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Cellular Respiration
Harvesting Energy From Food
Chapter 5
Obtaining Food
All organisms need food for energy and building materials. Biologists
classify organisms according to how they obtain food.
Autotrophs are organisms such as a
plant that makes its own food. For
example, during photosynthesis plants
use the sun's energy to convert water
and carbon dioxide into sugars.
Autotrophs are also called producers.
Heterotrophs are organisms that
cannot make their own food, such as
humans, meaning "other eaters."
Heterotrophs are also called
consumers.
Principles of Energy Harvest
Energy flow occurs through
the ecosystem
The products of photosynthesis
are the chemical ingredients for
cellular respiration, while the
products of cellular respiration are
the chemical ingredients for
photosynthesis.
Chemical Energy
Just like the molecules in gasoline and other fuels, organic compounds are a
form of potential energy called chemical energy.
The stored chemical energy of
foods such as peanuts can be
released through cellular
respiration.
Introduction to Energy
Energy is the ability to do work.
Can you identify examples of
these forms of energy?
kinetic energy: energy of
motion
potential energy: energy
stored due to an object's
position or arrangement
Putting Chemical Energy to Work
Potential energy is converted to Kinetic energy
Calories: Units of Energy
calorie: amount of energy required to raise the temperature of 1 g of water
1°C.
The "calories" shown on a food label are actually kilocalories. One
kilocalorie (kcal) equals 1,000 calories.
What factors contribute to the energy
(calorie) needs of a person?
ATP provides the energy for cellular work
ATP: (adenosine triphosphate) main energy source that cells use for most
of their work
An ATP molecule contains potential energy, much like a compressed
spring. When a phosphate group is pulled away during a chemical
reaction, energy is released.
The ATP Cycle
ATP is constantly recycled in your cells. A working muscle cell recycles all
of its ATP molecules about once each minute. That's 10 million ATP
molecules spent and regenerated per second!
ATP powers cellular work by coupling energy releasing to energy
using reactions
ATP + H2O  ADP + P
ATP and Cellular Work
Cells perform three main types of work: chemical work, mechanical work,
and transport work.
The transfer of the phosphates from ATP forming ADP provides the energy.
Relationship of Cellular Respiration to Breathing
Cellular respiration is an aerobic process, meaning that it requires oxygen
Breathing supports cellular respiration by providing the body with oxygen
and removing carbon dioxide.
Overall Equation for Cellular Respiration
In cellular respiration, the atoms in glucose and oxygen are rearranged,
forming carbon dioxide and water. The cell uses the energy released to
produce ATP.
Cellular respiration breaks down organic molecules to yield
energy.
Energy stored in organic compounds is released in a series of
enzymes controlled reactions. Similar to burning but…
"Falling" Electrons as an Energy Source
Food represents a source of high energy electrons similar to the potential
energy of being on top of a slide.
When the electrons pass from the high potential state of food to oxygen,
released energy is converted to other forms of energy.
How does burning compare
to cellular respiration?
When sugar is burned,
oxygen atoms pull electrons
from carbon and hydrogen,
forming new chemical bonds.
Burning releases energy in
the form of heat and light.
Burning Compared to Cell Respiration: The energy release is controlled by
enzymes and carrier molecules in a series of steps.
Electron Transport Chains
Compared with burning, cellular respiration is a more controlled. Energy is
released from glucose in small amounts that cells can put to productive
use—the formation of ATP molecules.
In Eukaryotic Cells, the reaction of Aerobic Respiration occur
Inside MITOCHONDRIA.
Structure of Mitochondria
Mitochondria are found in almost all eukaryotic cells. Its structure is key to its
role in cellular respiration.
Its complex folding pattern of membranes and spaces allows for many sites
where reactions can occur.
Respiration involves glycolysis, the Krebs cycle, and
electron transport
Stage I: Glycolysis
The first stage in breaking down a glucose molecule, called glycolysis (splitting
sugar), takes place outside the mitochondria in the cytoplasm of the cell.
Glycolysis harvests chemical energy by oxidizing glucose to
pyruvate
The energy input and
output of glycolysis.
Concentrate on the
totals, not the details!
Glycolysis movie
Stage 2: The Krebs Cycle
The Krebs cycle finishes the breakdown of pyruvic acid molecules to carbon
dioxide, releasing more energy in the process. The enzymes for the Krebs cycle
are dissolved in the fluid matrix within a mitchondrion's inner membrane.
Kreb’s Cycle:
Where does this occur?
Identify the products.
Kreb’s Cycle movie
Stage 3: Electron Transport Chain and ATP Synthase Action
The final stage occurs in the inner membranes of mitochondria. This stage has
two parts: an electron transport chain and ATP production by ATP synthase
The inner mitochondrial membrane couples electron transport
to ATP synthesis.
The Pathway of Electron
Transport
This energy change is used
to “pump” hydrogen to the
inner membrane space
creating a gradient which
can power cell processes.
.
Chemiosmosis couples the electron transport chain to ATP
synthesis
Chemiosmosis: The Energy-Coupling Mechanism
ATP synthase protein complex
functions as a mill, powered by
the flow of hydrogen ions.
This complex resides in
mitochondrial and chloroplast
membranes of eukaryotes and
in the plasma membranes of
prokaryotes..
The gradient of hydrogen ions
“pushes” the ATP synthesis.
Animation of ATP synthesis in Mitochondria
Copyright 1997. Thomas M.
Terry, The University of
Connecticut
Cellular respiration generates many ATP molecules for each sugar
molecule it oxidizes
During respiration, most energy flows in this sequence:
Glucose NADH  electron transport chain  protonmotive force  ATP
Harvesting Energy without Oxygen
Fermentation in Human Muscle Cells
When your lungs and bloodstream can't supply oxygen fast enough to meet
your muscles' need for ATP. Your muscle cells use fermentation, to make ATP
without using oxygen.
How does the energy production of Lactic Acid fermentation compare to
aerobic respiration?
Lactic Acid fermentation occurs in animal cells deficient in oxygen
Lactic Acid Fermentation movie
Fermentation in Microorganisms
Yeast (a microscopic fungus) is capable of both cellular respiration and
fermentation.
Fermentation in yeast produces ethyl alcohol. The carbon dioxide that is
released during fermentation creates bubbles and pockets that make bread
rise. The alcohol evaporates during baking.
Fermentation enables some cells to produce ATP without the
help of oxygen. Alcoholic fermentation occurs in yeast.
Alcoholic Fermentation movie
Pyruvate as a key juncture in catabolism. Glycolysis is common to
fermentation and respiration.
How does the net gain of
ATP compare in aerobic vs.
fermentation?
The catabolism of various
food molecules.
Carbohydrates, fats, and
proteins can all be used as
fuel for cellular respiration.