Mitochondria

How do catabolic pathways that decompose glucose produce energy?

- By transferring electrons during chemical reactions. - Oxidation of glucose transfers electrons to a lower energy state -> energy is available for ATP synthesis.

Cellular respiration

- CHO + O2 -> CO2 + H20 + Energy (ATP and heat). - breakdown of glucose is exergonic (a positive flow of energy from the system to the surroundings). - Reaction happens spontaneously, without input of energy. - Product stores less energy than the reactant.

What are the catabolic pathways and production of ATP?

- Cells systematically break down complex organic molecules -> work and heat. > Fermentation: partial degradation of sugars, without use of oxygen. > Aerobic respiration: oxygen is consumed along with the organic fuel (most efficient).

Give a comparison between cell respiration and fermentation

- Cellular transpiration harvests much more energy from each sugar molecule than fermentation can. - up to 16 times as much as fermentation does.

What is fermentation

- Enables cells to produce ATP without oxygen. - Consists of Glycolysis plus reactions that regenerate NAD+ by transferring electrons from NADH to Pyruvate. - Alcohol fermentation: Pyruvate -> reduced by NADH to Ethanol. - Lactate fermentation > Pyruvate -> reduced by NADH to Lactate.

Starch

- Energy rich compounds. - Consists of helical amylose *20-30%) and branched amylopectin (70-80%).

Where do mitochondria originate from?

- Eukaryotic cells evolved through serial endosymbiosis - Mitochondria found in eukaryotic cells. - Proposed ancestors of mitochondria were aerobic, heterotrophic prokaryotes.

What are the characteristics of the mitochondria's inner membrane?

- More complex in structure. - Folded into cristae, increased surface, enhanced ability of ATP production. - Two compartments (inter membrane space and mitochondrial matrix). - Permeable only to O2, CO2 and H2O, helps to regulate transfer of metabolites. - Types of proteins: > Perform the redox reactions of oxidative phosphorylation. > ATP synthase. > Specific transport proteins. > Protein import machinery.

Why do mitochondria retain their own genetic systems?

- Nucleus must provide > 90 genes just to maintain organelle's genetic system. - Mitochondria contain genes for proteins whose function in electron transfer demands rapid and direct regulatory control.

What is a mitochondrial genome

- Own genome -> relic of its evolutionary past. - Most of the genes encoding present-day mitochondrial proteins are located in the nucleus. - Extensive transfer of genes from organelle to nuclear DNA during eukaryote evolution. - Proteins are imported into the organelle from the cytosol after synthesised on cytosolic ribosomes. - Organelle DNA transcription, protein synthesis, and DNA replication: in the matrix of mitochondria. - Multiple copies of mitochondrial DNA attached to inner membrane. - Range in size >6-300kb. - Circular molecules. - Organelle DNA molecules double in every cell cycle -> to maintain constant amount of mitochondrial DNA.

What are characteristics of mitochondria?

- Range from 0.5 - 1.5 um. - Cell can have one single large mitochondrion or 100-1000, correlating with level of metabolic activity. - Generate most of cells supply of ATP. - Composed of compartments that carry out specialized functions. - Each membrane is a phospholipid bilayer with a unique collection of proteins. - Intermembrane space and mitochondrial matrix: respiratory enzymes. - Free ribosomes in the mitochondrial matrix. - Circular DNA molecules associated with the inner mitochondrial matrix.

What are the characteristics of the mitochondria's outer membrane?

- Smooth, phospholipids, proteins. - Large number of porins. - Channels for movement: molecules pass through it by diffusion. - Larger proteins: specific signalling sequence to be transported, bind to a protein called translocase (active transport). - Membrane is freely permeable to nutrient molecules, ions, energy molecules like ATP and ADP.

What is inter membrane space?

- Space between outer and inner membrane. - Same composition as the cell's cytoplasm.

What are the stages of cellular respiration?

- The harvesting of energy from glucose by cell respiration is a cumulative function of three metabolic stages. 1. Glycolysis 2. Pyruvate oxidation and the citric acid cycle. 3. Oxidative phosphorylation (electron transport + chemiosmosis). 1. Glycolysis (cytosol!): Glucose -> Pyruvate. 2. Pyruvate -> Acetyl CoA -> Citrate acid cycle. 3. Electron transport chain: H2O! Energy is stored as ATP. INDEPTH ON SLIDE

Transport chains in mitochondria?

- Uncontrolled reaction. > Explosive release of heat and light energy. - Cellular respiration. > Controlled release of energy for synthesis of ATP.

What is mitochondrial matrix?

- Viscous. - Enzymes are important for ATP synthesis, mitochondrial ribosomes, tRNAs and DNA. - Enzymes that catalyse cell respiration steps.

Metabolism in regards to catabolism and anabolism

Catabolism = oxidative, exergonic. - Energy rich -> low energy. > carbohydrates, fats/lipids, proteins -> H2O, CO2, NH3. Anabolism = reductive, endergonic. - Precursors -> macromolecules. - Amino acids, sugars, fatty acids, nitrogenous bases -> carbohydrates, fats, proteins, nucleic acids.