How Cells Harvest Chemical Energy

Global Athlete Outreach Program US CytoThesis Systems Medicine Center www.CytoThesis.US

US OncoTherapy Systems BioMedicine Group CytoThesis Bioengineering Research Group

General Biology – Dept Mathematics

• Long-distance runners have many slow muscle fibers in their muscles

– Slow muscle fibers break down glucose for ATP production aerobically using oxygen – These muscle cells can sustain repeated, long contractions

– Fast fibers make ATP without oxygen— anaerobically – They can contract quickly and supply energy for short bursts of intense activity

– The white meat consists of fast fibers (less myoglobin) – Wing muscles allow for quick bursts of flight

dark meat

white meat

• Nearly all the cells in our body break down sugars for ATP production • Most cells of most organisms harvest energy aerobically, like slow muscle fibers

– The aerobic harvesting of energy from sugar is called cellular respiration

– Cellular respiration yields CO2, H2O, and a large amount of ATP

• Breathing and cellular respiration are closely related

BREATHING O2 CO2

Lungs

CO2 Bloodstream O2

Muscle cells carrying out

CELLULAR RESPIRATION

Sugar + O2  ATP + CO2 + H2O Figure 6.1

• Cellular respiration breaks down glucose molecules and banks their energy in ATP

– The process uses O2 and releases CO2 and H2O

Glucose Oxygen gas Carbon Water Energy dioxide

Figure 6.2A

Energy released Energy released Gasoline energy from glucose from glucose converted to (as heat and light) banked in ATP movement 100% heat

About 40% 25% Burning glucose “Burning” glucose Burning gasoline in an experiment in cellular respiration in an auto engine

Figure 6.2B

• ATP powers almost all cell and body activities

Table 6.3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings BASIC MECHANISMS OF ENERGY RELEASE AND STORAGE 6.4 Cells tap energy from electrons transferred from organic fuels to oxygen

• Glucose gives up energy as it is oxidized

Loss of hydrogen atoms

Energy

Glucose Gain of hydrogen atoms

Figure 6.4

• 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, and the addition of electrons to another substance is called reduction • Enzymes remove electrons from glucose molecules and transfer them to a coenzyme Figure 6.5

OXIDATION

Dehydrogenase and NAD+

NAD+: nicotinamide adenine dinucleotide

REDUCTION

addition of electrons

Figure 6.5

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 6.6 Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen • NADH delivers electrons to a series of electron carriers in an electron transport chain – As electrons move from carrier to carrier, their energy is released in small quantities

En ergy Each carrier has a greater av rele ailab ased - le fo and affinity for e than its uphill r ma now king neighbor. ATP

E LEC TRO ele N CA ctro RR Electron flow n tra IERS nsp of t ort c he hain Figure 6.6

Energy released as heat and light

Figure 6.6B

High H+ concentration • Cells use the energy ATP synthase uses gradient released by “falling” energy to make ATP electrons to pump H+ Membrane

ions across a membrane Electron transport – The energy of the chain

gradient is harnessed ATP to make ATP by the synthase process of chemiosmosis Energy from Low H+ concentration

Figure 6.7A

Organic molecule (substrate) – This process is called Adenosine substrate-level

phosphorylation New organic molecule (product)

Figure 6.7B

• Cellular respiration oxidizes sugar and produces ATP in three main stages

– Glycolysis occurs in the cytoplasm – The Krebs cycle and the electron transport chain occur in the mitochondria

High-energy electrons carried by NADH

GLYCOLYSIS KREBS ELECTRON TRANSPORT CHAIN Glucose Pyruvic CYCLE acid AND CHEMIOSMOSIS

Cytoplasmic fluid Mitochondrion

Figure 6.8

Glucose Pyruvic acid

Figure 6.9A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings PREPARATORY Steps 1 – 3 A fuel Glucose PHASE molecule is energized, Step (energy investment) • Details of using ATP. 1 Glucose-6-phosphate glycolysis 2 Fructose-6-phosphate

Fructose-1,6-diphosphate Step 4 A six-carbon 4 intermediate splits into two three-carbon Glyceraldehyde-3-phosphate intermediates. (G3P)

