Lecture 5 - Eukaryotic Cell Structure

Question 1

Describe the origin of the eukaryotes referred to as The Endosymbiotic Hypothesis

Answer 1

• most common ancestor 2.1 bya
• oxygen was accumulating in the atmosphere 2.4 bya but all cells were toxic to oxygen
• eukaryotes evolved oxygen-neutralizing enzymes

Question 2

How did internal membranes form?

Answer 2

• the surface area of Archaean increased by the infoldings of membranes

Question 3

What are the steps of Eukaryote Evolution?

Answer 3

1) endomembrane system (infoldings of membranes)
2) endosymbiotic organelles (mitochondria and chloroplasts arose from a primitive prokaryote living inside a primitive eukaryote)

Question 4

What is the good roommate hypothesis? provide evidence

Answer 4

• bacteria are sensitive to rising oxygen
• Archaea have evolved enzymes to neutralize toxic oxygen and they also have lots of space
  evidence = mt and cp have: circular genome, bacterial-like gene organization, prokaryote-like ribosomes
  also, the bacteria was ingested and not digested

Question 5

What is the endomembrane system?

Answer 5

membrane-bound organelles that arose from infoldings of the membrane and are connected via vesicles

Question 6

What are vesicles?

Answer 6

membrane-bound compartments that contain cargo

Question 7

What are the organelles in the endomembrane system?

Answer 7

• outer nuclear membrane
• endoplasmic reticulum
• golgi
• lysosome

Question 8

What is the function and structure of the nucleus?

Answer 8

function: storage of DNA and the site of gene expression
structure: double-membrane bound, the outer membrane is continuous with the ER
- NPC = nuclear pore complexes (transmembrane complexes that span both bilayers, allow non-specific transport)

Question 9

What is the function of the nucleolus?

Answer 9

function: site of ribosomal subunit assembly
- ribosomes consist of two major protein components and associate with their rRNA at the nucleolus
- leave nucleus as independent subunits and come together in cytoplasm during translation

Question 10

What is the function and structure of the nuclear envelope?

Answer 10

function: separates nucleoplasm from the cytoplasm (protects DNA)
structure: two lipid bilayers + nuclear lamina

Question 11

Why do we need chromatin packaging?

Answer 11

• organize DNA

- protect from damage

Question 12

What is the order of packaging?

Answer 12

*refer to notes, too much to type out

Question 13

What is the function of the RER?

Answer 13

• covered in ribosomes
• enzymes of translation
• called bound ribosomes
• function: site of protein synthesis for a protein that functions within the endomembrane system and the site of protein quality control

Question 14

What is the function of the SER?

Answer 14

• ion storage
• phospholipid synthesis
• steroid synthesis
• detoxification of drugs and alcohol

Question 15

What is the function and structure of The Golgi Apparatus?

Answer 15

function: receives cargo from ER and sorta cargo to different destinations and then packages it into vesicles
structure: a set of flattened membrane sacs called cisternae

Question 16

What are the two models of Golgi Trafficking?

Answer 16

• Vesicle Trafficking
• Cisternal Maturation
• refer to notes for extra content

Question 17

What are lysosomes?

Answer 17

• ‘cell stomach’ = involved in digestion of macromolecules from endocytosis, contains many hydrolytic enzymes that function best at pH 5, lysosomes actively pump in H+ to maintain low pH to protect cells from accidental autophagy

Question 18

What is autophagy?

Answer 18

• lysosome is a site of organelle recycling

- cells can commit cell suicide (apoptosis)

Question 19

What organelles are not found in the endomembrane system?

Answer 19

• mitochondria and chloroplasts
• peroxisomes
• cytoskeleton

Question 20

What are peroxisomes?

Answer 20

• specialized metabolic compartment
• involved in the oxidation reactions that often produce toxic byproducts
• involved in the detox of alcohol and metabolism of fats

Question 21

What is the function and structure cytoskeleton?

Answer 21

• network of fibers extending throughout the cytoplasm
• three types: microtubules, microfilaments, and intermediate filaments
• function: support, motility, and cell shape
• structure: 3 components

Question 22

What is the function and structure of microtubules?

Answer 22

• function: compression resistance
• structure: polymers of tubulin
• tubulin is a dimer of alpha and beta-tubulin monomers and 13 protofilaments bundle to form a rigid tube

Question 23

What are associated motor proteins? What are Kinesin and Dynein?

Answer 23

• proteins that change shape with ATP hydrolysis that generates a force
• Kinesin = (+) end-directed MT motor
• Dynein = (-) end-directed MT motor

Question 24

What is the function and description of the Eukaroyitc Flagellum?

Answer 24

• function: cell movement
• whiplike
• powered by ATP hydrolysis
• membrane-bound
• single and long = flagellum
• short and numerous = cilia
• movement is generated by dynein

Question 25

What are the function and motor of microfilaments?

Answer 25

• polymer of actin
• function: tension resistance
• movement: cytokinesis, muscular contraction
• motor: myosin

Question 26

What is the function and structure of intermediate filaments?

Answer 26

• function: tension-resistance, not very dynamic, they have no associated motor proteins and low turnover
• structure: many different subunit types that form rope-like filaments