MCBG 3 Flashcards
How many purines can be found in a stretch of 100bp double stranded DNA
100 purines. 2 strands each nucleotide will have one purine
What is chromatin
A material that forms chromosomes in eukaryotes
How is DNA packaged ?
DNA DNA is wrapped around histones to form nucleosomes
These are then coiled into units call SOLENOIDS
Solenoids are then coiled into solenoid loops
Chromatin
Chromatin loops
Condensed chromatin loops
Chromosomes
What’s a nucleoside? Nucleotide
Nuceloside = base and sugar Nucleotide = phosphate base and sugar
What’s a exonuclease?
A protein that cleaves nucleotides fro, the end of the DNA chain
What’s a endonuclease?
An ezyme that cleaves a polynucleotidee by cleaving the chain at any point except the ends
In DNA polymerase what is the function of the exonuclease domain?
To act as a proof reader and cleave incorrectly assembled chains.
What demos DNA polymerase do?
It catalyses the formation of new DNA strands?
What are the three phases of interphase?
G1
Synthesis. DNA replication
G2
How are the arms of a chromosome labeled?
Top or small arm is P for petit
The longer arm is Q because is comes after P
How are chromosomes grouped?
In order of size. There are 9 groups A-G
What happens in prophase?
DNA condenses into chromosomes
Nucleolus decondenses
Centrosomes spindles start to form
Prometaphase?
Nuclear spindles connect to chromosomes
No nuclear membrane
Metaphase?
Chromosomes line up on the equator (metaphase plate)
Polar spindle fibres
This is a random alignment
Anaphase?
Centromeres divide
Spindles contract
Sister chromatids instantly become chromosomes
Telophase?
Nuclear membrane formation
Cleavage of cell begins
Decondensing of DNA
Spindles disappear
What happens in cytokinesis?
Cytoplasm divides
Parent cell becomes 2 daughter cells with identical genetic information
Do sister chromatids always have identical dna in mitosis?
Yes!
Non-sister chromatids have the same DNA?
Yes
Meiosis.
How many daughter cells are produced?
What’s the genetic material like?
4 genetically different daughter cells
Haploid
In meiosis when does crossing over occur?
Prophase 1
What happens in prometaphase in meiosis?
Nothing. There is no prometaphase. Bazinga
In meiosis what lines up at the metaphase plate?
A tetra. Two chromosomes with 4 chromatids
How does meiosis generate genetic diversity?
Random assortment of chromosomes. at the start of meiosis you have two chromosomes (4 chromatids). One chromosome is from your mother and then the other from your father.
Crossing over
What’s the cell pre meiosis called in a male?
What has this specialised from?
What is the name of the haploid cell
And these develope into mature?
Primary spermatocyte
Spermatogonium
Spermatids
Mature sperm
How long does spermatogenesis occur?
~60 days
What’s the cell pre meiosis called in a female?
What has this specialised from?
What is the name of the haploid cell
And these develope into mature?
Primary oocyte
Oogonium
Ovum + three polar bodies
Mature ovum
Length of oogenesis?
12-50 years
What’s a telomere?
Repetitive nucleotide sequence at the end of chromosomes
TTAGGG What does this code for?
Telomeres. This sequence is repeated 2500 time
What’s the “equator” called?
Metaphase plate
How is genetic diversity obtained in meiosis? 2
Randomly alignment (assortment) of chromosomes (metaphase I) Crossing over (prophase 1)
What’s slippage in DNA mutation?
An extra base is added and it loops out
DNA mutation: how can slippage cause an addition of a base and sometimes a removal?
Depends on which strand? New strand slippage causes an addition of a base. If slippage occurs on a template strand then a nucleotide will be missed
What’s the most dangerous type of DNA mutation?
Double stranded breaks. Hard to fix
