Proteins

Question 1

What are amino acids?

Answer 1

the monomers from which proteins are made

Question 2

How are dipeptides formed?

Answer 2

the condensation of 2 amino acids

Question 3

How are polypeptides formed?

Answer 3

the condensation of many amino acids

Question 4

How are peptide bonds formed?

Answer 4

a condensation reaction between 2 amino acids

Question 5

What are proteins made up of?

Answer 5

one or more polypeptides

Question 6

What is the amine group?

Answer 6

H2N

Question 7

What is the carboxyl group?

Answer 7

COOH

Question 8

What is the R group/ Variable group?

Answer 8

the 20 different options of amino acids that create the side chain - the only difference in amino acids

Question 9

What is the primary structure?

Answer 9

the sequence of amino acids in the polypeptide chain
- determines the final shape and function

Question 10

What is the secondary structure?

Answer 10

held together by hydrogen bonds between the carboxyl and amine group in the polypeptide backbone
- coil into alpha helix
= hydrogen bonds run parallel with long helical axis
= strong stable structure due to many hydrogen bonds
- polypeptide chain fold back on itself to form beta pleated sheets
= held together by hydrogen bonds

Question 11

What is the tertiary structure?

Answer 11

• final 3D structure formed by folding of polypeptide chains
• each protein has unique tertiary structure which is responsible for its specific properties and functions
  e.g. enzymes active site
• can be denatured by heat or pH - increased kinetic energy can break bonds - not reversible
• held together by bonds between the R groups of the amino acids so depends on the sequence of the amino acids

Question 12

What are the bonds in the tertiary structure?

Answer 12

hydrogen
- between slightly oppositely charged groups - forms slightly negative charge
- can be split by high temp of altered pH (weak)

ionic
- form between basic + acidic group
- between oppositely charged R groups
- can be split by changing pH (strong)

disulphide
- between 2 cysteine aa - covalent S-S
- can be split by reducing agents (strongest)

Van der Waal forces (extra reading)
- weak forces of attraction between non polar groups
- water excluded from hydrophobic side chains - helps keep side chains together
- split by rise in temp

Question 13

What is the quaternary structure?

Answer 13

• only found in proteins containing more than 1 polypeptide
  e.g. haemoglobin - 4 globular arranged in tetrahedral structure

Question 14

The final 3D structure can be?

Answer 14

globular or fibrous

Question 15

What is a globular protein?

Answer 15

• ball shaped
• water soluble - hydrophobic turn inwards and hydrophilic outwards
• have metabolic roles
• enzymes in all organisms
• plasma proteins and antibodies in mammals

Question 16

What are fibrous proteins?

Answer 16

• form fibres
• have regular or repetitive sequence of amino acids
• usually insoluble in water
• structural roles
• collagen in bonds and cartilage
• keratin in fingernails and hair

Question 17

How do you test for proteins?

Answer 17

biuret test
- add a few drops of sodium hydroxide solution to sample in test tube (must be alkaline)
- add copper sulphate solution and mix gently
- protein present = turns purples
- no protein = stays blue