DNA intro Flashcards
What is the smallest unit in DNA packaging?
A nucleosome
It’s DNA wrapped twice around one histone protein.
The DNA then links these nucleosomes together in a chain (beads on string)
What is a solenoid?
All the nucleosomes are linked like beads on a string. This string then could together tightly to form a solenoid (also called a fibre)
How are Heterochromatin a and euchromatin packaged differently?
The euchromatin sure like beads on a string it’s exposed and the genes can be expressed.
Heterodox chromatin is solenoid fibres, they are tightly bound so genes are not expressed.
In what form are genes when in a chromosome in replication ?
They are tightly packaged solenoids and so the genes are not expressible.
What are genes and where are they found?
They contain the coding for proteins and have a chromosomal location.
What is a genome?
The genome is the entire DNA sequence.
The human genome is 24 chromosomes (22 autosomes + 2 sex chromosomes)
What is the basic structure of DNA?
Bases, protected by a phosphosuagr backbone. Made from nucleotides and helixes
The strand run antiparrelel
Form a double right handed helix
What is a nucleotide?
Contains a single base + pentose sugar + phosphate
What is a nucleoside?
Base + pentose sugar (no phosphate)
What the difference between RNA and DNA?
The pentose sugar.
On RNA its ribose, on DNA it loses a H from the 2nd carbon to become 2-deoxyribose.
What is a purine?
A two ring base = adenine and guanine
What is a pyrimidine?
A one ring base. = thymine and cytosine and uracil
What is distinct about a DNA chain?
It has polarity 3” to 5”
The 3” is the OH end and the 5” is the P end.
How are bases paired?
Hydrogen bonds.
2 between T/U and A
3 between C and G
How is a DNA sequence written?
Conventionally it runs left to right 5” to 3”
What is the accepted model for DNA replication?
The semi-conservative model
What are the main points of DNA replication?
Catalysed by DNA polymerase Strands are separated It’s a stepwise reaction 1 base at time Reaction dire by pyrophosphate hydrolyses Chain grows from 5” to 3”
What are the 3 steps of DNA replication in prokaryotes?
Initiation
Elongation
Termination
(Of a circular naked chromosome)
What happens in the initiation step of prokaryotic DNA replication?
A replication fork forms and DNA polymerase joins the 3” end of the strand so it begins making 5” to 3”.
What happens in the elongation step of prokaryotic DNA replication?
The DNA polymerase runs along the DNA from 3” towards 5” creating a new strand for each template strand.
DNA ligase puts together the Osaka fragments that are formed in the lagging strand .
DNA helicase continues to unwind the double helix.
What happens in the termination stage of prokaryotic DNA replication?
The lagging strand and leading strand meet and are linked by DNA ligase, to form one strand.
