Proteins

Question 1

What are the monomers from which proteins are made called?

Answer 1

• Amino acids.

Question 2

How many types of amino acids are there in all organisms?

Answer 2

• 20 amino acids

Question 3

How is peptide bond formed?

Answer 3

• Peptide bond formed by condensation reaction between two amino acids.

Question 4

What are dipeptides formed by?

Answer 4

• Dipeptides formed by condensation reaction of two amino acids.
• Peptide bond forms between OH of carboxyl group (on amino acid) and H of the amine group.

Question 5

What are polypeptides formed by?

Answer 5

• Polypeptides are formed by the condensation of many amino acids.
• Peptide bond forms between OH (of carboxyl group) and H of the amine group.

Question 6

What is the only part of the amino acid monomer that changes depending on the type of amino acid?

Answer 6

• The R (variable) group.

Question 7

What are the components of an amino acid monomer, ie. the groups in an amino acid monomer?

Answer 7

• C and H atom in centre
• Amine group (NH₂)
• Carboxyl group (COOH)
• R- group (variable) side chain.

Question 8

What type of protein contains one or more polypeptides?

Answer 8

• Functional protein may contain one or more polypeptides.

Question 9

What is a hydrogen bond?

Answer 9

• Chemical bond often between slight negative oxygen atoms and slight positive hydrogen atoms (in water.) (oxygen = slightly negative as it has more electrons than hydrogen.)

() - extra info for clarification

Question 10

What are the 4 levels of structure in proteins?

Answer 10

1.) Primary
2.) Secondary
3.) Tertiary
4.) Quaternary

Question 11

Definition of primary structure of protein.

Answer 11

• The sequence of amino acids in a polypeptide chain.

Question 12

Definition of secondary structure of a protein.

Answer 12

• Sequence of amino acids (ie. primary structure) are bent into alpha helix shapes or folded into beta pleated sheets (this is known as secondary structure.)
• Hydrogen bonds hold the secondary structure of protein.

Question 13

Where are hydrogen bonds formed in the secondary structure of a protein?

Answer 13

• Hydrogen bonds form between the C=O groups (part of peptide bond of 1 amino acid) and the NH group (in the peptide bond of another amino acid.)

Question 14

Definition of** tertiary structure** of proteins.

Answer 14

• The further folding of the secondary structure (forms the tertiary structure.)
• Folding forms a unique 3D shape.
• Tertiary structure held in place by ionic, hydrogen and disulphide bonds/ bridges.

Question 15

What 3 types of bonds hold the tertiary structure of proteins in place?

Answer 15

• Ionic
• Hydrogen
• Disulphide

Question 16

Where are ionic and disulphide bonds formed in the tertiary structure?

Answer 16

• Ionic/ disulphide bonds = formed between the R groups of different amino acids.

Question 17

True or False

Disulphide bonds/ bridges are always present in the tertiary structure of a protein.

Answer 17

• False.
• Disulphide bridges only sometimes occur (when there is a sulphur in the R groups of the amino acids.)

Question 18

Definition of **quarternary structure ** of protein.

Answer 18

• More than one polypeptide chain.

Question 19

What happens to the tertiary structure of a protein when it is **denatured? **

Answer 19

• The bonds which hold the tertiary structure in place break (ionic/ hydrogen bonds break) and therefore the unique 3D shape is lost/ collapses back into the secondary structure.

Question 20

Two conditions that would denature a protein:

Answer 20

1.) Too high temperature ( too much kinetic energy - of amino acids - can cause bonds to break.)
2.) Too high/ low a pH (ie. too many H+ or OH- : will lead to imbalance in charge which can break the bonds.)

Question 21

What is the importance of the primary structure of a protein?

Answer 21

• Primary structure: sequence of amino acids.
• If sequence of amino acids changes (ie. from a mutation), it will cause the ionic/ hydrogen/ disulphide bonds to form in different locations (in the tertiary structure.)
• This will result in a different 3D shape.

Question 22

What is the issue with the shape of a 3D protein (ie. enzymes/ carrier proteins) changing ?

Answer 22

• Enzymes: will have different shapes active site (will be non-functioning.)
• Carrier proteins: will have different shapes binding site (molecules = no longer complementary/ cannot be transported across membranes.)

Question 23

What is the test for proteins?

Answer 23

• Add Biuret (solution) to sample.
• A positive result = Biuret goes from blue to purple.

Question 24

Atoms involved in peptide bond?

Answer 24

– COHN

Question 25

How does the charge of amino acids affect the protein?

Answer 25

- Change in charge of an amino acid may change the tertiary structure of the protein. - Ie. Ionic bond only between positively-charged/ negatively-charged amino acids. Mutation (change in amino acid to another amino acid) may change the charge so the ionic bond will break.