Bioenergetics How Do Organisms Acquire and Use Energy?
Metabolism • All of the chemical reactions that occur in cells. • Organic substances are converted to other organic molecules and energy is transformed. • Energy • Anything that can do work. • Example: move a muscle, make a protein
Laws of Thermodynamics • First Law: • Energy may change forms, but it is neither created nor destroyed. • Second Law: • Energy changes always occur in the direction in which the energy of the universe becomes more disordered.
Entropy • The amount of disorder or randomness in the universe. • Without the input of energy from outside the system, all systems are spontaneously moving closer to equilibrium at all times.
Uphill Struggle For Living Things • Living things must do biological work to keep the forces of the universe from dismantling their highly ordered bodies. • To do this, organisms need a constant supply of energy. • Autotrophs and heterotrophs either produce or obtain energy to overcome this struggle.
Animal Respiration, Like Fire, Is Oxidation • Joseph Priestly • Championed the idea of “phlogistron” • Phlogistron is the substance that flowed into the air when substances were burned.
Animal Respiration, Like Fire, Is Oxidation • Antoine Laurent Lavoisier • Disproved theory of phlogistron. • Hypothesized if burning substance releases phlogistron, then as the substance burns, its weight should decrease. • Found the total weight had increased. • He reasoned burning doesn’t add something to the air, it takes something out of the air. • First to recognize fire and breathing both require oxygen.
Animal Respiration, Like Fire, Is Oxidation • Types of energy: • Kinetic • Energy that is doing work • Potential • Stored or inactive energy
Metabolism is Efficient and Highly Specific • Can’t burn glucose as you would wood. • Need the process to be controlled to minimize the energy loss (entropy). • Also need it to be specific. • Need enzymes.
Metabolism is Efficient and Highly Specific • Enzymes • A class of proteins that catalyze, or speed up, the steps of metabolism • Cannot force a reaction to go in a direction that is not consistent with the laws of thermodynamics
How Do Enzymes Work? • They overcome the activation energy. • Barrier that prevents molecules from undergoing otherwise favorable reactions
Hallmarks of Enzyme-Catalyzed Reactions • Metabolic efficiency: • Cellular metabolism is characterized by metabolic pathways. • Sequences of enzyme-catalyzed reactions in which the product of one reaction serves as the reactant for the next.
Hallmarks of Enzyme-Catalyzed Reactions • Metabolic specificity • A given enzyme only binds to a specific kind of molecule, called its substrate
ATP: Energy Currency of Life • Adenosine Triphosphate: • Assembled by energy-yielding metabolic pathways. • “Used” to drive energy-consuming pathways. • A nucleotide.
Other Nucleotide-Based Compounds Shuttle Hydrogen • These molecules shuttle hydrogen atoms from one place to another and from one compound to another. • NAD+/NADH, • NAD+/FADH2, • NADP+/ NADPH • Play central role in metabolism.
How Do Organisms Use Energy? • Cellular Respiration • Metabolic pathways in which cells harvest the energy from the metabolism of food molecules • Occurs in three stages • Glycolysis • Krebs Cycle • Electron Transport Chain
Glycolysis • Occurs in the cytoplasm • Net reaction: 2 ADP 2 ATP 2 C3H16O3 Pyruvic Acid C6H12O6 Glucose 2 NAD+ 2 NADH
When Oxygen is Limited • Two problems with anaerobic cellular respiration: • 2 ATPs / glucose molecule will not sustain activity for long periods. • In the absence of oxygen, glycolysis converts all of the limited NAD+ to NADH. • With no more available NAD+, glycolysis ceases.
Lactic Acid Fermentation • H atoms are removed from NADH and added to pyruvic acid forming lactic acid. • Regenerates NAD+ in order for glycolysis to continue
With Oxygen Present • Transitional step before Krebs Cycle: • Accomplishes 3 things • 1. Hydrogen atoms removed from pyruvic acid and added to NAD+ making NADH • 2. Carbon atom is removed from pyruvic acid and lost as CO2 • 3. Resulting two-carbon molecule is attached to carrier molecule (coenzyme A) forming acetyl-CoA • Performed by large enzyme in the in mitochondria
Krebs Cycle • Occurs in mitochondria: • Entering cycle: • 1 acetyl-CoA, 3 NAD+, 1 FAD, 1ADP + Pi • Exiting the cycle: • 3 NADH, 1 FADH2, 1 ATP, 2 CO2
Electron Transport Chain • Occurs in mitochondria: • Have cristae • Folds of inner mitochondrial membrane • Contains energy transforming machinery needed to convert the energy stored in NADH and FADH2 to ATP
Electron Transport Chain • Components of the chain are enzymes • Grouped into 4 large complexes • On inner mitochondrial membrane • End products of the chain • Gradient of protons across the inner mitochondrial membrane • water
ATP is Made Using Energy From Proton Gradient • Proton gradient similar to dam • Hold water back until you need it to do work • As water rushes down its gradient toward equilibrium, • Use a coupling mechanism –a waterwheel or turbine-to put that energy to work for you.
