Download 2.A.2 Organisms Capture and Store Energy - kromko

2.A.2 Organisms Capture and Store
Energy Part II
(Cellular Respiration)
Organisms capture and store free
energy for use in biological processes.
Cellular respiration uses free energy available
from sugars to phosphorylate ADP, producing
the most common energy carrier, ATP.
The free energy available in sugars can be
used to drive metabolic pathways vital to
cell processes.
Cellular respiration involves a series of
enzyme-catalyzed reactions that harvest
free energy from simple carbohydrates.
Cell respiration is a catabolic pathway that
yields energy by oxidizing organic fuels.
LEO says GERRR
• Lose Electrons = Oxidized
• Gains Electrons = Reduced
The breakdown of organic molecules is
exergonic (G >0); the energy released can
be harnessed to phosphorylate ADP  ATP.
The Three Steps of Cellular Respiration
Glycolysis
Krebs
Cycle
Electron Transport Chain
Glycolysis: the breakdown of one glucose
molecule into two pyruvate. It occurs in
the cytoplasm and is anaerobic.
Glycolysis: Energy Investment Phase
• Glucose, a six carbon sugar, is split into two 3-carbon
molecules.
• Requires 2 ATP
Glycolysis: Energy Payoff Phase
• The two 3-carbon molecules are converted into two
pyruvate.
• Produces 2 NADH and 4 ATP
Glycolysis: Summary
Investment:
•
•
•
Glucose
4 ATP formed – 2 ATP used
2 NAD+
Payoff:
•
•
•
2 Pyruvate
2 ATP
2 NADH
Oxidation
Reaction
Pyruvate is transported from the cytoplasm
to the mitochondrion, where it is
converted to Acetyl CoA.
Transition Reaction:
Investment:
• 2 Pyruvate
Payoff:
• 2 Acetyl Coenzyme A
• 2 NADH
• 2 CO2 (waste product)
The Krebs Cycle
(Also known as the Citric Acid Cycle or the TCA Cycle)
The Krebs Cycle occurs in the matrix of the
mitochondria.
Matrix
The Krebs Cycle produces 2 ATP through
substrate-level phosphorylation. (Must
occur twice for one glucose to be
consumed).
The Krebs Cycle produces 2 ATP through
substrate-level phosphorylation.
During the Krebs Cycle , coenzymes NAD+
and FADH each receive high energy
electrons and become NADH and FADH2.
The Krebs Cycle Summary:
Investment:
• 2 Acetyl CoA
Payoff:
•
•
•
•
2 ATP
6 NADH
2 FADH2
4 CO2 (waste)
Substrate-Level
Phosphorylation
The Electron Transport Chain is imbedded
in the inner mitochondrial membrane.
Electrons that were extracted in the Krebs
cycle are carried by NADH and FADH2 to
the Electron Transport Chain.
The electrons are passed from one carrier to the
next until they are ultimately accepted by
oxygen, forming water. (Oxygen is the final
electron acceptor.)
The energy from the electrons is used to pump
protons into the intermembrane space, forming
an electrochemical gradient.
The protons diffuse through ATP synthase
(chemiosmosis), which uses the energy of the
gradient to synthesize ATP from ADP. This type
of ATP synthesis is called Oxidative
Phosphorylation.
The Electron Transport Chain occurs on the
cell membrane of prokaryotes.
The Electron Transport Chain Summary:
Investment:
• 10 NADH
• 2 FADH2
• Oxygen
Payoff:
• 32-34 ATP
• H 2O
Oxidative
Phosphorylation
Cellular Respiration Summary:
Investment:
• 1 glucose
• oxygen
Payoff:
• Water
• CO2
• 36-38 ATP
Yields 686 kcal
energy per mole of
glucose oxidized!
Cellular respiration also occurs in plants,
along with photosynthesis.
Endotherms can decouple oxidative
phosphorylation from the electron
transport to produce more body heat
instead of ATP.
Different energy-capturing processes use
different types of electron acceptors:
• NADP+ for photosynthesis
• Oxygen for cellular respiration
In the absence of oxygen, ATP production
can continue. This is called fermentation.
There are two types of fermentation:
Fermentation
Lactic Acid
Fermentation
Ethanol
Fermentation
Animals
Yeast
Fermentation produces ATP through
substrate-level phosphorylation when the
ETC cannot run due to lack of oxygen.
Lactic Acid Fermentation
Ethyl Alcohol Fermentation
Fermentation Summary:
Investment:
• 1 glucose
Payoff:
• 2 ATP
• 2 CO2
Anaerobic
Heterotrophs may metabolize
carbohydrates, lipids and proteins by
hydrolysis as sources of free energy.
Hydrolysis:
Photosynthesis and Cellular Respiration are
mirror reactions.
Photosynthesis:
Cellular Respiration:
Learning Objectives
LO 2.4 The student is able to use representations to
pose scientific questions about what mechanisms
and structural features allow organisms to
capture, store and use free energy. [See SP 1.4,
3.1]
LO 2.5 The student is able to construct explanations
of the mechanisms and structural features of cells
that allow organisms to capture, store or use free
energy. [See SP 6.2]