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Cell and Molecular Biology > The Nucleus and Chromosomes > Flashcards

The Nucleus and Chromosomes Flashcards

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1
Q

What is the role the nuclear envelope

A
  • a highly regulated membrane barrier that separates the nucleus from the cytoplasm in eukaryotic cells
  • encloses DNA
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2
Q

What are the 3 main differences between prokaryotes and eukaryotes?

A

prokaryotes: no nucleus + no compartmentalisation + smaller
eukaryotes: nucleus + compartmentalisation + larger

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3
Q

What is compartmentalisation

A

the separation of the cell’s interior into distinct compartments

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4
Q

What is the function of compartmentalisation

A
  • certain regions can focus on different cellular activities
  • prevent dangerous molecules from roaming freely within the cell
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5
Q

Why are eukaryotic cells larger than prokaryotic cells

A

compartmentalisation

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6
Q

What is the nuclear envelope composed of

A
  • inner membrane
  • outer membrane
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7
Q

What is the main characteristic of the outer membrane of the nuclear envelope

A

it is continuous to w/ the ER (studded with ribosomes)

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8
Q

What are the main characteristics of the inner membrane of the nuclear envelope

A

it contains specific proteins that act as binding sites for chromatin + nuclear lamina (structural support)

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9
Q

Why is nuclear transport important

A
  • mRNA has to be exprted out of the nucleus for translation
  • transcription + replication need enzymes that have to be imported into the nucleus
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10
Q

What is the main function of nuclear pores

A

regulates the transportation of molecules between the nucleus and the cytoplasm

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11
Q

True or False:
The more active the nucleus is in transcription, the greater the number of pore complexes its envelope contains

A

True
more transcription = greater number of enzymes needed to be imported into the nucleus

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12
Q

What are nuclear pore composed of

A
  • protein fibrils
  • aqueous channel proteins
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13
Q

What kind of molecules are able to freely pass through the nucleus

A

small molecules of 5000 daltons or less

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14
Q

What kind of molecules need to be actively transported through the nucleus

A

molecules of 60kD and more

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15
Q

What is NLS

A

an amino acid sequence that indicates a protein is destined for import into the nucleus by nuclear transport

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16
Q

What is NES

A

amino acid sequence that indicates a protein is destined for export from the nucleus into the cytoplasm by nuclear transport

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17
Q

Define Importins

A

they carry proteins into the nucleus

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18
Q

Define Exportins

A

they carry proteins out of the nucleus

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19
Q

Define nuclear transport receptors + give 2 examples

A

they escort large proteins through the nuclear pores
- importin & exportin

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20
Q

How do nuclear pores allow the necessary proteins into the nucleus

A

if the proteins have special sequences that indicate they belong in the nucleus –> NLS

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21
Q

What is a cargo protein

A

a protein that is transported within the cell by another molecule

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22
Q

What process favours the release of a cargo protein into the nucleus

A

When Ran-GTP is bound to an importin

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23
Q

What process stabilises the interaction w/ a cargo protein

A

When Ran-GTP is bound to an exportin

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24
Q

What is the main function of Ran-GEF

A

promotes the formation of Ran-GTP from Ran-GDP

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25
Q

What is the main function of Ran-GAP

A

promotes the formation of Ran-GDP from Ran-GTP

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26
Q

Where are the ribosomes exported and assembled

A

assembled: nucleus
exported: cytoplasm

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27
Q

What is the relationship between genome size and animal complexity

A

There is no correlation

28
Q

Why are eukaryotic genomes larger and more complex than prokaryotic genomes

A
  • more genes w/ introns
  • more regulatory sequences
29
Q

What is repetitive DNA + where are they found?

A

it has repeated sequences of nucleotides in the DNA and that doesn’t code for proteins –found in introns or heterochromatin

30
Q

What is single-copy DNA

A

a unique sequence that codes for proteins and undergoes transcription – found in exons or the euchromatin

31
Q

What are the 3 elements that are required for a functional chromosome

A
  • telomere
  • centromere
  • replication orgins
32
Q

What is the function of telomeres

A
  • stabilise the ends of chromosomes
  • prevent chromosomal damage
33
Q

What is the function of centromeres

A

separate the sister chromatids

34
Q

What happens to the size chromosomes during interphase

A
  • they are not visible
35
Q

What happens to the size chromosomes during mitosis

A

chromosomes condense

36
Q

What is the Rabl Configuration

A
  • it is the position of chromosomes after cell division
  • centromeres: clustered at one end
  • telomeres: orientated towards the border of the nucleus
37
Q

