Intro to DNA 1 Flashcards
What chromosomes do normal humans have?
22 pairs of autosomes and 1 pair of allosomes
What is heterochromatin?
DNA that is tightly packaged around the histone, so the genes are not expressed
What is euchromatin?
Beads on a string model of DNA, so genes are expressed as the DNA is loosely packaged
What is a nucleosome?
A section of DNA wrapped twice around a histone core
What is the DNA between histones called?
Linker DNA
How many proteins make up a histone?
8 (so it’s an octamer)
What is a solenoid?
A section of heterochromatin
Are genes expressed in chromosomes?
No
What’s the difference between nucleotides and nucleosides?
Nucleotides are a base + sugar + phosphate, whereas a nucleoside is only a base + sugar
What’s the difference between ribose and n-deoxyribose? What is n?
n=2, as the second carbon in ribose has an OH attached whereas in 2-deoxyribose it has a H
What’s the difference between purines and pyrimidines?
Purines have two rings (adenine, guanine) (nucleoside ends in -sine) whereas pyrimidines have just one (cytosine, uracil, thymine) (nucleoside ends with -dine)
Which nitrogenous bases are zwitterions?
Cytosine and guanine
How are nucleotides joined?
Phosphodiester bonds between C5 and C3 of the pentose sugar
Which way is the DNA chain usually written?
5’ (prime) to 3’
Only the top strand which runs 5’ to 3’ is written by convention
What is at each end of a DNA chain?
At 5’ end - phosphate group
At 3’ end - OH group
What is the name given to the way a DNA double helix twists?
Right handed helix
How does the secondary structure of DNA affect gene expression?
In the major groove (bigger gap) genes are expressed, in the minor groove they aren’t
Describe the cell cycle
1) Mitosis - cell division
2) G1 - cell content replication
3) S - DNA replication
4) G2 - double check and repair
How does DNA polymerase catalyse the start of DNA replication?
It separates DNA strands (dNMP)n and catalyses the reaction of adding a deoxynucleoside triphosphate (dNTP) to the 3’ end of a DNA strand, extending the chain ((dNMP)n+1 and releasing a pyrophosphate (PPi) which is then hydrolysed by DNA polymerase to break it down into inorganic phosphate to release energy
How did they first discover DNA replication?
Through circular DNA in prokaryotes
What are the three steps of DNA replication in prokaryotes?
Initiation, elongation, termination
What is initiation in terms of DNA replication in prokaryotes? What does it require?
Recognition of origin of replication
Requires recruitment of DNA polymerase plus other specific proteins
Requires a ‘kick-start’ by primase (as DNA polymerase can only extend a 3’ end)
Which way does DNA polymerase read DNA?
3’ to 5’, as it has to add a dNTP on the 3’ end
What breaks the bonds between base pairs, and what are those bonds called?
DNA Helicase
Hydrogen bonds
