7.1 DNA structure and replication Flashcards
(23 cards)
who discovered that DNA was hereditary not proteins?
Hershey and Chase designed a sophisticated investigation using bacteriophage viruses grown in different radio-labelled sulphur or phosphorus.
what was the use of photograph 51?
taken by rosalind franklin, it was crutial in the development of watson and cricks model of DNA.
what are the two types of bases and the pairing of them?
(bigger) purines - adenine and guanine
(smaller) pyrimidines - thymine and cytosine + uracil
how do the bases pair in a stable way?
thymine is positive charge and adenine is more negative - electrically compatible.
cytosine and guanine have three hydrogen bonds - structurally stable
how do you determine the 5’ and 3’ ends?
5’ is a phosphate attached to a carbon atom
3’ is a hydroxyl group attached to a carbon atom
DNA in eukaryotes, what are nucleosomes?
- associated with proteins called histones and they form nucleosomes
- has 8 histone proteins together called an octamer.
- section of DNA called linker connects it all together
- this helps it supercoil
what is the association between protein and DNA within a nucleosome?
- negatively charged DNA associates with positively charged amino acids on the surface of histones.
- histones have IV terminals that extrude out from the nucleosome.
- when chromosomes condense N-terminal tails from octamers lick to IV-terminals.
what is the direction of DNA replication?
- begins at sites called origins of replication.
- prokaryotes have 1 site and eukaryotes have multiple
- replication occurs away from the origin
- new nucleotides are added to the chain by an enzyme DNA polymerase.
- polymerase adds the phosphate group of a new DNA nucleotide to the 3’ carbon of the deoxyribose on the nucleotide.
what is the leading and lagging strand?
the leading strand is made continuously following the replication fork as it opens.
the lagging strand is made into small fragments moving away from the replication fork
what are the lagging strand fragments called?
Okazaki Fragments
what does helicase do?
it unwinds the DNA at the replication fork and breaks hydrogen bonds between the two DNA strands.
what does DNA Gyrase or topoisomerase do?
they release the strain that develops before helicase, which prevents supercoling of the DNA.
what do single-stranded binding proteins (SSBP) do?
they keep the two DNA strands separate for replication
what does DNA primase do?
it synthesises one RNA primer on the leading strand and many RNA primers on the lagging strand.
provided the RNA primers needed to start DNA polymerase activity.
What does DNA polymerase III do?
forms covalent links between the new nuleotide to the hydroxl group at 3’ carbon to extend the strand.
2 extra phosphates are removed (dNTP to dNMP) to provide energy
used first
what does DNA polymerase I do?
removes RNA primer and replaces it with DNA nucleotides.
what does DNA ligase do?
used to join the Okazaki fragments to create a continuous strand
what are coding sequences?
DNA sequences that code for new polypeptides
what are non-coding sequences?
- most eukaryotic genomes are non-coding sequences - they are used for gene expression
- introns are in the nucleus
- exons are out of the nucleus
- in eukaryotes genomes, there are repetitive sequences
what are telomeres?
- they are found at the ends of eukaryotic chromosomes
- they prevent loss of genes during gene replication
what is DNA sequencing?
- carried out with a method that uses fluorescence.
- unknown DNA to be sequenced are placed in test tubes with raw materials, deoxyribonucleotides and enzymes
what are the fluorescent labelled nucleotides?
- dideoxyribonucleotides
- they are added to the test tube and create a stop replication when they are added.
what is a VNTR?
a variable number of tandem repeat - DNA sequenc ethat is repeated between people
- how DNA profiling is done
- short tandem repeats are on Y chomosome
