H-B Woodlawn AP EXAM REVIEW

Part 2. Chapters 7-10 of Campbell 6th Ed. (Also found at

Chapter 7: A OVERVIEW OF THE CELL (Web activities 7C, 7D)

Prokaryotic and eukaryotic cells differ in size and complexity (FIGURES 7.4-7.6)
All cells are bounded by a plasma membrane.
Bacteria and archaea are prokaryotic cells, without nuclei or other membrane-enclosed organelles.
All other organisms have eukaryotic cells, with membrane-enclosed nuclei and other membranous organelles in their cytoplasm.
The need for a high surface-to-volume ratio limits cell size.
Internal membranes compartmentalize the functions of a eukaryotic cell (FIGURES 7.7, 7.8)
Plant and animal cells have most of the same organelles. Animals have no chloroplasts, central vacuaoles, cell walls, or plasmodesmata;
Plants have no lysosomes, centrioles, or flagella.

THE NUCLEUS AND RIBOSOMES (Web activities 7E)

The nucleus contains a eukaryotic cell’s genetic library (FIGURE 7.9)
DNA is organized with proteins into thin fibers of chromatin, which coil to form thick chromosomes in dividing cells.
One or more nuclei in nondividing cells are the sites of ribosome synthesis. Macromolecules and ribosomal subunits pass between nucleus and cytoplasm through pores in the nuclear envelope.
Ribosomes build a cell’s proteins (FIGURE 7.10)
Free ribosomes’ proteins are dissolved in the cytosol;
Bound ribosomes on the ER and the nuclear envelope make proteins for membranes or for secretion.

THE ENDOMEMBRANE SYSTEM

Many of the eukaryotic cell’s membranes are connected either by physical continuity or through transport vesicles made of pinched-off pieces of membrane.
The endoplasmic reticulum manufactures membranes and performs many other biosynthetic functions (FIGURE 7.11) Continuous with the nuclear envelope, the endoplasmic reticulum (ER) is a network of cisternae, membrane-enclosed compartments.
Smooth ER lacks ribosomes; it synthesizes steroids, metabolizes carbohydrates, stores calcium in muscle, and detoxifies poisons in liver.
Rough ER has bound ribosomes and produces cell membrane and secretory proteins. These products are distributed by transport vesicles budded from the ER.
The Golgi apparatus finishes, sorts, and ships cell products (FIGURE 7.12)
Stacks of separate cisternae make up the Golgi. The cis face of a Golgi stack receives secretory proteins from the ER in transport vesicles. The proteins are modified, sorted, and released in transport vesicles from the trans face. The Golgi also synthesizes some macromolecules on its own.
Lysosomes are digestive compartments (FIGURE 7.14) Lysosomes are membranous sacs of hydrolytic enzymes. They break down cell macromolecules for recycling as well as ingested substances.
Vacuoles have diverse functions in cell maintenance (FIGURE 7.15) A plant cell’s central vacuole functions in storage, waste disposal, cell growth, and protection.

OTHER MEMBRANOUS ORGANELLES

Mitochondria and chloroplasts are the main energy transformers of cells (FIGURES 7.17, 7.18)
Mitochondria, the sites of cellular respiration in eukaryotes, have an outer membrane and an inner membrane that is folded into cristae. Some reactions of respiration occur in the mitochondrial matrix enclosed by the inner membrane, and others are catalyzed by enzymes built into the inner membrane.
Chloroplasts contain chlorophyll and other pigments that function in photosynthesis. In chloroplasts, two membranes surround the fluid stroma, which contains thylakoids stacked into grana.
Peroxisomes generate and degrade H2O2 in performing various metabolic functions (FIGURE 7.19) Peroxisomes carry out processes that produce hydrogen peroxide (H2O2) as waste, and their enzymes convert the toxic peroxide to water.

THE CYTOSKELETON

The cytoskeleton provides structural support to the cell, and also functions in cell motility and regulation (TABLE 7.2, FIGURES 7.22-7.24)
The cytoskeleton is made of microtubules, microfilaments, and intermediate filaments.
Microtubules grow out from the centrosome, a region near the nucleus that includes two centrioles in most animal cells. Microtubules shape the cell, guide movement of organelles, and help separate the chromosome copies in dividing cells.
Cilia and flagella are motile appendages containing microtubule doublets that are moved past each other by the motor protein dynein.
Microfilaments are thin rods built from actin; they function in muscle contraction, amoeboid movement, cytoplasmic streaming, and support for microvilli.
Intermediate filaments support cell shape and fix organelles in place.

CELL SURFACES AND JUNCTIONS

Plant cells are encased by cell walls (FIGURE 7.28) Plant cell walls are composed of cellulose fibers embedded in other polysaccharides and protein.
The extracellular matrix (ECM) of animal cells functions in support, adhesion, movement, and regulation (FIGURE 7.29) Animal cells secrete glycoproteins that form the ECM. Important components include collagen, proteoglycan complexes, and fibronectin attached to integrins in the plasma membrane.
Intercellular junctions help integrate cells into higher levels of structure and function (pp. 133-134,FIGURE 7.30) Plants have plasmodesmata, channels that pass through adjoining cell walls. Animal cell contact is by tight junctions, desmosomes, and gap junctions.
The cell is a living unit greater than the sum of its parts (p. 135,FIGURE 7.31)

Chapter 8: MEMBRANE STRUCTURE (Web activity 8A)

Membrane models have evolved to fit new data (FIGURES 8.1-8.3) The Davson-Danielli model, placing layers of proteins on either side of a phospholipid bilayer, has been replaced by the fluid mosaic model.
Membranes are fluid (FIGURES 8.4, 8.5) Phospholipids and, to a lesser extent, proteins move laterally within the membrane. Cholesterol and unsaturated hydrocarbon tails in the phospholipids affect membrane fluidity.
Membranes are mosaics of structure and function (FIGURES 8.6-8.9) Integral proteins are embedded in the lipid bilayer; peripheral proteins are attached to the surfaces. The inside and outside membrane faces differ in composition. The functions of membrane proteins include transport, enzymatic activity, signal transduction, intercellular joining, cell-cell recognition, and attachment to the cytoskeleton and extracellular matrix.
Membrane carbohydrates are important for cell-cell recognition (pp. 143-144) Short chains of sugars are linked to proteins and lipids on the exterior side of the plasma membrane, where they can interact with the surface molecules of other cells.

TRAFFIC ACROSS MEMBRANES (Web activity 8B, 8C, 8D, 8E, 8F)

A membrane’s phospholipid bilayer molecular organization results in selective permeability
A cell must exchange small molecules and ions with its surroundings, a process controlled by the plasma membrane.
Hydrophobic substances are soluble in lipids and pass through membranes rapidly.
Polar molecules and ions generally require specific transport proteins to help them cross a membrane.
Passive transport is diffusion across a membrane (FIGURE 8.10)
Diffusion is the spontaneous movement of a substance down its concentration gradient.
Osmosis is the passive transport of water (FIGURE 8.11) Water flows across a membrane from the side where solute is less concentrated (hypotonic) to the side where solute is more concentrated (hypertonic). If the concentrations are equal (isotonic), no net osmosis occurs.
Cell survival depends on balancing water uptake and loss (FIGURE 8.12)
Cells lacking walls (as in animals and some protists) are isotonic with their environments or have adaptations for osmoregulation.
Plants, prokaryotes, fungi, and some protists have elastic cell walls, so the cells don’t burst in a hypotonic environment.
Specific proteins facilitate the passive transport of water and selected solutes (FIGURE 8.14)
In facilitated diffusion, a transport protein speeds the movement of water or a solute across a membrane down its concentration gradient.
Active transport is the pumping of solutes against their gradients (FIGURE 8.15) Specific membrane proteins use energy, usually in the form of ATP, to do this work.

Some ion pumps generate voltage across membranes (FIGURE 8.17) Ions can have both a concentration (chemical) gradient and an electrical gradient (voltage). These forces combine in the electrochemical gradient, which determines the net direction of ionic diffusion.
Electrogenic pumps, such as sodium-potassium pumps and proton pumps, are transport proteins that contribute to electrochemical gradients.
In cotransport, a membrane protein couples the transport of two solutes (FIGURE 8.18) One solute’s "downhill" diffusion drives the other’s "uphill" transport.

Exocytosis and endocytosis transport large molecules (pp. 151-152,FIGURE 8.19) In exocytosis, transport vesicles migrate to the plasma membrane, fuse with it, and release their contents. In endocytosis, large molecules enter cells within vesicles pinched inward from the plasma membrane. The three types of endocytosis are phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Chapter 9:CELLULAR RESPIRATION

THE PRINCIPLES OF ENERGY HARVEST

Chemical elements are recycled by respiration and photosynthesis, but energy is not (FIGURE 9.1)
Cellular respiration and fermentation are catabolic, energy-yielding pathways
The breakdown of glucose and other organic fuels to simpler products is exergonic, yielding energy for ATP synthesis.
Cells recycle the ATP they use for work (FIGURE 9.2) ATP transfers phosphate groups to various substrates, priming them to do work. To keep working, a cell must regenerate ATP. Starting with glucose or another organic fuel, and using O2, cellular respiration yields H2O, CO2, and energy in the form of ATP and heat.
Redox reactions release energy (FIGURE 9.3) when one substance partially or totally shifts electrons to another. The substance receiving electrons is reduced; the substance losing electrons is oxidized.
During cellular respiration, glucose (C6H12O6) is oxidized to CO2, and O2 is reduced to H2O. Electrons lose potential energy during their transfer from organic compounds to oxygen, and this energy drives ATP synthesis.

THE PROCESS OF CELLULAR RESPIRATION

Respiration involves glycolysis, the Krebs cycle, and electron transport: an overview (pp. 160-161,FIGURE 9.6) Glycolysis and the Krebs cycle supply electrons (via NADH) to the transport chain, which drives oxidative phosphorylation. Glycolysis occurs in the cytosol, the Krebs cycle in the mitochondrial matrix. The electron transport chain is built into the inner mitochondrial membrane.

Glycolysis harvests chemical energy by oxidizing glucose to pyruvate: a closer look (FIGURES 9.8, 9.9) Glycolysis nets 2 ATP, produced by substrate-level phosphorylation, and 2 NADH.
The Krebs cycle completes the energy-yielding oxidation of organic molecules (FIGURES 9.11, 9.12)
The conversion of pyruvate to acetyl CoA links glycolysis to the Krebs cycle. The two-carbon acetate of acetyl CoA joins the four-carbon oxaloacetate to form the six-carbon citrate, which is degraded back to oxaloacetate. The cycle releases CO2, forms 1 ATP by substrate-level phosphorylation, and passes electrons to 3 NAD+ and 1 FAD.
The inner mitochondrial membrane couples electron transport to ATP synthesis (FIGURE 9.15)
Most of the ATP made in cellular respiration is produced by oxidative phosphorylation when NADH and FADH2 donate electrons to the series of electron carriers in the electron transport chain. At the end of the chain, electrons are passed to O2, reducing it to H2O.
Electron transport is coupled to ATP synthesis by chemiosmosis. At certain steps along the chain, electron transfer causes electron-carrying protein complexes to move H+ from the matrix to the intermembrane space, storing energy as a proton-motive force (H+ gradient). As H+ diffuses back into the matrix through ATP synthase, its exergonic passage drives the endergonic phosphorylation of ADP.

Cellular respiration generates many ATP molecules for each sugar molecule it oxidizes: a review (pp. 169-170,FIGURE 9.16) The oxidation of glucose to CO2 produces a maximum of about 38 ATP.

RELATED METABOLIC PROCESSES

Fermentation enables some cells to produce ATP without the help of oxygen (FIGURES 9.17, 9.18)
Fermentation is anaerobic catabolism of organic nutrients, yielding ATP from glycolysis. Electrons from NADH made in glycolysis are passed to pyruvate, restoring the NAD+required to sustain glycolysis.
Yeasts and certain bacteria are facultative anaerobes, capable of making ATP by either aerobic respiration or fermentation. Of the two pathways, respiration is the more efficient in terms of ATP yield per glucose. Glycolysis occurs in nearly all organisms and probably evolved in ancient prokaryotes before there was O2 in the atmosphere.
Glycolysis and the Krebs cycle connect to many other metabolic pathways (FIGURE 9.19) T
hese catabolic pathways combine to funnel electrons from all kinds of food molecules into cellular respiration. Carbon skeletons for anabolism (biosynthesis) come directly from digestion or from intermediates of glycolysis and the Krebs cycle.
Feedback mechanisms control cellular respiration (FIGURE 9.20) Cellular respiration is controlled by allosteric enzymes at key points in glycolysis and the Krebs cycle. This helps the cell strike a moment-to-moment balance between catabolism and anabolism.

Chapter 10: Photosynthesis

PHOTOSYNTHESIS IN NATURE

Plants and other autotrophs are the producers of the biosphere (FIGURE 10.1)
Autotrophs nourish themselves without ingesting organic molecules. Photoautotrophs use the energy of sunlight to synthesize organic molecules from CO2 and H2O.
Heterotrophs ingest organic molecules from other organisms to get energy and carbon.
Chloroplasts are the sites of photosynthesis in plants (p. 178,FIGURE 10.2)
In autotrophic eukaryotes, photosynthesis occurs in chloroplasts, organelles containing thylakoid membranes that separate the thylakoid space from the chloroplast’s stroma. Stacks of thylakoids form grana.

THE PATHWAYS OF PHOTOSYNTHESIS

Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis (pp. 179-180,FIGURE 10.3) Photosynthesis is summarized by the equation
Experiments show that the chloroplast splits water into hydrogen and oxygen, incorporating the electrons of hydrogen into the bonds of sugar molecules.
Photosynthesis is a redox process: H2O is oxidized, CO2 is reduced.
The light reactions and the Calvin cycle cooperate in converting light energy to the chemical energy of food: an overview (FIGURE 10.4)
The light reactions in the grana produce ATP and split water, releasing O2 and forming NADPH by transferring electrons from water to NADP+.
The Calvin cycle in the stroma forms sugar from CO2, using ATP for energy and NADPH for reducing power.

The light reactions convert solar energy to the chemical energy of ATP and NADHP(FIGURES 10.12-16)
Light is a form of electromagnetic energy, which travels in waves. The colors we see as visible light are a part of the electromagnetic spectrum.
A pigment is a substance that absorbs visible light of specific wavelengths.

The action spectrum of photosynthesis does not exactly match the absorption spectrum of chlorophyll a, the main photosynthetic pigment in plants, because accessory pigments (chlorophyll b and various carotenoids) absorb different wavelengths of light and pass the energy on to chlorophyll a.
A pigment goes from a ground state to an excited state when a photon boosts one of its electrons to a higher-energy orbital.

The pigments of chloroplasts are built into the thylakoid membrane near molecules called primary electron acceptors, which trap the excited electrons before they return to the ground state.
Pigment molecules are clustered in an antenna complex surrounding a chlorophyll a molecule at the reaction center.
Photons absorbed anywhere in the antenna can pass their energy along to energize this chlorophyll a, which then passes an electron to a nearby primary electron acceptor.
The antenna complex, the reaction-center chlorophyll, and the primary electron acceptor make up a photosystem, a light-harvesting unit built into the thylakoid membrane. There are two kinds of photosystems. Photosystem I contains P700 chlorophyll a molecules at the reaction center; photosystem II contains P680 molecules.

(See page 187 – Cyclic electron flow)

Noncyclic electron flow involves both photosystems and produces NADPH, ATP, and oxygen.
Cyclic electron flow employs only photosystem I, producing ATP but no NADPH or O2. ATP production during the light reactions is called photophosphorylation.
The mechanism is chemiosmosis. The redox reactions of the electron transport chain that connects the two photosystems generate an H+ gradient across the thylakoid membrane. ATP synthase uses this proton-motive force to make ATP.

The Calvin cycle uses ATP and NADPH to convert CO2 to sugar (FIGURE 10.17) The Calvin cycle is a metabolic pathway in the chloroplast stroma.
An enzyme (rubisco) combines CO2 with ribulose bisphosphate (RuBP), a five-carbon sugar. Then, using electrons from NADPH and energy from ATP, the cycle synthesizes the three-carbon sugar glyceraldehyde-3-phosphate.
Most of the G3P is reused in the cycle to reconstitute RuBP, but some exits the cycle and is converted to glucose and other essential organic molecules.

Alternative mechanisms of carbon fixation have evolved in hot, arid climates (FIGURE 10.19)
On dry, hot days, plants close their stomata, conserving water. Oxygen from the light reactions builds up. When O2 substitutes for CO2 in the active site of rubisco, the product formed leaves the cycle and is oxidized to CO2 and H2O in the peroxisomes and mitochondria. This process, photorespiration, consumes organic fuel without producing ATP.
C4 plants avert photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells. These compounds are exported to photosynthetic bundle-sheath cells, where they release carbon dioxide for use in the Calvin cycle.
CAM plants open their stomata during the night, incorporating the CO2 that enters into organic acids, which they store in mesophyll cells. During the day the stomata close, and the CO2 is released from the organic acids for use in the Calvin cycle.