lecture 8 Flashcards
humans have how many chromosomes
46
humans have two copies of each chromosome, therefore they have
23
the complex of DNA, histones and non-histone proteins with in the nucleus of a eukaryotic cell. the material of which chromosomes are made
chromatin
one of the two copies of a replicated chromosome that is joined at the centromere to the other copy
chromatids
two identical chromatids
sister chromatids
center of sister chromatids that hold them together, where kinetochore forms
centromere
prokaryotes have chromatin?
no, they have chromosomes that are “naked” no proteins bonded. Chromosomes live in spaghetti form
three main things chromatin does
genome compaction
genome integrity
gene expression regulation
explain genome compaction
allows genome to fit into nucleus
- twice around nucleosome
- wrapped around itself- 20 nm fibers (might not exist)
- rope
- wrapped rope
- chromsome
can be open, closed and remodeled
-chromatin remodeling enzymes
Histones acetylation (becomes less + charged) loosens its grip on DNA and DNA can be moved around
explain genome integrity
protects genome from transposable elements (40% of genome) and DNA damage
when DNA is compacted bad things cant get in and TEs can’t react and cut itself out
explain gene expression regulation
two types of chromosomes
heterochromatin
dark are silent. chromosome is binded up and does not allow transcription factors to attach
euchromatin
light is active. chromosome is unbinded and allows transcription factor to attach
histone is made of
2 copies of H2A, H2B, H3 and H4
two copies of H3 and H4 bind to form H3-H4 tetramer
one copy of each H2A and H2B form a dimer
(happens twice)
H1 is a linker
explain 3 ways chromatin remodeling enzymes can work
sliding
histone exchange
nucleosome eviction
explain 3 ways chromatin remodeling enzymes can work
sliding
histone exchange
nucleosome eviction
TEs
transposable elements
have matching ends, can cut itself out and then can paste back into genome somewhere else
if DNA is compacted, TEs can not interact with each other
euchromatin
low nucleosomal density-
open
active transcription
light part of nucleus
heterochromatin
high nucleosomal density
closed
non active- silent transcriptionally
dark part of nucleus
histones tails
unfolded peptides that stick out
can have post translational modifications -(where acetylation occurs)
can activate or deactivate regions
chromosomes like to stay in ___
discrete territories and with limited intermingling
euchromatic regions like to be ___
close to the middle of the nucleus
heterchromatic regions like to be ___
at border of nucleus
explain DNA replication at the end. explain telomeres
DNA polymerase can only add to the 3’ has to go 5’ to 3’
RNA primers are added first and DNA polymerases extend the new strand after the primer
RNA primers are removed afterwards. DNA polymerase will fill in gaps where the primer was
at the end of the chromosome, primer is not added
therefore, at the end of DNA replication, 50-100 nucleotides are lost (BAD THING) too short=cell death
telomerase
telomerase has an associated RNA that complements the 3’ overhang at the end of he chromosome
the RNA template is used to synthesize the complementary strand
telomerase is shifted and process is repeated
primase and DNA polymerase synthesize the complementary strand
active typically only in germ cells and stem cells
improper activation is contributor as how cancer replicates
errors in telomerase
cancer- cells are replicated without shortening- can live forever!
down syndrome
trisomy 21- XXY
two many chromosome
deletion of one of two chromosomes
monosomy
chromosomal duplication
polyploidy
part of one arm of a chromosome is transferred to an arm or different chromsome
translocation
example of translocation error
blood cancers
t(15;17)(q24;a21)- acute promyelocytic leukemia (APL)
polyploidy and monosomy cause disease by generating
improper levels of gene expression
translocations cause diseased by creating
improper proteins
*** why does acetylation of histone N terminal tails correlate with high transcriptional activity?
acetylation neutralized the positive charge of the histone, decreasing the histones ionic interaction with the negative charge of DNA. This allows DNA to be exposed (TATA box, promoters) thus allowing transcription to occur
acetylation makes histone less +, loosens grip on -DNA, DNA can move/unbind and can be acted upon by transcription factors
