2.1.2 M) Levels of Protein Structure

Question 1

Primary protein structure:

Answer 1

sequence of amino acids bonded by covalent peptide bonds

Question 2

How is the primary structure of a protein formed?

Answer 2

• condensation reacts bonds amino acids together and water molecule(s) is released
• covalent peptide bond between the amino acids

Question 3

What is the primary structure specific for?

Answer 3

the primary structure us specific for each protein (one alteration in the sequence of amino acids can affect the function of the protein)

Question 4

What is the secondary protein structure?

Answer 4

• initial folding of the protein
• weak negatively charged nitrogen and oxygen atoms interact with weak positively charger hydrogen atoms to form hydrogen bonds which holds the initial folding in place

Question 5

What shapes are formed in the secondary structure?

Answer 5

• α-helixshape
• β-pleated sheetshape

Question 6

Which proteins have a secondary structure?

Answer 6

most fibrous proteins e.g. collagen and keratin

Question 7

How can the bonds in the secondary structure be broken?

Answer 7

the hydrogen bonds can be broken by high temperatures and pH changes

Question 8

Diagram of α-helixshape and β-pleated sheetshape

Question 9

Tertiary protein structure:

Answer 9

• 3D shape formed and held together by 4 bonds
• bonds formed between R groups of amino acids

Question 10

What bonds are formed in the tertiary protein structure?

Answer 10

• Hydrogen- between strongly polar R groups
• Disulphide bond/bridge- only occurs between 2 sulphurs on 2 R groups (only 3 types of amino acids contain sulphur so bond is rare)
• Ionic - between charged R groups
• Hydrophobic/philic interactions- between non-polar R groups within the interior of proteins

Question 11

What proteins is the tertiary structure common in?

Answer 11

common in globular proteins

Question 12

Order of weakest to strongest bonds in tertiary structure:

Answer 12

• H bond
• ionic bond
• disulphide bond/bridge

Question 13

What does tertiary structure determine?

Answer 13

• A polypeptide chain will fold differently due to the interactions (and hence the bonds that form) betweenR groups
• Each of thetwenty amino acidsthat make up proteins has a uniqueR groupand therefore many different interactions can occur creating a vast range of protein configurations and therefore functions

Question 14

How can a change in the amino acid sequence result in the formation of a non-functional enzyme?

Answer 14

• change in aa sequence
• leads to change in primary structure
• so dif. order of R groups
• dif. secondary structure - may change hydrogen bonding → H bonds may not form or form in different places
• dif. tertiary structure - R groups in dif. places so tertiary bonds may form differently
• 3D shape is different
• so active site no long complementary to substrate

Question 15

How is a proteins tertiary structure disrupted when heated to a high temp?

Answer 15

• increase in kinetic E of protein
• protein vibrates/moves more
• hydrophobic/philic / hydrogen / ionic bonds / interactions break
• change in 3D shape/conformation of protein
• denatures enzyme
• active site changes shape and is no longer complementary to substrate
• enzyme stops working

Question 16

What proteins have a tertiary structure?

Answer 16

most enzymes

Question 17

Quaternary protein structure:

Answer 17

• multiple tertiary structures/polypeptide chains joining together
• same 4 bonds as tertiary structure

Question 18

What is each polypeptide chain in the quaternary structure of a protein referred to as?

Answer 18

referred to as asubunitof the protein