proteins

Question 1

what elements do proteins contain

Answer 1

• carbon
• oxygen
• hydrogen
• nitrogen

Question 2

what makes amino acids different from each other

Answer 2

‘R’ groups
(side chains)

Question 3

how many different amino acids?

Answer 3

20
- 5 non essential as our body is able to make them from others
- 9 essential and can only be obtained from eating
- 6 conditionally essential as only needed by children

Question 4

how do amino acids join

Answer 4

• condensation reaction
• hydroxyl in the carboxyl group and hydrogen in amine group
• forms peptide bond
• water is produced

Question 5

what catalyses a condensation reaction for peptide bonds

Answer 5

enzyme called peptidyl transferase

(found in ribosomes-site of protein synthesis)

Question 6

what is the primary structure of a protein

Answer 6

the sequence in which amino acids are joined

peptide bonds only

Question 7

what influences the function of a protein

Answer 7

the particular amino acids in the sequence will influence how the polypeptide folds to the protein’s final shape

Question 8

secondary structure of a protein

Answer 8

• hydrogen bonds form within the chain
• pulling it into a coil shape (alpha helix)
  or
• forming sheet like structures by polypeptides lying parallel to each other (beta pleated sheet)

Question 9

tertiary structure of a protein

Answer 9

the folding of a protein into its final shape

• the coiling/folding of polypeptides into their secondary structure brings out R groups of different amino acids closer enough to interact and further folding occurs

Question 10

interactions in a protein’s tertiary structure

Answer 10

-hydrophobic/ hydrophilic interactions between polar and non-polar groups
- hydrogen bonds (weakest)
- ionic bonds (between oppositely charged R groups
- disulfide bonds (strongest covalent)

Question 11

quaternary structure of a protein

Answer 11

• association of 2 or more individual proteins called subunits
• interactions between subunits are the same as in tertiary structure except they are between protein molecules rather than within 1 molecule

Question 12

what subunits do enzymes often consist of

Answer 12

2 identical subunits

Question 13

where are proteins assembled

Answer 13

the aqueous environment of the cytoplasm

Question 14

where are hydrophobic/hydrophilic groups on a protein?

Answer 14

hydrophilic groups are on the outside of the protein
hydrophobic groups are on the inside of the protein, shielded from water in cytoplasm

Question 15

what catalyses a hydrolysis reaction for peptides

Answer 15

enzyme proteases

Question 16

what are features of globular proteins

Answer 16

compact
water soluble
roughly spherical

Question 17

when do globular proteins form

Answer 17

when proteins fold into their tertiary structures in such a way that they hydrophobic R groups are kept away from the aqueous environment, and hydrophilic R groups are on the outside of the protein

Question 18

what type of protein is insulin

Answer 18

globular

Question 19

why is insulin a globular protein

Answer 19

• hormones are transported in the bloodstream so need to be soluble
• hormones have to fit into specific receptors on membranes to have their effect so they need to have precise shapes

Question 20

what are conjugated proteins

Answer 20

globular proteins that contain a non-protein component called a prosthetic group

(proteins without prosthetic groups are called simple proteins)

Question 21

examples of types of prosthetic groups

Answer 21

• lipids/carbohydrates can combine with proteins to form lipoproteins or glycoproteins
• metal ions/molecules from vitamins (called co-factors if they are necessary for the protein’s function)
• Haem groups contain an iron 2+ ion (catalase, haemoglobin)

Question 22

structure of haemoglobin

Answer 22

• conjugated protein
• quaternary protein
• 4 polypeptides
• 2 alpha, 2 beta subunits
• each subunit has a prosthetic haem group
• iron ion is able to combine reversibly with an oxygen molecule

Question 23

structure of catalase

Answer 23

• enzyme
• conjugated protein
• quaternary protein
• 4 haem prosthetic groups
• iron ion allows catalse to interact with hydrogen peroxide and speed up its breakdown
• hydrogen peroxide is a byproduct of metabolism but damages cells

Question 24

structure of fibrous proteins

Answer 24

• long, insoluble molecules which aren’t folded into complex 3d shapes
• due to high proportion of amino acids with hydrophobic R groups in their primary structures
• limited range of amino acids with small R groups
• primary structure sequence is quite repetitive
• leads to very organised structures
  (keratin, elastin, collagen)

Question 25

what is keratin

Answer 25

fibrous protein

Question 26

where is keratin present

Answer 26

hair
skin
nails

Question 27

structure of keratin

Answer 27

• high proportion of cysteine (contains sulfur)
• many strong disulfide bonds forms strong, inflexible, insoluble materials
• degree of disulfide bonds determines flexibility
• hair contains fewer, nails contains more bonds

Question 28

what is elastin

Answer 28

fibrous protein

Question 29

structure of elastin

Answer 29

• found in elastic fibres
• present in walls of blood vessels, alveoli (gives flexibility to expand)
• quaternary protein
• made from tropoelastin

Question 30

what is collagen

Answer 30

fibrous protein

Question 31

structure of collagen

Answer 31

• connective tissue found in skin, tendons, ligaments, nervous system
• 3 polypeptides wound together in a long, strong rope-like structure
• flexible

Question 32

test for proteins and why

Answer 32

Biuret test

peptide bonds form violet complexes with copper ions in alkaline solutions

Question 33

how to carry out a test for proteins

Answer 33

• 3cm^3 of sample mixed with equal volume of 10% sodium hydroxide solution
• 1% copper sulfate solution added a few drops at a time until solution turned blue
• solution mixed and left for 5 minutes
• should turn lilac (positive test)