proteins

Question 1

what elements always and sometimes make up a protein?

Answer 1

always: carbon, hydrogen, oxygen, nitrogen
sometimes: sulfur

Question 2

what are amino acids? describe and draw their structure

Answer 2

amino acids are the basic building blocks of proteins

• each amino acid has one animo group (-NH2) and one carboxyl group (-COOH)
• the carbon atom next to the carboxyl group is called the α carbon
• each α carbon has a hydrogen atom, a carboxyl group, an animo group and a R group bonded to it
• all amino acids only differ in the R group

drawing

Question 3

what do amino acids join together to form?
describe the condensation reaction

Answer 3

they join together to form a polypeptide chain, joined by peptide bonds

the condensation reaction occurs between the animo group of one amino acid and the carboxyl group of another, to form a dipeptide where a peptide bond is formed between the 2 amino acids, which is accompanied by the elimination of one water molecule.

Question 4

briefly describe the polypeptide chains

Answer 4

• folded into three-dimensional shape, due to chemical bonds between various amino acid residues in polypeptide chains
• has an amino end (N-terminal) and carboxyl end (C-terminal)

amino terminal is the START of chain, c-terminal is end

Question 5

what is the characteristic three-dimensional shape and structure of protein know as?

Answer 5

conformation

Question 6

define primary structure

Answer 6

variety, number, and sequence of amino acids in a polypeptide chain

Question 7

what bonds are present in primary structure?

Answer 7

peptide bond

Question 8

describe the primary structure

Answer 8

• unique - proteins differ from each other in the variety, number and sequence of their consistuent amino acids
• slight change in primary structure of a protein can alter is properties drastically

Question 9

define secondary structure

Answer 9

localised, repetitive folding of the polypeptide chain

Question 10

what bonds are present in secondary structure?

Answer 10

it is stabilised by hydrogen bonds between peptide linkages of polypeptide backbone (R groups of amino acids are NOT involved)

Question 11

a) describe:
- the shape of α-helix
- the bonding in α-helix

b) provide an example of a protein which mainly has α-helix

Answer 11

a)
- extended spiral spring
- stabilised by hydrogen bonds between -C=O and N-H groups within polypeptide chain

b) keratin

hydrogen bonds are between -C=O and N-H groups for both secondary structures

Question 12

a) describe:
- the shape of β-pleated sheet
- the bonding in β-pleated sheet

b) provide an example of a protein which mainly has β-pleated sheet

Answer 12

a)
- two or more regions of polypeptide chain lie parallel to each other in flat, zig zag sheets. the polypeptide chains may run in the same direction (parallel β-pleated sheets) or in opposite direction (anti-parallel β-pleated sheet)
- stabilised by hydrogen bonds between the -C=O and N-H groups of one part of the backbone and the -C=O and N-H groups of an adjacent part in the parallel regions

b) fibroin (protein in silk) -> hence it has high tensile strength

hydrogen bonds are between -C=O and N-H groups for both secondary structures

Question 13

define tertiary structure

Answer 13

the polypeptide chain folds and bends into a precise, compact, globular three-dimensional shape, unique to the protein

Question 14

what are all the bonds present in tertiary structure?

Answer 14

stabilised by intramolecular R group interactions / (disulfide bonds, hydrogen bonds, ionic bonds and hydrophobic interactions) between R groups of amino acids at different regions of polypeptide chain

Question 15

define quaternary structure

Answer 15

combination of a number of polypeptide chains and may involve associated non-protein groups into a large, complex and functional protein molecule. each polypeptide chain in the protein is called a subunit

Question 16

what are the bonds present in quaternary structure?

Answer 16

subunits are held together by intermolecular R group interactions / (disulfide bonds, hydrogen bonds, ionic bonds and hydrophobic interactions)

Question 17

name a protein in RBC with a quaternary structure. briefly describe it.

Answer 17

haemoglobin
it has 4 subunits (4 polypeptide chains), with 2 α-chains and 2 β-chains each containing a heme group (non-protein group). the heme group has a Fe2+ ion.

Question 18

describe the functions of 8 types of proteins (in living organisms)

HEHE psst (mnemonic)

Answer 18

1) homeostatic: soluble proteins in blood plasma act as buffers to stabilise pH
2) enzymatic: catalyses and speed up the rate of chemical reactions in the cell
3) hormonal: hormones in the body like insulin and glucagon
4) source of energy: during extreme starvation when carbohydrates and fat reserves are depleted
5) protection:
- antibodies function as part of immune system
- blood clotting factors are important in blood clotting mechanism

6) storage:
- ferritin functions to store iron in liver
- myoglobin in skeletal muscle cells functions to store oxygen

7) support / structural:
- collagen as a component of connective tissue, cartilage, tendons and ligaments
- keratin in hair, hoofs and feathers

8) transport:
- proteins in plasma membrane function in transport of certain substances into and out of cell or membrane-bound organelle
- haemoglobin functions in transport of oxygen in vertebrates
- lipoproteins function in transport of cholesterol in blood

the examples or not very very important, but at least remember what named proteins function as.

Question 19

describe the test for proteins

Answer 19

1) to 2cm3 of test sample, add an equal volume of 5% sodium hydroxide solution
2) add two drops of 1% copper sulfate solution and mix
3) (observe any colour change)

expected results:
positive result: contents turned from light blue to violet
negative result: contents remained light blue

NOTE: this test tests for presence of peptide bonds, and individual amino acids won’t yield a positive result

Question 20

draw the condensation reaction between 2 amino acids

Answer 20

answer