AQA A Level Biology - Proteins

what is a protein?

a polymer made up of amino acids 

how many different amino acids are there?

20

what components do all amino acids have?

• amine group 

• carboxyl group 

• R group, which differentiates amino acids

• C-H

what is an amine group?

NH2

what is a carboxyl group?

-COOH

what is the structure of an amino acid?

what reaction joins two amino acids?

condensation

what is the bond between amino acids called?

peptide

what are two amino acids joined together called?

dipeptide

what are three or more amino acids joined together called?

polypeptide

what atoms are lost from each amino acid in a condensation reaction?

• OH from the carboxyl group on one

• H from amine group 

draw the condensation reaction of two amino acids and the resulting dipeptide 

what are the 4 structural levels of a protein?

• primary

• secondary

• tertiary

• quaternary 

what is the primary structure of a protein?

the specific sequence of amino acids in the polypeptide chain

what is the secondary structure of a protein?

• the shape of the amino acid chain

• 2 types: alpha helix or beta pleated sheet

what does an alpha helix and a beta plated sheet look like?

what type of bonds cause the secondary structure of a protein to develop?

• hydrogen bonds 

• alpha helix: hydrogen atom of amine group, oxygen atom of carboxyl group of another AA

what is the tertiary structure of a protein?

• the 3D structure of a protein - if made from aa single polypeptide chain, this is their final 3d structure

• caused by different bonds forming between amino acids

what bonds cause the tertiary structure of a protein to develop?

• ionic

• hydrogen

• disulfide bridges (strongest)

what do ionic bonds in proteins form between?

form between charged R groups

what do disulfide bridges in proteins form between?

two sulfur atoms in differing R groups of amino acids

what is the quaternary structure of a protein?

• some proteins have multiple polypeptide chains held together by bonds  - and also might have other things (haemoglobin also has haem (iron) group)

• QS is the way these are assembled together 

• determines the ultimate final 3D structure

what are the two types of quaternary structure?

• globular

  • ball shaped molecules

  • includes enzymes; haemoglobin; insulin

  • most are soluble in water

• fibrous 

  • long thin molecules

  • not soluble in water

  • includes collagen; keratin

what are some examples of proteins and their function?

• enzymes - spherical - catalyse reactions

• antibodies - made up of two light chains and two heavy chains - y shape 

• structural

• hormones

• transport

• contractile