PROTEINS

Question 1

Proteins

Answer 1

proteins are large molecules. all enzymes are proteins. protein is a polymer made up of large number of smaller sub units called amino acids.

Question 2

major component elements in protein

Answer 2

CHONS - carbon, hydrogen, oxygen, nitrogen and sulphur

Question 3

examples of protein

Answer 3

hormone - insulin and glucagon
- oxygen carrying pigments - myoglobin and haemoglobin
- structural protein - collagen found in connective tissues and keratin found in hair and nails.
- actin and myosin.

Question 4

feature of amino acids

Answer 4

amphoteric
can act as an acid or a base.

Question 5

what is the bond that joins amino acids?

Answer 5

peptide bonds

Question 6

peptide bonds

Answer 6

peptide bond is a chemical bond formed when two amino acids are joined together in a condensation reaction.

it is formed when oh group on acidic end of one amino acid reacts with h group on amino end of the next amino acid.

Question 7

structures of protein

Answer 7

primary, secondary, tertiary and quaternery

Question 8

primary structure of protein

Answer 8

it is the sequence of amino acids in a polypeptide chain.

Question 9

why is primary structure important?

Answer 9

because it is determined by the genetic code - determines the order and position of the R group - controls the shape - determines the function.

Question 10

secondary structure of protein

Answer 10

secondary structure of protein is the molecule which is resulted from the regular coiling or folding of chain of amino acids.

Question 11

what causes the chain to fold ? what shapes are formed?

Answer 11

the hydrogen bonds

as a result two shapes can be formed that is either alpha helix or beta pleats.

Question 12

what can break the hydrogen bonds

Answer 12

high temperature and pH.

Question 13

tertiary structure of protein

Answer 13

the way in which a protein coils to form a precise three dimensional shape. it is a result of much stronger bonds when there is attraction between alpha helices and beta pleats.

Question 14

bonds present in tertiary structure

Answer 14

1. hydrogen bonds
2. disulfide bridges
   3 ionic bond
3. hydrophobic interaction or weak vander waals force

Question 15

hydrogen bonds

Answer 15

not strong when isolated but really strong when together

Question 16

disulfide bridge

Answer 16

covalent bond between two cysteine molecules. ionic and disulfide bonds forms between different r groups of amino acids.

Question 17

ionic bond

Answer 17

formed between ionised amino group and ionised carboxylic group

Question 18

hydrophobic interactions

Answer 18

occurs between non polar r groups.

These strong covalent bonds holds the protein in its specific 3d shape. the 3d shape creates pockets or holes in protein surface which is very important for protein functioning.

Question 19

Quaternery structure of protein

Answer 19

it is when two or more tertiary structures stick together to form a large molecule. not all proteins have it. eg haemoglobin.

Question 20

Haemoglobin

Answer 20

haemoglobin carries oxygen and is found in red blood cells. it consists of 4 polypeptide chains. 2 of which are 141 amino acids long and other two are 146 amino acids long.

Question 21

structure of haemoglobin

Answer 21

• haemoglobin is nearly spherical in shape.
• the hydrophobic group are pointed inwards towards the centre wheras the hydrophilic groups are on the outside.
• the hydrophobic interactions on the inside are important for maintaining a precise 3d shape
• the hydrophilic gropups help to maintain solubility.

Question 22

what happens if a protein is denatured

Answer 22

if a protein is denatured then the bonds which hold the secondary and tertiary structure in shape breaks and therefore the unique 3d shape is lost. enzymes lose their unique active site.

Question 23

imp of primary structure

Answer 23

if even one amino acid sequence changes it will cause the ionic,hydrogen or disulphide bonds to form in a different location which results in a different 3d shape.

Question 24

test for protein

Answer 24

biuret test.
biuret reagent is added to the sample of protein that is to be tested.
lilac color indicates positive results.