L1 Mitochondrial and Plastid Genomes

Question 1

properties of outer membrane of mitochondria

Answer 1

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

Question 2

properties of inner membrane of mitochondria

Answer 2

lipid bilayer contains high proportion of phospholipids

higher proportion of proteins embedded in inner membrane than outer

contains many transport proteins

Question 3

proteins in the inner membrane

Answer 3

NADH dehydrogenase (complex I)

succinate dehydrogenase (complex II)

cytochrome c reductase (complex III)

cytochrome c oxidase (complex IV)

ATP synthase (complex V)

Question 4

what are plastids

Answer 4

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

Question 5

different types of plastids

Answer 5

storage plastid: stores fat, oil or starch

chromoplast: stores pigments

chloroplast: carries out photosynthesis

Question 6

how many chloroplast in a typical plant cell

Answer 6

50

Question 7

structure of chloroplast

Answer 7

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

Question 8

developmental process of thylakoid

Answer 8

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

Question 9

properties of thylakoid membrane

Answer 9

enclose a lumen: system of vesicles

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

Question 10

what does the stroma contain

Answer 10

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

special set of ribosomes, RNAs and chloroplast DNA

Question 11

which side of polypeptide enters mitochondria membrane first

Answer 11

transit signal sequence at N terminus

Question 12

how does protein get imported into the mitochondria

Answer 12

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

Question 13

difference between chloroplast and mitochondria

Answer 13

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

Question 14

genome sizes of mitochondria and chloroplast

Answer 14

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

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

Question 15

what is out of phase replication

Answer 15

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

Question 16

properties of mitochondrial DNA

Answer 16

mitochondria have their own dna and ribosomes

they can make some of their own proteins

still require nuclear dna for other proteins

Question 17

how many proteins does human mt dna encode

Answer 17

13

Question 18

how many mtDNA human mitochondrion contains

Answer 18

5, each is about 16,569bp

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

Question 19

what are the 13 polypeptides encoded in mt used for

Answer 19

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

Question 20

special features of human mitochondrial genome

Answer 20

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

Question 21

examples of mt-linked diseases

Answer 21

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

Question 22

what happens to old mitochondria

Answer 22

mt numbers controlled by autophagy

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

Question 23

do plastids have their own dna

Answer 23

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

Question 24

properties of chloroplast genome

Answer 24

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

Question 25

how are chloroplasts inherited

Answer 25

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

Question 26

where did mitochondria and chloroplasts come from

Answer 26

mitochondria of eukaryotes evolved from aerobic bacteria (rickettsias) living within their host cell chloroplasts of eukaryotes evolved from endosymbiotic cyanobacteria (autotrophic prokaryotes)

Question 27

properties of rickettsias

Answer 27

almost all are obligate intracellular parasites rickettsia prowazekii causes typhus fever when transmitted to humans by lice

Question 28

properties of cyanobacteria (blue-green algae)

Answer 28

photosynthetic prokaryotes use chlorophyll a use water as source of electrons to reduce CO2 to carbohydrate

Question 29

why is mitochondrial dna used for evolutionary trees

Answer 29

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

Question 30

which bcl-2 family proteins are anti and pro apoptosis

Answer 30

anti-apoptotic: bcl-2 and bcl-XL pro-apoptotic: Bad and Bax

Question 31

how does bcl-2 family help in apoptosis

Answer 31

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

Question 32

how are new mitochondria made

Answer 32

cells cannot make mitochondria from scratch mitochondria replicate like bacteria cells: divide by fission when grown into a certain size)