What is meant by mitotic chromosomes

A

highly condensed chromosomes in a dividing cell

38
Q

What is chromatin

A

a complex of DNA and proteins that form chromosomes found in eukaryotic cells

39
Q

What is the function of chromatin

A

packaging DNA into a unit capable of fitting within the tight space of a nucleus

40
Q

Outline the structure of chromatin

A

-DNA is compacted + wrapped with histone proteins = chromatin

41
Q

What are histones

A

positively charged proteins that help organise and package the negatively charged DNA

42
Q

What are the 2 main forms of chromatin

A
  • euchromatin
  • heterochromatin
43
Q

Outline euchromatin

A
  • less condensed + more accessible form of chromatin
  • associated w/ actively transcribed genes
44
Q

Outline heterochromatin

A
  • more condensed + less accessible form of chromatin
  • associated w/ genes not actively transcribed
45
Q

What is the role of Histone 1 (H1)

A
  • H1 compacts & stabilises DNA
  • It binds to the entry and exit sites of DNA + completes nucleosomes
46
Q

What are the different types of histone modifications

A
  • acetylation
  • methylation
47
Q

What are the consequences of acetylation

A
  • it causes DNA to be less tightly wrapped around histones
  • increases transcription/gene expression
48
Q

What are the consequences of methylation

A
  • it causes DNA to be more tightly wrapped around histones
  • decreases transcription/gene expression
49
Q

Outline the main steps of nuclear import

A
  1. importin + NLS protein bind and form a cargo protein
  2. cargo protein moves to the nucleus via nuclear pores
  3. Ran-GTP binds to cargo protein causing importin a conformation change –> protein is released
  4. Ran-GTP and importin move back to cytoplasm
  5. Ran-GAP binds and causes Ran-GTP and importin to dissociate
  6. Ran-GTP is converted into Ran-GDP
  7. Ran-GDP is then recycled back into Ran-GTP by Ran-GEF
50
Q

Outline the main steps of nuclear export

A

1.Exportin binds to proteins w/ NES and form cargo protein
2. Ran-GTP binds to cargo protein and causes it to move to the cytoplasm via nuclear pores
3.Ran-GTP is converted to Ran-GDP by Ran-GAP
4. changes the conformation of exportin releasing proteins

51
Q

What is the function of the small ribosomal unit

A

tRNA matches its codons to the anticodons on mRNA

52
Q

What is the function of the large ribosomal unit

A

forms peptide bonds between the amino acids brought by tRNA

53
Q

Are chromosomes visible during interphase

A

no

54
Q

What is acetylation

A

adding an acetyl group of DNA so DNA is less tightly wrapped

55
Q

What is methylation

A

adding a methyl group to DNA so DNA is more tightly wrapped

56
Q

What are two different types of regulatory transcription factors

A

activators and repressor proteins

57
Q

What are regulatory transcription factors

A

proteins that control the activity of genes by binding to specific DNA sequences near the genes they regulate

58
Q

What do activator proteins do

A

they bind to enhancer sequences and increase the rate of transcription

59
Q

What do repressor proteins do

A

they bind to silencer sequences and either block or decrease the rate of transcription

60
Q

where is Ran-GTP found

A

nucleus

61
Q

Where is Ran-GDP found

A

cytoplasm

62
Q

What is meant by rRNA genes are in tandem arrays

A
  • rRNA genes are located one after another
  • repeated several times (multiple copies of same gene next to each other)
63
Q

Why is it advantageous for the rRNA genes to be in tandem arrays

A

having multiple copies of the rRNA genes clustered together allows for more efficient/faster transcription and thus more ribosome production

64
Q

Outline how rRNAs are processed into ribosomes

A
  1. rRNA genes are transcribed into pre-rRNA in the nucleus
  2. introns of pre-rRNA are removed + chemical modifications
  3. pre-rRNA assemble the ribosome in the nucleus
  4. the ribosome (large + small) is exported into the cytoplasm
65
Q

What is a nucleosome

A

a fundamental unit of chromatin

66
Q

Why does X chromosome inactivation happen

A

it ensures that females don’t produce double the amount of proteins coded by X-linked genes (males only have 1 X chromosome)

67
Q

How does X chromosome inactivation happen

A
  1. one of the two X chromosomes in each female cell is randomly chosen for inactivation
  2. The inactive X chromosome undergoes heterochromatinization, where it becomes tightly packed and inactive
  3. this prevents transcription + silences genes

Cell and Molecular Biology (8 decks)

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