Prokaryote and eukaryotes: evolutionary relationships

Question 1

how big are prokaryotes?

Answer 1

small 1-10 u

membrane infolded in some species

Question 2

define invagination

Answer 2

infolding of membranes ie infolding of the mitochondria to form cristae

Question 3

define evagination

Answer 3

: out pocketing - plasma membrane folding out - ex. Esophagus bulging wall out in fetus develops into lungs

Question 4

what are the three common shapes of prokaryotes?

Answer 4

• Spiral, spherical, and cylindrical cell shapes

Some have square shapes

Question 5

how do antibiotics work?

Answer 5

Kills a bacterial cell by degrading the bacterial cell wall

Question 6

describe gram positive bacteria

Answer 6

Gram positive: peptidoglycan wall exposed and this retains violet stain - thick layer of peptidoglycan

Question 7

describe gram negative bacteria

Answer 7

• Gram negative: peptidoglycan wall not exposed and does not retain violet stain
  
  • Peptidoglycan- made of protein and a carbohydrate molecule joined together. Present in almost all bacteria cells.
  • Histology helps us to stain different parts of the cell
  • Gram negative: peptidoglycan wall not exposed and does not retain violet stain

Question 8

what features are found in eukaryotes but not prokaryotes

Answer 8

• Nucleus and nuclear membrane
  
  • Mitosis
  • Golgi, ER (complex membranes)
  • Cytoskeleton - made of microtubules that provide physical support
  • Organelles (mitochondria, chloroplast)
  • Membrane sterols (eg. Cholesterol)

Question 9

describe the eukaryotic flagellum

Answer 9

• Has a bunch of microtubules in its flagellum, organized in a 9 + 2 ultrastructure
• 9 microtubules on the perimeter of the inside and 2 on the inner
Not seen in bacterial flagellum

Question 10

when did prokaryotes evolve into eukaryotes?

Answer 10

• Happened about 2.8 bya (chemical evidence)

* Fossils found about 1.5 byo

Question 11

what is the hypothesis of why eukaryotes have golgi complex and ER?

Answer 11

• More complex membranes in a eukaryotic cell : golgi complex and ER
• Specialized double membrane organelles (mitochondria, chloroplast)
Probably have exogenic origin

Question 12

describe the autogenous model/hypothesis

Answer 12

• Invagination of cellular membrane might have led to ER, Golgi, and nuclear membrane
  
  • Ribosomes of prokaryote plasma membrane vs rough ER in eukaryote

Question 13

what is symbiosis?

Answer 13

An intimate association of two or more species

Question 14

describe commensalism

Answer 14

• Commensalism +/o
• Beneficial to one - commensal
• Apparently, no effect to the other - host
Egrets & grazing cattle

Question 15

describe mutualism

Answer 15

• Mutualism +/+
• Beneficial to both partners
• Microbes in the gut of termites and ruminant mammals
• Ie clown anemone fish and sea anemones (cnidaria)
Flagellates live inside of body of termites and have bacteria that contain cellulase and break it down which helps it and the termite survive

Question 16

describe parasitism

Answer 16

• Parasitism +/- 
	• Beneficial to one - parasite 
	• Harmful to the other - host 
	• Parasite derives nutrients from host and may cause damage 
Ex plasmodium cause malaria

Question 17

who was a major proponent of the endosymbiosis model? what was their hypothesis?

Answer 17

• Lynn Margulis (1981): “symbiosis in cell evolution”
  
  • Based on a large number of known symbiotic relationships
  • Hypothesis: mitochondria and chloroplasts evolved from bacterial symbionts of early eukaryotic cells
  Mitochondria and chloroplasts are probably derived from prokaryotes
  Oxygenic photosynthesis in cyanobacteria

Question 18

what is the theory of endosymbiosis?

Answer 18

• Theory of endosymbiosis
• Energy transducing organelles, chloroplasts and mitochondria, thought to have been derived from free living prokaryotic cells
• Mitochondria developed from ingested prokaryotes capable of using oxygen for aerobic respiration
Chloroplasts developed from ingested cyanobacteria

Question 19

what is the evidence for the theory of symbiosis?

Answer 19

• Frequent occurance of endosymbiotic relationships in living organisms
• Prokaryote like features of mitochondria and chloroplast
• Morphology: shape and size similar
• Circular DNA; no histone proteins
• Binary fission
• Protein synthesis machinery similar ( ribosomes, tRNA, polymerases)
• Electron transport similar to free - living prokaryotic cells
Sequence analysis: sequence of chloroplast rRNA close to xyanobacteria and mitochondria rRNA close to heterotrophic bacteria

Question 20

what is a critism of endosymbiosis?

Answer 20

• Mitochondrial and chloroplast DNA do not contain all genetic information necessary to function
Most are transcribed in nucleus and cytoplasm

Question 21

what are the missing links of endosymbiotic theory?

Answer 21

• Although well accepted, invagination and endosymbiosis models do not account for several eukaryotic features:
• Cillia /flagella different than (analogous to) prokaryotic flagella
• Mitosis and a large genome
• Meiosis and sex
Nucleus

Question 22

why are eukaryotes chimaera of prokaryotes?

Answer 22

imilarly the eukaryotic cell is a chimaera of prokaryotic parts:
• Mitochondria from one bacteria
• Plastids from another
• Nucleus from giant virus
• Nuclear genome from multiple host cells
• Additional endosymbiotic events and horizontal gene transfers
May have contributed to the large genomes and complex cellular structure of eukaryotic cells

Question 23

how did the eukaryotic flagella evolve?

Answer 23

• Some speculated that eukaryotic flagella and cilia evolved from symbiotic bacteria, based on symbiotic relationships between some bacteria and protozoans
But 9 + 2 microtubules arrangement is unique to prokaryotes

Question 24

why did eukaryotes evolve from prokaryotes?

Answer 24

• Ability of early eukaryotes to generate more ATP led to remarkable changes- cells could become larger and more complex
A wide variety of genes could be supported that led to eukaryotic specific traits: the cell cycle, sexual reproduction, phagocytosis, endomembrane trafficking, the nucleus, and multicellularity