D1.1 DNA replication Flashcards
dna replication
product of exact copies of dna with identical base sequences
semi conservative
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
why is replication important in multicellular organisms
- growth
- replacement of old cells
- reproduction
what does semi conservative allow
high degree of accuracy in copying base sequences
conservative replication
entirely new double helix is formed alongside the original with no unzipping of DNA
complimentary base pairing
Adenine with thymine
Cytosine with guanine
helicase enzyme
unwinds the dna double helix at one region breaking the hydrogen bonds that hold the strands together
where do hydrogen bonds form in DNA
between the template strand and new strand if the correct bases are paired up
what reaction does DNA polymerase catalyse
DNA polymerase links together the sugar and phosphate groups of adjacent nucleotides forming new strands
also a condensation reaction
polymerase other roles
replication where mistakes are corrected - proof-reading
results in 2 strands being formed which are identical to original strands
PCR - polymerase chain reaction
technique for amplifying selected regions of dna by multiple cycles of dna synthesis
which direction does polymerase work in
3’-5’ direction
adds the 5’ terminal to the new nucleotide
taq polymerase
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
Gel electrophoresis
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
what does the separation in electrophoresis occur because of
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
what is pcr used for
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
dna primer
short sequence of single stranded DNA
used in PCR
made synthetically
base sequences complementary to one end of DNA
what is gel electrophoresis used in
DNA sequencing - investigation of sequence of bases in particular lengths of DNA
genetic profiling - identification of individual organisms and species
how can fragments be identified after separation
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
Buffer solution
to provide the optimum pH for the reactions to occur in
Denaturation in PCR
first stage
the double-stranded DNA is heated to 95°C which breaks the hydrogen bonds that bond the two DNA strands together
Annealing
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
Elongation / Extension
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
southern blotting
extracted dna is cut into fragments with restriction enzyme
fragments are separated by electrophoresis
made single stranded by treatment of gel with alkali
applications of genetic fingerprinting
identification of suspects and corpses
determining paternity
