topic 1.3 - proteins

Question 1

primary structure of a protein

Answer 1

sequence of an amino acids that make up the polypeptide chain

Question 2

secondary structure

Answer 2

can either be alpha helix or beta pleated sheet

Question 3

what is the sequence of a protein determined by

Answer 3

the DNA of the gene that encodes the protein. Even changing just one amino acid in a protein’s sequence can affect the proteins overall structure and function

Question 4

importance of insulin and glucagon as proteins

Answer 4

control blood glucose concentration

Question 5

how is an α-helix formed

Answer 5

due to hydrogen bonds forming between the oxygen of -CO group of one amino acid and the hydrogen of the -NH group of the amino acid 4 places ahead of it

Question 6

how is a β-pleated sheet formed

Answer 6

two or more segments of a polypeptide chain line up next to each other forming a sheet like structure held together by hydrogen bonds

Question 7

tertiary structure

Answer 7

folding of the protein in order to form a precise 3D shape

Question 8

bonding in a tertiary structure

Answer 8

• hydrogen bonds : formed between polar groups like -NH, -CH, -OH groups (broken & reform by change in temp or pH)
• disulfide bonds : formed between two cysteine molecules which are close in strcuture of a polypeptide. Much stronger than hydrogen bonds as it is covalent. (broken by reducing agents)
• ionic bonds : between ionised amine (NH3+) and ionised carboxylic acid (COO-)

Question 9

quarternary structure

Answer 9

proteins are made up of two or more polypeptide chains

held together by hydrogen bonds, disulphide bonds & ionic bonds

Question 10

globular proteins

Answer 10

• proteins that curl up into a ball shape so their hydrophobic groups are in the centre while the hydrophilic groups remain on the outside and relate well to the blood
  
  • enzymes

Question 11

fibrous proteins

Answer 11

• molecules do not curl up
  
  • not soluble in water
  • role is mostly structural
  • e.g. collagen, keratin

Question 12

globular protein - haemoglobin

Answer 12

• carries oxygen and found in red cells
• 4 polypeptide chains
• each polypeptide chain is called a Globin held together by disulfide bonds
• each chain is arranged around a haem group (contains iron)
• iron enables haemoglobin to bind to and release oxygen molecules
• when haemoglobin binds to oxygen it is bright red, when there is no oxygen it is blue/purple

Question 13

fibrous protein - collagen

Answer 13

• most common protein found in animals
• not folded; form strands
• insoluble as it provides a structural function
• 3 polypeptide chains arranged in a triple helix held together by hydrogen and covalent bonds

Question 14

advantages of collagen

Answer 14

• flexible
• high tensile strength so not easy to break when pulled