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PSA712 Biochemistry > Nucleus > Flashcards

Nucleus Flashcards

1
Q

What is a chromosome?

How many pairs of chromosomes are there within the nucleus?

A

A defined region of chromatin that codes for a specific set of genes.

There are 23 pairs of chromosomes within the nucleus.

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2
Q

Chromatin is made from what?

A

Repeating nucleosome structures.

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3
Q

How are sister chromatids formed?

A

Two chromosomes are wedged together in their condensed form (metaphase of mitosis).

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4
Q

The description of a nucleosome refers to what?

A

The way in which our DNA is packaged.

Core consists of 8 histone proteins packed together (octamer), DNA wraps around the octamer.

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5
Q

What is a histone?

A

A protein which DNA wraps around within the nucleus.

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6
Q

DNA is converted to what in transcription?

Where does this occur and what enzymes are necessary?

A

mRNA

Occurs in the nucleus with the help from RNA polymerases.

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7
Q

mRNA is converted to a what in translation?

Where does this occur and on what structures?

A

Protein - polypeptide chain.

Occurs in the cytosol on ribosomes.

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8
Q

How is mRNA modified to enhance its binding to ribosomes after transcription?
There are 3 possible ways it is enhanced.

A
  1. Addition of a 5’ CAP.
  2. 3’ Polyadenylation - addition of adenine to the 3’ end.
  3. Splicing of introns.
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9
Q

When mRNA is modified, the modifications help with what in the process between transcription and translation?
List three advantages.

A
  1. mRNA is more stable.
  2. Helps mRNA to bind with the ribosome in the cytosol.
  3. Allows mRNA to be exported out the nucleus into the cytosol.
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10
Q

The nuclear envelope has a what membrane?

A

Double phospholipid bilayer membrane.

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11
Q

The outer membrane of the nuclear envelope is continuous with what organelle?

A

Endoplasmic Reticulum.

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12
Q

What is the nuclear lamina structure in the nuclear envelope?
What is its function?

A

The nuclear lamina is the criss-cross structure on the nuclear side of the envelope.

It gives the envelope structural support and is part of the cytoskeleton.

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13
Q

The NPC allows what?

A

Entry and exit of larger molecules into/out of the nucleus.

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14
Q

The NPC is made up from 30 different types of proteins, these proteins are known as what?

A

Nucleoporins.

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15
Q

Cytosolic fibrils are structures attached to NPCs, they reach into what part of the cell?

A

Cytosol.

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16
Q

The nuclear basket extends into what side of the cell?

A

Nucleus side.

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17
Q

What is the job of scaffold nucleoporins.

A

They anchor the NPC into the nuclear envelope.

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18
Q

What is the role of nuclear import receptors (importins)?

A

Importins bind to the protein’s nucleus localisation signal.

This creates a complex which moves through the NPC via FG repeats.

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19
Q

Proteins greater than what size cannot freely diffuse through the nucleus?

A

60KDa

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20
Q

GTP stands for what?

A

Guanosine Triphosphate

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21
Q

What is the role of a GTP binding protein?

A

Protein binds to GTP and acts as a GTPase (hydrolyses GTP).

Hydrolysis requires GAP.

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22
Q

What does GAP stand for and what is its function?

A

GTPase activating protein.

Binds to GTP binding protein and induces GTP hydrolysis.

23
Q

What does GEF stand for and what is its function?

A

Guanine nucleotide exchange factor.

Binds to GTP binding protein and causes it to release GDP.

24
Q

The protein ‘Ran’ is an example of what?

A

GTP binding protein.

25
Q

Where is Ran GDP found?

A

Cytosol.

26
Q

Where is Ran GTP found?

A

Nucleus.

27
Q

Large proteins enter the nucleus with the help of GTP binding proteins such as Ran.

Describe the Ran Cycle, once protein is in the nucleus.

A
  1. Ran GTP in the nucleus binds to nuclear import receptor which is bound to protein of interest.
  2. Conformation change, protein of interest is released into nucleus.
  3. Import receptor and Ran GTP diffuse back through the NPC to the cytosol.
  4. Ran binding protein binds to Ran GTP and releases import receptor.
  5. Ran GAP stimulates Ran GTP to hydrolyse.
  6. Ran GDP diffuses from cytosol to nucleus.
  7. Guanine exchange factor (GEF) exchanged GDP to GTP in cytosol.
28
Q

How are proteins exported OUT of the nucleus.

