Endosymbiosis

Question 1

What defines a eukaryotic cell?

Answer 1

The eukaryotic cell has internal membranes and organelles. These both lack in bacteria and achaea.

Question 2

What is endosymbiosis?

Answer 2

the engulfment of one cell by another

Question 3

The two membranes that chloroplasts have are believed to have derived from what?

Answer 3

the endosymbiosis procedure itself

Question 4

Of what origin are chloroplasts from?

Answer 4

Chloroplasts are specific plant organelles of prokaryotic origin.

Question 5

Where have the membranes of chloroplasts come from?

Answer 5

1. the inner membrane derives from the prokaryote ancestor
2. the outer membrane derives from the vacuolar membrane of the eukaryotic cell which was involved in engulfing the endosymbiont

Question 6

What is an endosymbiont?

Answer 6

An organism which has been engulfed by another organism, and now lives within that organism.

Question 7

Endosymbiosis step by step?

Answer 7

1) Ancestral eukaryotic cell with internal membrane system engulfs aerobic bacterium. This becomes a mitochondrion which allows it to use aerobic respiration.
2) The eukaryotic cell then engulfs a photosynthetic bacterium. This becomes a chloroplast allowing the cell to photosynthesise.

Question 8

Whats the advantage of a eukaryotic cell that engulfs a chloroplast?

Answer 8

Can photosynthesise

Question 9

Whats the advantage to the engulfed bacteria?

Answer 9

Protection

Question 10

define Genome ?

Answer 10

the sum total of all genes in an cell, tissue, organ, or organism.

Question 11

define gene?

Answer 11

a dna sequence which codes for a particular protein

Question 12

The closer organelles/species are evolutionarily…

Answer 12

…the closer their dna resemble eachother. This is why organellar DNA is circular like that of bacteria.

Question 13

What happens when we loot at genes in chloroplasts and mitochondria?

Answer 13

when we look at genes in chloroplasts and mitochondria they are more like their bacterial equivalents and not like eukaryotic genes, which reinforces the postulation that these organelles derive from prokaryotes.

Question 14

What did Ivan Wallin do?

Answer 14

Postulated that mitochondria may be bacteria in the 1920s. Tried to culture them. He Failed.

Question 15

mitochondria are believed to be descended from…

Answer 15

mitochondria are believed to be descended from aerobic bacteria

Question 16

Can mitochondria and chloroplasts be cultured?

Answer 16

Unlike free-living bacteria, chloroplasts and mitochondria cannot be cultured independently.

Question 17

How does bacteria reproduce?

Answer 17

Binary fission.

Question 18

What is the evidence for chloroplasts and mitochondria being of prokaryotic origin?

Answer 18

1 - mitochondria and chloroplasts are similar in size and morphology to prokaryotes

2 - both reproduce by binary fission as do bacteria

3 - organelles can only arise from pre-existing organelles

4 - mitochondria and chloroplasts have their own DNA

5 - organellar DNA is circular like that of bacteria

6 - organellar DNA has genes that resemble those of bacteria (DNA phylogeny)

7 - these organelles contain their own ribosomes (can make their own proteins)

8 - the organellar ribosomes resemble bacterial ribosomes (they are 70S not 80S)

9 - differences in the composition of the two membranes

10 - organelles can be targeted by
antibiotics specific to prokaryotes (due to their bacterial ribosomes)

Question 19

Why do antibiotics target mitochondria and chloroplasts?

Answer 19

Because of their “bacterial ribosomes”, they get attacked by antibiotics which aim to stop them from working.

Question 20

What did Ivan Wallin propose?

Answer 20

Ivan Wallin proposed that mitochondria may be bacteria in the 1920s

Question 21

What are mitochondria believed to be descended from?

Answer 21

Aerobic bacteria .

Question 22

Can mitochondria be cultured?

Answer 22

No. Unlike free living bacteria, chloroplasts and mitochondria cannot be cultured independently.

Question 23

What can we compare DNA sequences of?

Answer 23

we can compare DNA sequences of the same gene in different organisms – when we look at genes in chloroplasts and mitochondria they are more like their bacterial equivalents and not like eukaryotic genes

Question 24

Where might the outer membrane have come from?

Answer 24

one possibility is that the outer membrane is derived from a vacuolar membrane from the original host – the inner membrane from the ingested bacterial cell

Question 25

Why can organelles be targeted by antibiotics specific to prokaryotes?

Answer 25

because they have ‘bacterial ribosomes’ then they are prone to attack by the same antibiotics that stop bacterial ribosomes from working

Question 26

Why are the ribosomes of mitochondria and chloroplasts similar to those of bacteria?

Answer 26

the ribosomes of mitochondria and chloroplasts are similar to those of bacteria – produced from the same genes

Question 27

How many proteins involved in oxidative phosphorylation?

Answer 27

13

Question 28

How many genes in organelles?

Answer 28

22. Very few. Most are tRNAs.

Question 29

Many mutations linked to…

Answer 29

human diseases.