Presentation on theme: "PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth Edition REECE TAYLOR SIMON DICKEY HOGAN Chapter 6 Lecture by Edward J. Zalisko How."— Presentation transcript:
Activity Running (8–9 mph) Dancing (fast) Bicycling (10 mph) Swimming (2 mph) Walking (4 mph) Walking (3 mph) Dancing (slow) Driving a car Sitting (writing) kcal consumed per hour by a 67.5-kg (150-lb) person* *Not including kcal needed for body maintenance 979 510 490 408 341 245 204 61 28
Cells capture energy from electrons “falling” from organic fuels to oxygen How do your cells extract energy from glucose? The answer involves the transfer of electrons during chemical reactions.
Cells capture energy from electrons “falling” from organic fuels to oxygen During cellular respiration, electrons are transferred from glucose to oxygen and energy is released. Oxygen attracts electrons very strongly. An electron loses potential energy when it is transferred to oxygen.
Cellular respiration is a more controlled descent of electrons and like rolling down an energy hill. Energy is released in small amounts and can be stored in the chemical bonds of ATP.
The movement of electrons from one molecule to another is an oxidation-reduction reaction, or redox reaction. In a redox reaction, the loss of electrons from one substance is called oxidation, the addition of electrons to another substance is called reduction, a molecule is oxidized when it loses one or more electrons, and a molecule is reduced when it gains one or more electrons.
Oxidation States of Carbon - 4 Highest Energy Least Stable +4 Lowest Energy Most Stable In Respiration, Carbon Carbon is Oxidized from its highest energy to a lower one. The energy coming out is eventually trapped and held in the cells as ATP. ATP provides this energy to run all of life’s processes. In Fats, most of the carbon atoms are at the -4 level. In Sugars and starches, they are in the -2 or 0 level.
Cells capture energy from electrons “falling” from organic fuels to oxygen A cellular respiration equation is helpful to show the changes in hydrogen atom distribution. Glucose loses its hydrogen atoms and becomes oxidized to CO 2. Oxygen gains hydrogen atoms and becomes reduced to H 2 O.
NADH delivers electrons to a string of electron carrier molecules, which moves electrons down a hill. These carrier molecules constitute an electron transport chain. At the bottom of the hill is oxygen (1/2 O 2 ), which accepts two electrons, picks up two H +, and becomes reduced to water.
Cellular respiration occurs in three main stages Cellular respiration consists of a sequence of steps that can be divided into three stages. Stage 1: Glycolysis Stage 2: Pyruvate oxidation and the citric acid cycle Stage 3: Oxidative phosphorylation
Cellular respiration occurs in three main stages Stage 1: Glycolysis occurs in the cytosol, begins cellular respiration, and breaks down glucose into two molecules of a three- carbon compound called pyruvate.
Cellular respiration occurs in three main stages Stage 2: Pyruvate oxidation and the citric acid cycle take place in mitochondria, oxidize pyruvate to a two-carbon compound, and supply the third stage with electrons. The cell makes a small amount of ATP during glycolysis and the citric acid cycle.
Cellular respiration occurs in three main stages Stage 3: Oxidative phosphorylation NADH and a related electron carrier, FADH 2, shuttle electrons to an electron transport chain embedded in the inner mitochondrial membrane. Most ATP produced by cellular respiration is generated by oxidative phosphorylation, which uses the energy released by the downhill fall of electrons from NADH and FADH 2 to oxygen to phosphorylate ADP.
Stage 3: Oxidative phosphorylation As the electron transport chain passes electrons down the energy hill, it also pumps hydrogen ions (H + ) across the inner mitochondrial membrane, into the narrow intermembrane space, and produces a concentration gradient of H + across the membrane. In chemiosmosis, the potential energy of this concentration gradient is used to make ATP.
The steps of glycolysis have two main phases. In steps 1–4, the energy investment phase, energy is consumed as two ATP molecules are used to energize a glucose molecule, which is then split into two small sugars. In steps 5–9, the energy payoff phase, two NADH molecules are produced for each initial glucose molecule and four ATP molecules are generated. There is a net gain of two ATP molecules for each glucose molecule that enters glycolysis.
