Cell Biology: Mitochondria And Peroxisomes

Front 1

Fun facts about the mitochondria.

Back 1

1500 proteins in mitochondria, 13 are made by the mitochondria genome.

Functions as more than just for ATP production

Although many diseases are associated with abnormal mitochondrial function, they often represent a downstream effect of the original cause of the disease.

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Structure of mitochondria

Back 2

Outer membrane have non selective porin channels.

Intermembrane space is continuous with intracristal spaces

Cristae: Inner membrane fold extensions. Most cells have flat cristae. Steroid producing cells have tubular cristae.

Inner membrane contains protein complexes that have to do with electron transport chain. Also has cardiolipin, which has four fatty acid chains instead of 2, making the inner membrane more impermeable than usual to ions.

Matrix = intercristal space. Has enzymes of TCA cycle, DNA and ribosomes.

Front 3

Mitochondria and importation of proteins from the cytosol

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Very complex system of transport molecules exists to ferry newly made proteins to their destinations, mostly using protein complexes called TOM (translocase of the outer membrane) and TIM (translocase of inner membrane).

Front 4

Biogenesis of mitochondria

Back 4

Divide by fission. Can fuse with each other to make bigger structures.

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Function of mitochondria

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1. Energy metabolism
2. Steroid hormone biosynthesis
3. Apoptosis (cytochrome c)
4. Calcium sequestration

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Mitochondrial replication

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Only produced from replication of pre-existing mitochondria. Only passed through the mother.

Most lipids required for mitochondrial membranes are synthesized by ER

Front 7

Mitochondria and ischemic/anoxic injury

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O2 supply cut off, no oxidative phosphorylation, decrease ATP.

First, the cell swells because function of Na/K ATPase compromised.

Front 8

Mitochondria and poisoning

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Cyanide poisoning directly affects oxidative phosphorylation pathway, killing cells by shutting down energy production

Front 9

Structure of peroxisomes

Back 9

Diameter ~0.1-1um
Larger in liver and kidney cells
Single membrane
Matrix

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Components of peroxisomes

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Membranes contain: Docking proteins (shuttle in matrix proteins), ABC transporters and other small molecule transport proteins

Cytosolic receptor proteins that traffic into the matrix (Pex5, Pex7)

Soluable enzymes in matrix (catalase, amino acid oxidase, urate oxidase)

Peroxins: from PEX genes, synthesized on free ribosomes.

Front 11

Biogenesis of peroxisomes

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From ER or self replicating.

Matrix proteins: assembled on free ribosomes, shuttled.

Docking proteins and "translocon" assembly in peroxisomal membrane called peroxins.

Some membrane proteins are made on free ribosomes, carried to membrane by specific PEX proteins.

Proteins do not have to unfold to pass through membrane. Different from import to the mitochondria. Closely resembles nuclear import mechanism.

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Functions of peroxisomes

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Degrade fatty acids by B-oxidation (also occurs in mitochondria)

Degrade organic substrates/toxins (urate oxidase catalase, etc.) Turns peroxisomes made by other enzymes into H2O and O2

Synthesis of cholesterol and plasmalogens

Degradation of leukotrienes and D-amino acids

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Peroxisome diseases

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1. Deficient plasmalogens (major protein in myelin) leads to severe neurologic disorders.

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Zellweger syndrome

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"Empty" or no peroxisomes. Damage to brain, liver, kidney. Adrrenoleukodystrophy (progressive degenerative disease involving CNS and adrenal glands)