Cell Architecture

Question 1

Nucleus

Answer 1

• protects the genome
• has a continuous membrane with the ER
• nuclear pores govern movement in and out
• laminin proteins facilitate nuclear envelope breakdown for cell division
• nucleolus is within the nucleus and is not membrane bound

Question 2

Endoplasmic Reticulum

Answer 2

• net like maze of tubes and sacs in the cytosol
• composed of the rER and sER
• this organelle is very dynamic

Question 3

Golgi Apparatus

Answer 3

• smooth tubular flattened cisternae stacks
• sorts and packages proteins into vesicles
• intersection of vesicle pathways

Question 4

Lysosomes

Answer 4

• spherical lipid bilayer organelle

- low interior pH for hydrolytic enzymes for waste disposal

Question 5

Endosomes

Answer 5

• spherical internalising compartment sorting for degradation
• lipid bilayer
• 3 types: early (sorting), recycling (return to PM), late (degradation target)

Question 6

Peroxisomes

Answer 6

• spherical organelles with a lipid bilayer
• important for oxidative reactions using molecular oxygen
• takes organic substances and oxidises them to form hydrogen peroxide that degrades toxic substances

Question 7

Plastids

Answer 7

• double membraned organelles found in plant and algae cells

- usually ATP generation factors (similar to mitochondria) but also have storage/synthesis roles

Question 8

Endosymbiotic Theory

Answer 8

Theory of how eukaryotic cells and organelle compartmentalisation arose.
Says that one prokaryotic cell engulfed another to form a symbiotic relationship between organisms = driving force of evolution
There is physical evidence to support this
- double membranes around mitchondria and organelles
- mitochondria can only come from existing mitochondria and contain their own circular genome
- organelles contain 70s ribosomes similar to prokaryotic cells
Critiques
- some don’t have circular genomes
- replication is different from binary fission
- size/shape of mitochondria when viewed closely is less similar to that of a bacteria than previously thought

Question 9

Theory of endosymbiosis

Answer 9

1. loss of rigid cell wall in ancient anaerobic archaeans facilitated horizontal gene transfer
2. phagocytosis/digestion of prokaryotes greatly increases horizontal gene transfer (speeds up evolution)
3. membranes increasingly enclose the chromosome of anaerobic archaeans to help protect it
4. aerobic bacterium taken up intact to live symbiotically as promitocondrion
5. development of multiple mitochondrion provides energy