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Fundamentals Of Living Cells > The Cell Nucleus > Flashcards

The Cell Nucleus Flashcards

1
Q

What is the functional compartmentalisation?

A

How the nucleus contains no internal membranes but subnuclear compartments exists anyways

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2
Q

What are the functional elements of a chromosome?

A

A single molecule of DNA
Linear (in eukaryotes) and double stranded
Contains genes

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3
Q

What are the structural elements of a chromosome

A

Telomeres (protecting chromosome ends)
Centromere (needed during cell division)
Replication origins

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4
Q

What are the functions of a centromere?

A
  • Locks sister chromatids together
  • Attachment site for chromosomes to the mitotic spindle via a protein structure called the kinetochore
  • made up of megabuses of repetitive DNA, (majority of which is the alpha satellite DNA in humans)
  • all chromosomes have different satellite DNA configurations.
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5
Q

How many base pairs is alpha satellite DNA made up of

A

171

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6
Q

What is a hierarchy of repeats?

A

When you have one unit that is repeated, then the repeats get repeated etc etc etc

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7
Q

What is a telomere made up of?

A

Tandem repeat TTAGGG

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8
Q

What is the end replication problem?

A

With each round of replication we loose a bit of the end of the replication

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9
Q

What is the hayflick limit?

A

The number of times a cell can divide before it dies

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10
Q

What type of loop is a telomere? (Double or single strand)

A

Single stranded

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11
Q

Why does the telomere shorten after each round of replication?

A

Removal of the RNA primer on the lagging strand

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12
Q

What is telomerase?

A

An RNA dependant DNA polymerase that adds telomeric DNA to telomeres

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13
Q

How does telomerease work?

A

Uses an RNA template that follows the TTAGGG sequence, which is able to bind to the DNA which means the original length of the chromosomes is restored

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14
Q

How do you get a G banded metaphase spread?

A
  • take a blood sample
  • culture cells
  • add a cell cycle blocking agent to get lots of the cells in metaphase (the chromosomes are most condensed here)
  • add cells to hypertonic solution (swells cells)
  • drop them onto the slide so the cells burst open
  • end up with a karyotype
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15
Q

What are the 3 identifying features of chromosomes?

A
  • size
  • banding pattern
  • centromere position
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16
Q

What is G bonding

A

When chromosomes are partially digested and stained with giemsa

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17
Q

What does G dark mean?

A

Gene poor- lots of heterochromatin

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18
Q

What does G light mean?

A

Gene rich- lots of euchromatin

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19
Q

How are chromosomes organised in the interphase nucleus?

A

Heterochromatin on the outside and euchromatin on the inside

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20
Q

What does FISH stand for?

A

Fluorescent in situe hybridisation

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21
Q

What does FISH do?

A

Allows decondensed chromosomes to be visualised

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22
Q

Give the steps of FISH

A
  • stain metaphase chromosomes red by propidium iodide
  • as the cells enter G1 the chromosomes begin to decondense
  • when it is fully in G1, the whole nucleus fluoresces red and a chromosome pend is used to colour in entire chromosomes
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23
Q

What are the benefits of FISH?

A

Means you are able to see where specific chromosomes are in relation to one another and the cell in 3D

24
Q

What does spectral karyotyping allow?

A

You to see what happens to the chromosomes in interphase as it is coloured

25
Q

What happens to the arms and the bands of chromosomes in interphase?

A

They stay very distinct and mutually exclusive

26
Q

Where do gene poor/ gene rich chromosomes prefer to be?

A

Gene poor like to be on the outside (like heterochromatin) and gene rich like to be in the inside (like euchromatin)

27
Q

Where is an MHC (Major histocompatibility complex) gene cluster found in a territory?

A

At the surface

28
Q

What happens to the genes when interferon is added?

A

They loop out in response to transcriptional activation

29
Q

What is the largest substructure in the nucleus and what does it do?

A

Nucleolous is the site of ribosomal subunit production

30
Q

How are ribosomal subunits made?

