DNA replication Flashcards
What are the stages in DNA replication?
- DNA helices runs along phosphate backbone breaking the hydrogen bonds between the bases
- this causes the double helix to unwind
- each strand exposes nucleotides
- free nucleotides from the cytoplasm travel to the nucleoplasm via the nuclear pores and attach to their complementary bases
- hydrogen bonds form( 2 with AT and 3 with CG)
- DNA polymerase catalyses the formation of phosphodiester bonds to form the phosphate backbone
Why is it semi conservative replication?
- forms two identical helices of DNA
- Each molecule of DNA has one of the original strands of DNA and one new strand
- the original strand acts as a template
Which way is DNA synthesised and why?
- 5’ to 3’
- the enzyme DNA polymerase only runs in the 3’ to 5’ direction
What is the difference between a leading strand and a lagging strand?
- leading strand is due to continuous replication
- lagging strand is due to discontinuous replication
- this leads to Okazaki fragments which have to be joined by the enzyme DNA ligase
What is a mutation?
- a change in the sequence of bases
- mutations are spontaneous and random
Why is it important that DNA replication produced genetically identical DNA?
- for the continuation of species
- ensure that cells and structures are maintained within a species
How do two nucleotides join?
- formation of phosphodiester bonds from the hydroxyl group on the third carbon and phosphate group on the fifth carbon
- condensation reaction
- removal of water
How can DNA be extracted?
- grind with a pestle and mortar to break down cell walls
- add detergent to break down cell membrane and release cell’s contents into the solution
- add salt to break the hydrogen bonds between DNA and water
- add protease enzymes to break down the proteins associated with DNA
- add cold ethanol
- the DNA should precipitate and lie between the layer of ethanol and solution
- using a glass rod, spool the shite precipitate
Why should DNA extraction be done at high temperatures
- so there is a low rate of enzyme-controlled reactions that could break down the DNA
Why does cold ethanol have to be used?
- to reduce solubility of DNA
what acts as the template strand during transcription?
- antisense strand
what is splicing of pre mRNA?
- removal of non coding regions called introns to form mature mrNA
describe how mRNA is formed from DNA
- DNA helix unwinds due to DNA helicase
- the hydrogen bonds between the bases are broken
- free RNA molecules attach to their complementary base pairs on the DNA antisense strand
- adenine will bind with uracil as RNA nucleotides don’t contain the base thymine
- cytosine will bind to guanine and vice versa
- transcriptions stops at the end of the base sequence that codes for the gene
- RNA polymerase catalyses the formation of phosphodiester bonds between the RNA nucleotides
- mRNA detaches from DNA
- premRNa is spliced to remove introns and form mature mRNA
what feature of the DNA molecule provides stability?
- the double helix
- polynucleotide chain with phosphodiester bonds between the monomer nucleotides
What are the features of the genetic code?
- degenerate so more than one codon codes for the same amino acid
- universal so all organisms follow the same code
- triplet code so three bases code for an amino acid
- non overlapping so a base would not be involved in two different codons.. the sequence is read so that each base is only part of one codon
