L1 Mitochondrial and Plastid Genomes Flashcards

1
Q

properties of outer membrane of mitochondria

A

contains many transmembrane channel proteins called porins

outer membrane is permeable to molecules 5000Da or less

intermembrane space and cytosol contain similar concentration of small solutes and proteins

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2
Q

properties of inner membrane of mitochondria

A

lipid bilayer contains high proportion of phospholipids

higher proportion of proteins embedded in inner membrane than outer

contains many transport proteins

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3
Q

proteins in the inner membrane

A

NADH dehydrogenase (complex I)

succinate dehydrogenase (complex II)

cytochrome c reductase (complex III)

cytochrome c oxidase (complex IV)

ATP synthase (complex V)

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4
Q

what are plastids

A

develop from pro plastids which are small organelles found in plant cell

plant cell differentiation > undifferentiated pro plastid found in meristematic cells of shoot and root can differentiate into number of specialised plastid types

most common plastid: chloroplast

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5
Q

different types of plastids

A

storage plastid: stores fat, oil or starch

chromoplast: stores pigments

chloroplast: carries out photosynthesis

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6
Q

how many chloroplast in a typical plant cell

A

50

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7
Q

structure of chloroplast

A

smooth outer membrane freely permeable to molecules

smooth inner membrane with many transporters to regulate passage of molecules in and out of chloroplast

system of thylakoid membranes

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8
Q

developmental process of thylakoid

A

inner membrane folds inwards > pinches off to form thylakoid vesicles > thylakoid vesicles stick together to form thylakoid membrane

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9
Q

properties of thylakoid membrane

A

enclose a lumen: system of vesicles

4 types of protein assemblies embedded:
- photosystem I
- photosystem II
- cytochrome b6f complex
- ATP synthase

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10
Q

what does the stroma contain

A

enzymes needed to carry out the “dark” reactions of photosynthesis

special set of ribosomes, RNAs and chloroplast DNA

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11
Q

which side of polypeptide enters mitochondria membrane first

A

transit signal sequence at N terminus

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12
Q

how does protein get imported into the mitochondria

A

continuously through the TIM and TOM complexes, passing through inter membrane space in one motion

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13
Q

difference between chloroplast and mitochondria

A

chloroplast is generally larger

chloroplast has third set of thylakoid membrane

inner mitochondrial membrane folded into cristae but not for chloroplast

mitochondria import most of their lipids, chloroplast make most of theirs

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14
Q

genome sizes of mitochondria and chloroplast

A

mitochondria: 6000-300,000bp; average mitochondria genome is ~16,000bp

chloroplast: 70,000-200,000bp; average genome of land plants is ~151,000bp

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15
Q

what is out of phase replication

A

when replication of organelle DNA is not limited to S phase of cell cycle, but instead occurs throughout cell cycle

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16
Q

properties of mitochondrial DNA

A

mitochondria have their own dna and ribosomes

they can make some of their own proteins

still require nuclear dna for other proteins

17
Q

how many proteins does human mt dna encode

18
Q

how many mtDNA human mitochondrion contains

A

5, each is about 16,569bp

they encode for:
- 2 rRNA molecules
- 22 tRNA molecules
- 13 polypeptides

19
Q

what are the 13 polypeptides encoded in mt used for

A

to build several protein complexes embedded in inner mitochondrial membrane

7 subunits to make mitochondrial NADH dehydrogenase

3 subunits of cytochrome c oxidase

2 subunits of ATP synthase

cytochrome b

20
Q

special features of human mitochondrial genome

A

dense gene packing: nearly every nucleotide part of coding sequence > little or no regulatory elements

relaxed codon usage: only 22 tRNAs required for mitochondria

variant genetic code: some codons have different meanings from those of the same codons in other genomes

21
Q

examples of mt-linked diseases

A

Leber’s hereditary optic neuropathy: caused by mutations to genes encoding units of complex I

ragged muscle fibers: mutations of lysine tRNA

Kaerns-Sayre syndrome: several large deletions in mtDNA

22
Q

what happens to old mitochondria

A

mt numbers controlled by autophagy

double membrane wraps around mitochondrion > form autophagosome > fuses with lysosome > degradation

23
Q

do plastids have their own dna

A

they have their own dna which is a reduced “genome” derived from cynaobacterial ancestor that was captured early in evolution of the eukaryotic cell

24
Q

properties of chloroplast genome

A

circular DNA of 70,000-200,000bp

about 120 genes encoded

60 genes involved in rna transcription and translation

20 genes encode subunits of chloroplast photosynthesis ETC and F0F1 ATPase complexes

40 genes encode proteins of unknown functions

25
Q

how are chloroplasts inherited

A

maternally inherited in most plants

pollen grains (male reproductive cells) only contribute genetic information contained in nucleus but not in chloroplast to zygote

26
Q

where did mitochondria and chloroplasts come from

A

mitochondria of eukaryotes evolved from aerobic bacteria (rickettsias) living within their host cell

chloroplasts of eukaryotes evolved from endosymbiotic cyanobacteria (autotrophic prokaryotes)

27
Q

properties of rickettsias

A

almost all are obligate intracellular parasites

rickettsia prowazekii causes typhus fever when transmitted to humans by lice

28
Q

properties of cyanobacteria (blue-green algae)

A

photosynthetic prokaryotes

use chlorophyll a

use water as source of electrons to reduce CO2 to carbohydrate

29
Q

why is mitochondrial dna used for evolutionary trees

A

have their own genome

present in large numbers in each cell > fewer samples required

have higher rate of substitution than nuclear dna > easier to resolve differences between closely related individuals

inherited only from mother > allow direct tracing of genetic line

do not undergo recombination

30
Q

which bcl-2 family proteins are anti and pro apoptosis

A

anti-apoptotic: bcl-2 and bcl-XL

pro-apoptotic: Bad and Bax

31
Q

how does bcl-2 family help in apoptosis

A

pro-apoptotic bcl-2 proteins found in cytosol > act as sensors of cellular damage or stress

cellular stress > relocate to surface of mitochondria where anti-apoptotic proteins located

interaction between the two disrupts normal functions of anti-apoptotic protein > formation of pores > release of cytochrome c and other pro-apoptotic molecules from inter membrane space

formation of apoptosome > activation of caspase 9 and then 3 > activation of caspase cascade > digest and cause fragmentation of proteins > cell death

32
Q

how are new mitochondria made

A

cells cannot make mitochondria from scratch

mitochondria replicate like bacteria cells: divide by fission when grown into a certain size)