Refer to Ran as the binding protein.

A
  1. Nuclear export receptor binds to Ran GTP.
  2. Receptor-Ran GTP complex binds to protein of interest.
  3. Complex leaves nucleus via NPC using FG repeats.
  4. Ran GTP is hydrolysed to Ran GDP in the cytosol.
  5. Ran GDP diffuses back through the NPC to the nucleus and GEF exchanges GDP for GTP.
29
Q

When mature mRNA is complexed with numerous proteins, it is termed as what?

A

mRNP

30
Q

mRNP uses what receptors to be exported to the cytosol?

A

Nuclear export receptors (NER).

31
Q

Nuclear export receptors (used to transport mRNP) bind to what proteins which bind to the 5’ end of the mRNA?

A

Adaptor proteins.

32
Q

TRUE OR FALSE:

The nucleolus is membrane bound.

A

FALSE

The nucleolus is not membrane bound.

33
Q

The nucleolus appears darker because it is packed full of what?

A

RNA and protein.

34
Q

What macromolecular machines are synthesised in the nucleolus?

A

Ribosomes - new proteins can hence be synthesised in the nucleolus.

35
Q

Heterochromatin is tightly packaged, meaning what?

A

Transcription cannot take place.

36
Q

Euchromatin is loosely packaged, meaning what?

A

Transcription can take place.

37
Q

80S ribosomes (not found in the mitochondria) are composed of two sub-units. Using ‘S’ how large are they?

A
  1. Large sub-unit = 60S

2. Smaller sub-unit = 40S

38
Q

The large sub-unit of an 80S ribosome has how many ribosomal RNA strands and proteins?

A

3 ribosomal RNA strands

49 proteins

39
Q

The smaller sub-unit of an 80S ribosome has how many ribosomal RNA strands and proteins?

A

1 ribosomal RNA

33 proteins

40
Q

rRNA genes are clustered together on a DNA sequence. This cluster is known as what?

A

Tandem repeats.

41
Q

The 3 rRNA strands for the large subunit of the 80S ribosome are transcribed in the nucleolus by RNA polymerase I.

What size is each of the strand?

A

18S
5.8S
28S

42
Q

The 1 rRNA strand for the smaller subunit of the 80S ribosome is transcribed in the nucleoplasm by RNA polymerase III.

What size is the strand?

A

5S

43
Q

What separates each 45S pre-rRNA strands?

A

Transcribed spacers.

44
Q

What modification is made to the 45S rRNA to form the 90S pre-ribosome?

A
  1. Addition of ribosomal proteins during transcription of 45S pre-rRNA.

This forms a huge macromolecular structure termed the 90S pre-ribosome.

45
Q

At the 90S pre-ribosome, what happens to the rRNA strand?

A

Strand is split into 3 rRNA strands.

46
Q

What are snoRNPs?

A

Small Nuclear RNAs which recognise specific areas of rRNA that require modification.

47
Q

snoRNAs are complementary to target regions of the 45S pre-rRNA. They are complexed with what that enables modification of rRNA?

A

Structural proteins and enzymes.

48
Q

What are the three types of modification that snoRNPs can perform?

A
  1. Methylation of hydroxyl group on ribose.
  2. Conversion or uridine to pseudouridine.
  3. Cleavage of 45S pre-rRNA.
49
Q

The methylation of hydroxyl groups on ribose helps rRNA how?

A

Improves stability and acts as a tag to show rRNA is mature and structurally correct.

50
Q

The conversion of uridine to pseudouridine helps rRNA how?

A

Pseudouridine is an isomer as uridine.

It improves affinity of rRNA for tRNA during protein synthesis.

51
Q

The cleavage of 45S pre-rRNA helps rRNA how?

A

This is the final step - the removal of the transcribed spaces in pre-rRNA.

52
Q

What enzymes splice of the externally/internally transcribed spaces?

A

exo/endoribonucleases

53
Q

The 5S rRNA is exported out the nucleus into the cytosol and combines with what strand to form the 60S subunit.

A

5.8S rRNA strand.

PSA712 Biochemistry (11 decks)

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