Introduction to DNA Flashcards
What is heterochromatin and what does it look like under an electron microscope?
Densely packed form of chromatin
Looks darker
What is euchromatin and what does it look like under an electron microscope?
Lightly packed form of chromatin
Looks lighter
What is the shape of DNA?
Right handed double helix
What is a gene?
A section of DNA that codes for a protein
How do you fit 2 metres of DNA into a 6 micrometre cell nucleus?
DNA is wrapped around histones to form a nucleosome
30nm of nucleosomes is a solenoid
What is the human genome?
The entire DNA sequence of a human
22 and 2 sex chromosomes
What are the two nucleic acids?
DNA and RNA
What is a polynucleotide?
Linear polymer of nucleotides
E.g. DNA and RNA
What is a nucleoside?
Sugar and base
What is a nucleotide?
Sugar, base and phosphate
Which is the difference between ribose and deoxyribose?
Ribose has two OH on carbon 2 and 3
Deoxyribose has a H and OH on carbons 2 and 3
What bond links together nucleotides?
Phosphodiester bonds
What bases are purine?
Adenine and guanine
What bases are pyrimidine?
Thymine, cytosine and uracil
What is at the 5’ end of a DNA chain?
Phosphate
What is at the 3’ end of DNA?
OH
What are the complementary base pair rules and how many hydrogen bonds form between them?
Adenine and thymine or uracil- 2
Guanine and cytosine- 3
How do DNA strands connect?
Complimentary and antiparallel
Which way of a DNA strand is left to right?
5’ to 3’
By convention top strand is this direction
Where are cell cycle checkpoints?
Between G1 and S
Between G2 and mitosis
What is the name of DNA replication?
Semi-conservative
What enzyme catalyses DNA replication?
DNA polymerase
What happens in the initiation stage of DNA replication?
recognise origin of replication
primase kicks starts process as DNA polymerase can only extend the 3’ end and shows where to start
What happens in the elongation stage of DNA replication?
Moving replication fork Helicase unwinds double helix DNA polymerase extends 3' end only lagging strand uses fragments of DNA called ozkazaki fragments- use primers RNA Primers are replaced with DNA DNA ligaments joins the fragments
What happens in the termination stage of DNA replication?
When two facing replication forks meet DNA ligase joins final fragments
What is a chromatid?
When chromosomes are connected by the centromere, they are the two arms
If not connected by centromere a chromatid is a chromosome
