Transcript Cellular Respiration

Cellular Respiration
Learning objectives
 SWBAT: Understand that cellular respiration involves a
series of enzyme-catalyzed reactions that harvest free
energy from simple carbohydrates.
 SWBAT: Use representations (models) to demonstrate
the mechanisms and structural features of cells that
allow organisms to capture and use free energy
Cells do 3 kinds of work
 Chemical work- pushing endergonic reactions that
would not occur spontaneously. Often these are
anabolic pathways like creating polymers from
monomers.
 Transport work- pumping substances across
membranes against the gradient flow
 Mechanical work- movement of things like cilia,
muscle cells, or chromosomes
To accomplish work. . .
 Cells must couple (combine) exergonic reactions with
endergonic reactions to provide the needed energy.
 ATP is the energy source for most of this coupling.
 Catabolic reactions break down complex organic
molecules into simple molecules plus energy.
 Anabolic reactions are those that consume energy to
synthesize complex molecules from simpler ones.
Cellular respiration
In living cells, both plant and animal,
cellular respiration is an extremely
efficient catabolic pathway that
provides the energy necessary to do
work.
Figure 7.2
Light
energy
ECOSYSTEM
CO2  H2O
Photosynthesis
in chloroplasts
Cellular respiration
in mitochondria
ATP
Heat
energy
Organic
 O2
molecules
ATP powers
most cellular work
Basic equation
Organic compound + O2  CO2 + H2O + energy
We will focus on the breakdown of glucose:
C6H12O6 + 6O2  6CO2 + 6H2O + Energy (ATP&heat)
This is an exergonic reaction with ΔG= -686kcal/mole
Redox reactions
 Chemical reactions often yield energy by transferring
electrons.
 The transfers are called oxidation-reduction reactions =
“redox”
 Oxidation= the loss of electrons
 Reduction= the addition of electrons
 Electron donor= reducing agent
 Electron acceptor= oxidizing agent
Oxidized
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
Reduced
 Glucose has lots of electrons ready to be transferred to
oxygen.
 Why then does it not instantaneously do so?
 Why doesn’t a sugar cube ignite at room temperature?
 Combustion is an oxidation reaction with the sudden
release of energy in the form of heat and light.
 The answer lies in the very high
activation energy of this reaction.
 Even our body temperatures are not high
enough to supply enough energy to
overcome it.
Bring on the enzymes!
Enzymes decrease the activation energy
required to allow the oxidation of glucose in
a series of controlled steps to efficiently
capture the energy that it releases.
NADH
 A coenzyme that acts as an electron carrier
 At each step, as an electron is stripped from glucose, it
is often passed to a molecule called NADH
 Easily cycles between NAD+ (its oxidized form) and
NADH (its reduced form).
3 Steps of Cellular
Respiration
1. Glycolysis
1. Kreb Cycle / Citric Acid Cycle
1. Oxidative phosphorylation/ Electron Transport Chain
Glycolysis
 Occurs in the cytoplasm
 Breaks down glucose (a 6 carbon
molecule) into 2 molecules of
pyruvate (each with 3 carbons)
 Pyruvate (3 carbon) moves into the
matrix of the mitochondria where it is
further broken down into Acetyl CoA (2
carbons) and CO2
Kreb Cycle/ Citric acid cycle
 Occurs in the mitochondrial matrix
 Further breaks down Acetyl CoA and
transfers energy to NADH and FADH2
 Produces a small amount of ATP
Oxidative Phosphorylation
 Also known as the electron transport
chain
 Occurs in the inner membrane of the
mitochondria
 Produces 32- 34 molecules of ATP!
Learning objectives
 SWBAT: Understand that cellular respiration involves a
series of enzyme-catalyzed reactions that harvest free
energy from simple carbohydrates.
 SWBAT: Use representations (models) to demonstrate
the mechanisms and structural features of cells that
allow organisms to capture and use free energy