Exam # 3 Study Guide chapter 8-11Chapter 8 PhotosynthesisI. Overview of photosynthesis- In photosynthesis, water is oxidized to form oxygen, and carbon dioxide is reduced to form carbohydrates.- Photosynthesis consists of two sets of reactions: (1) the Calvin cycle, in which carbon dioxide is reducedto form carbohydrates, and (2) light-harvesting reactions, in which ATP and NADPH are generated to drive the Calvin cycle.- The evolution of photosynthesis involved horizontal gene transfer in bacteria and endosymbiosis in eukaryotes.- In eukaryotes, photosynthesis takes place in chloroplasts: The Calvin cycle occurs in the stroma, and thelight-harvesting reactions take place on the thylakoid membrane.II. The calvin cycle- The three steps of the Calvin cycle are (1) carboxylation; (2) reduction; and (3) regeneration.- The first step is the addition of CO2 to the 5-carbon sugar RuBP. This step is catalyzed by the enzyme rubisco, considered the most abundant protein on Earth. The resulting 6-carbon compound immediately breaks down into two 3-carbon compounds.- The second step is phosphorylation of the 3-carbon compounds by ATP followed by reduction by NADPH to produce 3-carbon triose phosphate molecules that are exported from the chloroplast to the cytosol, where they are used to build larger sugars.- The third step is the regeneration of RuBP from five 3-carbon molecules.- Starch formation provides chloroplasts with an osmotically inactive way of storing carbohydrates.III. light- Visible light is absorbed by chlorophyll. The absorbed light energy can be released as heat, reemitted aslight (fluorescence), or transferred to an adjacent chlorophyll molecule. Special chlorophyll molecules inthe reaction center transfer both energy and electrons, thus initiating the photosynthetic electron transport chain.- The electron transport chain consists of multisubunit protein complexes and diffusible compounds. Water is the electron donor and NADP+ is the final electron acceptor.- Antenna chlorophylls transfer absorbed light energy to the reaction center.- Reaction centers are located within pigment–protein complexes known as photosystems.- The linear transport of electrons from water to NADPH requires the energy input of two photosystems.- Photosystem II pulls electrons from water, resulting in the production of oxygen and protons on the lumen side of the membrane. Photosystem I passes electrons to NADP+, producing NADPH for use in the Calvin cycle.- The buildup of protons drives ATP synthase to produce ATP on the stroma side of the membrane, where it is used by the Calvin cycle.IV. Efficiency of photosynthesis- An imbalance between the light-harvesting reactions and the Calvin cycle can lead to the formation of reactive oxygen species.- Protection from excess light energy includes antioxidant molecules that neutralize reactive oxygen species and xanthophyll pigments that dissipate excess light energy as heat. BIOl 2107 1st Edition- Rubisco can act catalytically on oxygen as well as on carbon dioxide. When it acts as an oxygenase, there is a loss of energy and reduced carbon from the Calvin cycle.- Rubisco has evolved to favor carbon dioxide over oxygen, but the cost of this selectivity is reduced speed.- The synthesis of carbohydrates via the Calvin cycle results in significant energy losses, largely due to photorespiration.- The maximum theoretical efficiency of photosynthesis is approximately 4% of total incident solar energy.Chapter 9 I. Sending and receiving signals- There are four essential players in communication between two cells: a signaling cell, a signaling molecule, a receptor, and a responding cell.- The signaling molecule binds to its receptor on the responding cell, leading to receptor activation, signal transduction and amplification, response, and eventually termination of the signal and response.II. Distance between responding and receiving cells- Endocrine signaling takes place over long distances and relies on the circulatory system for delivery of signaling molecules.- Paracrine signaling takes place over short distances between neighboring cells.A. signals diffuse to/affect nearby cells- Autocrine signaling occurs when a cell signals itself.A. signals diffuse to/affect cells that synthesize them- Juxtacrine communication depends on physical contact between cells.III. Signaling molecules- A signaling molecule, or ligand, binds to the ligand-binding site of the receptor. Binding causes the receptor to undergo a conformational change that activates the receptor.- Receptors for polar signaling molecules, including growth factors, are located on the plasma membrane. Cell surface protein receptors interact with polar proteins- Receptors for nonpolar signaling molecules, such as steroid hormones, are located in the cytosol or in the nucleus.- There are three major types of cell-surface receptor: G protein-coupled receptors, receptor kinases, and ligand-gated ion channels. All act as molecular switches.- G protein-coupled receptors associate with G proteins, which are active when bound to GTP and inactive when bound to GDP.- Receptor kinases are activated by phosphorylation and inactivated by dephosphorylation.- Ligand-gated ion channels open in response to a signal, allowing the movement of ions across the plasma membrane.IV. Transmission of signals- G proteins are associated with G protein-coupled receptors that bind signaling molecules.- G proteins are composed of three subunits, denoted α, β, and γ. When a G protein encounters an activated receptor, the α subunit exchanges GDP for GTP, dissociates from the β and γ subunits, andbecomes active.- Second messengers like cAMP amplify the signal in the cytosol (brought to the cell by the extracellular first messenger).- Intracellular, cytosolic signals are short-lived before they are terminated.- Ligand binding to a receptor kinase causes it to dimerize with another receptor bound to the same ligand. The two receptor kinases become active when they phosphorylate each other’s cytoplasmic domains, allowing activation of intracellular signaling pathways.- The phosphorylated receptors are bound by other proteins, which cause the subsequent activation of other cytosolic signaling molecules, such as Ras.A. Example of Cytoplasmic signaling protein = RasActivated when bound to GTPTriggers phosphorylation (kinase) cascade within the