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. Even water molecules, which are very polar, cannot cross a lipid bilayer. Water flows through aquaporins, which are specialized channels for water. A simple experiment demonstrates this. If you place an amphibian egg in hypotonic spring water, it does not swell. If you then inject aquaporin mRNA into the egg, the cha... |
permeable membrane across its face; the membrane allows the passage of water molecules but not salt ions. (b) When this tube is immersed in a beaker of distilled water, the salt cannot cross the membrane, but water can. The water entering the tube causes the salt solution to rise in the tube. (c) Water will continue t... |
llular fluid, causing the cell to swell. The pressure of the cytoplasm pushing out against the cell membrane, or hydrostatic pressure, would increase. On the other hand, the osmotic pressure (figure 6.16), defined as the pressure that must be applied to stop the osmotic movement of water across a membrane, would also b... |
membrane firmly against the interior of the cell wall, making the cell rigid. The newer, softer portions of trees and shrubs depend on turgor pressure to maintain their shape, and wilt when they lack sufficient water. Osmosis is the diffusion of water, but not solutes, across a membrane. Chapter 6 Membranes 115 6.4 Bu... |
of a particular kind of cell contains a characteristic battery of receptor types, each for a different kind of molecule. The interior portion of the receptor molecule resembles a hook that is trapped in an indented pit coated with the protein clathrin. The pits act like molecular mousetraps, closing over to form an in... |
which carries the molecules into the cell. Coated pit Target molecule Clathrin Receptor protein Coated vesicle (a) (b) (c) (d) Plasma membrane Secretory product Secretory vesicle Cytoplasm (a) (b) FIGURE 6.19 Exocytosis. (a) Proteins and other molecules are secreted from cells in small packets called vesicles, whose m... |
Sodium-Potassium Pump The use of ATP in active transport may be direct or indirect. Lets first consider how ATP is used directly to move ions against their concentration gradient. More than onethird of all of the energy expended by an animal cell that is not actively dividing is used in the active transport of sodium ... |
ATP and cleaves it into adenosine diphosphate and phosphate (ADP + Pi). ADP is released, but the phosphate group remains bound to the protein. The protein is now phosphorylated. Step 3. The phosphorylation of the protein induces a second conformational change in the protein. This change translocates the three Na+ acro... |
, enabling each carrier to transport as many as 300 Na+ per second. The sodiumpotassium pump appears to be ubiquitous in animal cells, although cells vary widely in the number of pump proteins they contain. Active transport moves a solute across a membrane up its concentration gradient, using protein carriers driven by... |
simultaneously bind to the same transmembrane protein on the outside of the cell, called a symport (figure 6.22). Both are then translocated to the inside of the cell, but in the process Na+ moves down its concentration gradient while the sugar or amino acid moves up its concentration gradient. In effect, the cell use... |
lasm Conformation A Conformation B Conformation A FIGURE 6.23 The proton pump. In this general model of energy-driven proton pumping, the transmembrane protein that acts as a proton pump is driven through a cycle of two conformations: A and B. The cycle A→B→A goes only one way, causing protons to be pumped from the ins... |
are embedded within the plasma membrane have their hydrophobic regions exposed to the hydrophobic interior of the bilayer, and their hydrophilic regions exposed to the cytoplasm or the extracellular fluid. • Membrane proteins can transport materials into or out of the cell, they can mark the identity of the cell, or t... |
ocytosis • Exploration: Active Transport • Active Transport • Active Transport 7 Cell-Cell Interactions Concept Outline 7.1 Cells signal one another with chemicals. Receptor Proteins and Signaling between Cells. Receptor proteins embedded in the plasma membrane change shape when they bind specific signal molecules, tri... |
bacteria and protists lack? Your cells touch and communicate with one another. Sending and receiving a variety of chemical signals, they coordinate their behavior so that your body functions as an integrated whole, rather than as a massive collection of individual cells acting independently. The ability of cells to co... |
teins The characterization of receptor proteins has presented a very difficult technical problem, because of their relative scarcity in the cell. Because these proteins may constitute less than 0.01% of the total mass of protein in a cell, purifying them is analogous to searching for a particular grain of sand in a san... |
important interactions between cells in early development occur by means of direct contact between cell surfaces (figure 7.3a). We’ll examine contact-dependent interactions more closely later in this chapter. Secretory cell Gap junction Adjacent target cells (a) Direct contact (b) Paracrine signaling Hormone secretion... |
is called a chemical synapse. While paracrine signals move through the fluid between cells, neurotransmitters cross the synapse and persist only briefly. We will examine synaptic signaling more fully in chapter 54. Adjacent cells can signal others by direct contact, while nearby cells that are not touching can communi... |
protein Binds signal extracellularly, catalyzes response intracellularly Phosphorylation of protein kinases Seven-pass transmembrane protein with cytoplasmic binding site for G protein Binding of signal to receptor causes GTP to bind a G protein; G protein, cells in the eyes with attached GTP, detaches to deliver the ... |
, in a few instances, suppresses) a particular gene, usually located adjacent to the regulatory site. The lipid-soluble signal molecules that intracellular receptors recognize tend to persist in the blood far longer than water-soluble signals. Most water-soluble hormones break down within minutes, and neurotransmitters... |
, when the brain sends a nerve signal relaxing the smooth muscle cells lining the walls of vertebrate blood vessels, the signal molecule acetylcholine released by the nerve near the muscle does not interact with the muscle cell directly. Instead, it causes nearby epithelial cells to produce NO, which then causes the sm... |
are protein kinases, enzymes that add phosphate groups to proteins. Most enzymic receptors have the same general structure. Each is a singlepass transmembrane protein (the amino acid chain passes through the plasma membrane only once); the portion that binds the signal molecule lies outside the cell, and the portion t... |
protein, causing it to bind GTP. The G protein can now diffuse away from the receptor. The “activated” complex of a G protein with attached GTP is then free to initiate a number of events. However, this activation is short-lived, because GTP has a relatively short life span (seconds to minutes). This elegant arrangeme... |
of single-celled ancestors. Discovery of G Proteins. Martin Rodbell of the National Institute of Environmental Health Sciences and Alfred Gilman of the University of Texas Southwestern Medical Center received the 1994 Nobel Prize for Medicine or Physiology for their work on G proteins. Rodbell and Gilman’s work has pr... |
phosphorylation has on cell function depends on the identity of the cell and the proteins that are phosphorylated. In muscle cells, for example, the α-kinase phosphorylates and thereby activates enzymes that stimulate the breakdown of glycogen into glucose and inhibit the synthesis of glycogen from glucose. Glucose is... |
that relay messages from receptors to target proteins. Signal molecule Cell surface receptor Signal molecule Cell surface receptor Adenylyl cyclase Phospholipase C G protein ATP cAMP G protein Endoplasmic reticulum Inositol trisphosphate intermediary Target protein Cytoplasm Cytoplasm Nucleus Ca++ Nucleus Target prote... |
the signal as it is being relayed to the nucleus. How is the signal amplified? Imagine a relay race where, at the end of each stage, the finishing runner tags five new runners to start the next stage. The number of runners would increase dramatically as the race progresses: 1, then 5, 25, 125, and so on. The same sort... |
to amplify the signal. The Vision Amplification Cascade Let’s trace a protein amplification cascade to see exactly how one works. In vision, a single light-activated rhodopsin (a G-protein-linked receptor) activates hundreds of molecules of the G protein transducin in the first stage of the relay. In the second stage,... |
000 split cGMP molecules, which will then effect a change in the membrane of the rod cell, which will be interpreted by the organism as a visual event. Chapter 7 Cell-Cell Interactions 133 7.4 Cell surface proteins mediate cell-cell interactions. The Expression of Cell Identity With the exception of a few primitive typ... |
, even though they lack a complex immune system. Every cell contains a specific array of marker proteins on its surface. These markers identify each type of cell in a very precise way Light chain chain chain ss ss Heavy chains Cell membrane Constant region Variable region SS Disulfide bond chain chain s s s s s s Light... |
figure 7.17). This allows the sheet of cells to act as a wall within the organ, keeping molecules on one side or the other. Intracellular attachment proteins Transmembrane linking proteins Primary cell wall Plasma membrane Plasma membranes Middle lamella Lumen Tight junction Smooth ER Cell 1 Cell 2 Intercellular space ... |
ensure that materials move through the cells rather than between them. 136 Part II Biology of the Cell Anchoring Junctions Anchoring junctions mechanically attach the cytoskeleton of a cell to the cytoskeletons of other cells or to the extracellular matrix. They are commonest in tissues subject to mechanical stress, s... |
changes in cadherin expression may provide the migrating cells with a “roadmap” to their destination. Integrin-Mediated Links Anchoring junctions called adherens junctions are another type of junction that connects the actin filaments of one cell with those of neighboring cells or with the extracellular matrix (figure... |
ctions are composed of structures called connexons, complexes of six identical transmembrane proteins (figure 7.21). The proteins in a connexon are arranged in a circle to create a channel through the plasma membrane that protrudes several nanometers from the cell surface. A gap junction forms when the connexons of two... |
junctions readily allow the passage of small molecules and ions required for rapid communication (such as in heart tissue), but do not allow the passage of larger molecules like proteins. Vacuoles Nuclei Cytoplasm Primary cell wall Plasmodesmata Middle lamella FIGURE 7.22 Plasmodesmata. Plant cells can communicate thr... |
sheets, holding the cells together such that materials cannot pass between them. • Gap junctions (in animals) and plasmodesmata (in plants) permit small substances to pass directly from cell to cell through special passageways. 7. What are the functions of tight junctions? What are the functions of desmosomes and adhe... |
an input of energy is required to destabilize existing chemical bonds. In a chemical reaction, the energy released 8.2 Enzymes are biological catalysts. Enzymes. Globular proteins called enzymes catalyze chemical reactions within cells. How Enzymes Work. Enzymes have sites on their surface shaped to fit their substrat... |
converted into kinetic energy. Much of the work that living organisms carry out involves transforming potential energy to kinetic energy. Energy can take many forms: mechanical energy, heat, sound, electric current, light, or radioactive radiation. Because it can exist in so many forms, there are many ways to measure ... |
is the most common electron accep- (a) Potential energy (b) Kinetic energy FIGURE 8.2 Potential and kinetic energy. (a) Objects that have the capacity to move but are not moving have potential energy. The energy required to move the ball up the hill is stored as potential energy. (b) Objects that are in motion have ki... |
arts from one atom (oxidation) and moves to another (reduction), the electron’s added energy is transferred with it, and the electron orbits the second atom’s nucleus at the higher energy level. The added energy is stored as potential chemical energy that the atom can later release when the electron returns to its orig... |
Energy continuously flows through the biological world in one direction, with new energy from the sun constantly entering the system to replace the energy dissipated as heat. Heat can be harnessed to do work only when there is a heat gradient, that is, a temperature difference between two areas (this is how a steam en... |
form other chemical bonds, is called the free energy of that molecule. In a more general sense, free energy is defined as the energy available to do work in any system. In a molecule within a cell, where pressure and volume usually do not change, the free energy is denoted by the symbol G (for “Gibbs’ free energy,” wh... |
in the degree of disorder of the system (T ∆S). Any reaction whose products contain less free energy than the reactants (∆G is negative) will tend to proceed spontaneouslya) Product Energy must be supplied. Reactant Reactant Endergonic (b) Exergonic Energy is released. Product FIGURE 8.6 Energy in chemical reactions. ... |
the ball to move freely; gravity determines the direction it then travels. Lowering the resistance to the ball’s movement will promote the movement dictated by its position on the hill. Similarly, the direction in which a chemical reaction proceeds is determined solely by the difference in free energy. Like digging aw... |
+ H2O → H2CO3 carbonic carbon water acid dioxide This reaction may proceed in either direction, but because it has a large activation energy, the reaction is very slow in the absence of an enzyme: perhaps 200 molecules of carbonic acid form in an hour in a cell. Reactions that proceed this slowly are of little use to... |
within the cleft, some 1.5 nm from the surface, are located three histidines, their imidazole (nitrogen ring) groups all pointed at the same place in the center of the cleft. Together they hold a zinc ion firmly in position. This zinc ion will be the cutting blade of the catalytic process. Here is how the zinc catalyz... |
ates. This specificity is due to the active site of the enzyme, which is shaped so that only a certain substrate molecule will fit into it. Active site Substrate (a) (b) FIGURE 8.8 How the enzyme lysozyme works. (a) A groove runs through lysozyme that fits the shape of the polysaccharide (a chain of sugars) that makes ... |
Take Many Forms While many enzymes are suspended in the cytoplasm of cells, free to move about and not attached to any structure, other enzymes function as integral parts of cell structures and organelles. Multienzyme Complexes (a) Often in cells the several enzymes catalyzing the different steps of a sequence of reac... |
by RNA itself, rather than by enzymes. This initial observation has been corroborated by additional examples of RNA catalysis in the last few years. Like enzymes, these RNA catalysts, which are loosely called “ribozymes,” greatly accelerate the rate of particular biochemical reactions and show extraordinary specificit... |
catalysis. Above the temperature optimum, these forces are too weak to maintain the enzyme’s shape against the increased random movement of the atoms in the enzyme. At these higher temperatures, the enzyme denatures, as we described in chapter 3. Most human enzymes have temperature optima between 35°C and 40°C, a rang... |
). Enzyme inhibition occurs in two ways: competitive inhibitors compete with the substrate for the same binding site, displacing a percentage of substrate molecules from the enzymes; noncompetitive inhibitors bind to the enzyme in a location other than the active site, changing the shape of the enzyme and making it una... |
end and an organic base attached to the other end. The two nucleotides that make up NAD+, nicotinamide monophosphate (NMP) and adenine monophosphate (AMP), are joined head-to-head by their phosphate groups. The two nucleotides serve different functions in the NAD+ molecule: AMP acts as the core, providing a shape reco... |
ATP? The chief energy currency all cells use is a molecule called adenosine triphosphate (ATP). Cells use their supply of ATP to power almost every energy-requiring process they carry out, from making sugars, to supplying activation energy for chemical reactions, to actively transporting substances across membranes, t... |
iring Reactions Cells use ATP to drive endergonic reactions. Such reactions do not proceed spontaneously, because their products possess more free energy than their reactants. However, if the cleavage of ATP’s terminal high-energy bond releases 154 Part III Energetics FIGURE 8.14 The ATP molecule. (a) The model and (b)... |
By determining where many of the enzymes that catalyze these steps are located, we can “map out” a model of metabolic processes in the cell. How Biochemical Pathways Evolved In the earliest cells, the first biochemical processes probably involved energy-rich molecules scavenged from the environment. Most of the molecu... |
waste energy and raw materials that could be put to use elsewhere. It is, therefore, advantageous for a cell to temporarily shut down biochemical pathways when their products are not needed. Initial substrate Initial substrate Enzyme 1 End product + Enzyme 1 Intermediate A Intermediate A Enzyme 2 Enzyme 2 Intermediate... |
of a system. In cells, it is a measure of how much energy has become so dispersed (usually as evenly distributed heat) that it is no longer available to do work. exergonic reaction. An energy-yielding chemical reaction. Exergonic reactions tend to proceed spontaneously, although activation energy is required to initia... |
of life on earth, since this biochemical pathway has been retained by all living organisms. It is a chemical process that does not appear to have changed for well over 3 billion years. Anaerobic Photosynthesis The third major event in the evolution of metabolism was anaerobic photosynthesis. Early in the history of li... |
vests energy by stripping energetic electrons from organic molecules. Aerobic respiration employs the same kind of proton pumps as photosynthesis, and is thought to have evolved as a modification of the basic photosynthetic machinery. However, the hydrogens and their associated electrons are not obtained from H2S or H2... |
heat? What is entropy? What is free energy? 5. What is the difference between an exergonic and an endergonic reaction? Which type of reaction tends to proceed spontaneously? 6. Define activation energy. How does a catalyst affect the final proportion of reactant converted into product? • Enzymes are the major catalyst... |
-CoA. Stage Three: The Krebs Cycle. electrons are stripped from acetyl-CoA. Harvesting Energy by Extracting Electrons. The respiration of glucose is a series of oxidation-reduction reactions which involve stripping electrons from glucose and using the energy of these electrons to power the synthesis of ATP. Stage Four:... |
the energy autotrophs produce and are called heterotrophs (“fed by others”). At least 95% of the kinds of organisms on earth—all animals and fungi, and most protists and bacteria— are heterotrophs. Where is the chemical energy in food, and how do heterotrophs harvest it to carry out the many tasks of living (figure 9.... |
, and energy: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (heat or ATP) The change in free energy in this reaction is –720 kilocalories (–3012 kilojoules) per mole of glucose under the conditions found within a cell (the traditional value of –686 kilocalories, or –2870 kJ, per mole refers to standard conditions—room tempe... |
moved about, crawling over one another to reach new positions. Movement also occurs within cells. Tiny fibers within muscle cells pull against one another when muscles contract. Mitochondria pass a meter or more along the narrow nerve cells that connect your feet with your spine. Chromosomes are pulled by microtubules... |
surface of the same enzyme; they are physically linked, or “coupled,” like two legs walking. In other cases, a high-energy phosphate from ATP attaches to the protein catalyzing the endergonic process, activating it (figure 9.4). Coupling energyrequiring reactions to the splitting of ATP in this way is one of the key t... |
of extracting energy from glucose is a 10-reaction biochemical pathway called glycolysis that produces ATP by substrate-level phosphorylation. The enzymes that catalyze the glycolytic reactions are in the cytoplasm of the cell, not bound to any membrane or organelle. Two ATP molecules are used up early in the pathway,... |
Figure 9.6 provides an overview of aerobic respiration. Anaerobic Respiration In the presence of oxygen, cells can respire aerobically, using oxygen to accept the electrons harvested from food molecules. In the absence of oxygen to accept the electrons, some organisms can still respire anaerobically, using inorganic m... |
Cytoplasm Extracellular fluid CO2 O2 FIGURE 9.6 An overview of aerobic respiration. Chapter 9 How Cells Harvest Energy 163 Stage One: Glycolysis Priming The metabolism of primitive organisms focused on glucose. Glucose molecules can be dismantled in many ways, but primitive organisms evolved a glucose-catabolizing pro... |
carbon molecule glucose, producing a six-carbon molecule with two phosphates. Cleavage reactions. Then, the six-carbon molecule with two phosphates is split in two, forming two three-carbon sugar phosphates. FIGURE 9.7 How glycolysis works. 164 Part III Energetics 1. Phosphorylation of glucose by ATP. 2–3. Rearrangemen... |
vate kinase ADP ATP Pyruvate Pyruvate CHOH CH2 O P O– C O CHOH CH2 O P P P O– C C O O CH2OH O– C C CH2 O– C C CH3 O O O O FIGURE 9.8 The glycolytic pathway. The first five reactions convert a molecule of glucose into two molecules of G3P. The second five reactions convert G3P into pyruvate. Chapter 9 How Cells Harvest ... |
molecules. Like many biochemical pathways, glycolysis is believed to have evolved backward, with the last steps in the process being the most ancient. Thus, the second half of glycolysis, the ATP-yielding breakdown of G3P, may have been the original process early heterotrophs used to generate ATP. The synthesis of G3P... |
ycle NADH As long as food molecules that can be converted into glucose are available, a cell can continually churn out ATP to drive its activities. In doing so, however, it accumulates NADH and depletes the pool of NAD+ molecules. A cell does not contain a large amount of NAD+, and for glycolysis to continue, NADH must... |
, then look briefly at fermentation. Glycolysis generates a small amount of ATP by reshuffling the bonds of glucose molecules. In glycolysis, two molecules of NAD+ are reduced to NADH. NAD+ must be regenerated for glycolysis to continue unabated. FIGURE 9.10 Fermentation. The conversion of pyruvate to ethanol takes pla... |
coenzyme A (CoA), forming a compound known as acetyl-CoA: Pyruvate + NAD+ + CoA → Acetyl-CoA + NADH + CO2 This reaction produces a molecule of NADH, which is later used to produce ATP. Of far greater significance than the reduction of NAD+ to NADH, however, is the production of acetyl-CoA (figure 9.11, bottom). Acety... |
pyruvate is decarboxylated, yielding acetylCoA, NADH, and CO2. This process occurs within the mitochondrion. Stage Three: The Krebs Cycle After glycolysis catabolizes glucose to produce pyruvate, and pyruvate is oxidized to form acetyl-CoA, the third stage of extracting energy from glucose begins. In this third stage,... |
twocarbon fragment is transferred from acetyl-CoA to a four-carbon molecule (the starting material). FIGURE 9.12 How the Krebs cycle works. Chapter 9 How Cells Harvest Energy 169 The Reactions of the Krebs Cycle The Krebs cycle consists of nine sequential reactions that cells use to extract energetic electrons and dri... |
the four-carbon succinyl group and CoA is a high-energy bond. In a coupled reaction similar to those that take place in glycolysis, this bond is cleaved, and the energy released drives the phosphorylation of guanosine diphosphate (GDP), forming guanosine triphosphate (GTP). GTP is readily converted into ATP, and the f... |
to drive the synthesis of much more ATP. 170 Part III Energetics Oxidation of pyruvate NAD+ NADH Pyruvate CO2 S CoA C O CH3 Acetyl-CoA (2C) The cycle begins when a 2C unit from acetyl-CoA reacts with a 4C molecule (oxaloacetate) to produce citrate (6C). Mitochondrial membrane Krebs cycle COO– The dehydrogenation of ma... |
as they proceed through the cycle. Chapter 9 How Cells Harvest Energy 171 Harvesting Energy by Extracting Electrons To understand how cells direct some of the energy released during glucose catabolism into ATP production, we need to take a closer look at the electrons in the C—H bonds of the glucose molecule. We state... |
from a less electronegative atom and closer to a more electronegative atom, just as energy is released when a boulder is allowed to roll down a hill. In the catabolism of glucose, energy is released when glucose is oxidized, as electrons relocate closer to oxygen (figure 9.14). 172 Part III Energetics Glucose is an en... |
olecules and is reduced to NADH. more of the energy can be used to push the pistons and move the car. The same principle applies to the oxidation of glucose inside a cell. If all of the hydrogens were transferred to oxygen in one explosive step, releasing all of the free energy at once, the cell would recover very litt... |
discuss how this energy is put to work to drive the production of ATP. The catabolism of glucose involves a series of oxidation-reduction reactions that release energy by repositioning electrons closer to oxygen atoms. Energy is thus harvested from glucose molecules in gradual steps, using NAD+ as an electron carrier.... |
H+ H+ H+ Inner mitochondrial membrane C Q FADH2 NADH + H+ NAD+ NADH dehydrogenase Mitochondrial matrix bc1 complex 2H+ + O2 1 2 H2O Cytochrome oxidase complex FIGURE 9.16 The electron transport chain. High-energy electrons harvested from catabolized molecules are transported (red arrows) by mobile electron carriers (u... |
cytoplasm Acetyl-CoA NADH Intermembrane space H+ H+ H+ H+ H+ Inner mitochondrial membrane Na-K pump NADH NAD+ ADP + Pi H+ ATP synthase ATP Proton pump Mitochondrial matrix FIGURE 9.17 Chemiosmosis. NADH transports high-energy electrons harvested from the catabolism of macromolecules to “proton pumps” that use the ener... |
generated for each proton pump activated by the electron transport chain. Since the electrons from NADH activate three pumps and those from FADH2 activate two, we would expect each molecule of NADH and FADH2 to generate three and two ATP molecules, respectively. However, because eukaryotic cells carry out glycolysis i... |
32% of the energy available in glucose. (By comparison, a typical car converts only about 25% of the energy in gasoline into useful energy.) The efficiency of oxidative respiration at harvesting energy establishes a natural limit on the maximum length of food chains. The high efficiency of aerobic respiration was one ... |
well as pyruvate decarboxylase and two other Krebs cycle enzymes), shutting down the catabolic pathway. Relative levels of ADP and ATP regulate the catabolism of glucose at key committing reactions. Glucose Fructose 6-phosphate Phosphofructokinase ADP Activates Inhibits Fructose 1,6-bisphosphate Activates Pyruvate Pyr... |
