Two types of metabolic reactions
• Catabolism or catabolic reactions: chemical reactions that break down large molecules into smaller ones
• Anabolism or anabolic reactions (also called biosynthesis): chemical reactions that involve the synthesis of large molecules from smaller ones
Catabolic Reaction: Cell Respiration
C6H1206 + 6O2 6CO2 + 6H20 + ATP
Anabolic Reaction: Photosynthesis
6CO2 + 6H20 + ATP C6H12O6 +6O2
ATP
• Adenosine Triphosphate• Energy currency of the cell• Releases free energy when it’s phosphate
bonds are broken• Allows cells to do work• It takes work to stay alive• Therefore, without ATP, there is no life
Goal of this unit: to investigate how cells make ATP from compounds such as glucose
Oxidation- Reduction Reactions
• The production of ATP occurs by oxidation-reduction reactions
• Oxidation-reduction reactions: when one or more electrons are transferred from one substance to another
Oxidation-Reduction reactions
• Oxidation: the loss of electrons• Reduction: the gain of electrons• Redox reactions: when both occur at the same
time
• When electrons removed from a compound protons often follow (H+)
• Oxidation: loss of a hydrogen atom• Reduction: gain of a hydrogen atom
The role of electron carriers• Cells use ATP as carrier of energy
• Cells use certain molecules as carriers of electrons
• 3 different electron carriers :
Central Metabolic Pathways
• What do they do?
• Modify organic molecules in a step-wise fashion to form– Intermediates with high energy bonds that can
be used to synthesize ATP– Intermediates that can be oxidized to
generate reducing power– Intermediates and end products that function
as precursor metabolites
Glycolysis
• Primary pathway used by nearly all organisms to convert glucose to pyruvate
• 10 step pathway- can occur in presence or absence of oxygen
• 1 molecule of glucose split into 2 molecules of pyruvate
• Generates 2 molecules of ATP and 2 molecules of NADH
Glucose(6C) + 2NAD+ + 2ADP +2Pi 2 pyruvate(3C) + 2NADH + 2H+ + 2ATP
Transition Step
• Links Glycolysis to Krebs Cycle
• Pyruvate converted to acetyl Co-A
• NADH generated
• Net Yield of Transition Step:– 2 NADH
Krebs Cycle
• 8 steps of Krebs cycle complete the oxidation of glucose
• Incorporates the acetyl groups from transition step, releasing CO2
• Does not directly use oxygen
Oxidative Phosphorylation
• Uses NADH and FADH2 generated in glycolysis, the transition step, and the TCA cycle to synthesize ATP
• Occurs through a combination of two mechanisms
Electron Transport Chain
• As electrons fall from carrier to carrier, energy is used to form ATP
• This is done by pumping protons out of the cell as electrons move along
• This creates a proton gradient (proton motive force)
• Energy represented in this gradient used to synthesize ATP (ATP synthase is enzyme used)
Electron Transport Chain
• Oxidative phosphorylation in electron transport chain yields:
• Each NADH generates 3 ATPs
• Each FADH2 generates 2 ATPs
Net ATP yield from Aerobic Respiration:
• Glycolysis: 2 ATP, 2 NADH
• Transition Step: 2 NADH
• TCA cycle: 6 NADH, 2 FADH2, 2 ATP
• Electron Transport Chain:– Add all NADH: 10 X 3= 30
– Add all FADH2: 2 X 2= 4 38 ATP
– Add ATP from above = 4
Anaerobic Respiration
• The same as aerobic respiration, generating ATP by phosphorylation, but uses inorganic molecule other than O2 , such as nitrate, as terminal electron acceptor
• Anaerobic respiration produces less ATP than aerobic respiration
Fermentation
• Fermentation Produces ATP Using an Organic Electron Donors and Acceptors
• Fermentation is used when oxygen and other alternative electron acceptors are unavailable
• Generates 2 ATP by substrate level phosphorylation
• Also generates 2 NADH- must be recycled to NAD+
• Different end products based on which microorganism
Eukaryotes also perform fermentation, such as the yeast used in alcoholic fermentation to create
alcoholic beverages
Photosynthesis
• Starting substances: carbon dioxide, water• Ending substances: glucose and oxygen• Two types of organisms:• Oxygenic Photosynthesis:
– produces oxygen and glucose– Uses light energy from the sun
• Anoxygenic Photosynthesis:– Do not produce oxygen– Water not starting substance, instead hydrogen
sulfide