Lecture 15 - Mitochondria and peroxisomes Flashcards
Mitochondria (5)
An organelle found in large numbers in most cells, in which the biochemical processes of respiration and energy production occur. It has a double membrane; the inner part being folded inwards to form layers (cristae).
Rod shaped.
Diameter: 0.1 - 0.5 um.
Length: 1 -2 um.
Inner membrane contains proteins that transport electrons, and protein channels associated with ATP synthase enzyme that allow protons to diffuse through them.
Mitochondrial matrix (3)
The part of the mitochondria enclosed by the inner mitochondrial membrane which contains enzymes for the Krebs cycle and the link reaction.
e.g. Coenzymes NAD/FAD, Oxaloacetate.
Contains DNA and ribosomes.
Mitochondria - Outer membrane (2)
Separates the contents of the mitochondrion from the rest of the cell.
Ideal conditions for aerobic respiration.
Contains proteins, which form channels or carriers that allow the passage of molecules, such as pyruvate, into the mitochondrion.
Mitochondria - Inner membrane (3)
The inner most of the two mitochondrial membranes. Seperates the mitochondrial matrix from the intermembrane space. It is the site where the electron transport chain takes place involved in the final stage of aerobic respiration, oxidative phosphorylation.
The lipid bilayer is less permeable to small ions such as hydrogen ions (protons) than is the outer membrane.
The folds, cristae, give a large surface area for the electron carriers and ATP synthase enzymes embedded in them.
Mitochondria - Intermembrane space (2)
The intermembrane space between the outer and inner layers of the mitochondrial envelope is also involved in oxidative phosphorylation.
The inner membrane is in close contact with the mitochondrial matrix, so the molecules of reduced NAD and FAD can easily deliver hydrogens to the electron transport chains.
Mitochondrial morphology changes during… (4)
- Apoptosis
- Ca2+ transfer
- Cell cycle
- Nutrient starvation - induces mitochondrial tubulation.
Production of mitochondrial proteins by two separate genetic systems (2)
1) Genomic DNA (in nucleus) –> RNA –> leaves cytosol –> precursor protein –> imported protein in the mitochondria.
2) Organelle DNA –> RNA –> PS in organelle.
Mitochondria contain their own DNA (8)
mtDNA.
Located in the nucleus.
Chromosomes are circular.
Genes are inherited cytoplasmically from the mother.
Contains their own ribosomes.
16,569 base pairs that encoded 2 rRNAs, 22 tRNAs and 50 proteins.
Mitochondrial proteins are encoded in the nucleus, translated in the cytoplasm and imported into the mitochondria.
Mitochondrial genetic code differs from standard nuclear code.
e.g. UGA = Stop codon = Tryptophan in mitochondria.
e.g. AGA/AGG = Arginine = Stop in mitochondria.
Endosymbiosis theory - CHECK DIAGRAM
The endosymbiotic theory describes how a large host cell and ingested bacteria could easily become dependent on one another for survival, resulting in a permanent relationship. Over millions of years of evolution, mitochondria and chloroplasts have become more specialised and today they cannot live outside the cell.
Functions of mitochondria (6)
Forming acetyl CoA –> Breakdown of fatty acids. –> Decarboxylation.
Citric acid cycle –> ATP generation and metabolic intermediates for anabolic pathways.
Oxidative phosphorylation –> Formation of ATP and water.
Thermogenesis –> generation of heat.
Apoptosis (programmed cell death)
ATP-Generating metabolism in mitochondria (5)
Pyruvate and fatty acids into Acetyl CoA.
Acetyl CoA metabolised by the citric acid cycle.
Produces NADH (and FADH2).
During oxidative phosphorylation, high-energy electrons donated by NADH (and FADH2) are then passed along the ETC in the inner membrane.
Generates a proton gradient, which is used to drive the production of ATP by ATP synthase.
Localisation of mitochondria near sites of high ATP utilisation (4)
Cardiac muscle cell - near contractile apparatus - ATP hydrolysis provides energy for contraction.
Sperm - located in tail, wrapped around motile flagellum. ATP is required.
Beriberi (4)
Neurologic and cardiovascular disorder.
Caused by a dietary deficiency of thiamine (vitamin B1).
Thiamine pyrophosphate is a prosthetic group for two mitochondrial enzymes, pyruvate dehydrogenase and α-ketoglutarate dehydrogenase.
Patients have higher serum levels of these enzymes’ substrates (pyruvate and α-ketoglutarate).
Beriberi - Symptoms (5)
Damage to the peripheral nervous system. Pain in the limbs. Weakness of the musculature. Distorted skin sensation. The heart may be enlarged and the cardiac output inadequate.
Peroxisomes (10)
Small membrane-enclosed organelle that contains enzymes that degrade lipids and destroy toxins.
0.2 to 1 µm in diameter.
Surrounded by a single membrane – as they are NOT made by endosymbiosis.
Contain no DNA or ribosomes.
Most peroxisomal proteins are encoded in the nucleus, translated in the cytoplasm and then imported. Some originate in the ER.
Carry out oxidative processes.
Reactions produce hydrogen peroxide (H2O2), which is broken down to water by the enzyme catalase.
Important in the metabolism of long-chain fatty acids.
Perform critical steps in the synthesis of certain lipids, e.g. cholesterol, plasmalogens, bile acids.
Breakdown of excess purines (AMP, GMP) to uric acid.
