Comparative Anatomy of Prokaryotic and Eukaryotic Cells

Question 1

What are the major differences between eukaryotic and prokaryotic cells?

Answer 1

• Size
• Presence or lack of nucleus
• Compartmentalisation

Question 2

Nucleus

Answer 2

• Contains chromatin (DNA complexed with histones)

- Site of mRNA, tRNA and rRNA synthesis (rRNA in the nucleolus)

Question 3

Rough ER

Answer 3

• Membrane network covered with ribosomes
• Site of protein synthesis
• Specific sorting signals allow import into RER

Question 4

Smooth ER

Answer 4

• No protein synthesis
• Contributes to lipid synthesis (steroids)
• Toxin breakdown

Question 5

Golgi complex

Answer 5

• Carbohydrate synthesis (for cell walls, extracellular matrix)
• Modification of proteins for specific targeting (secretion/incorporation in membranes)

Question 6

Lysosomes

Answer 6

• Originate from Golgi
• Can fuse with other vesicles
• Contain digestive enzymes to hydrolyse macromolecules

Question 7

Peroxisomes

Answer 7

• Originate from ER
• Incorporate lipids and proteins from cytoplasm
• Oxidise alcohols and fatty acids (role in lipid metabolism)

Question 8

Mitochondria

Answer 8

• “Power house of the cell”
• Involved in respiration, oxidative phosphorylations, Krebs cycle
• Has its own genome
• Multiply by division

Question 9

Chloroplasts

Answer 9

• Made of thylakoids forming grana, found in storm (~matrix)
• Converts light into organic compounds via the Calvin cycle
• Has its own circular DNA and translation machinery
• Multiply by division

Question 10

Flagella/Cilia

Answer 10

• Consist of a bundle of 9 pairs of microtubules surrounding a central pair (axoneme) - microtubules are connected to adjacent ones via nexin molecules
• Motion is driven by ATP hydrolysis carried out by dynein molecules
• Microtubules slide against one another, giving a whiplike movement

Question 11

Nucleoid

Answer 11

• Usually a single, circular chromosome
• DNA complexed with histone-like proteins
• Genetic material also includes plasmids

Question 12

Cytoplasm

Answer 12

• Compartment enclosed by a membrane with a dedicated physiological function
• Contains proteins, tRNAs, mRNA and ribosomes
• Can contain several inclusion bodies (protein bound), e.g. carboxysomes (CO2 reduction in photosynthetic bacteria), storage granules (sulphur/phosphate/nitrogen) and gas vesicles

Question 13

Envelope

Answer 13

• Consisting of a cytoplasmic membrane, peptidoglycan, polymers covalently bound to peptidoglycan and an outer membrane

Question 14

Appendages

Answer 14

• Pilus
• Fimbriae (or pili)
• Flagella

Question 15

Pilus

Answer 15

• appendage dedicated to conjugation (plasmid exchange)

Question 16

Fimbriae (or pili)

Answer 16

• involved in adherence to host cells/surfaces; antigenic structures made of one major protein

Question 17

Flagella

Answer 17

• supramolecular assembly involved in bacterial motility

Question 18

Endosymbiotic Origin of Eukaryotes

Answer 18

• Stable incorporation of endosymbiotic bacteria resulted in the formation of mitochondria and chloroplasts
• Nucleus appears before the acquisition of mitochondria and chloroplasts by endosymbiosis
• Problem: does not account for the fact that both eukaryotes and prokaryotes have similar lipid composition

Question 19

Origin of Mitochondria

Answer 19

• from engulfment of a H2-producing bacterium by an H2-consuming Archae

Question 20

Origin of Lipid Synthesis

Answer 20

• Genes for lipid synthesis were transferred to host giving rise to the nucleus

Question 21

Origin of Chloroplasts

Answer 21

• Chloroplasts were acquired later by endosymbiosis leading to the first phototrophic eukaryotes

Question 22

Anatomy of Eukaryotes

Answer 22

• Nucleus (RNA transcription)
• RER (protein translation/modification)
• SER (lipid/steroid synthesis)
• 80S ribosomes
• Golgi body (carbohydrate synthesis, protein modifications)
• Mitochondria (power station, ATP synthesis)
• Chloroplasts (light-dependent CO2 assimilation)
• Peroxysomes (lipid metabolism, detoxification role; e.g. alcohol)
  Lysosomes (digestive organelle)
• Flagella/Cilia (made of microtubules)

Question 23

Anatomy of Prokaryotes

Answer 23

• Nucleoid and plasmids (ds DNA)
• 70S ribosomes
• Rare membrane-bound organelles, frequent protein bound vesicles
• Complex envelope (peptidoglycan + polymers/proteins, outer membrane)
• Appendages (pilus, flagella, fimbriae)

Question 24

Endosymbiotic Theory

Answer 24

• Both mitochondria and chloroplasts result from engulfment of prokaryotic cells by a deep branching ancestor that gave rise to Archaea and Eukarya