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KH8 Flashcards

1
Q

what does the genome of each species of eukaryote consist of

A

a characteristic number of independent linear DNA molecules

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2
Q

each linear DNA molecules is a

A

chromosome

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3
Q

what do chromosomes never exist as

A

naked DNA

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4
Q

what do chromosome always exist as

A

DNA/protein complex termed chromatin

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5
Q

describe a key feature of chromatin organization

A

condensation or compaction
DNA molecule in average human chromosome is 5 cm long if stretched out = ~5000 times longer than width of typical cell nucleus
So DNA molecule is highly folded/packed/coiled even in the interphase nucleus

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6
Q

when are chromosomes more tightly folded/packed/coiled

A

mitotic metaphase (more packed than interphase)

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7
Q

why are chromosomes more tightly packed during mitotic metaphase

A

to facilitate equal distribution between the 2 daughter cells

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8
Q

describe metaphase

A

highly condensed for transmission to daughter cells
no DNA replication or transcription
only concerned with getting chromosomes to right place

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9
Q

describe interphase

A

real functional chromosome
undergoing replication and transcription
where action is
chromatin fiber of chromosome unwinds to a degree (from metaphase to interphase) - never to DNA/simplest chromosome structure
dynamic and controlled

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10
Q

what is chromatin

A

eukaryotic DNA and associated proteins

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11
Q

how many base pairs of DNA in each chromosome for humans

A

~50-250 million base pairs

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12
Q

what are topological domains

A

folded domains with definite boundaries
interact among themselves

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13
Q

what is nucleosome

A

DNA wrapped around histone octamer

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14
Q

where are giant interphase chromosomes from

A

polytene chromosomes of the fly (drosophila) salivary galdn

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15
Q

describe polytene chromosomes - why they happen

A

cellular gigantism driven by DNA ~10 cycles of DNA replication without cell division
duplicates but chromosome does not separate

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16
Q

describe polytene chromosomes - physically

A

all ~1024 daughter chromatids are in perfect alignment making a giant chromosome with regional differences in chromatin condensation
many parallel chromatids

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17
Q

describe regional differences in chromatin condensation

A

dark bands = condensed chromatin (topological domains)
light bands = boundary elements

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18
Q

describe interphase chromatin organization

A

dynamic
polytene chromosome puffs show how chromatin decondensation with transcriptional activation

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19
Q

describe puffs of polytene chromosome

A

puff up = active transcription regions, open and close
associated with active form of RNA polymerase 2 = active transcription

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20
Q

describe puffs of polytene chromosome - colours

A

red = pol 2 phosphoCTD = active
green = non phosphorylated = inactive

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21
Q

name parts of metaphase chromosome

A

sister chromatids
centromere
telomere
chromatid

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22
Q

describe metaphase sister chromatids

A

identical products of the previous semiconservative replication of a single chromosomal DNA molecule