5 ENERGY PAYOFF Step 5 A redox PHASE reaction generates NADH. 1,3-Diphosphoglyceric acid (2 molecules) 6

Steps 6 – 9 ATP 3-Phosphoglyceric acid and pyruvic acid 7 (2 molecules) are produced. 2-Phosphoglyceric acid 8 (2 molecules)

2-Phosphoglyceric acid (2 molecules)

• Each pyruvic acid molecule is broken down to

form CO2 and a two-carbon acetyl group, which enters the Krebs cycle

Pyruvic Acetyl CoA acid (acetyl coenzyme A)

CO2 Figure 6.10

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 6.11 The Krebs cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules • The Krebs cycle is a Acetyl CoA series of reactions in which enzymes strip away electrons and + H from each acetyl KREBS 2 CO group CYCLE 2

FADH2 : flavin adenine dinucleotide -reduced FAD: flavin adenine dinucleotide -oxidized Figure 6.11A

Citric acid

5 CO2 leaves cycle KREBS 2 CYCLE

Malic acid

4 Alpha-ketoglutaric acid 3 CO2 leaves cycle Succinic acid

Step 1 Steps 2 and 3 Steps 4 and 5

Acetyl CoA stokes NADH, ATP, and CO2 are generated Redox reactions generate FADH2 the furnace during redox reactions. and NADH.

Figure 6.11B

• The electrons from NADH and FADH2 travel down the electron transport chain to oxygen • Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes • In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP

Protein complex

Intermembrane Electron space carrier

Inner mitochondrial membrane

Electron flow

Mitochondrial matrix

ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Figure 6.12

cyanide ， rotenone oligomycin carbon monoxide

ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.13

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 6.14 Review: Each molecule of glucose yields many molecules of ATP • For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules

Cytoplasmic Mitochondrion fluid Electron shuttle across membranes KREBS GLYCOLYSIS 2 KREBS CYCLEELECTRON 2 Acetyl Glucose Pyruvic CYCLE TRANSPORT CHAIN CoA AND CHEMIOSMOSIS acid

by substrate-level used for shuttling electrons by substrate-level by chemiosmotic phosphorylation from NADH made in glycolysis phosphorylation phosphorylation

Maximum per glucose: Figure 6.14

• Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP

– But a cell must have a way of replenishing NAD+

converted to CO2 and ethanol – This recycles NAD+ to keep glycolysis working

released

GLYCOLYSIS

2 Pyruvic 2 Ethanol Glucose acid

Figure 6.15A Figure 6.15C

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • In lactic acid fermentation pyruvic acid is converted to lactic acid – As in alcoholic fermentation, NAD+ is recycled • Lactic acid fermentation is used to make cheese and yogurt

GLYCOLYSIS

2 Pyruvic 2 Lactic acid acid Glucose

Figure 6.15B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS 6.16 Cells use many kinds of organic molecules as fuel for cellular respiration • Polysaccharides can be hydrolyzed to monosaccharides and then converted to glucose for glycolysis • Proteins can be digested to amino acids, which are chemically altered and then used in the Krebs cycle • Fats are broken up and fed into glycolysis and the Krebs cycle

Food, such as peanuts

Polysaccharides Fats Proteins

Sugars Glycerol Fatty acids Amino acids Amino groups

Pyruvic ELECTRON Glucose G3P Acetyl KREBS acid TRANSPORT CHAIN CoA CYCLE AND CHEMIOSMOSIS GLYCOLYSIS

• In addition to energy, cells need raw materials for growth and repair

– Some are obtained directly from food – Others are made from intermediates in glycolysis and the Krebs cycle • Biosynthesis consumes ATP

ATP needed to drive biosynthesis

GLUCOSE SYNTHESIS KREBS Acetyl Pyruvic G3P Glucose CYCLE CoA acid

Amino groups Amino acids Fatty acids Glycerol Sugars

Proteins Fats Polyscaccharides

Cells, tissues, organisms

• All organisms have the ability to harvest energy from organic molecules

– Plants, but not animals, can also make these molecules from inorganic sources by the process of photosynthesis

Figure 6.18