Biological Molecules - Proteins

Question 1

What are the monomers (the basic building blocks) of proteins?

Answer 1

amino acids

Question 2

What is the basic structure of an amino acid?

Answer 2

1. a carboxyl group -COOH
2. an amine group -NH₂
3. R-group (the variable side group)

Question 3

What’s a dipeptide?

Answer 3

two amino acids joined

Question 4

What’s polypeptide?

Answer 4

Many amino acids joined together.

Question 5

How many types of amino acids do living things use?

Answer 5

20

Question 6

Describe a peptide bond

Answer 6

When amino acids join together (covalently) they release a water molecule (condensation reaction)

The bonds formed are call peptide bonds

Question 7

Describe a protein primary structure

Answer 7

flat and straight

Question 8

Describe a protein secondary struture

Answer 8

Hydrogen bonds form between amino acids (slightly polar) which causes the chain to coil and bend into:

alpha helix structure

or beta pleated sheet

Question 9

Describe a tertiary protein structure

Answer 9

More bonds now operate - hydrogen and ionic bonding (and disulfide bonding bonds in the case of cysteine)

A 3-D structure now forms

Question 10

Describe a quaternary protein structure

Answer 10

several polypeptide chains all held by bonds in a basic origami mess!

Question 11

Name four functions of proteins

Answer 11

enzymes - break/synthesise large molecules

antibodies - immune response

transporting - sitting in cell membranes to help molecules and ions cross the membrane

structural - scaffolding jobs such as keratin (hair, fingernails), collagen (connective tissue)

Question 12

Explain the Biuret test

Answer 12

Into a test tube with the food sample

Few drops of an alkaline solution - sodium hydroxide

Add copper (II) sulfate solutions

turns purple if present, or stays blue if not

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Question 13

What are conjugated proteins?

Answer 13

A protein to which another chemical group or molecule has been attached, typically with covalent bonds to conjugate (join) molecules to proteins.

Conjugated proteins can be attached to carbohydrates, lipids, organic complexes and stabilized metal ions.

E.g., haemoglobin and myoglobin are associated with an iron containing group

Question 14

What are free proteins? (1pt)

Answer 14

Proteins that contain only amino acids (as opposed to conjugated proteins that contain other chemical groups)

Question 15

What are globular proteins?

Answer 15

Spherical protein structures (eg enzymes)

Question 16

Why are globular proteins useful? (2pts)

Answer 16

1. They are soluble (due to hydrophilic tails) and are hence important in metabolic reactions.
2. Being three dimensional, they have a critical role in binding to other substances

Question 17

Describe the haemoglobin structure (4 pts)

Answer 17

1. Haemoglobin transports oxygen so:
2. it has four polypeptide chains
3. each associating with an iron haem group
4. oxygen attaches to the iron groups

(it’s also known as a conjugated protein)

Question 18

Describe fibrous proteins

Answer 18

Long protein chains

There are polypeptide chains that cross link creating more strength

Insoluble

Examples: skin, tendons, bones, cartilage, blood vessel walls

Question 19

Describe collagen

Answer 19

1. Fibrous protein
2. Three polypeptide chains wind around each other creating a rope-like strand held by hydrogen bonds
3. The strands are also staggered creating more strength