Lecture 4 Flashcards
chromosome number and size
are species specific, but are not associated with the complexity of an organism
How many chromosomes do cats have?
38
How many chromosomes do carp have?
104
How many chromosomes do humans have?
46
What is a Karyotype?
An organized image of the chromosomes in a nucleus
What do chromosomes look like during interphase?
highly DEcondensed and difficult to visualize
In what phases can chromosomes be individually visualized and identified?
about mid-prophase to metaphase
Are centromeres always in the CENTER of a chromosome?
No, they are almost always of UNEQUAL lengths
What is a centromere?
What binds two chromatids together to form a chromosome. They determine chromosome shape.
What is chromatin?
nucleic acids (DNA) and proteins that make up chromosomes
What is euchromatin?
LOOSELY CONDENSED chromosome regions that are more ACTIVELY TRANSCRIBED
What is heterochromatin?
TIGHTLY CONDENSED chromosome regions with FEWER expressed genes
Why do euk. chrom. need to be compacted?
-essential for cell division
-regulating gene expression (position effect variegation- PEV, euch/hetero chromatin)
-saves space
In “beads on a string” what are the beads, and what is the string?
“beads”= nucleosome
“string”= linker DNA
What are the 5 components of a nucleosome core particle ?
1) 2 H2A
2) 2 H2B
3) 2 H3
4) 2 H4
5) 146s bps of “core” DNA
-(linker) DNA
What is PEV?
Position effect variegation: gene expression is controlled by the state of chromatin (euch/hetero) in which a gene is located, so if a gene is moved to a diff. region (euch/hetero) will change how it is expressed
What is facultative heterochromatin?
Can switch between euch/hetero-chromatin to activate genes at certain times (eg. development) on in certain tissues
What is constitutive heterochromatin?
Regions of the genome that are always heterochromatic and transcriptionally inert
What kind of chromatin does a centromere lie in?
Heterochromatic chromatin/ heterochromatin
At what point during the cell cycle are centromeres most important?
During metaphase, when the spindles attach to them
Define open promoters.
initiate transcription of genes for constitutively active genes
eg. basic cellular functions
Define closed/covered promoters.
-regulate transcription of genes by requiring chromatin remodeling (displacement or removal of nucleosomes) to enable RNA polymerase to bind
-generally contain TATA boxes
-competition of nucleosomes and transcript. factors for binding
Define open chromatin.
-relaxed nucleosomes
-allows access by regulatory proteins
-DNase 1 sensitive–> transcribable
Define closed chromatin.
-DNA covered by nucleosomes
-restrict access of regulatory to proteins–> transcriptionally silent
Where are DNase 1 hypersensitivity regions?
-at open regions
What does DNase 1 do?
-enzyme randomly cuts DNA in open regions
-used to test if a region is open (hypersensitive) or closed
What are “writers?”
Enzymes that ADD chemical groups that modify histones
What are “erasers?”
Enzymes that REMOVE chemical groups to modify histones
What are “readers?”
Proteins that recognized modified histones; active or deactivate the site
What are HATs?
-histone acetyltransferases
-writers
-ADD acetyl groups
–> euchromatin (increase transcription)
What are HDACs?
-histone deacetylases
-erasers
-REMOVE acetyl groups
–> heterochromatin (decrease transcription)
What are the two primary mods added to histones?
1) addition or removal of acetyl groups
2) addition or removal of methyl groups
What are HMTs?
-histone methyltransferases
-writers
-ADD methyl groups
What are HDMTs?
-histone demethylases
-erasers
Define epigenetic.
Heritable patterns or changes in gene expression that are not associated with any change in DNA sequence.
What is Nucleotide Methylation?
-epigenetic
-adds methyl group to usually to cytosine (C) in DNA and usually turns expression off
What does Histone 1 (H1) do?
Stabilizes the nucleosome core particles
Rank the condensation of DNA.
naked DNA–>histones–> nucleosomes–> solenoid–> loop domains–> chromatid–> metaphase chromosomes
