Proteins

Question 1

What are amino acids?

Answer 1

The monomers from which proteins are made.

Question 2

Describe the general structure of amino acids?

Answer 2

Amino acids contain an amino group (NH2), carboxylic acid group (-COOH) and a variable R group which is a carbon-containing chain.

Question 3

How many types of amino acids of there?

Answer 3

There are 20 different amino acids, each determined by their different R groups.

Question 4

How are amino acids formed?

Answer 4

Amino acids are joined by peptide bonds formed in condensation reactions. In this reaction a molecule of
water is formed.

Question 5

What is a dipeptide?

Answer 5

A dipeptide contains two amino acids

Question 6

What is a polypeptide?

Answer 6

Polypeptides contain three or more amino acids.

Question 7

Describe the structure of a protein

Answer 7

• determined by the order and number of amino acids, bonding present and the shape of the protein:

• Primary structure of a protein is the order and number of amino acids in a protein. This primary structure contains the initial sequence of amino acids and will
therefore determine the protein’s function in the end.

• The secondary structure is the shape that the chain of amino acids chains – either alpha helix or beta-pleated sheet. The hydrogen in the -NH has a slight positive charge whilst the oxygen in the -C=O has a slight negative charge.

As a result weak hydrogen bonds can form leading to alpha helices or beta-pleated sheets.

• Tertiary structure of proteins is the 3D shape of the protein and is formed from further twisting and folding.

A number of different bonds maintain the structure, these are:

• Disulfide bridges - interactions between the sulfur in the R group of the amino acid cysteine are strong and not easily broken.
• Ionic bonds - form between the carboxyl and amino groups that are not involved in the peptide bond. They are easily broken by pH and are weaker than disulfide
  bridges.
• Hydrogen bonds - numerous and easily broken.

Proteins can be globular or fibrous.

Question 8

What is a Globular protein?

Answer 8

Globular proteins such as enzymes are compact

Question 9

What is a fibrous protein?

Answer 9

Long and thus can be used to form fibres. eg keratin

Question 10

What test is used to find the presence of peptide bonds in a protein?

Answer 10

The Biuret test

Question 11

How do you carry out the Biuret test?

Answer 11

1. Place the sample to be tested in a test tube and add an equal volume of sodium hydroxide at room temperature.
2. Add a few drops of very dilute (0.05%) copper (II) sulfate soliton and mix gently.
3. A purple colouration indicates the presence of a peptide bond and hence a protein. A negative result would mean the solution remains blue.

Question 12

What are the four groups surrounding the central carbon atom in an amino acid?

Answer 12

1. Amine group
2. Carboxyl group
3. Hydrogen group
4. R group

Question 13

The two functional groups in amino acids are:

Answer 13

anime group & Carboxyl group

Question 14

What is the name of the structure of a protein represented by the sequence of the amino acids?

Answer 14

Primary structure

Question 15

What bonds form between amino acids to hold the secondary structure in place?

Answer 15

Hydrogen bonds

Question 16

The 4 Structural levels of proteins are:

Answer 16

Primary structure
Secondary structure
Quaternary structure
Tertiary Structure

Question 17

Primary structure

Answer 17

Sequence of amino acids

Question 18

Tertiary structure

Answer 18

3D structure of a polypeptide chain

Question 19

Quaternary structure

Answer 19

The final 3D structure of a protein. This may contain multiple polypeptides

Question 20

Secondary Structure

Answer 20

Local folding of the polypeptide chain

Question 21

How many amino acids are common in all organisms

Answer 21

20

Question 22

A sample is boiled in a test tube with ethanol. The sample is shaken and left to stand. The solution inside is then poured into a tube containing distilled water.

What would be observed if there is a lipid present in the tube

Answer 22

A white, milky layer

Question 23

Which amino acid does not have carbon in its R group

Answer 23

Glycine

Question 24

What molecule is released as a byproduct when the amino terminal of one amino acid reacts with the carboxyl terminal or another amino acid?

Answer 24

water

Question 25

What colour shows a positive result in the Biuret test for protein?

Answer 25

Violet

Question 26

What interactions are most important in protein tertiary structure?

Answer 26

Disulphides bridge

Ionic bonds

Question 27

Protein A contains four polypeptide ma in a quaternary structure surrounding a central harm group.

What is protein A?

Answer 27

Haemoglobin

Question 28

What is the name given to the part of the enzyme that catalysed the reaction and provides specificity?

Answer 28

Active site

Question 29

“Increasing the temperature of an enzyme catalysed reaction will always increase the rate of reaction as there is a higher chance of a collision having the activation energy”

Is this true or false?

Answer 29

False

Question 30

What sort of inhibitor binds to active site and has a similar structure to a normal substrate of the enzyme?

Answer 30

Competitive inhibitors

Question 31

What causes the changes in protein structure through the three or four levels of structure?

Answer 31

The primary chain forms a secondary a-helix and beta-pleated sheets which fold onto each other forming the tertiary structure.

Question 32

What structural level of proteins is functional? Why?

Answer 32

The tertiary structure is functional as it possess the geometric shape showing neccessary loops and bends

Question 33

How does a chaperone work with proteins?

Answer 33

Chaperone assist proteins when folding

Question 34

What enzyme is used to hydrolyse proteins

Answer 34

endopeptidases, exopeptidases and Dipeptidase

Question 35

Endopeptidases

Answer 35

Hydrolise internal bonds

Question 36

Exopeptidases

Answer 36

Hydrolyse bonds at the end of protein molecules.

Question 37

What enzyme increases the surface area of Exopeptidse to work on?

Answer 37

Endopeptidases