Unit 3

1. Unit 3 Topic 8 (Cell Respiration and Photosynthesis)

2. 8.1 – Cell Respiration • 8.1.1 Forms of oxidation and reduction. • 8.1.2 Glycolysis. • 8.1.3 Structure of the mitochondria. • 8.1.4 Aerobic respiration. • 8.1.5 Oxidative phosphorylation in terms of chemiosmosis • 8.1.6 Relationship between the structure and function of the mitochondria.

3. 8.1.1  State that oxidation involves the loss of electrons from an element, whereas reduction involves a gain of electrons and that oxidation frequently involves gaining oxygen or losing hydrogen, whereas reduction frequently involves losing oxygen or gaining hydrogen • Redox (reduction-oxidation) reactions are chemical reactions that involve the transfer of electrons (gain or loss) between species • Mnemonics for redox reactions include: • OIL RIG:Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons) • ELMO:Electron Loss Means Oxidation • LEO goes GER: Loss of Electrons is Oxidation, Gain of Electrons is Reduction • In metabolic reactions, a species that has been reduced has the ability to reduce other species (this is the predominant role of hydrogen carriers)

5. 8.1.2  Outline the process of glycolysis, including phosphorylation, lysis, oxidation and ATP formation • Glycolysis is the first stage of cell respiration and involves the breakdown of glucose into two molecules of pyruvate • It is an anaerobic reaction (does not require the presence of oxygen) and occurs in the cytoplasm • There are four main parts in glycolysis (not including intermediary steps): • 1.  Phosphorylation:  A hexose sugar is phosphorylated by two ATP to become hexosebiphosphate • 2.  Lysis:  The hexosebiphosphate splits into two triose phosphates (3C sugars) • 3.  Oxidation:  Hydrogen removed from the triose phosphates via oxidation (NAD is reduced to NADH + H+) • 4.  ATP Formation:  Four ATP molecules are released as the triose phosphates are converted into pyruvate • Overall:  One molecule of glucose results in 2 pyruvate, 2 (NADH + H+) and 2 ATP (net gain)

6. Glycolysis

7. 8.1.3  Draw and label a diagram showing the structure of a mitochondrion as seen in electron micrographs 2D representation Electron micrograph 3D representation

8. 8.1.4  Explain aerobic respiration, including the link reaction, the Krebs cycle, the role of NADH + H+, the electron transport chain and the role of oxygen • Aerobic respiration takes place in the mitochondria, using the pyruvate produced via glycolysis • It produces large amounts of ATP in the presence of oxygen via three main processes: 1) The Link Reaction • Pyruvate is transported from the cytosol to the mitochondrial matrix in a reaction that produces (one) NADH + H+ via oxidation • The pyuvate loses a carbon (as CO2) and the remaining two carbons are complexed with coenzyme A (CoA) to form acetyl CoA

9. 2) The Krebs Cycle • In the matrix, acetyl CoA combines with a 4C compound to form a 6C compound • Over a series of reactions the 6C compound is broken back down into the original 4C compound • These reactions result in the formation of 2 CO2 molecules, 1 ATP molecule and multiple hydrogen carriers, specifically 3 (NADH + H+) and 1 FADH2

10. 3) The Electron Transport Chain • The hydrogen carriers (NADH + H+ and FADH2) provide electrons to the electron transport chain on the inner mitochondrial membrane • As the electrons cycle through the chain they lose energy, which is used to translocate H+ ions to the intermembrane space (creating a gradient) • The hydrogen ions return to the matrix through the transmembrane enzyme ATP synthase, producing multiple ATP molecules (via chemiosmosis) • Oxygen acts as a final electron acceptor for the electron transport chain, allowing further electrons to enter the chain • Oxygen combines the electrons with H+ ions to form water molecules • The electron transport chain produces the majority of the ATP molecules produced via aerobic respiration (~32 out of 36 ATP molecules)

12. 8.1.5  Explain oxidative phosphorylation in terms of chemiosmosis • Oxidative phosphorylation describes the production of ATP from oxidized hydrogen carriers (as opposed to substrate level phosphorylation) • When electrons are donated to the electron transport chain, they lose energy as they are passed between successive carrier molecules • This energy is used to translocate H+ ions from the matrix to the intermembrane space against the concentration gradient • The build up of H+ ions creates an electrochemical gradient, or proton motive force (PMF) • The protons return to the matrix via a transmembraneenzyme called ATP synthase • As they return they release energy which is used to produce ATP (from ADP and Pi) • This process is called chemiosmosis and occurs in the cristae • The H+ ions and electrons are combined with oxygen to form water, allowing the process to be repeated anew

14. 8.1.6  Explain the relationship between the structure of the mitochondria and its function • Inner membrane:  Folded into cristae to increase surface area for electron transport chain • Intermembrane space:  Small space between inner and outer membranes for accumulation of protons (increases PMF) • Matrix:  Contains appropriate enzymes and a suitable pH for the Krebs cycle to occur • Outer membrane:  Contains appropriate transport proteins for shuttling pyruvate into the mitochondria

15. Animations • http://www.sumanasinc.com/webcontent/animations/content/cellularrespiration.html • http://www.mhhe.com/biosci/bio_animations/MH01_CellularRespiration_Web/index.html • Song – • https://www.youtube.com/watch?feature=player_embedded&v=VCpNk92uswY • https://www.youtube.com/watch?feature=player_embedded&v=3aZrkdzrd04

16. Extra credit poster • Poster depicting all four steps of Aerobic Cell Resp • Include diagrams on the front as well as ALL molecules (ATP, NADH, FADH2, CO2, O2, H2O) produced at each step • Include explanation of what is happening at each stage

17. 8.2 - Photosynthesis • 8.2.1 Chloroplast Structure. • 8.2.2 Stages of photosynthesis. • 8.2.3 Light-dependent reaction. • 8.2.4 Photophosphorylation. • 8.2.5 Light-Independent reaction. • 8.2.6 Structure and function of the chloroplast. • 8.2.7 Action spectrum and absorption spectrum. • 8.2.8 Limiting factors on the rate of photosynthesis.

