proteins

Question 1

fibrous proteins

Answer 1

insoluble in water
stable and tough
have structural function
polypeptide chains parallel with little or no tertiary structure
different proteins may have similar shapes, and the length of the same protein may vary
eg collagen

Question 2

globular proteins

Answer 2

soluble in water
not stable, as easily changed chemically
have metabolic function
polypeptide chains have tertiary structure and fold into compact shape
each protein has its own specific shape and length of chains
eg haemoglobin

Question 3

collagen

Answer 3

3 identical polypeptide chains
the 3 chains are twisted around each other to form a triple helix ie mainly 2 structure & 4 structure, very little 3 structure
no prosthetic group
35% of the amino acids are glycine
insoluble in water
function - connective tissue eg ligaments, tendons

Question 4

haemoglobin

Answer 4

4 polypeptide chains
the 4 chains form a globular protein showing 3 and 4 structure
contains the haeme prosthetic group which contains an FE2+ ion
a wide range of amino acids are used
soluble in water
function - transport of oxygen in red blood cells

Question 5

test for proteins

Answer 5

biuret test
add biuret solution/reagent to the sample & mic
if protein is present, the colour changes from blue to purple/lilac

Question 6

functions of proteins

Answer 6

fibrous proteins have a structural role - eg keratin in nails
enzymes eg amylase
protein hormones eg insulin
receptor proteins on cell membrane eg insulin receptor
antibodies - immunoglobulins to bind to antigens
channel proteins - transport polar substances across membranes by FD
carrier proteins - transport polar substances across membranes by FD and AT
glycoproteins - on cell membrane for cell-cell signalling
motor proteins - eg myosin and actin in muscle

Question 7

name two elements that are present in proteins that are not in lipids

Answer 7

nitrogen and sulphur

Question 8

why does a change in primary structure affect the function of haemoglobin

Answer 8

the change in the amino acid sequence causes a change in the R groups
H-bonds, ionic bonds, disulphide bonds form in different places
3 structure is changed
this means it cannot bind to O2

Question 9

amino acids

Answer 9

monomers from which proteins are made

Question 10

how is a dipeptide formed

Answer 10

a condensation reaction between two amino acids

Question 11

what is many amino acids joined

Answer 11

poly peptide

Question 12

what is the bond

Answer 12

peptide bond

Question 13

functional protein

Answer 13

one or more polypeptides

Question 14

primary structure

Answer 14

sequence of amino acids

Question 15

secondary structure

Answer 15

folding of amino acids into alpha helices or beta-pleated sheets
- hydrogen bonds hold them together

Question 16

hydrogen bonds

Answer 16

alone - weak

collective - strong

Question 17

tertiary structure

Answer 17

alpha-helices/beta sheets fold further to form a specific 3D structure
- ionic bonds and disulphide bridges hold the tertiary structure

Question 18

quaternary structure

Answer 18

consists of more than one polypeptide chain

polypeptide can bind to a prosthetic/non-peptide group