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23
Q

what do metaphase chromosomes show

A

karyotype (morphology)
chromosomal complement of the species

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24
Q

what characteristics of chromosomes vary

A

number
shape
size
species specific and sometimes sex specific

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25
describe ex of karyotype
human female karyotype revealed by fluorescence in situ hybridization (FISH) with a panel of probes representing sequences differentially distributed among the chromosomes "chromosome painting" - identification
26
what are chromosome rearrangements
breaks/translocation
27
describe chromosome rearrangements
chromosomes can break and rejoin giving translocations
28
when can translocations happen
mutations can happen during somatic cell division cycle in life and can cause disease like cancer also can occur in germ line
29
describe ex of chromosome rearrangements (cancer)
chronic myelogenous leukemia results of chromosome breakage and fusion in blood cells chromosome fusion generates chimeric gene encoding an oncogenic fusion protein creates protein that deregulated cell growth in blood cells with mutation = cancer called philadelphia chromosome
30
describe chromosome rearrangements in germ line
gives gametes - eggs or sperm - with variant chromosomes offspring often have reduced fertility usually a dead end this is why karyotype is so consistent across a species can happen that it is successful and passed on = rare and karyotype can evolve over time
31
describe evolution of human karyotype
from primate ancestral karyotype unchanged Chr 11 (=13) breakage Chr 14, 15 (=5) reciprocal translocation Chr 12, 22 (=14, 21) end-to-end fusion Chr 2 (=9 + 11)
32
what are the elements required for replication and stable inheritance of linear chromosomes - 3
origin of replication centromere 2 telomeres - ends
33
how do we learn about protein structure and function
by building artificial chromosomes
34
how did we discover elements required for chromosome function
Experimental discovery in a simple eukaryote: yeast
35
describe what yeast cells need
yeast leu- cells have LEU gene inactivated by a mutation and need exogenous leucine for growth
36
what does LEU gene code for
makes leucine
37
describe initial experiment done with yeast
wild type LEU gene cloned into circular bacterial plasmid introduce to yeast cells and ask if it rescues leucine independent growth aka does LEU plasmid replicate as cell grows
38
describe initial experiment done with yeast - results
LEU plasmid replicates well in bacteria BUT INCAPABLE OF REPLICATION IN YEAST since bacterial origins of replication do not work in eukaryotes
39
how do we fix plasmid not working in yeast
insert into plasmid a random piece of yeast DNA that happened to contain a yeast origin of replication now plasmid can support growth of leu - yeast in absence of leucine
40
describe origin of replication (yeast experiment)
ARS = autonomously replicating sequenced = yeast origin of DNA replication REQUIRED FOR REPLICATION but cells not portioned well between daughter cells - mitotic segregation is faulty
41
how to improve mitotic segregation
add centromere CEN = DNA sequence from yeast chromosome centromere drives good mitotic segregation
42
what is kinetochore
attached to centromere spindle microtubules attach here then 2 chromatids separate and walk in opposite directions
43
the centromere...
link to spindle microtubules
44
describe yeast CEN
sequences common to various yeast centromere present on nucleosome that includes a centromere specific histone variant CENP-A (centromeric protein A)
45
what does CENP-A do
recruits CBF3 complex which in turn recruits Ndc80 complex which attaches to microtubules initiates cascade of assembly
46
describe image of CENP-A
different colour since its a different histone tags it so it can recruit kinetochore apparatus - lateral attachment then to end on conversion Kinetochores attached here and migrates and microtubule dissolves behind it as it moves drags whole chromosome with it - this is how chromosome moves apart
47
what shape are yeast chromosomes
linear DNA molecules not circular Previously we used a plasmid in yeast experiment which is circular
48
how to convert circular plasmids to linear DNA molecules
cutting a single site with restriction endonucleases
49
Does a plasmid with ARS and CEN that works well as an experimental circular chromosome in yeast also work well as a linear chromosome?
nOOOOOOOOOO lose everything - linear does not work so add telomeres
50
what are telomeres
special sequences at ends of eukaryotic chromosomes cloning a bit of telomere DNA at end and it works - needed for linear molecules to survive
51
describe conclusions of yeast experiment - telomeres
cut plasmid without telomeres = unstable linear plasmids containing ARS and CEN act normal if genomic fragment telomeres added to both ends
52
name the functions of telomeres - 3
protect from exonuclease prevent end-to-end fusion solve a replication problem faced by linear DNA
53
what is telomere problem
because lagging strand synthesis cannot be completed - chromosomes shorten at ends in each replication unsustainable since at some point you will lose an essential gene 15-20 bases of RNA and no way to make it DNA
54
what is solution to telomere problem
telomerase DNA polymerase that can extend telomeres restores chromosome length to overcome lagging strand end shortening
55
what do telomeres contain
simple repeat DNA sequences ciliate protist tetrahymena (TTGGGG) human (TTAGGG)
56
describe telomerase
reverse transcriptase that carries its own template RNA complementary to the telomeric DNA repeat by extending template strand telomerase gives primase more template DNA to prime on
57
what is a reverse transcriptase
DNA polymerase that uses RNA as template
58
describe how telomerase works informally
binds to telomere complementary to telomere so reverse transcriptase can extend it slips so can extend next primer - adds telomere repeats
59
where is telomerase active
germ cells and stem cells not in somatic cells since divide only a few times (so existing telomeric repeats are long enough)
60
when is telomerase often reactivated
in cancer cells - a target for cancer therapy
61
describe mice lacking telomerase gene
ok for 3 generations then fertility decline has enough repeats so it can go through 3 generations before ends are shortened too much and a key gene is not replicated (it is lost)
62
describe ciliated protist tetrahymena
unusual gene expression mechanism does not express genes from its “main” genome. maintained in a non-transcribed form in the micronucleus transcription occurs in the macronucleus from millions of gene-sized DNA pieces. presence of so many DNA ends made it possible for researchers to identify the telomere sequence and to isolate telomerase

BIOL 200 (29 decks)

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