Chromosomes (7) Flashcards
Dyads
during S phase chromosomes duplicate forming dyads
sister chromatids
attached duplicated chromosomes
ploidy
increase the number of sets of chromosomes
Diploid
number of chromosomes per somatic cell
Haploid
number of chromosomes in gametes
karyotype
complete set of chromosomes in the cells of an organism (image)
trisomy
one extra c’some
monosomy
missing 1 c’some
How does aneuploidy arise?
nondisjunction
translocations
movement to a new c’some
transfer of a piece of one c’some to a non homologous c’some
inversions
portion of c’some is flipped
deletions
section of DNA excised
insertion
section of DNA inserted
What are 4 results of breakage & repair in c’some ?
translocations
inversions
insertions
deletions
normal recombination
translocation of a homologous c’some
How do translocations cause changes in the phenotype?
breaking a gene –> gene is non-functional
moving a gene to a region where it can be controlled by another regulatory sequence
Creating a hybrid gene –> brand new gene, may contain selectable trait & thrive
How does translocation cause CML?
c’abl gene encodes a kinase that regulates cell proliferation during the cell cycle
translocation causes the cable gene to be moved to another gene’s promoter, the bcr promoter
this promoter causes the gene to be promoted constantly & leading to constant division
CANCER
what is an ex of a positive outcome of translocation?
apes –> 48 c’somes
humans –> 46 c’some
we share all of our c’somes except 2
telomere of the ape’s c’some is in the middle of 2 of our c’some (seen in banding techniques)
therefore, there was a fusion of 2 of the ape’s c’some leading the humans
centromeres
constricted portion of each c’some
DNA contains alpha satellite DNA
alpha satellite DNA
made of non transcribed 171 base repetitive sequences
what is the role of centromeres?
enables kinetochore attachment
attach to kinetochores during M phase
telomeres
non coding regions at the ends of c’some
short repetitive sequences
include specialized PRO
form a capped end structure with a highly conserved sequence TTAGGG
what are the functions of telomeres?
protect end of c’some from nucleases (deoxynuclease) by folding over
allow cells to distinguish c’some ends from broken DNA
prevent c’some from fusing with each other
attachment to the nuclear scaffold (centromeres & telomeres)
What happens to telomeres in replication?
become progressively shorter
DNA polymerase
an enzyme that replicates DNA strands
how do telomeres become shorter?
DNA pol requires a primer
builds 5’-3’
RNA primer is removed leaving a small overhang (on strand that’s not replicated)
overhang folds over protecting the strand from nucleases
what dictates a cell’s life span?
the length of the telomeres
what end of the DNA is left unreplicated?
3’ end
cellular senscence
normal diploid cells seize to divide
when is cellular senscence triggered?
when telomere are too short to persist any longer
what type of cells have functional repair of telomeres?& what enzyme is involved?
stem cells & telomerase
telomerase
RNA containing enzyme that adds more nucleotides to the 3’ end of the telomere strand
What are the sets in telomerase repairment?
- telomerase binds to complementary sequence
- Nucleotides added to DNA 3’ terminus
- Telomerase slides over & its RNA binds to another complementary strand
- more nucleotides are added to DNA 3’ end
- other strand filled in using DNA pol
what type of genes can reactivate their telomerase?
cancer
Where is telomerase absent in ?
cultured cells from normal tissues
where is telomerase present in?
tumor cells
one celled organisms
primordial germ cells
tissue stem cells
what are the factors in cell aging? (4)
telomere shortening
accumulated errors
chromic risk exposures such as oxidants & UV
glycation
Who is Dolly?
1st cloned mammal from an adult cell
took nucleus from an udder (somatic tissue) & transplanted it into a de-nucleated embryo
What conditions did Dolly suffer from?
arthritis
premature aging
how do shortened telomeres cause aging?
not anchored properly, c’some moves around not expressing properly
why didn’t the de-nucleated embryonic cell restore the length of the telomeres in the 6 year old nucleus?
took away source of telomerasenexpression from the removed nucleus
what are the types of DNA sequences?
highly repeated sequences
moderately repeated sequences
non repeated sequences
highly repeated sequences
short sequences in clusters
mini-satellite & micro satellite (shorter that satellite)
what sequences are used in DNA fingerprinting?
highly repeated sequences
moderately repeated DNA
few copies to tens of thousands
some code for PROs needed in large quantities (ex: ribosomal PROs)
non repeated DNA
encodes PROs, build cells etc.
20% of genome codes for PROS
