04. Eukaryote Cell Structure 2

Question 1

What is the structure of the nucleus?

Answer 1

• Contains genetic information (DNA) of the cell
• DNA organised - chromosomes
• Has a nuclear envelope - double membrane
• Centre is the nucleolus, surrounded by chromatin (DNA+ protein)

Question 2

What is the structure of the nucleus?

Answer 2

• Nuclear Envelope - two membranes
  
  • Outer nuclear membrane
  • Perinuclear space
  • Inner nuclear membrane
• Nuclear pores

Question 3

What are Nuclear pores?

Answer 3

• Point of fusion between inner and outer membrane
• Has diameter of ~120nm
• Gated by Nuclear pore complex [NPC]
• Made up of 30 different proteins

Question 4

What can diffuse through a nuclear pore?

Answer 4

Small molecules (metal ions/ ATP).
Cut off is 30,000 Da (9 nm diameter)

Question 5

How do proteins get transported through the NPC?

Answer 5

They have a Nuclear Localisation Signal (NLS) - specific amino acid sequence
NLS is recognised by receptor protein - Importin
Importin binds to the NLS- containing protein.

Question 6

What is the process of nuclear importing?

Answer 6

• Requires Ran-GTPase (small protein, hydrolyse GTP)
• It switches between GTP and GDP-binding state
• Importin + Ran-GTP –> Release cargo (Inside nucleus)

Question 7

What is the process of nuclear exporting?

Answer 7

• Nuclear-Export Sequence (NES) - on protein to be exported
• NES binds to Exportin
• Requires gradient of Ran-GTP and Ran-GDP across nuclear membrane
• Exportin + Ran-GTP –> bind cargo
  Important for export of RNA

Question 8

What is the nuclear lamina?

Answer 8

• Tough fibrous mesh underneath inner nuclear membrane
• Made up of intermediate filament (10-40nm thick)
• Scaffold - maintains nucleus shape
• Disassemble and reform during cell division

Question 9

What are ‘Chromosome territories’ ?

Answer 9

Chromatins associate with the nuclear lamina, and each has its own discrete location.

Question 10

What is the function of the nucleolus?

Answer 10

• Centre of ribosomal RNA production
• Synthesis and assembly of RNA and protein to form ribosome
• Ribosome Protein translation
• Membrane less compartment, liquid like behaviour

Question 11

What is the structure of the Endoplasmic Reticulum?

Answer 11

• Continuous with outer nuclear membrane
• Organized into interconnected tubes and flatten sacs
• Share single internal space
• Have more than half the total membrane of average animal cell
• 10% of total cell volume

Question 12

What are the main types of Endoplasmic Reticulum?

Answer 12

• Rough ER - ribosomes on surface (protein synthesis)
• Smooth ER - biosynthesis and metabolism of lipid
• Transitional ER - vesicle export zone

Question 13

What is the function of Rough ER?

Answer 13

Proteins transolcated into ER lumen, being translated from mRNA. Simple modification of protein + folding quality check.

Question 14

What is the function of Smooth ER?

Answer 14

• Tubular, highly specialized
• Enriched in cell types involved in lipid metabolism
• Synthesis of lipid for production of lipoprotein
• Contains enzyme for drug detoxification
• Sarcoplasmic Reticulum - stores calcium ions

Question 15

What is the function of Transitional ER?

Answer 15

Exit sites of protein (vesicles) leaving rough ER.

Question 16

What is the structure of the Golgi apparatus?

Answer 16

• Collection of flattened, membrane enclosed sacs (cisternae)
• Cis-complex - adjacent to ER (recives proteins)
• Trans-complex - towards plasma membrane

Question 17

What is the function of the Golgi apparatus?

Answer 17

Protein modification and sorting for traffic within cell

Question 18

What is the Vesicular Transport model?

Answer 18

• Cargo proteins are moved between cisternae
• Resident enzymes stay in the same cisternae

Question 19

What is a Resident Enzyme?

Answer 19

Proteins that modify incoming cargo proteins

Question 20

What is the Cisternal Maturation Model?

Answer 20

• Cargo proteins stay in cisternae
• Resident enzymes move between cisternae

Question 21

What are the types of coated transport vesicles?

Answer 21

• Clathrin-coated - from Golgi, endosome, plasma membrane
• COPI-coated - from Glogi (retrograde movement)
• COPII-coated - from ER (anterograde movement)
• Retromer-coated - endosome retrieval to golgi apparatus

Question 22

What is the structure of a Clathrin-coated Vesicle?

Answer 22

Triskelion