3.1.4 Proteins

Question 1

how many types of amino acids are there?

Answer 1

20

Question 2

what are proteins made of?

Answer 2

C, H, O, N

Question 3

what are globular proteins?

Answer 3

round structures, metabollic function e.g. haemoglobin

Question 4

what are fibrous proteins?

Answer 4

long strands of polypeptide chains that have cross-linkages due to hydrogen bonds, structural function e.g collagen

Question 5

what are proteins made from?

Answer 5

amino acids (monomers)

Question 6

what is a dipeptide?

Answer 6

formed when 2 amino acids join together via condensation and form a peptide bond

Question 7

what is a polypeptide?

Answer 7

formed when more than 2 amino acids join together via condensation to form many peptides bonds

Question 8

what is the structure of amino acids?

Answer 8

amine group (H-N-H), variable group (R), carboxylic group (O=C-OH), a C and a H

Question 9

how do amino acids join?

Answer 9

condensation - removes 1 water molecule and joins carbon to the nitrogen forming a peptide bond

Question 10

how do amino acids break up?

Answer 10

hydrolysis - uses 1 water molecule to break up the amino acid

Question 11

how do you test for protein?

Answer 11

add sodium hydroxide solution
add copper (II) sulfate solution
positive test = purple
negative test = blue

Question 12

how does a purple colour form?

Answer 12

the nitrogen in the peptide bond forms a purple complex with copper (II) ions in biruets reagent, causing colour change - therefore, the colour change shows the presence of a peptide bond and therefore a protein

Question 13

why should you wear goggles?

Answer 13

sodium hydroxide is an irritant

Question 14

what is the primary structure of a protein?

Answer 14

the sequence of amino acids in the polypeptide chain (sequence determined by the DNA sequence)

Question 15

what is the secondary structure of a protein?

Answer 15

hydrogen bonds form between the amino acids in the chain which makes the automatically coil into an alpha chain or folded into a beta pleated sheet.
hydrogen bonds occur in C=O and N-H

Question 16

what is the tertiary structure of a protein?

Answer 16

the coiled/folded chain of amino acids is often coiled and folded further.
more bonds form between different parts of the polypeptide chain (disulphide bridge -> ionic bond -> hydrogen bond -> hydrophobic interactions) - bonds form between R groups
the way in which the polypeptide chain coils up forms a precise 3D shape which is specific and determines the biological function of the protein

Question 17

what is the quaternary structure of a protein?

Answer 17

for proteins with 2 or more polypeptide chains, this is their final structure
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