Key area 1.1 & 1.2 Flashcards
What are the repeating units that make up DNA
Nucleotides
What are DNA nucleotides comprised of
Phosphate
Deoxyribose sugar
Base
What does a sugar phosphate bond do?
A sugar phosphate bond links the phosphate of one nucleotide to the deoxyribose of the next nucleotide to form the sugar phosphate backbone
What is DNA
DNA is the genetic code for all living things
What joins the complementary base pairs together inbetween nucleotides
Hydrogen bonds
Why can DNA be described as anti-parallel
It’s strands run in opposite directions
What does the 3 prime end in?
&
What does the 5 prime end in?
3 prime - sugar
5 prime - phosphate
Where would DNA be found in prokaryotic cells
Large circular chromosomes and smaller rings of DNA called plasmids
Where would DNA be found in a eukaryotic cell
Linear chromosomes found in the nucleus
And
Small circles of DNA found in their chloroplast or mitochondria
How is DNA packaged inside a eukaryotic cell
And
Why is it packaged in this way
DNA is packaged around bundles of protein. This is to stop it from getting tangled and so it fits inside
What shape is DNA
Double stranded helix
What does replication mean
Replication is the process by which DNA makes an exact copy of itself
Why can DNA replication be described as semi-conservative
DNA has one original strand and one new strand
Why is DNA replication important
DNA replication is important for growth and repair.
For growth DNA must be able to pass on an exact copy of itself during mitosis
What is a replication fork
A replication fork is the area where the hydrogen bonds between bases are broken and the bases are exposed
What are the requirements for DNA replication
Primers
Free nucleotides
Enzymes (DNA Polymerase, ligase)
ATP
What is the function of DNA polymerase
DNA polymerase is the enzyme that joins complementary nucleotides to the 3 prime end
What is a primer
Shorts bits of DNA complementary to the DNA being copied
Describe the process of replication of the leading strand
- Hydrogen bonds between bases are broken leaving the bases exposed
The point where the bases are exposed is called the replication fork
- Primers attach complementary base pairs to the 3’ end of DNA
Free nucleotides align themselves to the rest of the exposed bases on the 3’ stand
- DNA polymerase catalyses the formation of the sugar phosphate bond between the 3’ end of the primer and the aligned free nucleotides
- DNA polymerase moves along the 3’ strand continuously adding nucleotides
Describe the process of replication of the lagging strand
(Already occurred)
- Hydrogen bonds broken bases are exposed
Replication fork is where the bases are broken
(Replication of lagging strand)
- Many primers attach along the strand.
DNA polymerase attaches nucleotides to these primers to form fragments
- The fragments are joined by the enzyme ligase
What strand is described as continuous and what strand is described as discontinuous
Continuous - 3’
Discontinuous - 5’
What does PCR stand for and why is it used
PCR stands for polymerase chain reaction and it is used for DNA amplification
Name some uses for PCR
- Paternity testing
- testing for genetic diseases
- identifying suspects from blood or semen
Describe the process of PCR
1) DNA is heated to 93 degrees to separate the stands by breaking weak hydrogen bonds
2) DNA is cooled to 55 degrees to allow the complementary primer to bind to specific sequence. This is know as annealing
3) temperature is them increased to 70 degrees and heat tolerant DNA polymerase is used to add nucleotides to the primers therefore replication section of DNA
Why does the DNA polymerase I’m PCR need to be heat tolerant
So it doesn’t denature
Name the two controls used in PCR
Negative control
Positive control
What is a negative control and why is it used
A negative control contains no DNA template.
Checks there is no contamination of the tubes
What is a positive control and why is it used
A positive control contains a DNA template that is guaranteed to be amplified
It is used to verify negative amplification results
