L5&6. Cell Cycle Flashcards
How are human chromosomes described
Diploid = 2 copies of each autosomal chromosome
What is the function of the centromere
Allow attachement if the mitotic spindle
What is the function of the replication origin
Allow DNA to be copied
What is the telomere
Short repeating sequences of non coding DNA
What is the function of the telomere
Every time a cell replicates a few bases are lost
So the telomeres are eroded until the chromosome can no longer be replicated
Acts as a replication counter
What is chromatin
DNA + associated proteins (histone and non)
Properties of nucleosomal histone proteins
High + charge
Lots of lysine and arganine
What are the 4 types of nucleosomal histone proteins
H2A
H2B
H3
H4
What is the large globular histone protein used for compaction
H1
Explain the packing process of DNA into histones
- 2 copies of each histone p associates forming the octameric core
- DNA winds round the core twice forming the nucelosome
- Forms beads on a string structure
Why is there strong attraction between histones and dna
Histone = high + charge DNA = high - charge
Describe the beads on a string structure
Nucleosomes joined by linker sequences
The nucleosomes and H1 associate pulling the chromomes together forming a compact structure
Each turn is 83bp
How does the tightness of association between histones snd DNA affect transcription
Tight association = DNA is highly condensed = repressed transcription because transcription machinery can’t acessDNA
How does HAT acetylase affect association between dna ans histone
Adds acyl groups of histones
Removes +ve charge on histones
Lowers association with -ve dna
How does HDAC deacetylase affect association between dna ans histone
Removes acyl groups
Increases +ve charge
Increase association
Explain G1
Cells increase in size and increase number of organelles
Explain S
DNA replicates
Explain G2
Allow cell to monitor if dna have been successfully replicated
Explain M
Condensing of chromatin
Cytokinesis
Nuclear division
Why can the length of a cell cycle vary between organism and cells
Amount of time in G1 can vary
What is G0
Specialised resting state
A cell can stay in for long periods of time
What is the function of checkpoint in the cell cycle
1 phase must completely finish before the next phase begins
In order to make sure the environment is favourable and the DNA is correctly replicated to stop the production of mutated cells
Why is G1 checkpoint important
After the g1 checkpoint the cell is committed to relocation of apoptosis because the cell would have the wrong genetic composition leading to cancer
