nab revision unit 1

Question 1

what happens during differentiation?

Answer 1

unspecialised cells become adapted or altered to perform a specific function as part of a permenant tissue

Question 2

why cant a specialised cell develop into different types of cells?

Answer 2

the genes needed are switched off and cant be turned back on

Question 3

what are stem cells?

Answer 3

relatively unspecialised cells which can develop into different types of cells because most of their genes are still switched on

Question 4

what are some therapeutic uses of stem cells?

Answer 4

corneal grafts, bone marrow transplants and skin grafts

Question 5

what are somatic cells?

Answer 5

differentiated cells that form different types of body tissue e.g. blood, bone, muscle, nerve

Question 6

what are germline cells?

Answer 6

the gametes and the cells that produce the gametes

Question 7

what are cancer cells?

Answer 7

cells which do no respond to normal regulatory signals that would instruct them to stop dividing when necessary

Question 8

how is a tumour formed?

Answer 8

when cancer cells continue to reproduce and form a mass of abnormal cells

Question 9

how are secondary tumours formed?

Answer 9

when cells from a tumour detach from their neighbours and spread throughout the body

Question 10

how many strands does dna consist of?

Answer 10

2

Question 11

what are the repeating units in dna called?

Answer 11

nucleotides

Question 12

what is the nucleotide made up of?

Answer 12

phosphate, deoxyribose sugar and a organic base

Question 13

what is the backbone of each dna strand made up of

Answer 13

deoxyribose and phosphate

Question 14

how are the strands held together?

Answer 14

weak hydrogen bonds between the bases

Question 15

what is the structure of dna?

Answer 15

the strands run anti-parallel to each other, double helix structure

Question 16

how are chromosomes formed?

Answer 16

dna is tightly coiled and packaged around bundles of protein which coil to form chromosomes

Question 17

replication stage 1

Answer 17

dna double helix unwinds

Question 18

replication stage 2

Answer 18

weak hydrogen bonds break causing the 2 strands to seperate

Question 19

replication stage 3

Answer 19

free dna nucleotide joins complimentary pair on open strand

Question 20

replication stage 4

Answer 20

weak hydrogen bonds reform between base pairs

Question 21

replication stage 5

Answer 21

strong chemical bond forms between both nucleotides controlled by the enzyme dna polymerase

Question 22

replication stage 6

Answer 22

newly formed daughter dna (identical to original) begins to wind into double helix

Question 23

what does dna polymerase do?

Answer 23

it can only add nucleotides to the free 3’ end of a growing strand and needs a primer to start things off

Question 24

what is a primer?

Answer 24

a piece of single-stranded dna which is complementary to a specific target sequence on the strand being replicated

Question 25

how is the 5' end of dna replicated?

Answer 25

the strand with the 5' end exposed is replicated in fragments starting at the 3' end, they are then joined together by then enzyme ligase

Question 26

what is a mRNA molecule?

Answer 26

a mRNA molecule carries the code from the dna in the nucleus to the ribosomes. mRNA is a single strand of nucleorides, which has no folding along its length, and therefore can have no base pairing

Question 27

what is a tRNA molecule?

Answer 27

a tRNA molecule carries a specific amino acid to the ribosomes. tRNA is a single strand of nucleotides which folds back on itself to make a 3D shape. base pairing occurs

Question 28

what is a substitution mutation?

Answer 28

one nucleotide swapped for another, so only one amino acid changed

Question 29

what is a insertion mutation?

Answer 29

one nucleotide added, sequence wrong from then on, so all amino acids altered from then on (frameshift)

Question 30

what is a deletion mutation?

Answer 30

one nucleotide lost, sequence wrong from then on, so all amino acids altered from then on (frameshift)

Question 31

what is a splice-site mutation?

Answer 31

a mutation occuring at a splice-site, which results in an intron remaining attached to the mRNA

Question 32

what is a missense mutation?

Answer 32

following a substitution, the altered codon codes for an amino acid that still makes sense but not the original sense

Question 33

what is a nonsense mutation?

Answer 33

an amino acid is substituted with a stop codon

Question 34

what is pcr used for?

Answer 34

to amplify (make copies of) a specific segment of DNA

Question 35

what does the amplification of dna involve?

Answer 35

the use of primers

Question 36

what is stage 1 of pcr?

Answer 36

melting; dna is heated to seperate the strands

Question 37

what is stage 2 of pcr?

Answer 37

annealing; dna is cooled for primer binding

Question 38

what is stage 3 of pcr?

Answer 38

extending; dna is reheated to allow heat tolerant dna polymerase to manufacture complementary strands

Question 39

what are inhibitors?

Answer 39

chemicals which slow down or stop an enzyme controlled reaction (competitive or non-competitive)

Question 40

what do competitive inhibitors do?

Answer 40

interfere with the active site of the enzyme so the substrate cannot bind

Question 41

what do non-competitve inhibitors do?

Answer 41

change the shape of the enzyme so it cannot bind to the substrate

Question 42

comparitive effects of increasing substrate concentration in the presence of inhibitors when enzyme concentration is limited

Answer 42

competitive; effect depends on relative concentration of substrate and inhibitor non-competitive; effect depends only on concentration of inhibitor

Question 43

what happens in an anabolic pathway?

Answer 43

small molecules are assembled into large ones. energy is required

Question 44

what happens in a catabolic pathway?

Answer 44

large molecules are broken down into small ones. energy is released

Question 45

what does the enzyme phosphofruktokinase do in stage 1 of respiration?

Answer 45

makes the intermediate compound irreversible and continues the process of glycolysis and is known as the key regulatory point

Question 46

what do dehydrogenase enzymes do?

Answer 46

remove hydrogen ions from substrate

Question 47

what are slow twitch muscle fibres good for?

Answer 47

endurance activities e.g. rowing, cycling and long distance running

Question 48

what are fast twitch muscle fibres good for?

Answer 48

bursts of energy e.g. sprinting and weightlifting