7. Endosymbiosis

Question 1

What evolutionary advantages might a cell with enclosed compartments have?

Answer 1

• Chemicals could be concentrated in particular regions of the cell allowing chemical reactions to proceed more effectively
• Biochemical processes could be segregated within an organelle creating more specific, favourable conditions for that cell
• Gene transcription could be separated from translation providing more spare control of the steps in gene expression

Question 2

What does the endosymbiosis theory state?

Answer 2

That mitochondria and chloroplasts originated when larger cells engulfed but did not digest smaller cells. Mutual benefits permitted this symbiotic relationship to be maintained, allowing the smaller cells to evolve in the eukaryotic organelles observed today.

Question 3

How have mitochondria evolved and what is their origins?

Answer 3

Billions of years ago mitochondria was a primitive prokaryotic microbe engulfed by eukaryotic cells, and could perform aerobic respiration, the most effective form of producing AtP. With a prokaryote inside it, the primitive eukaryote would have benefit as the mitochondria lived inside it. Over time these two cells lost the ability to live separately.

Question 4

How have chloroplasts evolved

Answer 4

Some time after eukaryotes acquired mitochondria, again a eukaryote engulfed but did not digest a prokaryote which had the ability to carry out photosynthesis (Cyanobacteria). The eukaryote and prokaryote evolved to become modern day plants.

Question 5

What features do mitochondria and chloroplasts have in common with a whole prokaryotic cell?

Answer 5

1. These organelles appear morphologically similar to bacteria
2. They are surrounded by an outer membrane similar to a cell membrane while their inner membrane invaginate to form lamellae or cristae. Derived from gram negative bacteria
3. Mitochondria and chloroplasts are semi-autonomous, retaining their own genome (DNA, RNA, proteins)
4. They also retain their own machinery for synthesising proteins, including ribsomes
5. Their metabolism is like existing prokaryotic organisms (cyanobacteria for chloroplasts and a purple bacterium for mitochondrion)
6. Some chloroplasts still have the bacterial peptidoglycan wall between the inner and outer membranes

Question 6

What is the inner membrane of the mitochondria for?

Answer 6

It is the primary barrier between the cytosol and mitochondrial enzymes

Question 7

What is the cristae for?

Answer 7

It contains key molecules for the generation of ATP from fuel molecules

Question 8

What is the matrix of the mitochondria for?

Answer 8

It is the space enclosed by the inner membrane which contains several of the enzymes for cellular respiration. It also contains ribosomes and DNA.

Question 9

What are some similarities between mitochondria and bacteria?

Answer 9

• Electron transport chain and turbine ATPase of inner membrane is the same as the plasma membrane of bacteria
• They have a circular DNA chromosome
• They both have smaller ribosomes sensitive to antibiotics
• They divide by binary fission using the FtsZ protein

Question 10

Which bacteria where mitochondria and chloroplasts believed to be derived from?

Answer 10

• Mitochondria thought to have originated as symbiotic aerobic bacteria (alpha purple)
• Chloroplasts believed to be derived from the symbiotic, photosynthetic bacteria (cyanobacteria)

Question 11

Where are the photosynthetic pigments located in the chloroplasts?

Answer 11

Thylakoids