W2L3 - Origin of eukaryotes Pt 1/2

Question 1

Properties of Eukaryotes (3)

Answer 1

• Nucleus
• Endomembrane system
• Linear Chromosomes (and >1 chromosomes)

Question 2

Differences between prokaryotes and eukaryotes

1. DNA
2. Histone proteins with DNA
3. Nuclear envelope with DNA
4. Multicellular
5. Size
6. Genome
7. Genes

Answer 2

Prokaryotes:

1. DNA: Circular (Singular)
2. Histone proteins with DNA: Yes/No
3. Nuclear envelope with DNA: No
4. Multicellular: No
5. Size: <10μm
6. Genome: <10⁶ bases (ATGC)
7. Genes: 4000 genes

Eukaryotes

1. DNA: Linear (Multiple)
2. Histone proteins with DNA: Yes
3. Nuclear envelope with DNA: Yes
4. Multicellular: Yes
5. Size: 3μm to 10mm
6. Genome: 10⁷ - 10¹⁰ bases (ATGC)
7. Genes: 6000-35000 genes

Question 3

5 Differences between prokaryotes and eukaryotes

Answer 3

1. Origin of nucleus
2. Endomembrane
3. Linear chromosomes
4. Large genome
5. More genes

Question 4

The function of histones in DNA.

Answer 4

Histone spools help keep long DNA from getting tangled

Question 5

What is the structure of the nuclear envelope?

Answer 5

• Outer and inner nuclear membrane (continuous)
• Nuclear pores allow U-turn
• The endoplasmic reticulum is continuous with the nuclear envelope
  
  • Ribosomes located: Insert protein into ER

Question 6

What is the nuclear envelope essentially (4) in eukaryotes

Answer 6

• The nuclear envelope is essentially rough endoplasmic reticulum (ER) pressed up against the DNA.
• Gaps in the appressed pieces of ER form pores
• Has ribosomes to insert protein into ER
• ER is connected to golgi apparatus

Question 7

What is the endomembrane system

Answer 7

Endomembrane system is a big plumbing system to deploy proteins within and to the outside of large cells

Question 8

What is the origin of a nucleus (prokaryotes)

Answer 8

Nucleus arose gradually by internalisation of plasma membrane

1. Prokayotes has a nucleoid (DNA). The prokaryotic plasma membrane has ribosomes attached and secretes proteins into the periplasmic space (outside cell).

• Dents in the cell become more elaborate and go into the cell, pressing against membrane against nucleoid.
  
  • By increasing dents, the extra surface-to-volume ratio allows greater interaction with the environment.
  • Since ribosomes are attached to indentations, ribosomes brought into the cell allow greater manipulation of environment

2. ER/nuclear envelope is essentially invaginations (folded out) of the plasma membrane (Still connected to the plasma membrane via Golgi and secretory vesicles)

Question 9

What is the origin of nuclear envelope? (3)

Answer 9

Created de novo after every cell division: Nucleus envelope disappears just before the chromosomes split but after separating into 2 daughter cells, it comes again.

• During nuclear division the envelope disintegrates
• Chromosomes divide & separate
• ER clusters around the chromosomes & forms a new envelope around DNA again

Question 10

Function of nuclear envelope (3). Include the junk hypothesis.

Answer 10

• Shields excessively long DNA during cell division (not necessary because of histone spooling. Moreover. the nuclear envelope disaggregates during nuclear division in some cells)
• In combination with the endomembrane system, it allowed for larger cells (Not necessary because it does not also have to come from envelope)
• Physically separates processes of transcription (RNA) & translation (Protein)
  
  • (PICERAS).