1. Energy, Enzymes, and photosynthesis

2. Basics of Photosynthesis
All cells need energy to carry out their activities
All energy ultimately comes from the sun
Photosynthesis—process in which some of the solar energy is captured by plants (producers) and transformed into glucose molecules used by other organisms (consumers).
6CO2 + 6H2O C6H12O6 + 6O2
Light energy
enzymes

3. Basics of Photosynthesis
Glucose is the main source of energy for all life. The energy is stored in the chemical bonds.
Cellular Respiration—process in which a cell breaks down the glucose so that energy can be released. This energy will enable a cell to carry out its activities.
C6H12O6 + 6O CO2 + 6H2O + energy
enzymes

4. Photosynthesis: redox process
Oxidation-reduction reaction:
Oxidation -loss of electrons from one substance
Reduction -addition of electrons to another substance

5. A Photosynthesis Road Map
Photosynthesis is composed of two processes:
The light reactions convert solar energy to chemical energy.
The Calvin cycle makes sugar from carbon dioxide.

6. Figure 7.4

7. Energy Energy —the capacity to do work
Kinetic energy —energy of motion (heat)
Potential energy —stored capacity to perform work (chemical energy stored in chemical bonds)
Figure 5.1x3
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

8. Chemical Reactions Cells carry out thousands of chemical reactions
The sum of these reactions constitutes cellular metabolism
Chemical reactions either store or release energy
Endergonic reactions —absorb and store energy in a reaction
Exergonic reactions —energy is released from reaction
Metabolism = endergonic rxns + exergonic rxns

9. Chemical Reactions Reactants —starting material
Products —ending material
Chemical Equation
Reactants → Products
Light energy
enzymes
6CO2 + 6H2O C6H12O6 + 6O2

10. Chemical Reactions
Occur when bonds between the outermost parts of atoms are formed or broken
Involve changes in matter, the making of new materials with new properties, and energy changes

11. Copyright © 2001 Pearson Education, Inc. publishing Benjamin Cummings

12. Energy in Cells ATP is used to shuttle chemical energy within the cell
ATP—energy-rich covalent bonds b/w outer 2 phosphate bonds

13. When ATP gives up its energy, it forms ADP and an energy shuttle, the phosphate group.
Energy coupling —using energy released from exergonic reactions to drive endergonic reactions
Copyright © 2001 Pearson Education, Inc. publishing Benjamin Cummings

14. For a chemical reaction to begin, reactants must absorb some energy
This energy is called the energy of activation (EA)
This represents the energy barrier that prevents molecules from breaking down spontaneously
EA barrier
Enzyme
Reactants 1
Products 2
Figure 5.5A
A protein catalyst called an enzyme can decrease the energy barrier
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

15. Enzyme —catalytic protein that speeds up the chemical reactions by lowering the activation energy (end with –ase)
Activation energy (EA)—amount of energy needed to start a chemical reaction before the reaction will proceed

16. Energy Profile
Copyright © 2001 Pearson Education, Inc. publishing Benjamin Cummings

17. Enzymes are Proteins Each amino acid contains: an amino group
a carboxyl group
an R group, which distinguishes each of the 20 different amino acids
Amino group
Carboxyl (acid) group
Figure 3.12A
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

18. Amino acids are linked by peptide bonds
Cells link amino acids together by dehydration synthesis
The bonds between amino acid monomers are called peptide bonds

19. Protein Structure Primary structure
The specific sequence of amino acids in a protein

20. Protein Structure
Secondary structure is polypeptide coiling or folding produced by hydrogen bonding
Primary structure
Amino acid
Secondary structure
Hydrogen bond
Pleated sheet
Alpha helix
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings
Figure 3.15, 16

21. Tertiary structure is the overall shape of a polypeptide—disulfide-bridges (covalent bonds), salt bridges (ionic attractions), H-bonds
Quaternary structure is the relationship among multiple polypeptides of a protein—stabilized by hydrogen-bonding, disulfide-bridges and salt bridges
Figure 3.17, 18
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

22. Overview: A protein’s specific shape determines its function
A protein, such as lysozyme, consists of polypeptide chains folded into a unique shape
The shape determines the protein’s function
A protein loses its specific function when its polypeptides unravel
Figure 3.14A
Figure 3.14B
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

23. Enzymes are substrate-specific —has unique 3-D shape which determines what the enzyme works on (substrate)
The 3-D shape of the enzyme creates a “pocket” called the Active Site in which the substrate binds
Active site has particular amino acid side-chains that match up with side-chains of substrate

24. ”Induced Fit Model” How an enzyme works
The enzyme is unchanged and can repeat the process
Copyright © 2001 Pearson Education, Inc. publishing Benjamin Cummings

25. Stop

26. Basics of Photosynthesis
Autotroph—organisms that synthesize organic molecules from inorganic materials (a.k.a. producers)
Photoautotrophs—use light as an energy source (plants, algae, some prokaryotes)
Heterotroph—organisms that acquire organic molecules from compounds produced by other organisms (a.k.a. consumers)

