Chromosomes and Cell Division Flashcards
Chromosomes and Cell Division
Primary function of genetic material
Store information
Chromosomes and Cell Division
Histone
Protein
DNA wrapped around it
Chromosomes and Cell Division
Why is the histone attracted to the DNA
DNA has a negative charge
Histone has a positive charge
Chromosomes and Cell Division
By how much does DNA wrapping around histone shorten it?
Sevenfold
Chromosomes and Cell Division
Nucleosome
Repeating unit of DNA wrapped around an octamer of histone proteins
Chromosomes and Cell Division
How are nucleosomes organised?
Into an even more compact structure
30nm fibre
Chromosomes and Cell Division
Radial loop domains
Chromosomes and Cell Division
Two proposed models for structure of 30nm fibre
Three dimensional zig-zag model
Solenoid model
Chromosomes and Cell Division
Why are we unsure about the structure of the 30nm fibre?
DNA conformation may be altered when extracted from living cells
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Types of compaction of chromosomes
Heterochromatin
Euchromatin
Chromosomes and Cell Division
Heterochromatin
Transcriptionally inactive
Very compact
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Echaromatin
Less condensed than heterochromatin
Capable of gene transcription
Chromosomes and Cell Division
Which type of chromsome compaction is most common in non-dividing cells?
Euchromatin
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What happens to chromatin compaction during cell division?
All Euchromatin converted to heterochromatin
Chromosomes and Cell Division
Individual chromosomes are located in their….
Discrete, non-overlapping territory
Chromosomes and Cell Division
Chromosome compaction at metaphase
Radial loops remain anchored to scaffold formed from proteins in the nuclear matrix
Chromosomes and Cell Division
How many different chromosomes do humans have?
23
Chromosomes and Cell Division
How many chromosomes do humans have in total?
46
Chromosomes and Cell Division
Haploid cells
Only have one member of a chromosome pair
Chromosomes and Cell Division
Diploid cells
Have full set of chromosomes
Chromosomes and Cell Division
When a species is diploid, members of a pair of chromosomes are called….
Homologues
Chromosomes and Cell Division
Homologues
Chromosomes and Cell Division
Cell cycle (time taken)
G1 (11 hours)
S (8 hours)
G2 (4 hours)
M (1 hour)
Chromosomes and Cell Division
Cell cycle (shorthand and long)
First gap (G1)
DNA synthesis (S)
Second gap (G2)
Mitosis (M)
Chromosomes and Cell Division
Shortest stage in cell cycle
Mitosis
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Checkpoint proteins
Act as sensors to determine if the cell is in proper condition to divide
Chromosomes and Cell Division
What happens if checkpoint proteins find a problem
Cell division is delayed until it’s sorted or stopped entirely
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What does a loss of checkpoint function lead to
Mutation and cancer
Chromosomes and Cell Division
3 checkpoints in eukaryotic cell division
G1 checkpoint/restriction point
G2 checkpoint
Metaphase checkpoint
Chromosomes and Cell Division
S phase of DNA replication
DNA is replicated
Sister chromatids formed
Chromosomes and Cell Division
Sister chromatids
2 identical chromosomes copies
Tightly associated at centromere
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Centromere
Acts as an attachment site for kinetochore
Chromosomes and Cell Division
What is responsible for organising and sorting chromosomes during miosis?
Mitotic spindle
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What is the spindle formed from?
Microtubules
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What are microtubules formed from?
Tybulin proteins
Chromosomes and Cell Division
3 types of microtubules
Astral
Polar
Kinetichore
Chromosomes and Cell Division
Astral microtubules
Position spindle in the cell
Chromosomes and Cell Division
Polar microtubules
Seperate the 2 poles