BioC2014 Mitochondria and Chloroplast Ultrastructure Lectures 3 + 4 (PDF)

BIOC2014 MITOCHONDRIA AND CHLOROPLAST ULTRASTRUCTURE DR. BRYAN  ENERGY CONVERSION Mitochondria convert the chemical energy of reduced carbon compounds into ATP. Chloroplasts convert light energy to the energy of reduced carbon compounds. Fundamental to both pr...

BIOC2014 MITOCHONDRIA AND CHLOROPLAST ULTRASTRUCTURE DR. BRYAN  ENERGY CONVERSION Mitochondria convert the chemical energy of reduced carbon compounds into ATP. Chloroplasts convert light energy to the energy of reduced carbon compounds. Fundamental to both processes is an electron transport chain, where energy is passed from compound to compound in coupled oxidation: reduction reactions. 2  MITOCHONDRIA STRUCTURE: Rod-shaped Two membranes (double membrane) - Outer membrane - Inner membrane (folded to form cristae). FUNCTION: “Powerhouse” of the cell. - Organelle where aerobic respiration occurs. It is the site of cellular respiration. - Breaks down glucose to produce ATP. 3  STRUCTURE OF MITOCHONDRIA OUTER MEMBRANE: Contains special pores. Has large aqueous channels made of a protein called porin. - Permeable to most small molecules and ions. INNER MEMBRANE: Specialized highly convoluted membrane that greatly increases surface area. - Impermeable to most small ions and molecules like H+, ATP and ADP. - Specialized transport systems (membrane-transport proteins) are necessary to move ions and molecules like ATP across the membrane. 4 STRUCTURE OF MITOCHONDRIA CONT’D INNER MEMBRANE: This is where you find the electron transport chain (ETC), ATP synthase and transport proteins to allow substances into the matrix. MATRIX (fluid) - which contains enzymes, coenzymes responsible for fatty acid oxidation etc, TCA (Krebs) cycle and DNA - several copies, ribosomes, tRNA. INTERMEMBRANE SPACE- Space between inner and outer membrane. 5 6  MITOCHONDRIA Cells vary in the number of mitochondria they have. More active cells like muscle, liver, kidney and sperm cells have large numbers of mitochondria. More metabolic activity = more energy needed = more mitochondria Present in every cell in the body, except for mature red blood cells. Both plants & animal cells have mitochondria. 7 CHLOROPLASTS Lens-shaped (oval) Found only in plant cells. In the mesophyll cells in the leaves of plants. Member of a group of organelles known as plastids. Contains a green pigment called chlorophyll (chlorophyll a and b) within thylakoids. Chlorophyll is essential for photosynthesis, captures sunlight. 8  CHLOROPLASTS Structure: Double membrane: -Inner/Outer Stroma (fluid) Grana Thylakoids (sacs) Function: Photosynthesis -conversion of light energy to chemical energy stored in the bonds of glucose (sugar). 9 10  CHLOROPLAST STRUCTURE Envelope (Outer membrane) – Semi-porous and is permeable to small molecules and ions, which diffuse easily. Not permeable to large proteins. Contains porins. Inner membrane – less permeable and studded with transport proteins. Regulates passage of materials in and out of the chloroplast. In addition to regulation activity, fatty acids, lipids and carotenoids are synthesized. Both membranes are primarily made of phospholipids and galactolipids. 11  CHLOROPLAST STRUCTURE Grana (thylakoids) – Provide large surface area for light absorption (extensively folded). Contains proteins of ETC, photosynthetic light-capturing systems, ATP synthase. Light dependent stage of photosynthesis Stroma – “Cytosol” of the chloroplast. Contains metabolic enzymes, starch granules, chloroplast DNA and ribosomes. Site for CO2 fixation and where synthesis of sugar, starch, fatty acids and some proteins occur. Enzymes for light independent stage of photosynthesis (Calvin cycle) 12  PHOTOSYNTHESIS Photosynthesis occurs in photo- autotropic organisms like plants. Carbon dioxide (CO2), water (H2O) and sunlight are used to produce oxygen and carbohydrates (with carbon dioxide as the only carbon source). Energy-poor compounds converted to energy-rich compounds. 13  *Key enzyme in Calvin cycle: Rubisco (ribulose-1,5- bisphosphate carboxylase/oxygenase) Responsible for the fixation of carbon derived from atmospheric CO2. Only plants, algae and certain bacteria are capable of conducting photosynthesis. Photosynthesis occurs in two stages: o Light Dependent Reactions o Light Independent Reactions 14  * RuBP- ribulose 1, 5- bisphosphate * G3P- glyceraldehyde 3-phosphate Energy trapped from sunlight by chlorophyll is used to excite electrons in order to produce ATP by photophosphorylation. Starch synthesis occurs within the stroma. 