A
  • RNA poll transcribes precursor rRNA
  • processed to 18s, 5.8s and 28s- endo and Exonuclease cleavage
  • 5s is transcribed in the nucleoplasm by RNA Poll2 and transported to the nucleolus
  • rRNA is folded and associated with 79 ribosomal proteins to assemble the 40 and 60s ribosomal subunits
  • subunits transported to the cytoplasm
31
Q

What are the three distinct zones of the nucleolus (seen by electron microscopy)

A

Fibrillar centre- ribosomal RNA genes
Dense fibril or component - processing and assembly
Granular component - processing and assembly

32
Q

Where does the nucleolus form around?

A

The Nuclear organising regions (NORS) location of the rRNA genes

33
Q

What are NORS the location of?

A

rRNA genes

34
Q

How many rRNA gene copies per haploid genome and where are they located?

A

200- in tandem copies on the Acrocentric chromosomes

35
Q

Which chromosomes are acrocentric?

A

13, 14, 15, 21, 22

36
Q

What is a tandem copy of genes?

A

Copies that follow on from each other along the length of the chromosome

37
Q

When would a single mRNA molecule be translated many time to give amplification of the final product?

A

on Single copy genes

38
Q

Give the features of a splicing speckle

A

20-50 per cell
146 known proteins
Composed of splicing factors and other mRNA processing factors
Variable size and shape used as a model system to study nuclear organisation

39
Q

What is nucleolus proteomics analysis?

A

Mass spectrometry organelle proteomics

40
Q

Give some other functions of the nucleolus (not subunit production)

A
  • role in processing of endogenous nuclear siRNAs
  • assembly of the six proteins and RNA molecules making up the signal recognition particles
  • biogenesis of other classes of RNPs such as the spliceosome small nuclear snRNP and telomerase
41
Q

Do slicking speckles contain DNA?

A

No, but they are associated with active transcription sites

42
Q

What happens when you inhibit transcription in speckles and what does this show?

A

The speckles round up and become larger, which shows they support speckles as a storage/assembly compartment not a direct site of splicing

43
Q

What happens when you add more intron genes to cells and what does this show?

A

Splicing factors redistribute to transcription sites and the speckles get smaller. This shows that the speckles are a reservoir of splicing factors and the spicing factors are shuttled between the speckles and transcription sites

44
Q

What defines nuclear body size/shape and pool in the nucleoplasm?

A

The continuous association and dissociation of components

45
Q

What does more recent research suggest about the speckles?

A

They may play a role in regulating access to splicing factors

46
Q

What is the predicted number of replicons firing at the same time and what does this mean?

A

5149- this challenges conventional interpretation of nuclear replication foci as replication factories

47
Q

How can transcription factories be visualised

A

Pulse labelled with BrUTP to detect nascent RNA or by immunofluorescence to active elongating RNA poll1

48
Q

What is pulse labelling?

A

Incorporating a tag into the RNA thats being transcribed so the mRNA takes it

49
Q

What do we think transcription factories do?

A
  • sites where multiple active RNA polymerases are concentrated
  • termed transcription factories and proposed that genes pass through the factory as they are transcribed
  • genes from the same or different chromosomes may associate at the same factory
50
Q

How has super-resolution microscopy disproved the transcription factory theories?

A
  • spacial organisation of RNA Poll1 mediated transcription
  • transcription foci consist of only one RNA poll2 molecule
  • no clustering, no factories
  • transcription machinery assembling at the site of transcription
51
Q

How many nuclear pore complexes does a typical mammalian cell contain?

A

3000-4000

52
Q

What is the nuclear envelope made up of?

A

Two lipid bilayers

53
Q

Are nuclear pores an open space?

A

No, more like a gateway- only small water soluble molecules can diffuse freely through the pore

54
Q

What do nuclear exports (give some examples) need to get through the nuclear pore?

A

Ribosomal subunits and mRNA need a nuclear export signal

55
Q

What do nuclear imports (give some examples) need to get through the nuclear pore?

A

Histones, DNA/RNA polymerases and other nuclear proteins need a nuclear localisation sequence

Fundamentals Of Living Cells (41 decks)

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