Chapter foci: Chemical bonds and ion gradients are cellular energy

1. Chapter Summary: The Big Picture (1) • Chapter foci: • Chemical bonds and ion gradients are cellular energy • Membrane transport proteins play a role in energy transduction • Energy transduction pathways in the chloroplast • Energy transduction in the mitochondria with an emphasis on glucose metabolism • Energy transduction in bacteria are diverse

2. Chapter Summary: The Big Picture (2) • Section topics: • Cells store energy in many forms • Gradients across cellular membranes are essential for energy storage and conversion • Storage of light energy occurs in the chloroplast • Cells use a combination of channel, carrier, and pump proteins to transport small molecules across membranes • The first phase of glucose metabolism occurs in the cytosol • Aerobic respiration results in the complete oxidation of glucose

3. logE survival: maintenance: growth 1:103:106

4. 1-4 =100% efficient E: cellular energy supply Fs: substrate flux (FS), G'rxn: free energies for catabolism G'ATP: free energy for ATP synthesis ADP + Pi = ATP (60 kJ mol-1) -n: translocated H+ for ATP synthesis E < ME= inactivity or death ME: maintenance energy

5. Cells store energy in many forms • Key Concepts (1): • Energy exists in three forms: kinetic, potential, and heat. • The laws of thermodynamics define the rules for energy transfer. • Cells remain alive by converting environmental energy sources into cell-accessible energy forms. • High-energy electrons and ion gradients are the most common forms of cellular energy storage. • The amount of energy in an ion gradient is expressed as an electrical potential. .

6. Cells store energy in many forms • Key Concepts (1): • Cells remain alive by converting environmental energy sources into cell-accessible energy forms. . O2 CO2 H2O

7. Cells store energy in many forms • Key Concepts (1): *High-energy electrons and ion gradients are the most common forms of cellular energy storage. *The amount of energy in an ion gradient is expressed as an electrical potential. .

8. The laws of thermodynamics define the rules for energy transfer • H2S released through volcanic activity • H2S dissolves in H2O and reacts with metals to form precipitates • 2 S-2 + Fe+2 FeS2 (pyrite) • SO2-2 + Ca+2  CaSO4 (gypsum)

9. Fats and polysaccharides are examples of long-term energy storage in cells

10. High-energy electrons and ion gradients are examples of short-term potential energy

11. How cells store potential energy with gradients ATP + H2O =ADP + Pi DGo’ =-30.5KJ/mole ADP + H2O= AMP + Pi DGo’ = -28.4KJ/mole • Cells couple energetically favorable and unfavorable reactions • Nucleotide triphosphates store energy for immediate use • The amount of potential energy stored in an ion gradient can be expressed as an electrical potential

12. Gradients across cellular membranes are essential for energy storage and conversion • Key Concepts: • Membrane transport proteins are responsible for moving ions through the phsopholipid bilayer of cellular membranes. • Membrane transport proteins are organized into three groups: channels, carriers, and pumps. • All channels dissipate gradients, all pumps build gradients, and most carriers only dissipate gradients. Some carriers can build gradients as well, using indirect active transport.

13. Phospholipid bilayers are semi-permeable barriers Figure 10.01: Permeation of lipid bilayers by biologically important molecules.

14. Protein channels, carriers, and pumps regulate transport of small molecules across membranes • Protein channels dissipate gradients Figure 10.02: Different views of a Cl- transporter. Note how several transmembrane alpha helices combine to form the pore, including the selectivity filter.

15. Channel types Ligand-gated Voltage-gated Figure 10.03: Three methods for controlling the opening and closing of channels. Ca+2 channels are used as examples. Figure 10.04: Three models for how voltage across a membrane controls the shape of voltage-gated channels. Different types of K+ channels are shown as examples.

16. Passive carrier proteins dissipate gradients Figure 10.05: A comparison of channel and carrier proteins. Figure 10.06: An example of a conformation change in a carrier protein.

18. Symport and Antiport Figure 10.07: Some examples of Na+-dependent transporters.

19. Energy-coupled carrier proteins (pumps) build gradients Direct active transport Indirect active transport Figure 10.08: The relationship between direct and indirect active transport.

20. PUMPS, CHANNELS AND TRANSPORTERS

21. Transporters

22. Membrane Transporter Proteins: Classification Primary active transport: Transport depends on the energy from the hydrolysis of ATP Secondary active transport: Use of energy from a secondary diffusion gradient set up across the membrane using another ion. Because this secondary diffusion gradient initially established using an ion pump, as in primary active transport, the energy is ultimately derived from the same source-ATP hydrolysis.

