DNA Structure Flashcards
How many forms of DNA are there and what are they called?
3: B, A and Z
What’s the difference between the 3 forms of DNA?
B and A are wound round the right hand and A is more tightly wound
Z is wound round the left hand and found inside cells
Give the Features of a DNA helix
Two antiparallel polynucleotide chains forming a RH helix
Bases on the inside and phosphate and sugar on the inside
10 base pairs in each turn (B form)
What’s weird about the Z form of DNA?
It winds round the left and formed by GCGCGCGCGC OR GTGTGTGTGTGT
What’s a tetraplex DNA?
4 stranded DNA helix formed at telomeres which generally involve G- rich sequences
What’s a Holliday junction?
When two homologous chromosomes exchange strands
Describe the levels of DNA structure and how you can see them
Primary- base sequence (DNA sequencing)
Secondary- helical structure (x-ray and chemistry)
Tertiary- DNA supercoiling ( electron microscopy)
Quaternary- chromosomes are interlocked (in bacteria after a round of replication)
How does Sanger sequencing work
- a strand is copied with DNA polymerase in the presence of inhibitors that stop DNA synthesis at a specific base.
- the strands are separated by length onto a gel
- if the DNA or inhibitor is fluorescent, the DNA bands can be visualised and the sequence read
How else (not Sanger) can you sequence DNA
Automation
What causes bacterial DNA to be supercoiled?
DNA gyrase uses ATP to take the DNA from its relaxed state to its supercoiled state
What’s the opposite of DNA gyrase?
Topo IV and topo I
How to get a karyotype
get a cell in mitosis and spread out all the chromosomes. Then you attach a dye to each and identify and sort out all the chromosomes ( on a computer)
Give Another name for chromatin
Nucleoprotein complex
What is chromatin?
DNA + histones
What is a Nucleosome?
Basic building block of chromatin
