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CELLULAR
RESPIRATION
(The process of converting glucose into
ATP)
I. Overview
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Both autotrophs and heterotrophs break
down glucose to get energy. This energy is
used to fuel life processes.
Review and be familiar with the following
terms:
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Autotrophs
Heterotrophs
1. ATP (adenosine triphosphate)
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ATP: A modified nucleotide molecule that
powers all cellular work directly.
Its structure: adenine, ribose and three
phosphates are combined by dehydration
synthesis
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ATP molecules release phosphate groups to
various other molecules. These molecules
take in the phosphate by phosphorylation
and get excess energy to perform various
processes.
When ATP releases a phosphate + energy it
produces ADP (adenosine diphosphate)
ADP can turn back to ATP by taking in a
phosphate and energy by phosphorylation
2. Electron Carrier Molecules
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There are two different molecules that are
used to carry electrons and hydrogen ions to
the last step cellular respiration.
NAD+ carries 2 electrons and a hydrogen ion
at a time – NADH
FAD carries 2 electrons and two hydrogen
ions at a time -- FADH
3. The Basics of Cellular Respiration
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Cellular respiration – releases energy by
breaking down glucose and other food
molecules in the presence of oxygen.
6 O2 + C6H12O6 → 6 CO2 + 6 H2O + Energy
Cellular respiration takes place in small steps to
minimize the loss of energy in the form of heat or
light.
Processes that require oxygen to take place are
called aerobic.
Processes that do not require oxygen to take
place are anaerobic.
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Cellular respiration consists of three major
steps if oxygen is present:
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Glycolysis – in the cytoplasm
The Krebs cycle (citric acid cycle) – in the
mitochondrion
Oxidative phosphorylation – in the mitochondrion
Cellular respiration is a collection of enzyme
catalyzed reactions of oxidation (the loss of
electrons or hydrogen from an element, or
the gain of oxygen) and reduction (the
gaining of an electron, or hydrogen or losing
oxygen by an element)
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ATP molecules can be produced in two ways:
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Substrate level phosphorylation -- when
enzymes directly transfer phosphate to ADP
during chemical reactions.
Oxidative phosphorylation – When ATP
synthesis is fueled by creating a concentration
difference of H ions between two sides of a
membrane.
II. The Steps of Cellular Respiration –
Glycolysis
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The process in which one molecule of glucose is
broken in half, producing two molecules of
pyruvic acid.
This process will also produce 2 ATP and 2
NADH molecules.
ATP is used in other life processes
NADH moves 2 electrons and 1 H+ per molecule
to the last step of cellular respiration
The initial investment of 2 ATP molecules are
needed
http://programs.northlandcollege.edu/biology/Biology1111/animations/glycolysis.html
http://www.wwnorton.com/college/biology/discoverbio4/animations/main.aspx?chno=ch08p02a
III. Fermentation (an alternative if
oxygen is not present)
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After glycolysis fermentation will take place if
oxygen is not present in the organism.
Fermentation will recycle the used NADH into
NAD+.
Fermentation forms a total of 2 ATP
molecules from one glucose.
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Types of fermentation:
 Alcoholic fermentation – Yeast and other
organisms form alcohol and CO2 by the
following process:
Pyruvic acid + NADH2 → CO2 + ethanol + NAD+
 Lactic acid fermentation – Skeletal muscle
cells of mammals and some bacteria produce
lactic acid. Lactic acid is a harmful chemical
than needs to be removed from the muscle
cells:
Pyruvic acid + NADH2 → lactic acid + NAD+
http://www.wwnorton.com/college/biology/discoverbio4/animations/main.aspx?chno=ch08p02d
IV. The Krebs Cycle – The Second Step
of Cellular Respiration
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Aerobic process that takes place in the matrix
of the mitochondrion.
During this process, pyruvic acid is broken
down into carbon dioxide and ATP in a series
of reactions.
Requirements:
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Electron carriers (NAD+, FAD)
ADP molecules
Enzymes
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The first step of this process is to break down
pyruvic acid into an acetyl group that binds
with a Coenzyme-A the complex that is
formed is called Acetyl-CoA. – This is called
the intermediate step. This is not part of the
citric acid cycle but comes before it.
Acetyl-CoA starts the Krebs cycle that will
extract energy and electrons from organic
molecules.
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During the citric acid cycle, the carbon atoms
from Acetyl – CoA form CO2 – released into
the atmosphere
Hydrogen ions and electrons bind to NAD+
and FAD and move to the oxidative
phosphorylation
1 ATP per cycle is also produced.
The cycle takes place twice per glucose
V. Oxidative Phosphorylation
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NADH and FADH2 molecules from the Krebs
cycle pass their electrons through an electron
transport chain. This uses the high energy
electrons to convert ADP into ATP.
This process takes place on the inner
membrane of the mitochondrion (cristae).
Requirements:
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10 NADH, 2 FADH2
Enzymes
32 ADP
Oxygen (from breathing)
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Products:
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6 H2O
32 ATP molecules
The movement of hydrogen ions from the
matrix to the intermembrane space of the
mitochondrion fuels the movement of high
energy electrons and the production of ATP.
We are going to look at the picture on the next
slide together and form the steps of the
electron transport chain and oxidative
phosphorylation together
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http://vcell.ndsu.nodak.edu/animations/etc/movie.htm
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http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm
VI. Comparing Aerobic Respiration and
Fermentation
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While fermentation can take place without
oxygen and is a simpler process, it produces
only 2 ATP molecules from glucose. It also
produces some harmful chemicals (ethanol or
lactic acid) that the body needs to break
down.
Cellular respiration produces a total of 36
ATP molecules from one glucose. Other
producs include CO2 and H2O that are
released into the environment.
VII. Energy and Exercise
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When the body needs energy quickly, it starts
to break down the available ATP molecules,
than glucose. If oxygen is not present
fermentation will take place. If enough
oxygen is present in the cell, cellular
respiration takes place.
If enough glucose is not available, the body
starts to break down the stored glycogen than
fats finally proteins.