ATP is Made Using Energy From Proton Gradient • The basic components of a dam are: • 1. Potential energy in the form of a water gradient • 2. An opening that directs the water flow in a specific path • 3. A coupling mechanism to do the work
ATP is Made Using Energy From Proton Gradient • Synthesis of mitochondria uses same basic components. • Protons moving down their gradient fuels the synthesis of ATP by • Mitochondrial ATP synthase • This mechanism of ATP synthesis is called chemiosmosis.
Net Overall Yield of Cellular Respiration • Net yield of ATP production from one glucose molecule • Glycolysis: 2 ATP • Krebs Cycle: 2 ATP • Electron Transport Chain • Converting the energy stored in NADH and FADH2 to ATP: 32 ATP • Total: 36 ATP
How Do Organisms Acquire Energy? • Only photosynthetic organisms can make organic molecules from sunlight, CO2 and H2O. • Heterotrophic organisms obtain organic molecules by consuming photosynthetic organisms.
Pigments absorb the Energy of Light • Light is a form of energy called electromagnetic radiation. • Occurs in a vast spectrum of size and energy • Shorter wavelength radiation has more energy than long wavelength radiation.
Pigments absorb the Energy of Light • Photosynthetic tissues appear green because they contain pigments. • Molecules that absorb some wavelength of light and reflect others. • Green plants have the pigment chlorophyll • Absorbs red and blue parts of the spectrum and reflects the green wavelength.
Pigments absorb the Energy of Light • If a beam of blue light is aimed at a test tube containing chlorophyll, the solution fluoresces. • Light is briefly absorbed and emitted at a different wavelength.
Photosynthesis • Consists of two types of reactions: • Light-dependent reactions • Produce ATP and NADPH • Light-independent reactions • Also known as the Calvin-Benson Cycle. • Use ATP and NADPH to produce carbohydrates.
Light Reactions Make ATP and NADPH • Chloroplasts • Large, green, membrane-bound organelles. • Site of photosynthesis • Thylakoids • Contain the light-harvesting pigments. • Stroma • Internal space of chloroplast.
Noncyclic vs. Cyclic Phosphorylation • Noncyclic: • Flow of electrons follow a linear noncyclic pathway: • Produce more NADPH than ATP. • Problem: Calvin–Benson cycle requires 3 ATP for every 2 NADPH to make carbohydrate. Light energy 2 H2O + 2 NADP+ + ADP + Phosphate O2 + 2 NADPH + ATP
Noncyclic vs. Cyclic Phosphorylation • Cyclic: • Depending on the need for ATP, electrons can bypass the NADP+ and be passed back to the chlorophyll molecule from which they originally came. • Still creates proton gradient.
Calvin-Benson Cycle • Discovered in late 1940s-1950s • Used paper chromatography and radioactive carbon. • Depicted carbon-fixation in green algae • Sugar-producing process of photosynthesis.
What Do Humans Need to Eat? • Macronutrients supply energy for our metabolism. • Macronutrients: dietary components that are needed in relatively large quantities for proper body function. • Three kinds: • Protein • Fats • Carbohydrates
Proteins • Make up the main structural components of our bodies. • Made of 20 amino acids. • Our body can produce 12 from fats and carbohydrates • The other 8, essential amino acids, have to be obtained from our diet • Dietary proteins that provide all of the essential amino acids in the proper proportions are called complete proteins or high-quality proteins.
Fats • Main structural component of cell membranes • Two groups of essential fats: • Omega-3 and omega-6 fatty acids must be obtained from diet. • Healthiest way to to obtain fat is to avoid foods rich in saturated fat (butter, lard) and cholesterol and concentrate on foods with unsaturated fats (vegetable oils).
Carbohydrates • Main source of calories is most diets. • Not all are equally healthy. • Healthy carbohydrates are those not heavily processed. • Examples: fruits, vegetable, whole grains • Highly processed carbohydrates cause drastic spikes in insulin levels. • Followed by unstable blood glucose levels and sensations of false hunger.
Micronutrients • Include vitamins and minerals. • Needed as cofactors for many enzymes. • In order for enzymes to catalyze cellular reactions. • Serve as building materials for bone and blood. • Required in small amounts. • Crucial for health and well-being.