The cell - WK3.docx

The cell – Metabolic Pathway and energy conversion Metabolic Organelles: Specialized compartments where many metabolic activities take place Mitochondria and Chloroplast are devoted to energy metabolism and ATP production. Overall Mitochondrion and Chloroplasts Mitochondrion generate energy from l...

The cell – Metabolic Pathway and energy conversion Metabolic Organelles: Specialized compartments where many metabolic activities take place Mitochondria and Chloroplast are devoted to energy metabolism and ATP production. Overall Mitochondrion and Chloroplasts Mitochondrion generate energy from lipid to carbohydrate breakdown Chloroplasts use energy captured by sunlight to generate energy ATP and the reducing power needed to synthesize carbohydrates CO2 and H2O Grow and divide in a coordinated process that requires the contribution of two separate genetic systems Most of the proteins in these organelles are encoded by nuclear DNA Some organelle proteins and RNAs are encoded by the organelle DNA Human mitochondrial genome contains about 16,500 nucleotides and encodes 2 ribosomal RNAs, 22 transfer RNAs, and 13 different polypeptide chains. Chloroplast genomes are about 10 times larger and contain ~120 genes. Phylogenetic tree of the evolution of mitochondria and Chloroplasts Properties and Functions of Chloroplasts: Found in plant cells Comparable in size of whole bacterial cell Provides energy by converting solar energy into chemical energy Generates ATP to convert CO2 to sugar Electron-transport processes occurs in thylakoid membrane Stroma is internal Space enclosed by membranes CHO, along with other chloroplast products, exported to cell cytosol Energy Conversion in Mitochondria and chloroplast ATP is generated from chemical energy or sunlight Two processes primarily responsible for the conversion Aerobic oxidation (aerobic respiration), conducted in mitochondria. Photosynthesis conducted in chloroplasts of plants. Glycolysis and the citric acid cycle are also important direct and indirect sources of ATP production Both organelles contain two Internal compartments Mitochondrial oxidation begins when large amounts of acetyl CoA are produced in the matrix space from fatty acids and pyruvate The citric acid cycle (TCA / Kreb cycle) oxidizes the acetyl group on acetyl CoA to generate NADH and FADH2 for the respiratory chain Electrons are transferred from NADH to oxygen through 3 respiratory enzyme complexes Energy released by the passage of electrons along the respiratory chain is stored as an electrochemical proton gradient across the inner membrane A chemiosmotic process converts oxidation energy into ATP on the inner mitochondrial membrane The rapid conversion of ADP to ATP in mitochondria maintains a high ratio of ATP to ADP in cells Aerobic Oxidation and photosynthesis: Despite the diversity of life on the planet, many of the basic structures and life processes are just variations on common theme. The two most important energy reactions in eukaryotes are aerobic oxidation and photosynthesis Glycolysis is catabolic and the Calvin cycle is anabolic The overall reactions are the reverse of each other Properties and functions of the Mitochondria Found in most Eukaryotic cells Comparable in the size of whole bacterial cell Site of aerobic respiration and energy production Surrounded by 2 membranes Matrix containing, Enzymes, DNA, mRNA, ribosomes Mitochondria are inherited only through Mother Grow and divide in a coordinated process that requires the contribution of two separate genetic systems Most of the proteins in these organelles are encoded by nuclear DNA Some organelle proteins and RNAs are encoded by the organelle DNA Human mitochondrial genome contains about 16,500 nucleotides and encodes 2 ribosomal RNAs, 22 transfer RNAs, and 13 different polypeptide chains. Chloroplast genomes are about 10 times larger and contain ~120 genes. Mitochondrial Organisation: Localisation of metabolic functions within the mitochondria Membrane or Compartment Metabolic Functions Outer membrane Phospholipid synthesis Fatty acid desaturation Fatty acid elongation Inner membrane Electron transport Proton translocation for ATP synthesis Oxidative phosphorylation Pyruvate import Fatty acyl CoA import Metabolite transport Matrix Pyruvate oxidation Citric acid cycle ATP synthesis β-oxidation of fats DNA replication RNA synthesis (transcription) Protein synthesis (translation) Matrix: Mitochondrial genetic system DNA and ribosomes Enzymes for central reactions of oxidative metabolism Conversion of pyruvate and fatty acids (imported from cytosol) to Acetyl CoA Oxidation of Acetyl CoA to CO2 via the citric acid cycle (Krebs cycle and tricarboxylic acid (TCA) cycle) Inner Membrane: Principal site for ATP production Surface area substantially increased by folding into cristae >70% protein Electron transport chain and oxidative phosphorylation Metabolite transport proteins Essentially impermeable to most ions and small molecules - maintains proton gradient Outer Membrane: Highly permeable to small molecules Integral transmembrane channel proteins (porins) allow the free diffusion of small molecules (<1000Da) The major permeability barrier between the cytosol and mitochondrial matrix Intermembrane space: Has a similar composition to cell cytosol with respect to ions and small molecules Proton gradient – Acidic, high H+ concentration ATP – universal energy carrier This is where ATP is currency for energy Conversion of ATP – ADP: ATP – derives energetically unfavourable process…why? Cells use energy released this hydrolysis of the terminal phosphoanhydride bond of ATP to power energetically unfavourable processes within cell Proton pump and ATP synthase: Aerobic oxidation of glucose and fatty acids: Glucose is converted to pyruvate and fatty acids to fatty acyl CoA in cytosol Stage 1: Glycolysis Conversion of glucose into fructose 1,6-bisphosphate: Phosphorylation Isomerization Second phosphorylation Stage 2: Glycolysis Cleave of the fructose 1,6 Bisphosphate into two 3 carbon fragments. Step 3: Glycolysis ATP is harvested when 3 carbon fragments are oxidized to pyruvate Glycolysis and Gluconeogenesis Glycolysis and gluconeogenesis are regulated in a reciprocal manner. Regulation involves allosteric activation (+) or inhibition (–) of enzymes that catalyze reactions unique to each pathway. For glycolysis, the key regulatory enzymes are those that catalyze the three irreversible reactions unique to this pathway (blue). For gluconeogenesis, two of the four bypass enzymes (tan) that are unique to this pathway are the main sites of allosteric regulation Fatty acid Oxidation: Cells can take up free fatty acids from their extracellular environment, with the help of specific transporter proteins, and convert them to Fatty acyl CoA in a reaction coupled to ATP hydrolysis to yield AMP + PPi. Link reaction: Pyruvate dehydrogenase catalyses the conversion of pyruvate to Acetyl CoA in the link reaction. Aerobic oxidization of glucose and fatty acid: TCA cycle: Electron Transport Chain: Electron Carriers: Anaerobic oxidation of glucose: Aerobic metabolism: Anaerobic metabolism: Chemiosmosis and energy conversion: One of the processes by which ATP is synthesised. In eukaryotes, it takes place in the mitochondria during cellular respiration, and in the chloroplasts during photosynthesis. In prokaryotes, it occurs in the cell membrane. This process is called chemiosmosis because the chemical ions move from an area of higher concentration to an area of lower concentration across a semipermeable membrane, similar to the movement of water molecules by osmosis. Plant cells – on powerpoint