2.3 nucleic acids and enzymes

Question 1

what is the structure of nucleotides

Answer 1

a phosphate
5 carbon sugar
nitrogenous base

Question 2

name the pentose sugars in RNA and in DNA

Answer 2

deoxyribose
ribose

Question 3

describe how polynucleotide strands are formed and broken down

Answer 3

condensation reactions form strong phosphodiester and glycosidic bonds

hydrolisis reactions use a molecule of water to break these bonds

Question 4

describe the structure of DNA

Answer 4

molecule twists to form a double helix of 2 deoxyribose polynucleotide strands that are anti parallel to each other

a-t
c-g

Question 5

name the purine bases and describe their structure

Answer 5

adenine
guanine
two ring molecules

Question 6

name the pyrimidine bases and describe their structure

Answer 6

thymine
cytosine
uracil
one ring molecules

Question 7

why is DNA replication described as semi conservative

Answer 7

strands from original DNA molecule act as a template

new DNA molecule contains 1 old strand and 1 new strand

Question 8

explain the role of helicase in semi conservative replication

Answer 8

breaks hydrogen bonds between base pairs to form 2 single strands, each of which can act as a template

Question 9

how is a new strand formed during semi conservative replication

Answer 9

DNA gyrase unwinds and helicase unzips DNA

primase adds a primer so that DNA polymerase knows where to start adding nucleotides

ligase sticks together the fragments

Question 10

what is the lagging strand

Answer 10

DNA polymerase only goes in the 5’3’ direction so okozaki fragments are made in the lagging strand and stuck together by ligase

Question 11

identify features of genetic code

Answer 11

non overlapping - each triplet is only read once

degenerate - more than one triplet codes for the same amino acid (64 possible triplets for 200 amino acids)

universal - same bases and sequences used by all species

Question 12

how does a gene determine the sequence of amino acids in a protein

Answer 12

consists of base triplets that codes for specific amino acids

Question 13

describe how DNA could be purified through precipitation

Answer 13

add ethanol and salt to aqueous solution, nucleic acids precipitate out of solution

centrifuge to obtain a pellet of nucleic acid then wash and centrifuge again

Question 14

what does transcription produce and where does it occur

Answer 14

produces mRNA and occurs in the nucleus

Question 15

outline the process of transcription

Answer 15

RNA polymerase binds to the DNA strand and unwinds a short section

this then travels along the DNA strand building an RNA molecule from the template strand

splicing removes non-coding strands of mRNA (introns)

mRNA leaves through the nuclear pores and attaches to the ribosomes

Question 16

what does translation produce and where doe it occur

Answer 16

produces proteins and occurs in the cytoplasm on ribosomes

Question 17

outline the process of translation

Answer 17

tRNA carries specific individual amino acids
tRNA carries an anti codon that matches up to the corresponding bases on mRNA

process continues to form polypeptide chain until ‘stop’ codon is reached

Question 18

what is a mutation

Answer 18

an alteration to the DNA base sequence

Question 19

when does DNA replicate

Answer 19

during interphase

Question 20

describe enzymes

Answer 20

biological catalysts used to spead up reactions

Question 21

what is the difference between intra and extracellular enzymes

Answer 21

intracellular enzymes are inside the cell e.g DNA polymerase
whereas extracellular enzymes are outside the cells e.g. protease

Question 22

define turnover number

Answer 22

number of reactions an enzyme can catalyse per second

Question 23

define anabolic reaction

Answer 23

building up

Question 24

define catabolic reactions

Answer 24

breaking down

Question 25

describe the lock and key theory

Answer 25

substrate molecules fit into the active site and are then released

Question 26

describe the induced fit hypothesis

Answer 26

when the substrate molecules fit into the enzymes active site, the active site changes shape slightly to mould itself around the substrate molecule