Download Electron Transport

Cellular Energy
and Metabolism
Law of Thermodynamics
 In your body, energy is required to assemble/break
down molecules, transport molecules, and transmit
genetic instructions.
“Energy can be converted from one form to
another, but it cannot be created or destroyed.”
Autotrophs and Heterotrophs
 (Review) Some organisms make their own food
automatically, while others must obtain it from other
organisms (heterotrophs).
 Chemoautotrophs – use inorganic substances such as
hydrogen sulfide as a source of energy.
Metabolism
 All chemical reactions
in a cell
 Catabolic v. Anabolic
 Catabolic – release
energy by breaking
down larger molecules
into smaller ones.
 Anabolic – use this
energy to build large
molecules from smaller
ones.
ATP: The Unit of Cellular Energy
Cellular Respiration
What do we think of when we
think of respiration?
Three Stages
 Glycolysis – no oxygen required (anaerobic)
 Krebs Cycle
 Electron Transport
oxygen required
(aerobic)
Glycolysis
 Glucose is broken down in the cytoplasm through
glycolysis.
 Net yield: two molecules of ATP, two molecules of
NADH, two molecules of pyruvate
Three Stages
 Glycolysis
 Krebs Cycle
 Electron Transport
Krebs Cycle
 Pyruvate (from glycolysis) is broken down into
carbon dioxide (CO2) through a series of reactions.
 In the presence of oxygen (aerobic)
 Basic steps:
1. Pyruvate reacts with coenzyme A (CoA) to form
acetyl CoA.
 Carbon Dioxide is released
 NAD+ is converted to NADH
2. Acetyl CoA moves to the mitochondrial matrix.
Krebs Cycle - continued
 Acetyl CoA combines with a 4-carbon
compound to form a 6-carbon compound called
citric acid.
 Citric acid is broken down in a series of steps
releasing the following molecules:
 2 CO2
 1 ATP
 3 NADH
 1 FADH2 – similar to NADH
 Ends with four carbon compound
 Cycle continues with the production of a new
acetyl CoA
Krebs Cycle – Net Yield
 Keep in mind some of these are produced “precycle”
 6 CO2
 2 ATP
look out for these
 8 NADH
again!
 2 FADH2
Three Stages
 Glycolysis
 Krebs Cycle
 Electron Transport
Electron Transport
 The stage where the most ATP is produced – 32!
 High energy electrons and hydrogen ions from
NADH and FADH2 are put to work.
 Electrons move along membrane from one protein
to another.
 This release of electrons also causes NADH and
FADH2 to lose a proton (H+)
 These protons are pumped into intermembrane
space from the mitochondrial matrix
Electron Transport - continued
 The protons (H+) then diffuse back down their
concentration gradient through ATP synthase
 This flow of protons causes the formation of ATP
 Oxygen is the final electron acceptor
 Some prokaryotes also go through aerobic
respiration (utilizing their cell membrane)
 Cellular Respiration Net Yield: 36 ATP
Anaerobic Respiration
 Done by many prokaryotes, and on occasion by
eukaryotes.
 A pathway by the name of fermentation follows
glycolysis in anaerobic respiration.
 Produces limited ATP
 Replenishes NAD+ (see next slide)
 Lactic Acid Fermentation – muscles!
 Alcohol Fermentation – yeast and bacteria.
Lactic Acid
Fermentation
Alcohol
Fermentation