27. Leaf Anatomy

28. The Nature of Sunlight Sunlight is a type of energy called radiation
Or electromagnetic energy.
The full range of radiation is called the electro-magnetic spectrum.
Light may be reflected, transmitted, or absorbed when it contacts matter

29. Chloroplasts: Nature’s Solar Panels
Chloroplasts absorb select wavelengths of light that drive photosynthesis.
Thylakoids trap sunlight

30. Photosynthetic Pigments
Pigments-substances that absorb light (light receptors)
Wavelengths that are absorbed disappear
Wavelengths that are transmitted and reflected as the color you see

31. Plant Pigments
Chlorophyll a – absorbs blue-violet and red light, thus appears green
Accessory pigments
Absorb light of varying wavelengths and transfer the energy to chlorophyll a
Chlorophyll b-yellow-green pigment
Carotenoids-yellow and orange pigments

32. Photosynthesis: 2 stages
Light reactions—convert light energy to chemical bond energy in ATP and NADPH
Occurs in thylakoid membranes in chloroplasts
Calvin Cycle—carbon fixation reactions assimilate CO2 and then reduce it to a carbohydrate
Occurs in the stroma of the chloroplast
Do not require light directly, but requires products of the light reactions

33. Light reactions produce: ATP and NADPH that are used by the Calvin cycle; O2 released
Calvin Cycle produces: ADP and NADP+ that are used by the light reactions; glucose produced

34. How Photosystems Harvest Light Energy
Photosystem: assemblies of several hundred chlorophyll a, chlorophyll b, and carotenoid molecules in the thylakoid membrane
form light gathering antennae that absorb photons and pass energy from molecule to molecule
Photosystem I—specialized chlorophyll a molecule, P700
Photosystem II—specialized chlorophyll a molecule, P680

36. Light Reactions Light drives the light reactions to synthesize
NADPH and ATP
Includes cooperation of both photosystems, in
which e- pass continuously from water to
NADP+

37. Chemiosmosis
Energy released from ETC is used to pump H+ ions (from the split water) from the stroma across the thylakoid membrane to the interior of the thylakoid.
Creates concentration gradient across thylakoid membrane
Process provides energy for chemisomostic production of ATP

38. Light reactions produce: ATP and NADPH that are used by the Calvin cycle; O2 released
Calvin Cycle produces: ADP and NADP+ that are used by the light reactions; glucose produced

40. The Calvin Cycle: Making Sugar from Carbon Dioxide
Carbon enters the cycle in the form of CO2 and leaves in the form of sugar (glucose)
The cycle spends ATP as an energy source and consumes NADPH as a reducing agent for adding high energy e- to make sugar
For the net synthesis of this sugar, the cycle must take place 2 times

41. The Calvin Cycle: Carbon Fixation
3 CO2 molecules bind to 3 molecules of ribulose bisphosphate (RuBP) using enzyme, RuBP carboxylase (rubisco)
Produces 6 molecules of phosphoglycerate (3-PGA)

42. The Calvin Cycle: Reduction
6 ATP molecules transfer phosphate group to each 3-PGA to make 6 molecules of 1,3-diphosphoglycerate
6 molecules of NADPH reduce each 1,3-bisphosph. to make 6 molecules of glyceraldehyde 3-phosphate (G3P)

43. The Calvin Cycle: Regeneration of RuBP
One of the G3P exits the cycle to be used by the plant the other 5 molecules are used to regenerate the CO2 acceptor (RuBP): 3 molecules of ATP are used to convert 5 molecules of G3P into 3 RuBP

44. The Calvin Cycle: Regeneration of RuBP
3 more CO2 molecules enter the cycle, following the same chemical pathway to release another G3P from the cycle.
2 G3P molecules can be used to make glucose

45. Calvin Cycle

48. Special Adaptations that Save Water
C3 Plants=plants that only use Calvin Cycle to fix carbon
During dry conditions C3 plants conserve water by closing stomata
Plants then fix O2 to RuBP rather than CO2, since CO2 can’t enter the plant (photorespiration)
This yields no sugar molecules or ATP

49. How Photosynthesis Moderates Global Warming
Photosynthesis has an enormous impact on the atmosphere.
It swaps O2 for CO2.

50. How Photosynthesis Moderates Global Warming
Greenhouses used to grow plant indoors
Trap sunlight that warms the air inside.
A similar process, the greenhouse effect,
Warms the atmosphere.
Is caused by atmospheric CO2.

51. Global Warming
Greenhouse gases (CO2, CH4, CFC’s) are the most likely cause of global warming, a slow but steady rise in the Earth’s surface temperature.
Destruction of forests may be increasing this effect.
Combustion of fossil fuels

52. Global Warming Consequences
Polar ice caps melting
Rise in sea level and flooding of current coastline
New York, Miami, Los Angeles underwater
Change in types of plants—more adapted to warmer temps. and less water

53. References
Unless otherwise noted, pictures are from Essential Biology with Physiology, 2nd edition. Campbell, Reece, and Simon. (2007).