15  MITOCHONDRIA & CHLOROPLAST: ENDOSYMBIOSIS Both are semi-autonomous organelles. They have their own DNA, RNA and are able to conduct protein synthesis. Having similar DNA structure is explained by the theory of endosymbiosis. First proposed by Lynn Margulis in 1960s. States that some of the organelles in eukaryotic cells were once prokaryotic microbes. 16  Endosymbiosis is a mutually beneficial relationship in which one organism inhabits the body of another. 17 SUMMARY: COMPARISON 18 OVERVIEW OF METABOLISM 19  METABOLISM Sum of all the chemical transformations taking place in a cell or organism. Metabolism occurs through a series of enzyme-catalyzed reactions that constitute metabolic pathways. Each step in a metabolic pathway brings about a specific, small chemical change: usually the removal, transfer or addition of a particular atom or functional group. 20  METABOLITES Metabolic intermediates and products of metabolism. Metabolites have various functions: fuel, structure, signalling, stimulatory and inhibitory effects on enzymes, catalytic activity of their own, defence and interactions with other organisms. Categorized as: primary and secondary metabolites 21  METABOLISM Metabolic fuels such as carbohydrates, lipids and proteins are broken down and are built up from smaller units such as glucose, fatty acids and amino acids by several metabolic pathways. The body uses glucose and fatty acids as the primary fuels to obtain energy. Only under dire circumstances, are amino acids used for this purpose. 22 WHAT MOLECULE IS THIS? 23  Adenosine triphosphate (ATP) ATP is the principal energy-carrying molecule; removal of a phosphoryl group to give ADP releases free energy. Universal energy currency for metabolism. Breaking down glucose releases energy, which is captured by the cell in the form of ATP. 24 25  METABOLISM Most pathways can be classified as either: Anabolic (synthetic) Catabolic (degenerative) 26  Catabolic vs Anabolic Pathways Anabolic pathway: Building up of complex molecules from simple ones. eg. the synthesis of a polysaccharide such as glycogen from glucose. Consume energy (endergonic) Catabolic pathway: Breaking down complex molecules such as proteins, polysaccharides and lipids into simpler ones. eg. CO2, ammonia (NH3) and H2O. Release energy (exergonic) 27 28  PHOTOSYNTHESIS VS CELLULAR RESPIRATION Photosynthesis uses energy. Anabolic pathway in which light energy from the Sun is converted to chemical energy. 6 C02 + 6 H2O ----→ C6H12O6 + 6 O2 Cellular respiration: the breakdown of glucose in the presence of oxygen Catabolic pathway used in organisms to produce energy. C6H12O6 + 6 O2 ----→ 6 CO2 + 6 H2O + ENERGY (ATP) Energy released drives anabolic reactions. 29 30 31  CARBOHYDRATE METABOLISM ❑ Primarily glucose -Fructose and galactose enter the pathways at various points. ❑ All cells can utilize glucose for energy production. -Glucose uptake from blood to cells usually mediated by insulin and transporters. ❑ Liver is a central site for carbohydrate metabolism. 32  CARBOHYDRATE METABOLISM Glucose can be obtained from other carbohydrates, glucogenic amino acids and the glycerol portion of lipids. When energy consumed is in surplus, the body converts all the three major nutrients into stored fat. 33 34  GLYCOLYSIS Glycolysis literally means “splitting sugars” and is the process of releasing energy within sugars. Oxidation of glucose to pyruvate in presence of O2 or lactate in absence of O2. Site: cytosol of all cells 35  GLYCOLYSIS ▪ Glucose (six carbon sugar) breaks down in ten steps in glycolysis to give: - 2 molecules of pyruvate (3 carbon sugar) - 2 ATP formed in step 10 and 2 NADH = the energy product of the glycolysis process. NOTE: 2 ATP molecules are used up in steps 1 and 3 are replaced in step 7 of Glycolysis. 36 PHASE 1: ENERGY INVESTMENT (ENERGY UTILIZATION PHASE) 37  PHASE 2: ENERGY PAY-OFF (ENERGY RECOVERY PHASE) 38 39 40 41 42  GLUCONEOGENESIS Synthesis of glucose from non-carbohydrate precursors. Its main function is to supply blood glucose in cases of carbohydrate deficiency (fasting, starvation and low carbohydrate diet). If glycogen stores are depleted, then liver cells synthesize glucose by gluconeogenesis. 43  GLUCONEOGENESIS The brain relies on glucose (120 g/day) as a source of energy, hence glucose must be synthesized from molecules other than carbohydrates. Non-carbohydrate precursors: Lactate, pyruvate, glucogenic amino acids, glycerol and propionate. 44 45 46  CARBOHYDRATE METABOLISM DISORDER Diabetes mellitus is a group of metabolic diseases characterized by elevated levels of glucose in the blood. DM results from defects in: Insulin secretion Insulin action or both Types of DM: Type 1, Type 2, Gestational diabetes and other types. 