23. Membrane Transporter Proteins: Classification Facilitated diffusion: Transport from higher concentration to lower concentration. It does not require the expenditure of metabolic energy

24. Channels • Selective transport water or ions down their concentration or electric potential gradients • Highly regulated • Energetically favorable reaction • A passageway across the membrane through which multiple water molecules or ions move simultaneously at a very rapid rate—up to 108 per second

25. Transporters: Uniporters • Transport is specific and saturable • Facilitated “low resistance” diffusion: • Down the concentration gradient • Reversible • Rate much higher than passive diffusion

26. Transporters:Secondary transporters • Couple the movement of one type of ion or molecule against its concentration gradient to the movement of a different ion or molecule down its concentration gradient • Mediate coupled reactions in which an energetically unfavorable reaction coupled to energetically favorable reaction

27. Transporters:Secondary transporters • Catalyze “uphill” movement of certain molecules often referred to as “active transporters”, but unlike pumps, do not hydrolyze ATP (or any other molecule) during transport

28. Pumps • P, F, and V classes transport ions only, whereas the ABC superfamily class transports small molecules as well as ions.

29. Pumps • Use the energy of ATP hydrolysis to move ions or small molecules across a membrane againsta chemical concentration gradient or electric potential. • Overall reaction—ATP hydrolysis and the “uphill” movement of ions or small molecules—is energetically favorable

30. Storage of light energy occurs in the chloroplast • Key Concepts (1): • Chloroplasts capture kinetic energy in photons of sunlight and convert it into an ion gradient and high energy electrons, which are stored on the electron carrier NADPH. • The machinery that converts sunlight into these energy forms is a cluster of proteins in the thylakoid membrane inside chloroplasts. Collectively, they are known as the thylakoid electron transport chain.

31. Storage of light energy occurs in the chloroplast • Key Concepts (2): • The ion gradient energy is converted into ATP by an enzyme called ATP synthase. • The energy in ATP and NADPH is used to convert atmospheric CO2 into carbon-containing macromolecule called glyceraldehydes 3-phosphate via set of chemical reactions called the Calvin cycle.

32. Chloroplasts have three membrane-bound compartments

33. Chloroplasts convert sunlight into the first forms of cellular energy • Light reactions - energy transduction reactions • Dark reactions - carbon assimilation reactions

34. The energy transduction (light) reactions convert sunlight into stored potential energy

35. The electron transport chain in the thylakoid membrane.

36. The “Z” scheme

37. The carbon assimilation (dark) reactions convert stored potential energy into macromolecules Figure 10.14: The synthesis of glucose and sucrose from G3P in the cytosol. Figure 10.13: An overview of the Calvin cycle.

38. The carbon assimilation (dark) reactions convert stored potential energy into macromolecules

39. The synthesis of glucose and sucrose from G3P in the cytosol.

40. Cells use combination of channel, carrier, and pump proteins to transport small molecules across membranes • Key Concepts: • The majority of the macromolecules made by cells can serve as food energy for other cells. To access this energy, the chemical bonds holding these macromolecules must be broken. • In animals, macromolecules are broken into cellular building blocks (via digestion) in the extracellular space. • Cellular building blocks (e.g., glucose) are transported across the plasma membrane by an integrated system of channels, carriers, and pumps.

41. Macromolecule Transport leaky K+ channel, Na+/glucose symporter, and passive glucose carrier work together to move glucose from gut lumen to bloodstream

42. The cholera toxin: when things go wrong with membrane function cholera toxin A Lumen Gs Cytosol G protein 1.Cholera toxin subunit A crosses the membrane and activates a G protein

43. A Lumen Gs AC Cytosol ATP cAMP 2. G protein activates adenyl cyclase to produce cAMP

44. Lumen cAMP K+ Cl- Na+ Cytosol HCO3- 3. cAMP activates a Cl- channel. K+, Na+ Cl- and HCO3- are secreted to the intestinal lumen. The lumen osmotic pressures rises

45. Lumen cAMP K+ Cl- Na+ Cytosol HCO3- water flow 4. A large osmotic pressure gradient is established between the cytosol and the lumen causing large amounts of water to go to the lumen. This produces diarrhea and dehydration

46. glucose Na+ Water flow Lumen Lumen Na+/glucose symporter Cytosol Cytosol Oral rehydration: Gatorade 5. : The Na+/glucose symporter binds Na+ and glucose in the lumen and transports both to the cytosol. This increases the osmotic pressure in the cell making water return to cell by osmosis

47. The first phase of glucose metabolism occurs in the cytosol • Key Concepts (1): • The steps taken to extract energy from glucose are very similar to the steps chloroplasts use to build glucose from G3P, only in reverse order. • The first 10 enzymatic steps in the digestion of glucose are called glycoslysis.

48. The first phase of glucose metabolism occurs in the cytosol • Key Concepts (2): • The products of glycolysis include the molecule pyruvate, which must be metabolized to keep glycolysis from stalling. • In the absence of molecular oxygen (O2), pyruvate is metabolized by a process called fermentation. Two different methods of fermentation have evolved in different organisms.

49. Glycolysis is subdivided into 3 stages • The 10 chemical reactions in glycolysis convert glucose into 2-three-carbon compounds (pyruvate), two NADH molecules, and two ATP molecules

50. In the absence of O2, pyruvate undergoes fermentation Figure 10.18: Three fates of pyruvate.