D1.1 DNA replication

Question 1

dna replication

Answer 1

product of exact copies of dna with identical base sequences

Question 2

semi conservative

Answer 2

each strand of an existing dna double helix acts as the template for the synthesis of a new strand from free nucleotides

one strand comes from the original chromosome and the other is newly synthesised

Question 3

why is replication important in multicellular organisms

Answer 3

• growth
• replacement of old cells
• reproduction

Question 4

what does semi conservative allow

Answer 4

high degree of accuracy in copying base sequences

Question 5

conservative replication

Answer 5

entirely new double helix is formed alongside the original with no unzipping of DNA

Question 6

complimentary base pairing

Answer 6

Adenine with thymine
Cytosine with guanine

Question 7

helicase enzyme

Answer 7

unwinds the dna double helix at one region breaking the hydrogen bonds that hold the strands together

Question 8

where do hydrogen bonds form in DNA

Answer 8

between the template strand and new strand if the correct bases are paired up

Question 9

what reaction does DNA polymerase catalyse

Answer 9

DNA polymerase links together the sugar and phosphate groups of adjacent nucleotides forming new strands

also a condensation reaction

Question 10

polymerase other roles

Answer 10

replication where mistakes are corrected - proof-reading

results in 2 strands being formed which are identical to original strands

Question 11

PCR - polymerase chain reaction

Answer 11

technique for amplifying selected regions of dna by multiple cycles of dna synthesis

Question 12

which direction does polymerase work in

Answer 12

3’-5’ direction

adds the 5’ terminal to the new nucleotide

Question 13

taq polymerase

Answer 13

heat stable DNA polymerase enzyme used in pcr

This means it does not denature at the high temperature involved during the first stage of the PCR reaction

Question 14

Gel electrophoresis

Answer 14

analysis of DNA, RNA, and proteins

the molecules are separated with an electric current according to their size or mass and their net (overall) charge

Question 15

what does the separation in electrophoresis occur because of

Answer 15

electrical charge - positively charges molecules will move towards negative pole and visa versa

different sizes of molecules - tiny pores in gel result in smaller molecules moving quickly and visa versa

types of gel - different sized pores can affect the speed at which molecules can move through the gel

Question 16

what is pcr used for

Answer 16

to amplify the number of dna molecules

it is used to produce large quantities of specific fragments of DNA or RNA from very small quantities

Using PCR, scientists can produce billions of identical copies of the DNA or RNA samples within a few hours, these can then be used for analysis

Question 17

dna primer

Answer 17

short sequence of single stranded DNA
used in PCR
made synthetically
base sequences complementary to one end of DNA

Question 18

what is gel electrophoresis used in

Answer 18

DNA sequencing - investigation of sequence of bases in particular lengths of DNA

genetic profiling - identification of individual organisms and species

Question 19

how can fragments be identified after separation

Answer 19

gene probes - radioactive label which causes the probes to emit radiation that makes the X-ray film go dark, creating a pattern of dark bands

stains - fluorescent stain or dye which shines when exposed to ultraviolet light, creating a pattern of coloured bands

Question 20

Buffer solution

Answer 20

to provide the optimum pH for the reactions to occur in

Question 21

Denaturation in PCR

Answer 21

first stage

the double-stranded DNA is heated to 95°C which breaks the hydrogen bonds that bond the two DNA strands together

Question 22

Annealing

Answer 22

second step of pcr where the temperature is decreased to between 50 - 60°C so that primers can anneal to the ends of the single strands of DNA

Question 23

Elongation / Extension

Answer 23

third stage of pcr
the temperature is increased to 72°C
this is the optimum temperature for Taq polymerase to build the complementary strands of DNA to produce the new identical double-stranded DNA molecules

Question 24

southern blotting

Answer 24

extracted dna is cut into fragments with restriction enzyme

fragments are separated by electrophoresis

made single stranded by treatment of gel with alkali

Question 25

applications of genetic fingerprinting

Answer 25

identification of suspects and corpses
determining paternity