1.4 Proteins

Question 1

What are proteins made up from?

Answer 1

Monomers called amino acids

Question 2

What elements do proteins contain?

Answer 2

C,H,O,N and S

Question 3

What is the structure of an amino acid?

Answer 3

R
|
H2N— C —-COOH
|
H

Question 4

What is the COOH group called?

Answer 4

Carboxyl group

Question 5

What is the H2N group called?

Answer 5

Amino group

Question 6

What does the R mean in an amino acid?

Answer 6

-Any possible number of chains
- it’s a side chain

Question 7

What is the simplest amino acid and what is its structure?

Answer 7

Glycine

   H    H   O
   |     |   || H—N—C—C—OH
          |
          H

Question 8

What forms a peptide bond?

Answer 8

A condensation reaction between two amino acids

Question 9

What forms from a condensation reaction between two amino acids?

Answer 9

A peptide bond

Question 10

How are dipeptides formed?

Answer 10

Formed by the condensation of two amino acids.

Question 11

How are polypeptides formed?

Answer 11

Formed by the condensation of many amino acids.

Question 12

What may a functional protein contain?

Answer 12

One or more polypeptides.

Question 13

What 4 levels does protein structure occur at?

Answer 13

-Primary Structure
-Secondary structure
-Tertiary structure
-Quaternary structure

Question 14

What is primary structure?

Answer 14

The number and sequence of amino acids in a polypeptide chain

Question 15

What is secondary structure?

Answer 15

The secondary structure is made when hydrogen bonds form between some of the atoms in the polypeptide chain, this pulls the chain into a shape, there are two shapes that are generally made - alpha helix or beta pleated sheets

Question 16

What is tertiary structure?

Answer 16

The folding of the polypeptide chain into a 3D shape, this is held in place by hydrogen bonds and disulfide bridges

Question 17

What is quaternary structure?

Answer 17

One or more polypeptide chains joined together to make a fully functional protein. Often there are prosthetic groups with quaternary structure. In haemoglobin the prosthetic group is iron

Question 18

What is the test for proteins?

Answer 18

The Biuret Test - Which detects peptide bonds

Question 19

What is the method of the Biuret test?

Answer 19

-Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature
-Add a few drops of very dilute copper sulfate solution and mix gently
-A purple colouration indicates the presence of peptide bonds and hence a protein. If no protein is present, the solution remains blue

Question 20

How many amino acids are there and how do they differ from one another?

Answer 20

20
differ only by side ‘R’ group

Question 21

What is the structure and function of globular proteins?

Answer 21

• spherical and compact
• hydrophilic R groups face outwards and hydrophobic R groups face inwards = usually water-soluble
• involved in metabolic processes

Question 22

What is the structure and function of fibrous proteins?

Answer 22

• can form long chains or fibres
• insoluble in water
• useful for structure and support

Question 23

How could chromatography be used to identify the amino acids in a mixture?

Answer 23

1. use a capillary tube to spot mixture onto pencil origin line and place chromatography paper in solvent
2. Allow solvent to run until it almost touches other end of paper. Amino acids move different distances based on relative attraction to paper and solubility in solvent
3. use revealing agent to see spots
4. Calculate Rf values and match to database

Question 24

Describe each type of bond in the tertiary structure of proteins.

Answer 24

• Disulfide bridges - strong covalent S-S bonds between molecules of the amino acid cysteine
• Ionic bonds - relatively strong bonds between charged R groups (pH changes cause these bonds to break)
• Hydrogen bonds - numerous and easily broken