GMan - Chapter 7

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Chromatin

DNA and proteins of chromosomes
When do chromosomes develop

When chromatin condenses prior to division
Chromosome morphology
- p (short arm) - centromere- q (long arm)
Four types of chromosome morphology
- Metacentric (equal length p and q arms)
- Submetacentric (Slightly longer q arms)
- Acrocentric (Much longer q arms)
- Telocentric (Little-to-no p arm)
Differences between Eukaryote and Bacterial chromosomes
- Bacterial DNA is associated with less protein
- Bacterial DNA is found in the Nucloid
- Bacerial cells do not contain chromatin
Function of chromatin
- Strength
- Packaging
- Regulation
Chromomeres

Dark bands associated with differential compacting of DNA
Polytene Chromosomes
- Large
- Multiple strands of DNA
- Paired homologs
Puff regions
- Areas of uncoiled DNA
- Associated with high expression/activity
Hitsone composition
- Basic/Positively charged
- Lots of lys and arg residues
Nucleosome
- Beads of histones and DNA (Beads on a string)
- Contain 8 histone proteins (Octamer)
- DNA is wound around 1.7 times (Left handed)
Proteins of the Histone octamer
- H2A-H2B Dimers
- H3-H4 Dimers
Core particle
- Histone octamer
- 146 BP of DNA
Chromatin fibre
- A length of Nucleosomes
- And intervening linkers ~ 54bp
Histone H1
- 50% as common as other histones
- Links nucleosomes (30nm fibre)
300nm Fibre

Series of looped domains of the 30nm fibre
Heterochromatin
- Tightly packed
- Transcriptionally inactive
- 700nm fibre
Euchromatin
- Looser packing
- Active transcription
Packing ration calculation

Length of DNA/Length of fibre
Constitutive heterochromatin

Highly condensed simple repeats
Facultative heterochromatin
- Variably condensed
- Includes heterochromatin and euchromatin
Chromosome territories

Regions occupied by decondensed chromosomes during interphase
Average human gene density
- 1 Gene per 100kb
- Protein coding genes are only 1.5% of the DNA
Perecentage of the human genome containing repeating sequences
- 50%
- Believed to be the result of transposons
Three main categories of repetitive DNA
- Satellite DNA - Centromeres
- Tandem repeats - Telomeres
- Interspersed elements - Transposons
What does VNTR mean?
- Variable number tandem repeats
- Applies to mini- & micro- satellites
S- and L- INES, meaning
- Short Interspersed elements
- Long Interspersed elements
Interspersed repetitive elements
- SINES and LINES
- Dispersed throughout the genome (not tandem repeats)
- 1/3 of human genome
- Jumping genes/retrotransposons
Three noncoding sequences required for replication
- Centromere
- Origin of replication
- Centromere
Centromeres
- Attached to kinetochores
- Mediate chromosomal migration
- Composed of satellite DNA
Telomere sequence

TTAGGG
Telomerase
- Restores telomerase
- Ribonucleoprotein
- Reverse transcriptase activity
Hayflick limit

Number of replications before senescence
How is gene diversity maximized

Alternative splicing

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GMan - Chapter 7

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GMan

Updated

2017-04-15T20:41:21Z

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