47  LIPID METABOLISM Lipids are available to the body from three sources: Ingested in the diet Stored in the adipose tissue of the body Synthesized in the liver When glucose levels are low, triglycerides can be converted into acetyl CoA and used to generate ATP through aerobic respiration. 48  LIPID METABOLISM Fats (or triglycerides) within the body are ingested as food or synthesized by adipocytes or hepatocytes from carbohydrate precursors. Oxidation of fatty acids: to generate energy or synthesize new lipid molecules. The main lipids in foods are fats = triglycerides 49  LIPID METABOLISM Pancreatic lipase partially hydrolyses triglycerides to mono- and di-glycerides, glycerol and free fatty acids. This process is called lipolysis which takes place in the cytoplasm. Glycerol and fatty acids are absorbed, taken to the liver for use in the production of energy. Glycerol may be used to produce glucose. 50  LIPOLYSIS Glycerol directly enters the glycolysis pathway as dihydroxyacetone phosphate (DHAP). Lipids are an important source of energy for the human body. Triglycerides yield more than twice the energy per unit mass when compared to carbohydrates and proteins. 1 molecule of a 12-Carbon fatty acid gives 78 ATP total energy versus glucose which gives 32 ATP. 51  LIPOGENESIS On the other hand, when glucose levels are plentiful, the excess acetyl CoA generated by glycolysis can be converted into fatty acids, triglycerides, cholesterol, steroids and bile salts. This process creates fat from the acetyl CoA and takes place in the cytoplasm of adipocytes or hepatocytes. Triglycerides and lipids are stored in adipose tissue until they are needed. 52 53  General Metabolism of Amino Acids Dietary proteins and body proteins are broken down to amino acids (catabolic reaction). In transamination reactions, the amino group of an amino acid is removed to produce the carbon skeleton (keto acid). The amino group is excreted as urea. The carbon skeleton is used for synthesis of non-essential amino acids. It is also used for gluconeogenesis or complete oxidation. Amino acids are used for synthesis of body proteins (anabolic reaction). 54  AMINO ACID DEGRADATION 10–15% of amino acids are broken down to CO2 and H2O and the free energy harvested. The rest enter the TCA cycle in one of two ways: Glucogenic amino acids are degraded to pyruvate or other TCA intermediate that will become glucose. Ketogenic amino acids are degraded to acetyl-CoA or acetoacetate and thus can be made into fatty acids or ketone bodies. 55 56 57  AMINO ACID METABOLISM DISORDERS Phenylketonuria (PKU): absence or deficiency in the hepatic enzyme phenylalanine hydroxylase (PAH). When PAH is deficient, phenylalanine (Phe) accumulates because it cannot be converted to tyrosine. Symptoms: Small head, delayed mental and social skills, seizures and a “musty odour” to the baby’s sweat, skin and urine due to conversion of Phe to phenylacetate (a ketone). Other disorders: Alkaptonuria (black urine) Maple syrup urine disease 58 NUCLEIC ACID METABOLISM 59 60  NUCLEOTIDE METABOLISM Synthesis of Nucleotide: 1. De novo Synthesis (biochemical pathway where nucleotides are synthesized new from simple precursor molecules). 2. Salvage Pathway (recycling bases and nucleosides formed during nucleic acid breakdown) 61 Metabolic Disorders: Nucleotide metabolism Human diseases that involve abnormalities in purine metabolism: Gout- painful form of arthritis. Caused by excess uric acid in the blood and tissues. 62 SUMMARY: Metabolic Pathways of Glucose Name Derivation of Name Function Glycolysis Glyco- glucose Conversion of glucose to pyruvate Lysis - decomposition Gluconeogenesis Gluco – glucose Synthesis of glucose from amino Neo – new acids, pyruvate, lactate and other Genesis - creation non-carbohydrates eg. Glycerol *Not the EXACT REVERSE of Glycolysis Glycogenesis Glyco (gen) – glycogen Synthesis of glycogen from glucose Genesis – creation Glycogenolysis Glycogen – glycogen Breakdown of glycogen to glucose Lysis – decomposition Pentose phosphate Pentose – a five carbon Conversion of glucose to the 5-C pathway sugar Phosphate sugar phosphate 63  Study Check Identify each process: 1) glycolysis 2) glycogenesis 3) glycogenolysis 4) gluconeogenesis A. the synthesis of glucose from non-carbohydrates B. the breakdown of glycogen into glucose C. the oxidation of glucose to two pyruvate D. the synthesis of glycogen from glucose 64  Solution Identify each process. 1) glycolysis 2) glycogenesis 3) glycogenolysis 4) gluconeogenesis A. the synthesis of glucose from noncarbohydrates 4) gluconeogenesis B. the breakdown of glycogen into glucose 3) glycogenolysis C. the oxidation of glucose to two pyruvate 1) glycolysis D. the synthesis of glycogen from glucose 2) glycogenesis 65