Pyruvate does not enter the citric acid cycle but undergoes some chemical grooming in which a carboxyl group is removed and given off as CO 2, the two-carbon compound remaining is oxidized while a molecule of NAD + is reduced to NADH, and coenzyme A joins with the two-carbon group to form acetyl coenzyme A, abbreviated as acetyl CoA. Then two molecules of acetyl CoA enter the citric acid cycle.
The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH 2 molecules The citric acid cycle is also called the Krebs cycle (after the German- British researcher Hans Krebs, who worked out much of this pathway in the 1930s), completes the oxidation of organic molecules, and generates many NADH and FADH 2 molecules.
The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH 2 molecules During the citric acid cycle the two-carbon group of acetyl CoA is joined to a four-carbon compound, forming citrate, citrate is degraded back to the four-carbon compound, two CO 2 are released, and one ATP, three NADH, and one FADH 2 are produced.
The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH 2 molecules Thus, after glycolysis and the citric acid cycle, the cell has gained 4 ATP, 10 NADH, and 2 FADH 2. To harvest the energy banked in NADH and FADH 2, these molecules must shuttle their high- energy electrons to an electron transport chain.
Most ATP production occurs by oxidative phosphorylation The final stage of cellular respiration is oxidative phosphorylation, which involves electron transport and chemiosmosis and requires an adequate supply of oxygen. The arrangement of electron carriers built into a membrane makes it possible to create an H + concentration gradient across the membrane and then use the energy of that gradient to drive ATP synthesis.
Scientists have discovered heat-producing, calorie-burning brown fat in adults Mitochondria in brown fat can burn fuel and produce heat without making ATP. Ion channels spanning the inner mitochondrial membrane allow H + to flow freely across the membrane and dissipate the H + gradient that the electron transport chain produced, which does not allow ATP synthase to make ATP.
Scientific studies of humans indicate that brown fat may be present in most people and when activated by cold environments, the brown fat of lean individuals is more active.
NADH FADH 2 CO 2 Maximum per glucose: + 2 ATP Glycolysis Glucose 2 Pyruvate Pyruvate Oxidation 2 Acetyl CoA Citric Acid Cycle by substrate-level phosphorylation by oxidative phosphorylation Oxidative Phosphorylation (electron transport and chemiosmosis) C YTOSOL MITOCHONDRION 2 NADH 2 6+ 2 ATP + about 28 ATP About 32 ATP O2O2 H2OH2O
F ERMENTATION : A NAEROBIC H ARVESTING OF E NERGY
Fermentation enables cells to produce ATP without oxygen Your muscle cells and certain bacteria can regenerate NAD + through lactic acid fermentation, in which NADH is oxidized back to NAD + and pyruvate is reduced to lactate.
Fermentation enables cells to produce ATP without oxygen Lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells. The dairy industry uses lactic acid fermentation by bacteria to make cheese and yogurt. Other types of microbial fermentation turn soybeans into soy sauce and cabbage into sauerkraut.
The baking and winemaking industries have used alcohol fermentation for thousands of years. In this process, yeast (single-celled fungi) oxidize NADH back to NAD + and convert pyruvate to CO 2 and ethanol.
Obligate anaerobes require anaerobic conditions, are poisoned by oxygen, and live in stagnant ponds and deep soils. Facultative anaerobes can make ATP by fermentation or oxidative phosphorylation and include yeasts and many bacteria.
Cells use many kinds of organic molecules as fuel for cellular respiration Although glucose is considered to be the primary source of sugar for respiration and fermentation, ATP is generated using carbohydrates, fats, and proteins.
Food, such as peanuts Carbohydrates Fats Proteins Oxidative Phosphorylation SugarsGlycerolFatty acidsAmino acids Amino groups GlucoseG3PPyruvate Glycolysis Acetyl CoA Citric Acid Cycle ATP
Organic molecules from food provide raw materials for biosynthesis A cell must be able to make its own molecules to build its structures and perform its functions. Food provides the raw materials your cells use for biosynthesis, the production of organic molecules, using energy-requiring metabolic pathways.
Organic molecules from food provide raw materials for biosynthesis Metabolic pathways are often regulated by feedback inhibition in which an accumulation of product suppresses the process that produces the product.