L1 Mitochondrial and Plastid Genomes Flashcards
properties of outer membrane of mitochondria
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
properties of inner membrane of mitochondria
lipid bilayer contains high proportion of phospholipids
higher proportion of proteins embedded in inner membrane than outer
contains many transport proteins
proteins in the inner membrane
NADH dehydrogenase (complex I)
succinate dehydrogenase (complex II)
cytochrome c reductase (complex III)
cytochrome c oxidase (complex IV)
ATP synthase (complex V)
what are plastids
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
different types of plastids
storage plastid: stores fat, oil or starch
chromoplast: stores pigments
chloroplast: carries out photosynthesis
how many chloroplast in a typical plant cell
50
structure of chloroplast
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
developmental process of thylakoid
inner membrane folds inwards > pinches off to form thylakoid vesicles > thylakoid vesicles stick together to form thylakoid membrane
properties of thylakoid membrane
enclose a lumen: system of vesicles
4 types of protein assemblies embedded:
- photosystem I
- photosystem II
- cytochrome b6f complex
- ATP synthase
what does the stroma contain
enzymes needed to carry out the “dark” reactions of photosynthesis
special set of ribosomes, RNAs and chloroplast DNA
which side of polypeptide enters mitochondria membrane first
transit signal sequence at N terminus
how does protein get imported into the mitochondria
continuously through the TIM and TOM complexes, passing through inter membrane space in one motion
difference between chloroplast and mitochondria
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
genome sizes of mitochondria and chloroplast
mitochondria: 6000-300,000bp; average mitochondria genome is ~16,000bp
chloroplast: 70,000-200,000bp; average genome of land plants is ~151,000bp
what is out of phase replication
when replication of organelle DNA is not limited to S phase of cell cycle, but instead occurs throughout cell cycle
properties of mitochondrial DNA
mitochondria have their own dna and ribosomes
they can make some of their own proteins
still require nuclear dna for other proteins
how many proteins does human mt dna encode
13
how many mtDNA human mitochondrion contains
5, each is about 16,569bp
they encode for:
- 2 rRNA molecules
- 22 tRNA molecules
- 13 polypeptides
what are the 13 polypeptides encoded in mt used for
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
special features of human mitochondrial genome
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
examples of mt-linked diseases
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
what happens to old mitochondria
mt numbers controlled by autophagy
double membrane wraps around mitochondrion > form autophagosome > fuses with lysosome > degradation
do plastids have their own dna
they have their own dna which is a reduced “genome” derived from cynaobacterial ancestor that was captured early in evolution of the eukaryotic cell
properties of chloroplast genome
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
how are chloroplasts inherited
maternally inherited in most plants
pollen grains (male reproductive cells) only contribute genetic information contained in nucleus but not in chloroplast to zygote
where did mitochondria and chloroplasts come from
mitochondria of eukaryotes evolved from aerobic bacteria (rickettsias) living within their host cell
chloroplasts of eukaryotes evolved from endosymbiotic cyanobacteria (autotrophic prokaryotes)
properties of rickettsias
almost all are obligate intracellular parasites
rickettsia prowazekii causes typhus fever when transmitted to humans by lice
properties of cyanobacteria (blue-green algae)
photosynthetic prokaryotes
use chlorophyll a
use water as source of electrons to reduce CO2 to carbohydrate
why is mitochondrial dna used for evolutionary trees
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
which bcl-2 family proteins are anti and pro apoptosis
anti-apoptotic: bcl-2 and bcl-XL
pro-apoptotic: Bad and Bax
how does bcl-2 family help in apoptosis
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
how are new mitochondria made
cells cannot make mitochondria from scratch
mitochondria replicate like bacteria cells: divide by fission when grown into a certain size)
