Lecture 3: Origins and importance of organelles Flashcards

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1
Q

Origins of chloroplasts & mitochondria:

A

Endosymbiotic Theory

-idea that ancestral eukaryotic cells engulfed bacterium ‘cells’

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2
Q

steps of endosymbiotic theory:

A

-Ancestral eukaryotic cell (got internal membrane system)
-englufs an aerobic bacterium –> endosymbiosis occurs = mitochondrion
-englufs photosynthetic bacterium –> endosymbiosis occurs = chloroplast
== Eukaryotic cell with mitochondrion and chloroplast

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3
Q

Evidence for prokaryotic origins of chloroplasts and mitochondria: DNA

A

Prokaryotes, chloroplasts & mitochondria: 1 single, circular chromosome

Eukaryotes: Multiple linear chromosomes in nucleus

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4
Q

Evidence for prokaryotic origins of chloroplasts and mitochondria: Replication

A

Prokaryotes, chloroplasts & mitochondria: Binary fission (1 cell splits into 2)

Eukaryotes: Mitosis

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5
Q

Evidence for prokaryotic origins of chloroplasts and mitochondria: Ribosomes

A

Prokaryotes, chloroplasts & mitochondria: 70S

Eukaryotes: 80S

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6
Q

Evidence for prokaryotic origins of chloroplasts and mitochondria: Size (approx)

A

Prokaryotes, chloroplasts & mitochondria: 1-10 micrometres

Eukaryotes: 50-500 micrometres

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7
Q

Evidence for prokaryotic origins of chloroplasts and mitochondria: Porins

A

Prokaryotes, chloroplasts & mitochondria: present

Eukaryotes: not present

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8
Q

Evidence for prokaryotic origins of chloroplasts and mitochondria: Initiating amino acid

A

Prokaryotes, chloroplasts & mitochondria: N-formylmethionine

Eukaryotes: methionine

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9
Q

Cardiolipin constitutes about 20% of..

A

the inner mitochondrial membrane lipids. Only found elsewhere in bacteria… evidence for endosymbiotic theory

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10
Q

Genes for cyanobacteria peptidoglycan (cell wall) synthesis is still

A

present in Arabidopsis… evidence for endosymbiotic theory

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11
Q

Secondary endosymbiosis: alga steps

A

Cyanobacterium engulfed –> Alga

Alga then engulfed by secondary host –> algae. Plastids with 3 or 4 envelopes are common in algae

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12
Q

Porins

A

transport across membrane (channels)

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13
Q

Repeated endosymbiosis has led to

A

plant and algal diversity. Depending upon how many stages of endosymbiosis (up to tertiary) & at each stage what cells fuse

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14
Q

Apicocomplexa are

A

animal parasite, including Plasmodium (malaria)

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15
Q

Some sea slugs run on

& young..

A

Solar power by ingesting chloroplasts. If young animals are fed algae for 2 weeks, they can survive 8-10 months without eating.

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16
Q

Endosymbiotic zooxanthellae in..

A

coral polyps

17
Q

The transfer of organelle DNA…

A

has abolished organelle autonomy & increased nuclear complexity

18
Q

~4,500 (~18% of total) Arabidopsis protein-coding genes..

A

were acquired from cyanobacteria

19
Q

Gene transfer from organelles to the nucleus is a..

A

continuing process

20
Q

Arabidopsis..

A

(rock cress) small flowering plant related to cabbage & mustard

21
Q

Mitochondria DNA:

A

encodes rRNAs, tRNAs, and 13 out of ~85 components of the oxidative phosphorylation system

22
Q

Chloroplasts DNA;

A

encodes some rRNAs, tRNAs, ribosomal proteins, RNA polymerase subunits & some genes for photosynthesis

23
Q

Maternal inheritance of mitochondrial (and plastid) genome

A
  • simple dilution
  • degradation of sperm mtDNA in the fertilised egg
  • failure of sperm mtDNA to enter the egg
24
Q

egg & sperm contains mtDNA molecules

A
  • egg contains 100,000 to 1,000,000 mtDNA

- sperm 100 to 1000 mtDNA

25
Q

3 person IVF is use to stop

A

mother passing on faulty mtDNA

26
Q

3 person IVF steps:

A

Step 1: parents embryo (unhealthy mitochondria) and healthy donor embryo (healthy mitochondria)
Step 2: Parents’ nucleus removed & donor nucleus removed & destroyed.
Step 3: Parents nucleus now in donor embryo

27
Q

How do proteins cross chloroplast membranes?

A

Most proteins are nuclear encoded. A signal peptide is a target sequence of amino acids that is recognized and cleaved by a signal peptidase at the chloroplast envelope (for thylakoid: two signal sequences)

28
Q

How do proteins cross chloroplast membranes? entering molecule

A
        • > Top;
  • chloroplast signal sequence
  • thylakoid signal sequence
  • thylakoid precursor proteins
29
Q

Plants without plastids: Rafflesia lagascae

A

a parasite that has plastid‐like structures but no intact plastid genome.

30
Q

Plants without plastids: Polytomella

A

a freshwater alga. Has a plastid but no trace of a plastid genome

31
Q

Apicomplexa

A
  • parasitic single‐celled eukaryotic organisms deriving from red algae
  • 1.2 ‐ 10 million apicomplexan species, only about 0.1% described to date?
  • apical complex of microtubules
  • 200 million people incapacitated by malaria; 600,000 die annually
  • Eimeria spp. responsible for annual $1.5 billion loss to the poultry industry worldwide
32
Q

Apicomplexa - MAlaria

A
  • Plasmodium still retains its plastid genome
  • Apicoplasts of Plasmodium falciparum have four membranes
  • Suitable target for drug treatments
33
Q

Apicomplexa - Cryptosporidium

A
  • Parasite which causes sever infection sin young children and people with weak immune systems
  • -infection begins with the ingestion of water or food containing spore-like oocysts
  • parasite enter cells of small intestine
  • simple single-host life cycle
  • oocysts pass into the colon and are released in the faeces
  • crypto infects others
34
Q

Advantages of chloroplasts and mitochondria: The cellular power struggle

A
  • Energetic cost of genes is trivial (2% of cell’s energy budget), but cost of expressing them as protein is 75% of the energy budget. An average bacterium (E. coli) has ~ 13,000 ribosomes, whereas a human liver cell has 13 million on the rough ER alone.
  • Mitochondrial genes enabled a 200,000‐fold rise in genome size in eukaryotes compared with bacteria by allowing oxidative phosphorylation across a large area of internal membranes.
  • Mitochondria increased the number of proteins that a cell can evolve, inherit and express by 4‐6 orders of magnitude.