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Definition
| is the genetic term for any complex of DNA and protein found in a nucleus of a cell |
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| are the separate pieces of chromatin that behave as a unit during cell division |
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| 1/3 DNA, 1/3 histones, and 1/3 nonhistone proteins |
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| DNA INTERACTIONS W/ HISTONES AND NONHISTONE PROTEINS |
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Definition
| produces sufficient level of compaction to fit into a cell nucleus |
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Definition
small, positively charged, highly conserved
- bind to & neutralize (-) charged DNA
- 5 types-> H1,H2A,H2B,H3, & H4
-core histones make up the nucleosome |
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Definition
| 200-200000 molecules of each kind |
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| LARGE VARIETY OF FUNCTION |
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Definition
structural role-> chromosome scaffold
chromosome replicaiton -> DNA polymerase
chromosome segregation->kinetochore protein
active in transcription |
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| DIFFERENT LEVELS OF CHROMOSOME COMPACTION |
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Definition
when stretched out, the DNA in a single cell would be about 6 ft long
compaction allows the DNA to fit in a cell nucleus |
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a fundamental unit of chromosomal packing
resemble beads on a string |
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| SPACING AND STRUCTURE OF NUCLEOSOME AFFECT GENETIC FUNCTION |
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Definition
-accessibility for proteins that initiate transcription, replication, and further comp.
-arrangement along chromatin is highly defined & varies in diff cell types &under diff conditions |
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| THE NUCLEOSOME IS AN OCTAMER OF 2 EACH OF HISTONES H2A,H2B,H3, &H4 |
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Definition
160 bp of DNA wraps 2x around a nucleosome core
40bp linker DNA connects adj. nucleosomes
histone H1 associates w/linker DNA as it enters & leaves nuclesome core |
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Term
| XRAY CRYSTALLOGRAPHY OF NUCLEOSOME |
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Definition
-DNA bends sharply at several places as it wraps around the core histone ocatmer
- base seq. dictates preferred nucleosome potisions along the DNA |
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Term
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Definition
model of higher-order packaging
100 A nucleosomal chromatin is compacted in to 300A fiber by supercoiling |
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Definition
model for higher level of compaction
several nonhistone proteins bind to chromatin every 60-100 kb and tether the 300A fiber into structure loops |
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Definition
| may further condense chromosomes into a compact bundle for mitosis |
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| KARYOTYPE OF A HUMAN FEMALE EXAMINED BY HIGH RESOLUTION G BANDING |
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Definition
-metaphase chromosomes stained w/ giemsa have alternating bands of light and dark stain
-each contains many loops 1-10 mb long
-banding patterns on each chromosome are highly reproducible |
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| LOCATIONS OF GENE IN RELATION TO CHROMOSOMAL BANDS |
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Definition
short arm = p arm
long arm = q arm
w/in each arm, light and dark bands numbered |
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| FLUORESCENT IN SITU HYBRIDIZATION (FISH) |
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Definition
| depends on hybridization btwn metaphase chromosomes and a labeled DNA sequence |
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Definition
| spread on a glass slide and denatured to make them single stranded |
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Definition
| is labeled w/ fluorescent tag to make a probe |
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Definition
| hybridizes to chromosomes at complementary regions |
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Definition
- is a variation of FISH
- probes specific for each chromosome are labeled w/ different fluorescent dye |
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Definition
-highly condensed, usually inactive transcriptionally
-darkly stained regions of chromosomes |
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Definition
condensed in all cells
- most of the Y chromosome and all pericentromeric regions |
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Definition
condensed in only some cells and relaxed in others
- position effect variegation, x chromosome in female mammals |
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Definition
relaxed, usually active transcriptionally
- lightly stained region |
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Definition
| changes in chromatin structure |
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Term
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Definition
| of inactive genes are hidden in nucleosomes |
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Definition
| transcription factors bind to enhancers and recruit chromatin remodeling proteins |
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Definition
| exposed by removing or repositioning nucleosomes |
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Definition
| white+ (w+) is normally located in euchromatin |
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Definition
| can result in w+ gene being located adjacent to heterochromatin |
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Definition
-can be caused by spreading of heterochromatin into nearby gene
-spreading can occur over > 1000 kb of chromatin
- heterochromatin spreads further in some cells than in others |
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Definition
| were used to identify genes involved in chromatin modification |
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Definition
-looked for changes in the amount of position effect variegation
-mutations that enhanced heterochromatin formation made eyes more white
-mutations that suppressed heterochromatin formation make less white eyes |
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Term
| SOME GENES ENCODE PROTEINS |
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Definition
| that localize to heterochromatin |
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Term
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Definition
-can be modified w/ chemical groups
-tails extend outward from nucleosome |
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| ENZYMES CAN ADD CHEMICAL GROUPS |
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Definition
methyl group, phosphate group, ubiquitin
modified tails can alter nucleosomes and bind chromatin modifier proteins |
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Term
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Definition
-histone acetyltransferases add acetyl group to histone tails
-prevent close packing
-favor expression of gene in euchromatin
-reversed by histone deacetylases |
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Term
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Definition
-histone methyltransferases add methyl groups
- affect depends on specific amino acid mod.
-adding to H3 lysine 9 favors heterochromatin
- reversed by methyltransferases |
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Term
| X-CHROMOSOME INACTIVATION |
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Definition
-in female mammals through heterochromatin formation
-ex of facultative heterochromatin
-x-linked genes in XX & XY express same level
-random inactivation except x chromosome
-Barr body |
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Term
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Definition
-early embryos bot X chromosomes are active
-in humans random x inactivation 2 wks after fertilization
-some maternal inactivation and some paternal
adult females are mosaic X-linked |
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| X-INACTIVATION IS INITIATED |
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Definition
| by expression of the Xist gene |
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Term
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Definition
-x inactivation specific transcription
-expressed on the inactive x, but not the active x |
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Term
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Definition
-is large, non-coding, cis-acting regulatory RNA
-binds to the x-chromosome which expressed
-initiates histone modification that result in heterochromatin formation |
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Definition
| in human cells is 50 nt/sec |
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Definition
-800 hrs to replicate the human genome if there was only one origin of replication
-most mammalian cells have 10000 origins
-many origins are active at same time
-accessible regions of DNA devoid in nucleosomes |
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Term
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Definition
| DNA being replicated in both directions |
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Definition
| disassembled and reformed during DNA replication |
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Definition
| in nucleosomes w/in minutes of synthesis |
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Definition
| associates w/DNA followed by 2 dimers of H2A and H2B |
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Definition
| are composed of recycled and new histones |
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Definition
| open to histone modification just after replication |
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Definition
| that protect the ends of eukaryotic chromosmoes |
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Term
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Definition
-specific repetitive sequences and dont contain genes
-Species-specific
-TTAGGG in humans -> tetrahymena
-250-1500 repeats w/ variable # btwn diff cells |
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Term
| REPLICATION AT ENDS OF CHROMOSOMES |
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Definition
-RNA primers used during DNA replication are removed, leaving a unreplicated DNA at 5' end
-w/o a special mechanism, DNA would be lost from every new DNA strand at each cell |
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Term
| ARTIFICIAL CHROMOSOMES REQUIRE 3 KEY ELEMENTS |
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Definition
centromeres
telomeres
origins of replication |
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| CONSEQUENCES OF DELETING KEY ELEMENTS |
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Definition
-no centromere no telomere - replicate segregation errors
- no telomere - replicate degrade if linear |
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