Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BIOL200 > Oct 13, KH8, Chromosomes > Flashcards

Oct 13, KH8, Chromosomes Flashcards

1
Q

what does the genome consist of?

A

characteristic number of independent linear molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is each of these linear molecules called?

A

a chromosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what do chromosomes exist as?

A

never as naked DNA
DNA/protein complex called chromatin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is a key feature of chromatin organisation?

A

condensation/compaction
DNA molecule of average chromosome is 5cm long, 5000 times larger than typical nucleus
tightly folded/packed/coiled

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

when are the chromosomes even more compactly folded than during interphase? and why?

A

during mitotic metaphase
facilitates equal distribution between the two daughter cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what happens in metaphase?

A

highly condensed for transmission to daughter cells
no DNA replication, no transcription

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what happens in interphase?

A

the real functional chromosome
replication, transcription and all the action

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what happens in the transition from metaphase to interphase?

A

the chromatin fiber of the chromosome unwinds to a degree

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is a chromatin?

A

eukaryotic DNA and associated proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is a nucleosome?

A

DNA wrapped around a histone octamer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

how many base pairs of DNA in each chromosome in humans?

A

~50-250 million

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are polytene chromosomes?

A

giant interphase chromosomes
have thousands of DNA strands
many parallel identical chromatids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what do the dark bands represent?

A

condensed chromatin (topological domains)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what are metaphase sister chromatids?

A

identical products of the previous semi conservative replication of a single chromosomal DNA molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what are the ends of the sister chromatids called?

A

telomeres

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what do metaphase chromosomes show?

A

the karyotype

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is the karyotype?

A

the chromosomal complement of the species

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what characteristics are species specific? (and sometimes sex specific)

A

number, shape and size of chromosomes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

how can chromosomes rearrange, when does it happen and what does this do?

A

chromosomes can break and rejoin, which gives translocations
these mutations can happen during a somatic cell division cycle in the life of an organism
can cause disease (ie cancer)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is the germ line?

A

refers to the sex cells (eggs and sperm) that sexually reproducing organisms use to pass on their genomes from one generation to the next (parents to offspring)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what happens when chromosome rearrangement occurs in the germ line?

A

this gives gametes (egg or sperm) with variant chromosomes
offspring arising from such variant gametes often have reduced fertility
usually germ line chromosome rearrangements are a dead end
this is why the karyotype is so consistent across a species

21
Q

what happens when a chromosomal rearrangement variant is successfully passed on from one generation to the next?

A

the karyotype can evolve over evolutionary time

22
Q

what are the elements required for the replication and stable inheritance of linear chromosomes?

A
  1. origin of replication
  2. centromere
  3. 2 telomeres (ends)
23
Q

how does yeast demonstrate the elements required for chromosome function?

A

yeast leu- cells have the LEU gene inactivated by a mutation, and therefore require exogenous leucine for growth
wild type yeast LEU gene is cloned into a circular bacterial plasmid
introduce LEU plasmid into leu- yeast cells and ask if this “rescues” leucine-independent growth
such rescue would require the LEU plasmid to replicated as the cells grow
the LEU plasmid replicates well in bacteria, but incapable of replication in yeast because bacterial origins of DNA replications do not work in eukaryotes
this plasmid cannot support leu- yeast growth in absence of leucine
BUT suppose the plasmid is inserted in a random piece of yeast DNA that happened to contain a yeast origin of replication
now the plasmid can support leu- yeast growth in the absence of leucine

24
Q

what is that yeast origin of DNA replication called?

A

ARS = autonomously replicating sequence
it is required for plasmid replication

25
Q

how does mitotic segregation compare from when the plasmid has LEU and when it has LEU +ARS?

A

mitotic segregation does not happen when only LEU is present because there is no growth of that plasmid
in presence of ARS, plasmid replication occurs but mitotic segregation is faulty (5-20% of cells have the plasmid)

26
Q

what is the CEN?

A

the DNA sequence from a yeast chromosome centromere

27
Q

what does the CEN do when added to the plasmid?

A

increases mitotic segregation (>90% of cells have plasmid)

28
Q

what is the kinetochore?

A

a complex of proteins associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach.

29
Q

where do the spindle microtubules attach?

