Topic 1---A: Biological molecules- 5. proteins

Question 1

What are the monomers of proteins?

Answer 1

Amino acids

Question 2

How is a dipeptide formed?

Answer 2

When two amino acids join together

Question 3

How is a polypeptide formed?

Answer 3

When more than 2 amino acids join together

Question 4

What are proteins made up of?

Answer 4

1 or more polypeptides

Question 5

Amino acid (structure)

Answer 5

• Carboxl group (COOH)
• Amine group (H2N)
• R GROUP (1 of 20 varieties) attached to a carbon
• R GROUP consists of 1 hydrogen atom
  H H O
  \ I //
  N -C-C
  / I \ OH
  H R

Question 6

How are amino acids linked together to form dipeptides and polypeptides?

Answer 6

By condensation reaction between amine and carboxyl group so a molecule of water is released during the reaction.
- Peptide bond is formed between the amino acids

Question 7

What are the bonds between amino acids called?

Answer 7

Peptide bonds

Question 8

When does hydrolysis happen?

Answer 8

When dipeptides and polypeptides are broken down

Question 9

How is there 20 different amino acids?

Answer 9

-Because there are 20 different R groups
- Each R group is slightly different so each amino acid has different properties so proteins have a wide range of properties.

Question 10

What are the 4 levels of structure in a protein?

Answer 10

• Primary
• Secondary
• Tertiary
• Quaternary

Question 11

Primary structure (proteins)

Answer 11

This is the sequence of amino acids in a polypeptide chain

Question 12

Secondary structure (proteins)

Answer 12

• Hydrogen bonds form between the amino acids in the chain between the amine and carboxyl groups
• This makes it automatically coil into a alpha helix or fold into a beta pleated sheet
• Hydrogen bonds hold the secondary structure in place

Question 13

Tertiary structure (protein)

Answer 13

• The coiled or folded chain of amino acids is often coiled and folded further.
• More bonds form between different parts of the polypeptide chain including hydrogen and ionic bonds.
• Disulphide bonds also form whenever 2 molecules of the same amino acid cysteine come together
• For proteins made from a single polypeptide chain the tertiary structure forms their final 3D structure

Question 14

Quaternary structure (protein)

Answer 14

-Protein made up of several different polypeptide chains held together by bonds
- It’s the way the polypeptide chains are assembled together

Question 15

What is an example of a quaternary structure?

Answer 15

Haemoglobin (4 polypeptide chains associated together)

Question 16

Why is the sequence of amino acids important?

Answer 16

• They determine the tertiary structure so therefore the overall 3D shape of the molecule due to the bonds forming in different locations.

Question 17

What does a proteins shape determine?

Answer 17

Their function

Question 18

Enzymes (protein example)

Answer 18

• Usually spherical in shape due to the tight-folding of the polypeptide chains.
• Their soluble and have roles in metabolism like breaking down large food molecules.

Question 19

Transport proteins (protein example)

Answer 19

• Channel proteins are present in cell membranes
• They contain hydrophobic and hydrophilic amino acids
• This causes the protein to fold up and form a channel so they can transport molecules and ions across cell membranes.

Question 20

Structural proteins (protein example)

Answer 20

• Physically strong
• Consist of long polypeptide chains lying parallel to each other with cross links between them.
• E.g. keratin and collagen

Question 21

What happens when a protein denatures?

Answer 21

• Hydrogen and ionic bonds in secondary and tertiary structure break
• Lose the 3D shape
• E.g. from changes in temperature/ PH

Question 22

Biuret test (proteins)

Answer 22

1. Test solution needs to be alkaline so first you add a dew drops of sodium hydroxide solution
2. Then add some copper (II) sulfate solution.
3. If protein is present it will go from blue to purple

Question 23

Ionic bonds

Answer 23

• Quite Strong
• Form between R groups

Question 24

Hydrogen bonds

Answer 24

• Weak
• Easily broken by temperature or pH

Question 25

Disulphide bridges

Answer 25

• Covalent (very strong)
• Form between sulphur atoms in the R group of cysteine