DNA & Genetics - Outcome 1 Flashcards
what does a DNA nucleotide consist of?
- deoxyribose sugar
- phosphate group
- base
what are purines?
- adenine
- guanine
what are pyrimidines?
- cytosine
- thymine
what does a nucleoside consist of?
- deoxyribose sugar
- base
what is the bond between a deoxyribose sugar and a base called?
N-glycosidic bond
how is a nucleotide produced?
condensation reaction between nucleoside on carbon 5 and phosphate group
what is the bond between a deoxyribose sugar and phosphate group called?
phosphoester bond
what bond is between carbon 3 of one nucleotide and the phosphate group of the next nucleotide called?
phosphodiester bond
what are the complementary DNA base pairs?
A - T and C- G
how many bonds are formed when guanine and cytosine pair together?
3
how many bonds are formed when adenine and thymine pair together?
2
what does it mean if a region on double stranded DNA features an unusually high number of guanines and cytosines? (G-C)
the strands will be relatively hard to separate as more bonds must be broken
how are the two DNA strands in a double helix aligned?
in an antiparallel fashion
- 5’ to 3’
- 3’ to 5’
what is the mechanism for replication and how does it work?
- semi-conservative replication
- two parental strands separate and duplicate to each produce a complementary daughter strand
- new double helix consists of one parental strand and one daughter strand
describe the steps in DNA replication?
- parental strands begin to separate
- parental strand acts as templates - free nucleotides pair with complementary bases on the template strands
- nucleotides bond to form sugar-phosphate backbone
- newly formed DNA strands separate forming two new double helices
describe what happens in the separation of DNA strands
- helices unwinds double helix
- hydrogen bonds break
- replication fork forms
describe what happens during addition of complementary nucleotides
- primase synthesise a primer
- primer is complementary to DNA template strand
- primer acts as start point for DNA polymerase
- DNA polymerase adds complementary DNA nucleotides to primer to extend daughter strand
what is a primer?
a short sequence of nucleotides joined together
what is the leading strand?
template strand with a 3’ to 5’ orientation that can easily grow in 5’ to 3’ direction
what is the lagging strand?
template strand with 5’ to 3’ orientation and requires extension in a 3’ to 5’ direction
what is continuous replication?
nucleotides are continuously added to the ;ending strand as replication fork opens up
describe discontinuous replication
- 1000 nucleotides on template strand are exposed before an RNA primer is added
- daughter strand synthesised ‘backwards’ in 5’ to 3’ direction
- entire lagging strand is synthesised in fragments known as Okazaki fragments
- each Okazaki fragment requires own primer
- lagging strand contains small stretches of RNA that must be replaced with DNA
- ligase repairs gaps In backbone between each fragment by formation of phosphodiester bond
what is the polymerase chain reaction (PCR)?
a lab technique that allows a single strand of DNA to be amplified into millions of copies
whats an example of PCR being beneficial?
forensics
- DNA at crime scene can be amplified to produce sufficient DNA to allow characterisation
what are the stages of PCR?
- denaturation
- annealing
- elongation
what happens during denaturation of PCR?
- RNA primers attach to single stranded template DNA
- strands separated by helicase
- double stranded DNA converted to single strand by heating to 95°C
what happens during annealing of PCR?
- entire DNA strand is copied
- DNA primers anneal to sites close to 3’ end of required gene
- ideal temperature is 55°C
what happens during elongation of PCR?
- DNA polymerase catalyses formation of DNA strand by addition of DNA nucleotides complementary to bases on template strand
- ideal temperature is 72°C.