A

the kinetochore at the centromere

30
Q

explain how the centromere is the link to spindle microtubules

A

there are sequences common to the various yeast centromeres
present on a nucleosome that incudes a centromere specific histone variant CENP-A (centromeric protein A)
CENP-A recruits the CBF3 complex which in turn recruits the Ndc80 complex, which attaches the microtubules

31
Q

how can circular plasmids be converted to linear DNA molecules?
and what’s the issue with that?

A

by cutting at a single site with a restriction endonuclease
BUT these do not work well as linear chromosomes (no growth without leucine and no mitotic segregation)

32
Q

how can the issue of circular plasmids not working well as linear DNA molecules be fixed?

A

add genomic fragment TEL (telomeres) to both ends
there will be growth without leucine and there will be good mitotic segregation

33
Q

what do telomeres do?

A

protect from exonuclease
prevent end to end fusion
solve a replication problem face by linear DNA

34
Q

what is the telomere problem and what is the solution?

A

because the lagging strand cannot be completed, chromosomes should shorten at the ends of each replication
unsustainable because at some point you will lose an essential gene
telomerase is the solution
a DNA polymerase that can extend telomeres, restoring chromosome length to overcome lagging strand end shortening

35
Q

what do telomeres contain

A

simple repeat DNA sequences

36
Q

where is telomerase active and why?

A

only active in germ cells and stem cells
somatic cells divide only a few times, so existing telomeric repeats are already long enough

37
Q

where is telomerase often re-activated?

A

in cancer cells
–> divide too much
telomerase is a target for cancer therapy

38
Q

what are topological domains?

A

folded domains that have somewhat of a definite structure but have definite boundaries
these regions have regulatory DNA sequences and interact within each other

39
Q

how is the DNA arranged around the histone proteins, and how are they positioned relative to each other?

A

around 100 base pairs wrapped twice around histone protein (octomer)
the nucleosomes
forms “beads on a string” shape

40
Q

how are polytene chromosomes created?

A

DNA over-replication
happens when the DNA replicated but chromosomes do not separate

41
Q

how are regional differences in chromatin condensation seen under a microscope?

A

dark bands = topological domains
light bands = boundary elements

42
Q

what are boundary elements?

A

region between each topological domain
separate neighboring genes to ensure their independent regulation

43
Q

what does it mean exactly “replication but chromosomes do not separate”?

A

the replication fork doesn’t go all the way to the end
another round start, the replication fork once again doesn’t go to the end, stops before where the previous replication fork had stopped
replication without separation (see slide 6)

44
Q

what happens in interphase chromatin organisation?

A

it is dynamic
polytene chromosome puffs show chromatin decondensation when transcription occurs (puff out)

45
Q

how can those puffs be shown?

A

puffs associated with active form of RNA polymerase II are undergoing active transcription
red puffs= polll phosphoCTD = active
green = non phosphorylated = inactive

46
Q

what is chromosome paiting?

A

fluorescent in situ hybridisation (FISH) with a panel of probes which represent sequences differently distributed among the chromosomes
color in the repeating DNA sequences

47
Q

explain how a cancer (name it) is caused by chromosome rearrangement

A

chronic myelogenous leukemia
in blood cells there is a break on chromosome 22 and on chromosome 9
the broken off end of chromosome 22 joins to 9 and the broken off of chromosome 9 goes on 9 (the ends swap)
creates a chimeric gene which codes for a protein that deregulates cell growth (cancer)

48
Q

what are some changes that happened in the karyotype of ancestral primates to bring that of humans?

A

there are several changes which lead to the karyotype that we see in humans now
those changes were preserved through evolution
some chromosomes were unchanged
some chromosomes (14 and 15) came from the same ancestral chromosomes (5) –> there was a break
there is reciprocal translocation (switching) chromosome 12,22 (=14,21)
and end to end fusion chromosome 2 = chr 9+11

49
Q

what DNA does the centromere contain?

A

contains DNA that can drive mitotic segregation

50
Q

how do the microtubules join at the centromeres initially and then finally?

A

first there is a lateral joining which turns into a end to end joining

51
Q

explain the structure of telomerase and how it works

A

telomerase is a reverse transcriptase which carries its own template RNA complementary to the telomeric DNA repeat
it is made up of part protein and part RNA
the complementary RNA template binds to the telomeric DNA end
slips/shifts over to match somewhere else
from there reverse transcriptase can extend that and and make a complete telomere repeat

BIOL200 (29 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions