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. Energyreleasing 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 sixcarbon 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 enzymecatalyzed 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.
Chemiosmotic Theory
of ATP Production
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.
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 5.2 The
stages of mitosis.
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 5.8
The cell cycle.
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.