Microanatomy: Mitochondria

why do H+ ions go to intermembrane space?

because an electrochemical proton gradient is created across the inner membrane.

how do mitochondria divide

by fission

how are metabolites transported across the relatively impermeable inner mitochondrial membrane

by specific transporter proteins; Symporters and Antiporters

antiporters; examples

carry 2 different solutes in opposite directions. examples: ADP/ATP antiporter moves ADP3- into the more negatively charged matrix and ATP4- into the more positively charged intermembrane space.

Symporters; examples of symporters

carry 2 different solutes in the same direction. examples are pyruvate transporter carries pyruvate into matrix along with H+; phosphate transporter carries Pi- into matrix along with H+

what is caused by primary hyperoxaluria

caused by improper targeting of a peroxisomal enzyme to the mitochondria where it can't carry its normal function. this misdirects the mutated peroxisomal enzyme to the mitochondria

what are heritable metabolic disorders caused by

caused by mutation of mitochondrial or nuclear DNA; mutations of nuclear DNA show Mendelian inheritance

Role of mitochondria in apoptosis

cytochrome c in cytosol binds to a protein called Apaf1. Apaf-1/cytochrome c monomers associate to form a complex called apoptosome (ATP and multiple molecules of inacive enzymes procaspase 9). procaspase autocatalzes into caspase-9 which triggers apoptosis.

what is a way to see the localization of mitochondrial enzymes

cytochrome oxidase, mitochondrial succinate dehydrogenase

where is mitochondrial DNA synthesized

cytosol

where are different chaperones located

cytosol, intermembrane space, matrix

what are examples of chaperones

cytosolic HSP 70 and mitochondrial HSP 70 in matrix

where are mitochondria usually found

found near sites of high ATP utilization

what is in the intermembrane space of the mitochondria

it contains enzymes that use ATP to phosphorylate other nucleotides.

what is something special about the transport of the protein into the intermembrane space

it has a peptidase cleavage site

how does the OXA translocase work

it recognizes a noncleaveable N-terminal signal, and inserts the protein into the inner membrane; -signal sequence anchors the protein in the membrane.

how do mitochondria move long distances? shorter distances? stationary?

long: along microtubules shorter: along microfilaments stationary : in cardiac muscle and in flagellar axoneme.

how are mitochondrial genes inherited

maternally

what has a higher mutation rate, mitochondrial DNA or nuclear DNA

mitochondrial DNA

what are the kinds of cell death mitochondria are involved in

necrotic, apoptic cell death, autophagy

Are H&E stains good to see mitochondria?

not really; they are difficult to see since a lot of mitochondria will cause the cytoplasm to stain eosinophilic with H&E because of high protein content.

where is mitochondrial DNA encoded

nucleus

What is the general morphology of mitochondria?

occupy about 20% of volume in cells; can be spherical to filamentous and long 0.5-1.0 micrometer in diameter and up to 10 micrometers in length; move about cytoplasm, and move long distance along microtubules and short distance along microfilaments .

role of mitochondria in autophagy

occurs during starvation; normal process that occurs in healthy cells

What substrate is used in oxidative phosporylation

pyruvate and fatty acids

how does mitochondria correlate with aging

respiratory enzymes function declines with age, while frequency of certain mutation of mitochondrial DNA increases.

necrosis

response to cell injury or disease; a pathologic form of cell death. occurs when there is insufficient amount of ATP available

What is the best way to see mitochondria?

the best way to see it is through EM, but this is not quickest. usually use iron hematoxylin

What happens to chaperones when protein reaches its final destination

the chaperones dissociate and protein folds into its final conformation

where are metabolite carrier proteins destined for

the inner membrane

what is in the inner membrane of the mitochondria?

the inner membrane is usually folded to form cristae. it is enriched in an unusual lipid called cardiolipin, which makes the membrane highly impermeable to macromolecules and ions unless a transporter protein is present. The inner membrane has three major types of proteins (1. proteins for ETC, 2. enzyme ATP synthase, 3. transport proteins)

What makes up the mitochondria

the mitochondria is a double membrane that has an outer membrane, inner membrane, intermembrane space, and matrix.

what makes up the lipid bilayer?

the outer membrane and the inner membrane make up the lipid bilayer.

