 10

What is the process known as when amino acids are joined up?

Answer 10

Polymerisation. Amino acid molecules are joined through a series of condensation reactions.

Question 11

What is a the name of a chain of many hundred amino acids?

Answer 11

Polypeptide

Question 12

What is the primary structure of a protein?

Answer 12

Basic sequence of amino acids in the polypeptide chains,

Question 13

How is the sequence of amino acids determined?

Answer 13

by the DNA.

Question 14

What determines the ultimate shape and function of a protein?

Answer 14

The multiple combinations of a polypeptide chain determines shape and function of a protein.

Question 15

Why is it significant that a protein’s shape is significant to its function?

Answer 15

A change in just a single amino acid in the primary sequence can change the shape of a protein and may stop it carrying out its function.

Question 16

What is the secondary structure of proteins?

Answer 16

Hydrogen on the - NH group of an amino acid chain has an overall positive charge, whereas the - O of the carboxyl group has an overall negative charge. These chains form weak hydrogen bonds between them.

Question 17

What do the weak hydrogen bonds make the secondary structure result in?

Answer 17

Long polypeptide chain twists into a 3-D shape, such as the coil known as the a-helix.

Question 18

What is the tertiary structure of proteins?

Answer 18

The chains are twisted and folded even more to give a complex and specific 3-D structure to each protein which is maintained by a number of different bonds.

Question 19

What are disulphide bridges in the tertiary structure?

Answer 19

Fairly strong bonds that are not easily broken.

Question 20

What are ionic bonds in the tertiary structure?

Answer 20

Formed between any carboxyl and amino group that are NOT involved in the peptide bond. They are weaker than disulphide bridges and are easily overcome by changes in pH.

Question 21

What are hydrogen bonds in the tertiary structure?

Answer 21

Numerous but easily broken.

Question 22

Why is the 3-D shape of a protein important to the function?

Answer 22

It makes each protein distinctive and allows it to recognise and be recognised by other molecules. It can then interact with them in a very specific way.

Question 23

What is the Quaternary structure of proteins?

Answer 23

Large proteins forming complex molecules with numbers of different polypeptide chains linked in various ways. May also be non-protein groups present, known as prosthetic groups.

Question 24

Test for Proteins : Biuret Test

Answer 24

• Place equal volumes of sample and sodium hydroxide solution (at room temperature) in a test tube.
• Add a few drops of very dilute (0.05%) Copper II Sulphate solution and mix gently.
• Purple colouration indicates peptide bonds. If no protein is present, solution remains blue.

Question 25

What does the biuret test, test for?

Answer 25

Detects peptide bonds showing amino acids are present.