Lecture 5

Microbe Metabolism

Metabolism

• Metabolism:

• Metabolic Pathway:

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

The use of ATP in Metabolism

ATP

ADP + Pi

Energy fromCatabolism

Energy for cellular work(Anabolism)

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

Using ATP for energy

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

Figure 5.9

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

Aerobic Respiration

Formula for Aerobic Respiration

C6H12O6 +6O2 6CO2 + 6H2O +38 ATP

Steps of Aerobic Respiration

• Glycolysis

• Transition Step

• Krebs Cycle

• Electron Transport

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

Glycolysis

• Net Yield of glycolysis:

–2 ATP

–2 NADH

–2 pyruvate

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

Krebs Cycle

• Net Yield of Krebs Cycle:– 2 ATP– 6 NADH

– 2 FADH2

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

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)

Figure 5.16 (2 of 2)

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

Lactic Acid Fermentation

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