Protien Structure and Function

Question 1

Under what conditions do amino acids act as a base ?

Answer 1

• in low pH

- excess H+

Question 2

Under what condition do amino acids act as a acid

Answer 2

• excess OH-

- High PH

Question 3

Describe the structure of the L isomer of amino acids

Answer 3

• When viewed along the hydrogen-carbon alpha bond from the hydrogen CoRN read in a clockwise direction
• All amino acids incorporated into proteins in living organisms are in L form

Question 4

Describe the structure of D isomers of amino acids

Answer 4

• When viewed along the hydrogen in the hydrogen-carbon alpha
• CoRN is read in a anti-clockwise direction
• Forms bacterial cell wall

Question 5

What is the most common conformation of the amino acid side chain R in a polypeptide chain?

Answer 5

Trans is the most common conformation where the R side chain are altering sides along the polypeptide chain

Question 6

What are peptide residues?

Answer 6

Each repeating unit of the polypeptide is termed a residue. Each residue consists of an invariable unit and a variable R chain - amino acid.

Question 7

Which conformation of variable regions is less energetically favourable? Cis or Trans

Answer 7

Cis

Question 8

Describe the structure of a beta pleated sheet?

Answer 8

• Secondary protein structure - folding of polypeptides
• Hydrogen bonds are present between beta strands
• Parallel or antiparallel arrangement of beta pleated sheets
• In the parallel arrangement the beta strands are connected together by longer loops
• In the antiparallel arrangement the beta strand are connected together by short strand Beta-turns

Question 9

Describe the structure of the alpha helix protein structure

Answer 9

• Right handed helix

- Stabilised by hydrogen bonds - H bonds are 4 residues apart

Question 10

What are 2 important feature os secondary structure proteins ?

Answer 10

• Arrangement of side chains gives the proteins their protiens their properties and are important for structure and function
• Side chains protrude outwards from both beta pleated sheets and alpha helix

Question 11

What are tertiary protein structures composed of?

Answer 11

• Combining secondary structures gives rise to tertiary structures - INTRACHAIN
• Many weak chemical bonds sometimes stabilised by covalent bonds

Question 12

Describe the tertiary structure of proteins

Answer 12

• Globular structure

- Formation depends on interactions of outward facing chains

Question 13

Describe the quaternary structure of proteins

Answer 13

• Made of 2 or more polypeptide chains
• Same bonds as in tertiary structure but are INTERCHAIN
• Protein structure may comprise single or multiple subunits
• Can contain organic or inorganic cofactors

Question 14

Describe the structure of water soluble proteins

Answer 14

• Hydrophilic residues are mostly on the external surface
• Hydrophobic residues are mostly on the internal surface
• Some can assemble into filaments or tubes or coiled coils