Metabolic Pathways
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Several steps
Oxidations paired with reductions
Specific enzymes for each step
Multiple ways to “enter” or “exit” pathway
Allows links to other pathways
Thermodynamics
• First law?
– All about energy TRANFER, need to be able
to trace where all the energy ends up
– Usually a partial transfer
– Combustion on a SLOW scale
• Energy coupling
Figure 6.9 Energy coupling by phosphate transfer
Basic Energy molecules
• ATP/GTP
• Electron Carriers – NADH, FADH2,
NADPH
– Ways of moving energy around;
Figure 9.7 Substrate-level phosphorylation
Oxidative phosphorylation
• Involves the oxidation of electron carriers, chemiosmosis
and oxygen.
• We’ll elaborate more on this later.
Figure 9.2 A review of how ATP drives cellular work
Oxidation and Reduction
• Always Paired together
• What happens in a reduction reaction?
• What happens in an oxidation?
• What happens to the free energy of a molecule when it is
reduced? VERY IMPORTANT!!!!
Figure 9.3 Methane combustion as an energy-yielding redox reaction
We can summarize the two energy-coupling coenzymes as follows:
1. ADP traps chemical energy to make ATP.
2. NAD+ traps the energy released in redox reactions to make NADH
Catabolism vs. Anabolism
- What’s going on with the energy?
- Which would be paired with ATP  ADP
- Which might be paired with NAD+  NADH
BUT energy in NADH can not be used directly
• Oxidative Phosphorylation couples the
oxidation of NADH (energy out) with the
Phosphorylation of ADP (energy in)
• Requires Chemiosmosis – using potential
energy in H+ gradient to drive ADP  ATP
• This process is essential to both photosynthesis
AND aerobic cell respiration
Figure 9.1 Energy flow and chemical recycling in ecosystems
Aerobic Cell Respiration
• Complete oxidation of glucose
– Glucose  CO2
endo or exo?
– What are the reactions that break glucose down likely to be paired
with?
• Reduction or oxidation of electron carriers?
• Phosphorylation or hydrolysis of ATP?
Figure 9.6 An overview of cellular respiration (Layer 3)
Figure 9.8 The energy input and output of glycolysis
Figure 9.9 A closer look at glycolysis: energy investment phase (Layer 2)
Figure 9.9 A closer look at glycolysis: energy payoff phase (Layer 4)
Know your enzymes
• Kinases
– Linked with?
• Isomerases
• Dehydrogenases
– Linked with?
Glycolysis Summary
• Started with?
• Ended with?
• Where is the bulk of the energy?
• Location?
• Aerobic?
Figure 9.10 Oxidation of Pyruvate
** remember we have TWO pyruvates per glucose, so
everything from here on out is doubled!!**
Keep the tally going!
• What do we have now?
Krebs Cycle (a.k.a.
citric acid cycle)
- complete
oxidation of Acetyl
CoA’s carbons into
CO2
Figure 9.12
So after Krebs what are
we left with?
Where is the energy?
Can we use it all?
Electron carriers need to be oxidized
• NADH + H+ + ½ O2  NAD+ + H2O
• Requires Electron Transport Chain (respiratory chain)
– Electrons are passed from membrane bound protein to
membrane bound protein in a series of oxidations
– EXERGONIC!
• Energy released actively transports H+ across
membrane establishing a gradient
Figure 9.14 ATP synthase, a molecular mill
Final Tally
• What do we have now?
• Why is oxygen needed?
• What happens in absence of O2?
• Solution?
Figure 9.18 Pyruvate as a key juncture in catabolism
Figure 9.20 The control of cellular respiration
Figure 9.19 The catabolism of various food molecules
Figure 10.2 Focusing in on the location of photosynthesis in a plant
Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the
Calvin cycle (Layer 3)
Figure 10.5 The electromagnetic spectrum
Figure 10.6 Why leaves are green: interaction of light with chloroplasts
Figure 10.7 Determining an absorption spectrum
Photons absorbed by molecules
raise the molecule to an excited
state.
Figure 10.8 Evidence that chloroplast pigments participate in photosynthesis:
absorption and action spectra for photosynthesis in an alga
Figure 10.9 Location and structure of chlorophyll molecules in plants
Figure 10.10 Excitation of isolated chlorophyll by light
Figure 10.11 How a photosystem harvests light
Figure 10.12 How noncyclic electron flow during the light reactions generates ATP
and NADPH (Layer 5)
Figure 10.13 A mechanical analogy for the light reactions
Figure 10.14 Cyclic electron flow
Figure 10.15 Comparison of chemiosmosis in mitochondria and chloroplasts
Figure 10.16 The light reactions and chemiosmosis: the organization of the thylakoid
membrane
Figure 10.17 The Calvin cycle (Layer 3)
Figure 10.19 C4 and CAM photosynthesis compared
Figure 10.18 C4 leaf anatomy and the C4 pathway
Figure 10.20 A review of photosynthesis