Proteins

Question 1

What are proteins made up of?

Answer 1

Amino acids

Question 2

What are the bonds that hold together amino acids?

Answer 2

peptide bond

Question 3

Name the parts that make up amino acids (draw a simple diagram)

Answer 3

Amino group
Carboxylic acid group
Alpha-carbon
R chain

Question 4

How many amino acids are there?

Answer 4

20

Question 5

Name what is formed when a series of amino acids are joined together

Answer 5

Polypeptide (polymer)

Question 6

Describe the meaning of polymerisation

Answer 6

The joining of many monomers into a polymer

Question 7

Describe the primary structure (of protein)

Answer 7

Sequence of amino acids into a polypeptide chain.

• As each amino acid has a different molecular structure in their R group + as these molecular differences affect all bonds that the polypeptide chain will be able to make
• The primary structure determines the ultimate shape + functionality of the protein

Question 8

Describe the secondary structure (of protein)

Answer 8

Polypeptide chain twisted into a 3D shape
Occurs as H bonds form between the ‘+’ charged H of the NH group and the ‘-‘ charged C=O group (H bonds relatively weak)
E.g an a-helix or B-pleated sheet

Question 9

Describe the tertiary structure (of protein)

Answer 9

• It is the result of further twisting of secondary structure
• It can be complex + is specific to protein
• Also plays significant role in determining the behaviour of the protein

Question 10

Name the 3 types of bond that is maintains the tertiary structure

Answer 10

Disulfide bonds - fairly strong + not easily broken
Ionic bonds - form between any carboxyl groups + amino groups not involved in peptide bonds. Weaker than disulfide bonds + easily broken by changes in pH
Hydrogen bonds - numerous but easily broken

Question 11

Describe the quaternary structure

Answer 11

Multiple polypeptides bond together e.g haemoglobin (large protein) - the haem group is not a protein

Question 12

Describe the test for proteins

Answer 12

Biuret test (which detects peptide bonds):

1. Place sample of the solution to be tested into a test tube + add equal volume of NaOH solution at room temp.
2. Add a few drops of very dilute (0.05%) copper (II) sulfate solution + mix gently
3. A purple colouration indicates the presence of peptide bond and hence a protein (if protein is not present it remains blue)

Question 13

What is the difference between fibrous and globular proteins? Give an example of each

Answer 13

Fibrous proteins: have structural functions e.g collagen is found in tendons which join muscles to bones
Globular proteins: perform metabolic reactions e.g enzymes + haemoglobin

Question 14

Describe the difference between the shapes/structure of fibrous and globular proteins

Answer 14

Fibrous: long polypeptide strands/chains twisted together (tightly wound around one another) - form long parallel chains. Chains are linked by cross-bridges + so form very stable molecules
Globular: not long but polypeptide chains wrapped around one another in a ball/bundle shape

Question 15

Describe the structure and function of the fibrous protein collagen

Answer 15

• Primary structure is a polypeptide chain
• Secondary structure is that it is very tightly coiled
• Higher concentration of glycine (an amino acid) helps it to pack closer together
• Tertiary structure is also a helix shape
• Quaternary structure is 3 double coiled polypeptide chains wound together