Term
| Histone complexes (name of basic structural unit of chromatin, # of bp/turns per complex, # of bp between complexes |
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Definition
- nucleosome
- 146bp and 1.8 turns around each histone core
- 20 - 60 bp spacer
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Term
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Definition
- double helix - 2nm
- nucleosome fiber - beads on a string - 10nm
- solenoid - 30 nm fiber
- solenoid packed in loops and attached to protein scaffold/ nuclear matrix at fixed locations - attachment intervals ~100kb
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Term
| Specialized histones/ Histone code |
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Definition
- H3 + H2A: confer specific characteristics - genomic DNA
- H3 + H4: can be modefied by chemical changes
- Post-translational modifications chng properties of nucleosomes that contain them
- histone code: pattern of major and specialized histone types and their modifications
- Varies from cell type to cell type, specifies packaging, and allows DNA to be accessible to regulatory molecules that determine gene expression
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Term
| Types of histone modifications |
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Definition
- acetylation
- methylation
- ubiquitination
- sumoylation
- phosphorylation
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Term
| Is DNA packaged the same in all cell types? |
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Definition
- No! Sperm cells highly specialized
- Histone proteins replaced with specialized protamines at late spermatogenesis
- Protamines are argenine rich and enable tighter packaging essential for sperm head condensation and DNA stabilization
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Term
| How does chromatin condensation chng with cell cycle? |
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Definition
- interphase - decondensed solenoid loops
- condenses as mitosis begins
- fully condensed at metaphase
- decondenses again toward interphase
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Term
| Telomeres and Centromeres |
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Definition
- Telomeres: seal chromosome ends preventing fusion with other chromosomes (TTAGGG repeats)
- Centromeres: specialized region of DNA (constriction along chromosome) - During cell division provides site at which spindle apparatus is anchored - essential for correct chromosome segregation
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Term
| Chromosome Preparation Procedure |
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Definition
- blood sample (WBC)
- cell culture - PHA (phytohemaglutinin) induce mitosis (condensation)
- treat with colchicine (dissolves spindle apparatus) and hypotonic soln.
- centrifuge
- fix cells (methanol + acetic acid)
- spread cells on slides, stain, microsopy
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Term
| types of chromosome banding methods |
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Definition
- G-banding - Giemsa - stains AT rich regions - most common in karyotyping
- c-banding - distinguish heterochromatin regions - favors areas like centromeres
- q-banding - quinacrine - fluorescent, similar to G bands
- r-banding - reverse of C banding, stains non-centromeric regions
- Reverse DAPI banding - similar to G banding
- Ag-NOR active nucleolar organising region
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Term
| names for diff centromere position |
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Definition
- metacentric - 1/2
- submetacentric - 1/3
- acrocentric - small piece of DNA on one side of centromere
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Term
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Definition
- p = short arm (petite)
- q = long arm (p+q = 1)
- cen = centromere
- ter = terminal/ telomere
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Term
| dark vs light bands in G-banding |
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Definition
- Dark bands - more condensed, A-T rich regions, heterochromatin, gene poor regions
- Light bands - less condensed, G-C rich regions, euchromatin, gene rich regions
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Term
| indications for karyotyping |
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Definition
- Probs in early growth + development (malformation, short stature, retardation
- stillbirth + neonatal death
- fertility probs (amenorrhea, hx of infertility, recurrent miscarriage)
- family hx of chromosome abnormality in 1st deg. relative
- neoplasia - cancer
- pregnancy > 35 yrs of age - fetal chromosome analysis
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Term
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Definition
- chromosome prep on slide
- denature DNA in situ
- label by incorp. nucleotides with attached flourophore or single probe for specific sequence
- allow to anneal, expose to UV, and visualize in situ
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