2.11

Question 1

a gene is a

Answer 1

length of DNA that codes for one polypeptide

Question 2

alleles are

Answer 2

different forms of a gene

Question 3

changes in DNA that makes up one gene will result in

Answer 3

new allele

Question 4

DNA is made of a double helix and is like a ‘twisted-rope-ladder’ with pairs of

Answer 4

organic bases forming the ‘rungs’ of the ladder

Question 5

Four bases:

Answer 5

Adenine
Thymine
Cytosine
Guanine

Question 6

The sequence of these four bases A,C,G,T carries the coded information that cells use to make

Answer 6

polypeptides and proteins

Question 7

Whenever DNA replicates, there is a risk that a

Answer 7

mistake may be made

Question 8

Almost all mistakes in copying DNA are corrected by the

Answer 8

DNA polymerase enzyme that copy the DNA

Question 9

Uncorrected errors in the DNA are called

Answer 9

mutations

Question 10

A mutation is a

Answer 10

permanent change in the amount or arrangement of a cell’s DNA

Question 11

Some mutations will have no effect, because they occur in so-called

Answer 11

‘junk’ DNA

Question 12

The mutation where one base pair has been deleted is known as

Answer 12

deletion

Question 13

one base pair missed out changes the way the code is

Answer 13

read

Question 14

deletion mutation is known as

Answer 14

frame-shift mutation

Question 15

deletion is called frame-shift mutation as

Answer 15

all the triplets are changed after the point of mutation

Question 16

frame-shift mutation produces a very big change in the

Answer 16

primary structure of the protein that is coded for by the mutated allele

Question 17

as a result of frame-shift mutation the resulting protein will have a very different

Answer 17

tertiary structure and is likely to be non-functional

Question 18

(EXAMPLE OF DELETION) most common mutation of CFTR gene is the deletion of just 3 nucleotides that code for the amino acid

As a result the CFTR protein coded for has an

Answer 18

phenylalanine

altered tertiary structure

Question 19

the mutation where one base has been changed to another is known as

Answer 19

substitution

Question 20

substitution will only affect a single triplet, therefore, just one

Answer 20

amino acid in the whole protein will be altered

Question 21

Example of substitution is

Answer 21

sickle-cell anaemia

Question 22

Sickle-cell anaemia results from haemoglobin S, which differs from normal haemoglobin by a change in just

Answer 22

one amino acid in 2 of its 4 polypeptide chains

Question 23

Sickle-cell anaemia: the triplet code CTT (codes for glutamate) in the DNA has changed to CAT (codes for valine). These amino acids have very different R-groups, making haemoglobin S much less

Answer 23

soluble than normal haemoglobin

Question 24

It is possible for a substitution mutation to occur, but without causing any change in the protein coded for as there are more

Answer 24

triplet codes than amino acids, so some amino acids have more than one DNA triplet code

Question 25

Example of no change in protein due to substitution is if triplet code CTT changed to CTC, there would be no change in the amino acid coded for, this is because they both code for

Answer 25

glutamate

Question 26

When substitution results in a base that still codes for the same amino acid as the original base it is a

Answer 26

silent mutation

Question 27

Silent mutations are possible due to the

Answer 27

degenerate nature of the genetic code

Question 28

Silent mutations would have no effect on the

Answer 28

final polypeptide

Question 29

changes in the base sequence of genes are usually referred to as

Answer 29

point mutations

Question 30

chromosome mutations may also occur. these are changes in the

Answer 30

number and structure of chromosomes

Question 31

an example of chromosome mutation is

Answer 31

non-disjunction

Question 32

non-disjunction is

Answer 32

the failure of one or more pairs of homologous chromosomes to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei

Question 33

when a substitution of a base occurs leading to a premature ‘stop-codon’ being coded for is known as a

Answer 33

non-sense mutation

Question 34

a non-sense mutation would lead to the

Answer 34

premature end to the synthesis of a polypeptide and the final protein would be almost certainly not able to function normally

Question 35

stop codons are:

Answer 35

UAA
UAG
UGA

Question 36

A mutation that occurs when a change in a base leads to a different amino acid being coded for is known as

Answer 36

mis-sense

Question 37

a mis-sense mutation is due to

Answer 37

substitution

Question 38

mis-sense mutation causes the polypeptide to have a single amino acid that is different and the effect is determined by the role of the

Answer 38

amino acid in the final polypeptide. it maybe that it was involved in the formation of bonds to structure the active site of an enzyme - if this changes so does active site, therefore substrate no longer fits.

Question 39

DNA mutations occur naturally at a very

Answer 39

low rate

Question 40

The rate at which mutations occur may be increased by environmental factors known as

Answer 40

mutagens

Question 41

a mutagen is an

Answer 41

agent, such as radiation, which causes genetic mutation

Question 42

Mutagens include:

Answer 42

Radiation - UV, X-rays, alpha and beta
Chemicals - nitrous acid
Carcinogens - diesel exhaust and cigarette smoke