BSCI 105 – SESSION 3- CLICKER 1: energy available to a cell to do work = free energyENZYMES AND METABOLISM- Metabolism: the sum of all biochemical reactions going on in every cello Anabolic reactions – biosynthetic (building molecules; using energy)o Catabolism reactions – degradative (breaks things down)- Metabolic pathways: reactions that occur one after another in orderly fashion- Metabolism is all about ENERGY- Energy: capacity to do worko Types: Kinetic (being currently used) + potential (stored) energyo Units: kilocalorie (kcal) or joules- 1st Law of Thermodynamicso Energy can be converted from one form to another, but can’t be created or destroyed Conservation of Energy- 2nd Law of Thermodynamicso Entropy in the universe always increaseso Entropy – a measure of disordero Energy used to increase order in the system (to decrease entropy)o Energy made available to do work as order decreases in the system > entropy increases- Energy = “Free Energy”o Energy AVAILABLE to do worko G (Gibbs free energy) T and P constant in a system (system = cell)o G (free energy) = H (enthalpy) – T(temp)S(entropy) G = H – TSo Enthalpy (H) = energy stored in the system Contained in chemical bondso Delta () = “change” G = G(products) – G(reactants)o Positive G Products of the reaction contain MORE free energy than the reactants Endergonic (endothermic) – energy needs to go in Input of energy is required for reaction to occuro Negative G Products of reaction contain LESS free energy than the reactants Exergonic (exothermic) Energy is released that is available to do work Spontaneous- Chemical Equilibriumo Chemical reactions are reversibleo If you know Keq, you can calculate G- Activation Energy (free energy of activation)o Energy required before a chemical reaction will starto In biological systems, enzymes lower the energy of activationo Enzymes DO NOT affect Keq or Go Enzymes speed up reaction Do not change thermodynamics- Enzymeso Biological catalystso Usually proteinso Reactants of enzyme – substrateso Area of interaction with substrates – active siteo Enzyme itself is unchanged after reaction and can be used againo Name tells us what reaction it catalyzes (-ase)- Properties of enzymeso Specificity Due to shape Active site and induced fit- Activity of enzymeso Influenced by: Temperature pH Co-factors (metal ions, coenzymes) Inhibitors (competitive, non-competitive)- Control of enzymeso Allosteric control Allosteric site is where “effector” molecules bind Binding of effector molecule changes the conformation of the enzyme Effector can be activator or inhibitor11/10/10- CLICKER 1: preferred starting point for cellular respiration = GLUCOSE- Metabolic pathwayso How chemical energy is obtained Autotrophs – make their own food Heterotrophs- Harvest energy from electronsGlucose Metabolism – Cellular respiration- Cellular energy currency = ATP (adenosine triphosphate)- Need energy to do work- ATP carries energyo In cells, energy released from hydrolysis of ATP is coupled with a second, endergonic reaction- ATP important in coupled reactions- ATP comes from ADP/ATP cycle; 3 ways to make ATP from ADP:o Substrate level phosphorylation (no oxygen required)o Oxidative phosphorylation (requires oxygen)o Photophosphorylation (only in plants)- Substrate-level phosphorylationo ANAEROBICo Energy released when certain covalent bonds are broken and is coupled with the remaking of ATP from ADP and Pi- Cellular Respirationo Harvest energy to make ATP from complete aerobic breakdown of glucoseo 3 main stages: Glycolysis: glucose pyruvate Kreb’s cycle (citric acid cycle): pyruvate carbon dioxide Electron transport chain (Also extra transition step – links glycolysis to kreb’s cycle)- Pathways:o What steps require energy?o What step is controlled (allosteric)?o What are the redox reactions?o What are the starting points (substrate) and final products?- Glycolysiso Starting point – GLUCOSE Other sugars can enter at other pointso End point – 2 molecules of PYRUVATEo 10 biochemical reactions First 5 are endergonico Takes place in cytosolo DOES NOT REQUIRE OXYGEN!o All enzymes free in cytoplasmo Not associated with any organelles Any cells can do it!o ATP made using SUBSTRATE LEVEL PHOSPHORYLATIONo Downside: at end, <4% of potential energy has been harvested from glucoseo Overall reaction: Glucose + 2 ADP + 2 Pi + 2 NAD + 2 pyruvate + 2 ATP + 2 NADHo Net ATP = 2 ATP (plus 2 pyruvate and 2 NADH)- Gluconeogenesis Reverse Pathwayo Making glucose from pyruvate Fasting, prolonged exerciseo Requires energy (takes 6 ATP molecules)- When pyruvate enterst he mitochondria it is converted into Acetyl CoA for use by the Kreb’s cycleTHE KREBS CYCLE- Fate of pyruvateo Major crossroad in metabolismo If cell needs energy – goes into Krebs cycleo If cell doesn’t need energy – converted into glucose, then glycogeno If cell doesn’t have oxygen – goes into fermentation- Transport of pyruvateo Pyruvate must be actively transported from cytosol into mitochondrial matrix- Conversion of pyruvateo Pyruvate Acetyl Coenzyme A (Acetyl CoA)o 3 step process using a single multi-enzyme complex **Pyruvate dehydrogenase complexo Occurs in mitochondrial matrixo Step 1: oxidation of pyruvate Yields 1 CO2o Step 2: oxidation of 2C fragment acetate Yields 1 NADHo Step 3: conversion of pyruvate- Acetyl CoAo Produced by oxidation of pyruvateo Product of metabolism of: proteins, fats, lipidso Can be used: For fat synthesis For ATP production- Cycleo Yield per turn: 1 ATP, 3 NADH, 1 FADH2, 2 CO2o Recycling- Glycolysis + Krebs cycleo Glucose + 4 ADP + 4 Pi + 10 NAD+ + 2 FAD o 6 CO2 + 4ATP + 10 NADH + 2 FADH2- Enzymeso Many classes of enzymes used in cellular respirationo Kinase – transfers phosphate group between moleculeso Dehydrogenase – oxidizes a molecule (removes hydrogen atom)o Decarboxylase – removes carboxyl group from molecule (makes CO2)o Isomerase – catalyses structural rearrangement of a molecule11/15/10- CLICKER: chemical energy carried by electrons is “harvested” through a series of ______________ reactions: reduction-oxidation- So far:o Started in cytosol with glucoseo Now we have: From glycolysis 2 ATP, 2 NADH From transition – 2 NADH From Krebs – 2 ATP, 6 NADH, 2 FADH2o NADH and FADH2 have
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