Cool Fires Attract Mates and Meals Fireflies use

Cool “Fires” Attract Mates and Meals • Fireflies use light to signal to potential mates • attract males of other species — as meals • luciferin-luciferase system Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Energy and cells • What is energy? Why do we need it? • How do chemical reactions use or produce energy? • How does ATP transfer energy? • How do enzymes affect rates of chemical reactions?

• Energy is the capacity to perform work

Chemical energy is due to the arrangement of atoms in molecules Rearrangement of atoms will either store or release energy chemical reaction = rearrangement of atoms Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Potential energy of molecules – Endergonic reactions absorb energy and yield products rich in potential energy Products Amount of energy INPUT Reactants Figure 5. 3 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Potential energy of molecules – Exergonic reactions release energy and yield products that contain less potential energy than their reactants Reactants Amount of energy OUTPUT Products Figure 5. 3 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Energy content of common chemicals (foods) Energy used in activities

ATP shuttles chemical energy within the cell • In cellular respiration, some energy is stored in ATP molecules • ATP powers nearly all forms of cellular work • ATP is key to energy coupling Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• This reaction supplies energy for cellular work: Phosphate groups Adenine Hydrolysis Energy Ribose Adenosine triphosphate Adenosine diphosphate (ADP) Figure 5. 4 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Fig. 5. 8

How do enzymes work? • For a chemical reaction to begin, reactants must absorb some energy – energy of activation (EA) = energy barrier Enzymes lower energy barriers Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• enzymes can decrease the energy barrier Enzyme EA barrier Reactants 1 Products Figure 5. 5 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2

• enzyme is unchanged and can repeat the Glucose process Enzyme (sucrase) Fructose 4 Active site Substrate (sucrose) 1 Enzyme available with empty active site Products are released 3 A specific enzyme catalyzes each cellular reaction Substrate is converted to products Figure 5. 6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 Substrate binds to enzyme with induced fit

The cellular environment affects enzyme activity • Enzyme activity is influenced by – temperature – salt concentration – p. H • Reaction rate is affected by amount of substrate • Allosteric regulation by other factors Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Some enzymes require nonprotein cofactors Ex. zinc, iron coenzymes = cofactors that are organic molecules Ex. vitamins Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

A. Cellular respiration 1. Glycolysis 1. Kreb cycle 1. Electron transport chain 2. B. Fermentation

• Cellular respiration breaks down glucose molecules and banks their energy in ATP – uses O 2 and releases CO 2 and H 2 O Glucose Oxygen gas Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Carbon dioxide Water Energy

Redox reactions are linked oxidations and reductions • Glucose gives up energy as it is oxidized oxidation = loss of H Oxygen is reduced (gains H) Loss of hydrogen atoms Energy Glucose Gain of hydrogen atoms Figure 6. 4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS Glucose Pyruvic acid Cytoplasmic fluid Figure 6. 8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion

Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid Glucose Figure 6. 9 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvic acid

Pyruvic acid is chemically groomed for the Kreb cycle • Each pyruvic acid molecule is broken down to form CO 2 and a two-carbon acetyl group, which enters the Kreb cycle Pyruvic acid Figure 6. 10 Acetyl Co. A (acetyl coenzyme A) CO 2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Kreb cycle completes the oxidation of organic fuel Acetyl Co. A • enzymes strip away electrons and H+ from each acetyl group, generating many NADH and FADH 2 molecules KRES CYCLE Figure 6. 11 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 CO 2

• Electron Transport System and chemiosmosis in the mitochondrion Protein complex Intermembrane space Electron carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN Figure 6. 12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings ATP SYNTHASE

cell outer membrane inner membrane mitochondrion

glycolysis inner membrane outer membrane H+ + H H+ H+ + H electron transport chain Krebs cycle + H H+ e. O 2 outer compartment H 2 O inner compartment H+ + H

: Certain poisons interrupt critical events in cellular respiration Rotenone Figure 6. 13 Cyanide, carbon monoxide ELECTRON TRANSPORT CHAIN Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Oligomycin ATP SYNTHASE

• An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS Glucose Pyruvic acid Cytoplasmic fluid Figure 6. 8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion

Fermentation is an anaerobic alternative to aerobic respiration • Without oxygen, cells can use glycolysis alone to produce small amounts of ATP – But a cell must replenish NAD+ Glucose Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvic acid

• In alcoholic fermentation, pyruvic acid is converted to CO 2 and ethanol – This recycles NAD+ to keep glycolysis working FERMENTATION GLYCOLYSIS released 2 Pyruvic Glucose acid 2 Ethanol Figure 6. 15 C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• In lactic acid fermentation, pyruvic acid is converted to lactic acid – NAD+ is recycled • Produces cheese and yogurt GLYCOLYSIS 2 Pyruvic Glucose Figure 6. 15 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings acid 2 Lactic acid

Cells use many kinds of organic molecules as fuel for cellular respiration • Polysaccharides glucose for glycolysis • Proteins • Fats monosaccharides amino acids acetyl-Co A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Krebs cycle

• Pathways of molecular breakdown Food, such as peanuts Polysaccharides Fats Proteins Sugars Glycerol Fatty acids Amino groups Glucose G 3 P Pyruvic acid Acetyl Co. A GLYCOLYSIS Figure 6. 16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS

Food molecules provide raw materials for biosynthesis • cells need raw materials for growth and repair – Some directly from food – Others made from intermediates in glycolysis and the Krebs cycle • Biosynthesis uses ATP (endergonic) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Biosynthesis of macromolecules from intermediates in cellular respiration ATP needed to drive biosynthesis KREBS CYCLE GLUCOSE SYNTHESIS Acetyl Co. A Pyruvic acid G 3 P Glucose Amino groups Amino acids Fatty acids Glycerol Sugars Proteins Fats Polyscaccharides Cells, tissues, organisms Figure 6. 17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings