Figure 10.5 (a) The energy of activation is a barrier that prevents molecules from undergoing otherwise favorable reactions. (b) Enzymes lower the energy of activation barrier, allowing the reaction to proceed.
Figure 10.6 Enzymes catalyze only those reactions involving their specific substrates. Other molecules do not react because they do not fit into the active site on the enzyme.
Figure 10.7 Adenosine triphosphate (ATP) is an important nucleotide in cellular metabolism. When the terminal phosphate on ATP is cleaved leaving ADP and a free phosphate, a small packet of energy is released that can be used by the cell to fuel metabolic processes.
Figure 10.8 The ATP cycle. Biological work uses the energy that is released when ATP is dephosphorylated; the chemical bond between the last two phosphates on ATP is broken, yielding ADP and a free phosphate. In cellular respiration, ADP is again phosphorylated to ATP. The total amount of adenosine stays constant.
Figure 10.9 An overall view of animal metabolism. Energy-releasing pathways break down foods to produce ATP. ATP is used to do biological work and to fuel the energy-consuming pathways that synthesize the macromolecules that form cellular structures. How would this figure change if we were to show plant metabolism?
Figure 10.11 An overview of cellular respiration showing the three main stages: glycolysis, the Krebs cycle, and the electron transport system. The synthesis of ATP in the mitochondrion is called oxidative phosphorylation. These are the major pathways organisms use to synthesize ATP.
Figure 10.12 The steps of glycolysis. In this metabolic pathway, the six-carbon sugar, glucose, is broken down into two three-carbon pyruvic acid molecules, with a net production of two molecules of ATP.
Figure 10.13 The fate of pyruvic acid depends on whether or not oxygen is present in the cell. When oxygen is absent, pyruvic acid is converted to lactic acid, and NAD+ is regenerated from NADH. When oxygen is present, pyruvic acid enters the mitochondrion. In the mitochondrion, an enzyme removes one carbon from pyruvic acid, and hydrogen is transferred to NAD+ to make NADH. The resulting two-carbon molecule is attached to a carrier forming acetyl CoA, which takes the carbons into the next stage of respiration, the Krebs cycle.
Figure 10.14 The steps of the Krebs cycle. Pyruvic acid enters the mitochondrion, where it loses a molecule of CO2 and is linked to a carrier molecule called CoA. The resulting compound, acetyl CoA joins with a four-carbon compound and, through several enzyme-catalyzed steps, the result is one molecule of ATP, three NADH molecules, and one FADH2 molecule.
Figure 10.16 The four enzyme complexes of the electron transport system are embedded in the inner membrane of the mitochondrion. NADH gives up hydrogens, which split into their respective electrons and protons. The electrons enter the electron transport system, where they are passed from carrier to carrier within the four complexes, giving up energy at each step. The energy is used to pump protons from inside the mitochondrion to the space between the two mitochondrial membranes. More protons are moved out of the mitochondrion by the other enzyme complexes. Finally, the electrons join with protons and oxygen to make water. The end result is a gradient of protons across the inner mitochondrial membrane.
Figure 10.17 (b) Analogy between a hydroelectric dam and the mechanism of oxidative phosphorylation. By opening a hole in the dam, the flow of water can be coupled to a generator that makes electricity. Electricity is used to do work. (d) Potential energy is stored in the proton gradient across the inner mitochondrial membrane. The F0 subunit of the ATP synthase opens a hole in the membrane, allowing protons (yellow balls) to flow through. The F1 subunit couples the flow of protons to the synthesis of ATP. Chemiosmotic Theory of ATP Production
Figure 10.18 The wavelengths of electromagnetic radiation. Our eyes can detect only a small segment of the spectrum, the portion called visible light. Chlorophyll absorbs light in the blue and red regions of the visible spectrum.
Figure 10.20 A generalized chloroplast.(note also outer and inner membrane)
Figure 10.21 The light-dependent reactions of photosynthesis. Light raises the energy of electrons, which then pass from carrier to carrier, releasing energy as they move. The energy is used to pump protons into the lumen of the thylakoid, creating a gradient of protons across the thylakoid membrane. The electrons finally join NADP+ and, along with protons, form NADPH. The chloroplast ATP synthase uses the potential energy in the proton gradient to make ATP. Both NADPH and ATP are used in the light-independent reactions to make sugars.
Figure 10.22 In cyclic photophosphorylation, electrons energized by light leave chlorophyll and pass through several carriers, ending up where they started. As electrons move, protons are pumped into the thylakoids. The proton gradient is used to make ATP. Chemiosmotic Theory of ATP Production
Figure 10.24 The steps of the Calvin-Benson cycle. Carbons enter the cycle as carbon dioxide. The enzyme rubisco combines each CO2 with a five-carbon compound called RuBP. The resulting six-carbon compound quickly splits into two three-carbon PGA molecules. Each PGA gains a phosphate from ATP and hydrogens from NADPH, making an energized three-carbon compound, called GAP. When the cycle has turned six times and 12 molecules of GAP have accumulated (GAP buildup), two GAPs are joined to make a six-carbon sugar. The other 10 GAP molecules are converted back into RuBP to continue the cycle.
Figure 5.5 A map of the many genes that have thus far been found on human chromosome 11. Notice that all the traits that have been mapped to the chromosome are hereditary diseases. Sometimes many traits or genetic diseases map to a small area of a chromosome, as illustrated by brackets. Maps such as this one exist for all of the human chromosomes, and new genes are being located on chromosomes every day.
Figure 5.7 A comparison between the steps of mitosis and the steps of meiosis.
Figure 5.9 Control of the cell cycle occurs at two checkpoints. The first checkpoint occurs just before the genetic material is synthesized; the second just before the cell enters the M phase of the cell cycle. If we unravel the cell cycle and portray it as a time line, we see that the checkpoints correspond to the highest concentrations of regulating proteins (red line).
Figure 5.10 Punnett square illustrating how sex is determined in fruit flies. Females have a matched pair of X chromosomes, and males have one X and one Y chromosome. During meiosis, all of a female's eggs get an X chromosome, but only half of a male's sperm get an X. The other half get a Y. The sex of the offspring is determined by the sex chromosome that is contributed by the sperm.
Figure 5.11a Crossing over between chromatids of homologous pairs of chromosomes.