topic 1 - proteins

Question 1

what are proteins made from

Answer 1

long chains of amino acids

Question 2

what is a monomer of proteins

Answer 2

amino acids

Question 3

how is a dipeptide formed

Answer 3

when two amino acids join together by a peptide bond

Question 4

what are protein made up of

Answer 4

one or more polypeptides

Question 5

what is an amino acids general structure

Answer 5

a carboxyl group (-COOH)
an amine/ amino acid group (-NH²)
an R group/ variable side group

Question 6

what is the only difference between the 20 amino acids

Answer 6

the R group

Question 7

how are polypeptides formed

Answer 7

when more than two amino acids are joined together by peptide bonds

Question 8

how do two amino acids become a dipeptide (detailed)

Answer 8

amino acids are linked together by condensation reactions to form a dipeptide - a molecule of water is released during the reaction - the bonds formed between amino acids are called peptide bonds

Question 9

how many structural levels do proteins have

Answer 9

four

Question 10

what are the proteins four structures

Answer 10

primary, secondary, tertiary, quaternary structures

Question 11

what is the proteins primary structure

Answer 11

this is the sequence of amino acids in the polypeptide chain

Question 12

what is the proteins secondary structure

Answer 12

the polypeptide chain doesn’t remain flat and straight - hydrogen bonds form between the amino acids in the chain, making it automatically coil into an alpha helix or fold into a beta pleated sheet

Question 13

what is the tertiary structure

Answer 13

the coiled or folded chain of amino is often coiled and folded further - more bonds form between different parts of the polypeptide chain, including hydrogen bonds and ionic bonds (attractions between negative and positive charges on different parts of the molecule)
disulphide bridges also form when two molecules of the amino acid cysteine come close together - the sulfur atom in one cysteine bond to the sulfur atom in the other
for proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure

Question 14

what is the quaternary structure

Answer 14

some proteins are made of several different polypeptide chains held together by bonds
the quaternary structure is the way these polypeptide chains are assembled together
for proteins made from more than one polypeptide chain the quaternary structure is the protein’s final 3D structure

Question 15

four examples of proteins

Answer 15

enzymes, antibodies, transport proteins, structural proteins

Question 16

how do enzymes structure make them specialised to carry out its particular job

Answer 16

enzymes - soluble and often have roles in metabolism, some hep synthesize large molecules
structure: usually roughly spherical in shape due to the tight folding of the polypeptide chain

Question 17

how do antibodies make them specialised to carry out its particular job

Answer 17

antibodies - involved in the immune response
structure: made of two light polypeptide chains and two heavy polypeptide chains bonded together
antibodies have variable regions - the amino acid sequences in these regions vary greatly

Question 18

transport proteins make them specialised to carry out its particular job

Answer 18

transport protein - transport molecules and ions across membranes
structure: channel proteins are present in cell membranes - channel proteins contain hydrophobic and hydrophilic amino acids, causing the protein to fold up and firm a channel

Question 19

structural protein make them specialised to carry out its particular job

Answer 19

structural proteins - physically strong
structure: consist of long polypeptide chains lying parallel to each other with cross links between them
include keratin and collagen

Question 20

what test do you use for proteins

Answer 20

biuret test

Question 21

what does a biuret test find out

Answer 21

if a substance contained protein

Question 22

what are the two stages to a biuret test

Answer 22

(1) test solution needs to be alkaline, so you add a few drops of sodium hydroxide solution
(2) add copper (II) sulfate solution
- if protein is present the solution turns purple
- if no protein solution stays blue