18. 8.2.1  Draw and label a diagram showing the structure of a chloroplast as seen in an electron micrograph

19. 8.2.2  State that photosynthesis consists of the light-dependent and light-independent reactions • Photosynthesis is a two-step process: 1.  The light dependent (light) reactions convert the light energy into chemical energy 2.  The light independent (dark) reaction uses the chemical energy to make organic molecules

20. 8.2.3  Explain the light dependent reactions • The light dependent reactions occur on the thylakoid membrane and may occur by either cyclic or non-cyclic processes • In both processes, light excites chlorophyll (clustered in photosystems) which release electrons that pass through an electron transport chain, making ATP (photophosphorylation) • Non-Cyclic Photophosphorylation • Chlorophyll in photosystems I and II absorbs light, which triggers the release of high energy electrons (photoactivation) • The electrons from photosystem II pass along a series of carriers (electron transport chain), producing ATP via chemiosmosis • The electrons from photosystem I reduce NADP+ to generate NADPH + H+ • Electrons lost from photosystem I are replaced by electrons from photsystem II • Electrons lost from photosystem II are replaced by electrons generated by the photolysis of water (oxygen is produced as a by-product)

22. Cyclic Photophosphorylation • Only photosystem I is involved in cyclic photophosphorylation • The high energy electrons released by photoactivation pass along an electron transport chain (producing ATP) before returning to photosystem I • Cyclic photophosphorylation does not produce NADPH + H+, which is needed for the light independent reactions • Thus while cyclic photophosphorylation can make chemical energy (ATP) from light, it cannot be used to make organic molecules

24. 8.2.4  Explain photophosphorylation in terms of chemiosmosis • As the electrons (released from chlorophyll) cycle through the electron transport chains located on the thylakoid membrane, they lose energy • This free energy is used to pump H+ ions from the stroma into the thylakoid • The build up of protons inside the thylakoid creates an electrochemical gradient (or proton motive force) • The H+ ions return to the stroma via the transmembrane enzyme ATP synthase, which uses the potential energy from the proton motive force to convert ADP and an inorganic phosphate (Pi) into ATP • This process is called chemiosmosis

26. 8.2.5  Explain the light independent reaction • The light independent reaction occurs in the stroma and uses the ATP and NADPH + H+ produced by the light dependent reaction (non-cyclic) • The light independent reaction is also known as the Calvin cycle and occurs via three main steps: 1.  Carbon Fixation • The enzyme rubisco (RuBPcarboxylase) catalyses the attachment of CO2 to the 5C compound ribulosebisphosphate (RuBP) • The unstable 6C compound that is formed immediately breaks down into two 3C molecules called glycerate-3-phosphate (GP)

27. 2.  Reduction • Each GP molecule is then phosphorylated by ATP and reduced by NADPH + H+ • This converts each GP molecule into a triose phosphate (TP) called glyceraldehyde phosphate

28. 3.  Regeneration of RuBP • For every six molecules of TP produced, only one may be used to form half a sugar molecule (need 6 cycles of Calvin cycle to form a complete glucose) • The remaining TP molecules are reorganized to regenerate stocks of RuBP in a reaction that involves ATP • With RuBP regenerated, this cycle will repeat many times and be used to construct chains of sugars (e.g. sucrose) for use by the plant

30. 8.2.6  Explain the relationship between the structure of the chloroplast and its function • Thylakoids:  Small lumen means small changes in proton concentration have a large effect on the proton motive force • Grana: Thylakoids arranged in stacks to greatly increase surface area available for light absorption (chlorophyll located in thylakoid membrane) • Stroma:  Contains appropriate enzymes and suitable pH for the light independent reaction to occur

31. 8.2.7  Explain the relationship between the action spectrum and absorption spectrum of photosynthetic pigments in green plants • Pigments absorb light as a source of energy for photosynthesis • The absorption spectrum indicates the wavelengths (frequency) of light absorbed by each pigment • The action spectrum indicates the rate of photosynthesis for each wavelength / frequency • There is a strong correlation between the cumulative absorption spectrum of all photosynthetic pigments and the action spectrum • Both display two main peaks - a larger peak at ~450 nm (blue) and a smaller peak at ~670 nm (red) with a decrease in between (green)

33. 8.2.8  Explain the concept of limiting factors in photosynthesis, with reference to light intensity, temperature and concentration of carbon dioxide • The law of limiting factors states that when a chemical process depends on more than one essential condition being favorable, its rate will be limited by the factor that is nearest its minimum value • Photosynthesis is dependent on a number of favorable conditions, including: • Light Intensity • Light is required for the light dependent reactions (photoactivation of chlorophyll and photolysis of water molecules) • Low light intensities results in insufficient production of ATP and NADPH + H+ (both needed for the light independent reaction)

34. Temperature • Primarily affects the light independent reaction (and to a lesser extent the light dependent reactions) • High temperatures will denature essential enzymes (e.g. rubisco), whereas insufficient thermal energy will prohibit reactions from occurring

35. Concentration of Carbon Dioxide • Carbon dioxide is required for the light independent reaction to occur (carbon fixation of RuBP by rubisco) • At low levels, carbon fixation will occur very slowly, whereas at higher levels the rate will peak as all rubsico are being used

36. Animations • http://www.mhhe.com/biosci/bio_animations/02_MH_Photosynthesis_Web/index.html • Song - https://www.youtube.com/watch?feature=player_embedded&v=_IV-E68rh18