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Biochemistry and Cell Biology Year 1 > The nucleus > Flashcards

The nucleus Flashcards

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1
Q

Define histone

A

Protein that binds to DNA to form eukaryotic chromosomes

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2
Q

Define nucleosome

A

A protein- DNA complex containing 8 histone proteins

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3
Q

Define chromatin

A

Repeating nucleosome structure like beads on a necklace bound to non histone proteins

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4
Q

Define chromosome

A

Defined region of chromatin that carries info relating to a specific set of genes. 1/3 DNA 2/3 protein

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5
Q

Define sister chromatids

A

Identical copies of the same chromosome seen in DNA replication - metaphase

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6
Q

What is the central dogma of molecular biology?

A

DNA to mRNA to Proteins
Transcription and translation

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7
Q

What is the nucleus?

A

The biggest single organelle and contains DNA and separates this from the cytoplasm

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8
Q

Outline the structure of the nucleus

A

Nuclear membrane has a double membrane - perinuclear space between the 2
Nucleolus - no membrane
Nuclear lamina- network of intermediate filaments
Ribosomes on the RER
Nuclear pores - perforate the nuclear envelope - channels that allow communication between the nucleoplasm and the cytoplasm

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9
Q

Outline the structure of the nuclear pore complex

A

Ordered 8 fold symmetry - formed by proteins called nucleoporins - scaffold - outside and channel - line channel - middle of the channel is a disordered region of channel nucleoporins
Nuclear basket - proteins form a cage like structure
Cytosolic fibrils - long proteins that reach into the cytosol
30 different types - 500 - 1000 proteins in each NPC - mammalian cells contain 3000- 20,000
1000 macromolecules per sec

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10
Q

What can diffuse through the NPC?

A

Less than 5000 Da freely diffuse
60KDa takes longer
Greater than 60KDa requires a specialised mechanism and energy

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11
Q

What is a nuclear localisation signal?

A

Tells a protein e.g. DNA polymerase to go into the nucleus

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12
Q

Outline the process of nuclear import

A
  1. Nuclear import receptor detects the NLS and binds to the protein
  2. Protein complex binds to cytosolic fibres of NPC
  3. Moves through by binding and dissociating with FG repeats
  4. In the nucleoplasm Ran-GTP binds to the NIR releasing the protein
  5. Empty receptor with Ran-GTP moves back to the cytoplasm
  6. A Ran binding protein binds to Ran-GTP and releases the NIR
  7. Ran-GAP hydrolyses Ran-GTP to Ran-GDP +Pi
  8. Ran-GDP moves back into the nucleus and is converted to Ran-GTP by Ran-GEF
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13
Q

Outline the process of nuclear export

A
  1. Ran-GTP binds to a nuclear export receptor
  2. Protein binds to the NER
  3. This complex bind to the nucleoporins on the nuclear basket
  4. Complex moves through by binding and dissociating with FG repeats
  5. In the cytoplasm, Ran-GAP binds to the complex releasing the protein and hydrolysing Ran-GTP to Ran-GDP
  6. Ran-GDP moves back to the nucleoplasm via the NPC
  7. Ran-GEF coverts Ran-GDP to Ran-GTP
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14
Q

What is the nucleolus?

A

Where ribosomal biogenesis occurs
No membrane
Contains RNA’s and proteins

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15
Q

What is the ribosome?

A

Site of protein synthesis
Small - 40S and large 60S subunit
40S contains - 18S rRNA and 33 proteins - transcribed in nucleoplasm by RNA polymerase III
60S contains - 5S rRNA, 5.8S rRNA, 28S rRNA and 49 proteins - transcribed in the nucleolus by RNA polymerase I

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16
Q

What are tandem repeats?

A

Genes are clustered together on a DNA sequence - speeds up rRNA transcription

17
Q

What are the spacer regions?

A

Non coding DNA sequence

18
Q

Outline the process of ribosomal biogenesis

A
  1. RNA polymerase I transcribes pre-rRNA in the nucleolus
  2. Ribosomal proteins enter via the NPC and move to the nucleolus
  3. They associate with the 45S pre-rRNA forming the 90S pre- ribosome
  4. snoRNPs modify the rRNA
  5. RNA polymerase III transcribes 5S rRNA in the nucleoplasm this is transported to the nucleolus and associates with the 28S and 5.8S rRNA to form the 60S subunit.
  6. 40S and 60S leave via the Ran Cycle.
19
Q

What are snoRNPs?

A

RNA complexes with proteins to help stability and function
They recognise areas of the rRNA that require modification

20
Q

In what 3 ways do snoRNPs modify rRNA?

A
  1. Methylate hydroxyl groups on ribose
  2. Convert (isomerise) uridine to pseudouridine
  3. Cleave 45S pre-rRNA
21
Q

How is the 45S pre ribosomal RNA cleaved?

A

Exoribonucleases remove externally transcribed spacers
Endoribonucleases remove internally transcribed spacers

Biochemistry and Cell Biology Year 1 (11 decks)

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