topic 2.4- proteins

Question 1

define denaturation

Answer 1

a change to the conformation of the protein

Question 2

why does a denatured protein normal not return to its original structure?

Answer 2

denaturation is permanent.

Question 3

why does heat cause denaturation?

Answer 3

it causes vibrations within the molecule that can break intermolecular bonds or interactions

Question 4

why does change in pH cause denaturation?

Answer 4

the charges on R groups are changed, breaking ionic bonds within the protein or causing new Ionic bonds to form

Question 5

what property of proteins usually changes after denaturation and why?

Answer 5

soluble proteins often become insoluble and form a precipitate; this is due to the hydrophobic R groups in the centre of the molecule becoming exposed to the water around by the change in conformation

Question 6

how are amino acids linked together?

Answer 6

by condensation to form polypeptides

Question 7

define a polypeptide

Answer 7

a chain of amino acids held together by peptide bonds; these are the main component of proteins

Question 8

describe the condensation reaction to form polypeptides from amino acids

Answer 8

• involves the amino group (NH2) of one amino acid and the carboxyl group of (-COOH) of another
• water is eliminated
• peptide bond formed

Question 9

how many different amino acids are there in polypeptides synthesised on ribosomes?

Answer 9

20

Question 10

state the features that all amino acids have in common

Answer 10

a carbon atom in the centre of the molecule is bonded to an amine group, a carboxyl group and a hydrogen atom, as well as a variable R group

Question 11

what allows for the huge range of possible polypeptides?

Answer 11

amino acids can be linked together in any sequence

Question 12

for a polypeptide of n amino acids, there are ? possible sequences

Answer 12

20^n

Question 13

what codes for the sequence of amino acids in a polypeptide?

Answer 13

genes- the base sequence that codes for a polypeptide is known as the open reading frame

Question 14

a protein may consist of —-

Answer 14

a single polypeptide or more than one polypeptide linked together

Question 15

what determines the three-dimensional conformation of a protein?

Answer 15

the amino acid sequence

Question 16

what is the conformation of a protein?

Answer 16

its 3 dimensional structure

Question 17

describe how R groups influence a protein’s solubility

Answer 17

soluble in water, there are hydrophilic R groups on the outside of the molecule and usually hydrophobic groups on the inside

Question 18

give 12 functions of proteins in humans

Answer 18

1. catalysis- enzymes to catalyse chemical reactions
2. muscle contraction- actin and myosin cause contractions used in motion/transport in the body
3. cytoskeletons- tubulin is the subunit of microtubules
4. tensile strengthening- fibrous proteins give tensile strength needed in skin, tendons, ligaments and blood vessel walls
5. transport of nutrients and gases- proteins in blood help transport O2, CO2, Fe and lipids
6. cell adhesion- membrane proteins cause adjacent cells to stick to each other
7. hormones- some such as insulin, FSH and LH are proteins
8. receptors- act as binding sites in membranes/cytoplasm for hormones, neurotransmitters
9. blood clotting- plasma proteins act as clotting factors to help blood go from liquid to gel
10. packing of DNA- histones associated with DNA in eukaryotes, help chromosomes condense during mitosis
11. immunity- antibodies

Question 19

give 6 proteins that demonstrate the range of protein functions

Answer 19

• rubisco
• insulin
• immunoglobins
• rhodopsin
• collagen
• spider silk

Question 20

rubisco

Answer 20

catalyses the reaction that fixes carbon dioxide from the atmosphere

Question 21

insulin

Answer 21

hormone secreted by beta cells in the pancreas that signals to cells in the body to absorb glucose and help reduce the glucose conc in the blood

Question 22

immunoglobin

Answer 22

antibodies- bind to antigens on bacteria/other pathogens

Question 23

rhodopsin

Answer 23

one of the pigments that absorbs light for vision- membrane protein of rod cells of retina

Question 24

collagen

Answer 24

1/4 of all the protein in the human body
- forms a mesh of fibres in skin/ blood vessel walls/ligaments that resists tearing
- also part of teeth and bones

Question 25

spider silk

Answer 25

used to make the spokes of spiders’ webs

Question 26

define a proteome

Answer 26

all of the proteins produced by a cell, tissue or an organism

Question 27

what is the difference between the genome and the proteome of an organism?

Answer 27

whereas the genome of an organism is fixed, the proteome is variable because different cells in an organism make different proteins.

Question 28

define a genome

Answer 28

all of the genes of a cell, tissue or organism

Question 29

why does everyone have a unique proteome?

Answer 29

• because of differences in activity
• because of small differences in the amino acid sequence of proteins