What is in the outer membrane of the mitochondria

the outer membrane has pores composed of channel-forming proteins called porin; highly permeable to molecules of 5,000 daltons or less; it also has enzymes involved in lipid synthesis.

what allows cyctochrome c to escape from mitochondrion into cytosol

the transition pore being modified; mitochondrial permeability transition pore.

is there greater "wobble" in the codon-anticodon recognition of mitochondrial tRNAs or in tRNA derived from nuclear genome

there is greater "wobble" in the mitochondrial tRNA because binding specificity is for the first two bases pairs and the third can be any of four which permits fewer tRNA.

Describe heritable metabolic disorders of oxidative phosphorylation

they affect tissues with high energy requirements (nervous system, muscle, liver, kidney)

where are B-Barrels proteins destined for? their properties; example

they are destined for the outer membrane. they have a B signal near their carboxy terminus; they require both TOM and SAM complex an example is porin

Describe the Iron Hematoxylin staining

they are more specialized for staining mitochondria by light microscopy, they stain other cellular components like nuclei

How are mitochondrial proteins synthesized?

they are synthesized on free polysomes in the cytosol, released from the polysome after synthesis has been fully completed, and then imported post-translationally into the mitochondria.

What do chaperone proteins do?

they bind to the protein being transported and keep it in unfolded configuration. Prevent it from folding into mature conformation prematurely. assist in transporting protein across the membrane

properties of metabolite carrier proteins; example

they carry multiple internal signals require both TOM and TIM 22 complexes ex. ATP/ADP antiport is example.

what do symporters act to create

they create a pH gradient

what are some classic qualities of mitochondrial proteins located in the outer mitochondrial membrane

they do not have a signal sequence; they bind to recepter near contact site; insert into membrane (hydrophobicity) and assume final configuration in membrane.

what is required for proteins to go into the mitochondrion

they need both the TOM and TIM 23 complexes. They have a cleavable signal sequence (presequence) and have a matrix signal peptidase cleavage site.

what do the cristae provide

they provide an increased surface area for the reaction that occcurs there.

What is the association between Parkinsonism

they think there is a association between Parkinsonism and a reduced function of respiratory enzyme complex (including cases induced b toxin MPTP)

How is transport mediated ?

translocator complexes TOM Complex TIM 23 Complex TIM 22 complex OXA Complex SAM Complex

what is important in generating heat in newborns and hibernating animals?

uncoupling of Oxidation from ATP Synthesis in mitochondria of brown fat cells.

apoptosis

"programmed cell death"; naturally occuring form of cell death; occurs during embryonic development or in the normal turnover of epithelial cells lining the intestines; involves ATP-dependent steps

Where does the energy used in importing cytosolic proteins into mitochondria come from?

-ATP hydrolysis required for functioning of many chaperone proteins -electrochemical gradient across the inner membrane

Steps in the transport of proteins into the inner membrane

-TOM complex recognizes the cleavable presequence -Protein is partially transported through the TOM and TIM 23 such that the presequence is exposed to matrix. -presequnce is cleaved by signal peptidase, exposing "stop-transfer" signal -Stop transfer signal halts transfre through TIM 23 and anchors the protein in inner membrane -protein completes its passage through TOM

What determines where a protein goes in the mitochondria?

-matrix: proteins with only the presequence are imported into the matrix. -inner membrane: proteins with presequence plus a noncleavable "stop- transfer" sequence are imported into the inner membrane -intermembrane space: proteins with the presequence and a cleavable "stop-transfer" sequence are imported into the intermembrane space

what is the evidence supporting endosymbiotic hypothesis

-mitochondria have their own genome and protein synthetic machinery (bacterial like) -mitochondrial proteins resemble bacterial homologues (superoxide dismutase) -mitochondria are size of bacteria -translation of mitochondrial RNA is sensitive to antibiotics

steps of transport of metabolite carrier proteins

-noncleavable signal sequence is recognized by TOM -Protein passes through TOM in a loop conformation -Chaperone proteins in the intermembrane space guide the protein to TIM 22 -the elctrochemical gradient drives positively charged sequences into inner membrane via TIM 22.

what is oxidative phosphorylation

-process of ATP production in mitochondria; metabolism of pyruvate, fatty acid -generates 30 mlc of ATP

Steps in the transport of proteins to intermembrane space

-protein is transported to the inner membrane as described (TOM and TIM 23) -signal peptidase on the inner membrane cleaves the stop-transfer signal and releases the protein into the intermembrane space.