Other organic molecules than glucose, particularly proteins and fats, are also important sources of energy (figure 9.21). Cellular Respiration of Protein Proteins are first broken down into their individual amino acids. The nitrogencontaining side group (the amino group) is then removed from each amino acid in a proce... |
yl groups from the end of each fatty acid tail until the entire fatty acid is converted into acetyl groups (figure 9.23). Each acetyl group then combines with coenzyme A to form acetyl-CoA. This process is known as oxidation. How much ATP does the catabolism of fatty acids produce? Let’s compare a hypothetical six-carb... |
ATP and generates one molecule each of FADH2 and NADH, not including the molecules generated from the Krebs cycle. H Fatty acid C H H C H C O OH CoA ATP AMP + PPi O C H C H CoA FAD FADH2 H C O C CoA H Fatty acid C H H Fatty acid C CoA H2O HO Fatty acid C H O C H C H CoA NAD+ NADH O H Fatty acid C C O C CoA H Acetyl-Co... |
there would not support enough zebras and other herbivores to maintain the number of lions needed to feed the human population. Thus, the ecological complexity of our world is fixed in a fundamental way by the chemistry of oxidative respiration. Stage 1: Photosynthesizers Stage 2: Herbivores Stage 3: Carnivore Stage 4... |
type, which occurs in single-celled fungi called yeast, the molecule that accepts hydrogen from NADH is pyruvate, the end product of glycolysis itself. Yeast enzymes remove a terminal CO2 group from pyruvate through decarboxylation, producing a two-carbon molecule called acetaldehyde. The CO2 released causes bread mad... |
. However, lactate is still toxic enough to produce a painful sensation in muscles during heavy exercise, when oxygen in the muscles is depleted. In fermentation, which occurs in the absence of oxygen, the electrons that result from the glycolytic breakdown of glucose are donated to an organic molecule, regenerating NA... |
Electron Transport and ATP • Glycolysis • Krebs Cycle • Electron Transport 9.3 Catabolism of proteins and fats can yield considerable energy. • The catabolism of fatty acids begins with -oxidation and provides more energy than the catabolism of carbohydrates. 6. How is acetyl-CoA produced during the aerobic oxidation ... |
How the Two Photosystems of Plants Work Together. Photosystems II and I drive the synthesis of the ATP and NADPH needed to form organic molecules. 10.4 Cells use the energy and reducing power captured by the light reactions to make organic molecules. The Calvin Cycle. ATP and NADPH are used to build organic molecules,... |
ynthetic process. No other structure in a plant cell is able to carry out photosynthesis. Photosynthe- Cuticle Epidermis Mesophyll Vascular bundle Bundle sheath Stoma Chloroplasts Vacuole Nucleus Cell wall Outer membrane Inner membrane Granum Stroma Thylakoid FIGURE 10.2 Journey into a leaf. A plant leaf possesses a th... |
molecule to another. A crude analogy to this form of energy transfer is the initial “break” in a game of pool. If the cue ball squarely hits the point of the triangular array of 15 pool balls, the two balls at the far corners of the triangle fly off, but none of the central balls move. The energy passes through the ce... |
the water he had been adding accounted for the plant’s increased mass. A hundred years passed before the story became clearer. The key clue was provided by the English scientist Joseph Priestly, in his pioneering studies of the properties of air. On the 17th of August, 1771, Priestly “accidentally hit upon a method of... |
and others then worked out the basic chemical reaction. Discovery of the Light-Independent Reactions Ingenhousz’s early equation for photosynthesis includes one factor we have not discussed: light energy. What role does light play in photosynthesis? At the beginning of the previous century, the English plant physiolog... |
2 H2S + light energy → (CH2O) + H2O + 2 S (a) The striking parallel between this equation and Ingenhousz’s equation led van Niel to propose that the generalized process of photosynthesis is in fact CO2 + 2 H2A + light energy → (CH2O) + H2O + 2 A In this equation, the substance H2A serves as an electron donor. In photo... |
used to synthesize other organic molecules. The Role of Reducing Power In his pioneering work on the light reactions, van Niel had further proposed that the reducing power (H+) generated by the splitting of water was used to convert CO2 into organic matter in a process he called carbon fixation. Was he right? In the 1... |
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