Transcript Lecture 8 - Harford Community College

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
Energy for
cellular work
(Anabolism)
Energy from
Catabolism
ADP + Pi
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
– Add ATP from above = 4
 38 ATP
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