What are the things that are required to import cytosolic proteins into mitochondria

-signal sequences -translocases -chaperones -energy from one or both of the following sources

steps of the transport of proteins into the matrix

-the TOM complex recognizes the cleavable presequence -Protein is transported through transiently coupled TOM and TIM 23 complexes -presequence is cleaved by a signal peptidase in matrix.

steps for importation of B-barrel proteins to outer membrane

-these proteins have a noncleavable Beta signal at C-terminus -signal recognized by TOM -chaperone proteins in intermembrane space guide protein to SAM -SAM inserts the protein into the outer membrane (after SAM form fully folded protein)

what is in the matrix of the mitochondria?

-they have enzymes of the citric acid cycle (TCA) -DNA that encodes mitochondrial genes -mitochondrial RNA's, rRNA, tRNA, and mRNA -mitochondrial ribosomes -calcium granules (matrix granules) that precipitate after calcium is transported from cytosol.

Where are mitochondrial proteins targeted for?

1. Outer mitochondrial membrane 2. Inner mitochondrial membrane 3. Intermembrane space 4. Matrix

Some of main functions of mitochondria

1. produce ATP (aerobic metabolism via oxidative phosphorylation) 2. Sequester calcium (protect from toxic levels of calcium, release calcium into cytosol where it can act in calcium signaling) 3. play role in cell death (necrosis, apoptosis, autophagy) 4. Generate heat via aerobic metabolism in brown fat cells 5. tissue specific functions (enzymes of urea cycle sequestered in mitochondria)

Describe the steps of oxidative phosphorylation

1. substrate is transported into mitochondria and converted to acetyl CoA in matrix 2. acetyl CoA enters citric acid cycle( which generates NADH, FADH2 which act as electron donors) 3. Electrons enter the ETC composed of protein complexes associated with inner membrane (I, III, IV) 4. as electrons are transferred along the chain, protons are moved from matrix to intermembrane space making a electrochemical proton gradient across inner membrane. 5. ATP is synthesized from ADP and Pi by ATP synthase on the inner membrane, using energy from protons flowing down their electrochemical gradient. 6. ATP is shuttled out of mitochondria and enters the cytosol

What are mitochondrial proteins coded by?

99% of time coded for by nuclear DNA

what are some non-mitochondrial pathways to apoptosis

ATP-independent Caspase dependent, death receptor mediated Cross-talk between death receptor-mediated and mitochondrial pathways.

What is it called when proteins imported from the cytosol lack the cleavable signal sequence, but have noncleavable signals

B-barrel proteins Metabolite carrier proteins

what release cytochrome c

Bcl2 family of proteins; Bax and Bak enhance release and thus stimulate apoptosis.

Role of mitochondria in Necrosis

In necrosis cell damage causes calcium levels in cytosol to rise and then mitochondria take up the calcium and water follows. The mitochondria swells and bursts and releases toxic levels of calcium into cytoplasm. Porins in the outer mitochondrial membrane align with transport proteins and release more calcium into cytosol. Mitochondria also make a lot of free radicals and if they are not eliminated they damage the mitochondria and lead to necrosis.

ruptures the cell membrane; intracellular components are released into extracellular environment where they stimulate inflammatory response.

Necrosis

what are the significant difference between the morphology of apoptosis and necrosis

Necrosis: ruptures the cell membrane; intracellular components are released into extracellular environment where they stimulate inflammatory response. Apoptosis: fragmentation into 'apoptotic bodies' that are phagocytized by macrophages. there is little inflammation.

what are some major differences between nuclear genome and mitochondrial genomes

Nuclear genomes: have introns, 31 tRNAs, transcribed individually, UGA codon for stop codon, only S phase Mitochondrial Genome: few if any intron, 22 tRNA, entire genome is transcribed, UGA codes for tryptophan, oxidative damage is very high and high mutation rate, replicates throughout the cycle

what about OXA translocase?

OXA translocase is involved in proteins that are coded for by the mitochondrial genome and synthesized in the matrix

what happens in the ETC?

The ETC includes respiratory enzyme complexes that transport protons into the intermembrane space when electrons pass through them. Ubiquinone and cytochrome c carry electrons from one complex to the next. Cytochrome c also plays a role in cell death mechanisms.

what is thought to contribute to aging

a gradual decline in mitochondrial function

what is the endosymbiotic hypothesis

a hypothesis that early prokaryotic (bacterium like) cell was internalized by an anaerobic eukaryotic cell as a symbiotic relationship. the prokaryote provided an efficient energy source from oxidative phosphorylation,the eukaryote provided nutrients.

what do antiporters act to create

a voltage gradient

wat are the features that autophagy shares of necrosis and apoptosis

as in necrosis, large vacuoles form as in apoptosis, there can be caspase activation (can also be caspace-independent mechanism) as in apoptosis there is little or no inflammation.