Cellular Respiration
Chapter 7 pgs 131-147
Food to energy
• Autotrophs
– “Self-feeders”
– Plants and other organisms that make all their
own organic matter from inorganic nutrients
• Heterotrophs
– “Other-feeders”
– Humans and other animals that cannot make
organic molecules from inorganic ones
Harvesting Chemical Energy
• From photosynthesis
we get carbohydrates
(glucose)
• Cellular respiration:
Breaking down the
carbohydrates
(glucose) to make ATP
and NADH
– NADH is an electron
carrier
• Starts with glycolysis
– Glyco = sugar
– Lysis = breaking
– Breaking down sugars
• Producers
– Biologists refer to
plants and other
autotrophs as the
producers in an
ecosystem
• Consumers
– Heterotrophs are
consumers, because
they eat plants or
other animals
Figure 6.2
Sunlight
energy
Ecosystem
Photosynthesis
(in chloroplasts)
Glucose
Oxygen
Carbon dioxide
Water
Cellular respiration
(in mitochondria)
for cellular work
Heat energy
Figure 6.3
The Relationship Between
Cellular Respiration and
Breathing
• Cellular respiration and breathing are closely
related
– Cellular respiration requires a cell to exchange
gases with its surroundings
– Breathing exchanges these gases between the
blood and outside air
The Overall Equation for
Cellular Respiration
• A common fuel molecule for cellular
respiration is glucose
– This is the overall equation for what happens to
glucose during cellular respiration
Glucose
Oxygen
Carbon
dioxide
Water
Energy
Unnumbered Figure 6.1
The Role of Oxygen in Cellular
Respiration
• During cellular respiration, hydrogen and its
bonding electrons change partners
– Hydrogen and its electrons go from sugar to
oxygen, forming water
Redox Reactions
• Chemical reactions that transfer electrons
from one substance to another are called
oxidation-reduction reactions
– Redox reactions for short
– The loss of electrons during a redox reaction is
called oxidation
– The acceptance of electrons during a redox
reaction is called reduction
– G.E.R. L.E.O.
– O.I.L. R.I.G.
Oxidation
[Glucose loses electrons (and hydrogens)]
Glucose
Oxygen
Carbon
dioxide
Water
Reduction
[Oxygen gains electrons (and hydrogens)]
Unnumbered Figure 6.2
A Road Map for Cellular Respiration
Cytosol
Mitochondrion
High-energy
electrons
carried
mainly by
NADH
High-energy
electrons
carried
by NADH
Glycolysis
Glucose
2
Pyruvic
acid
Krebs
Cycle
Electron
Transport
Figure 6.7
What Carries the Electrons?
NAD+ (nicotinadenine dinucleotide) acts as
the energy carrier
NAD+
It’s
is a coenzyme
Reduced to NADH when it picks up
two electrons and one hydrogen ion
Glycolysis
• 1 six carbon
glucose broken
down into 2
three carbon
pyruvic acid
molecules
• Happens out in
the cytoplasm
2 Pyruvic acid
Glucose
Figure 6.8
What
happens
next
depends on
whether
there is
oxygen
present or
not.
What happens after Glycolysis?
• Chemicals can take
one of two pathways
– Anaerobic (no oxygen
present) fermentation
• Makes no ATP, but
keeps the cycles going
– Aerobic respiration
• Makes a lot of ATP
EVOLUTION CONNECTION:
LIFE ON AN ANAEROBIC EARTH
• Ancient bacteria probably used glycolysis to
make ATP long before oxygen was present
in Earth’s atmosphere
– Glycolysis is a metabolic heirloom from the
earliest cells that continues to function today in
the harvest of food energy
Fermentation in Human Muscle Cells
• Human muscle cells can make ATP with and
without oxygen
– They have enough ATP to support activities
such as quick sprinting for about 5 seconds
– A secondary supply of energy (creatine
phosphate) can keep muscle cells going for
another 10 seconds
– To keep running, your muscles must generate
ATP by the anaerobic process of fermentation
Fermentation
• If there is no oxygen some cells can
convert pyruvic acid into other compounds
and get some more NAD+
• No ATP is made, but the NAD+ can keep
Glycolysis going to make a little ATP
• 2 kinds of fermentation: Lactic acid
fermentation and Alcoholic
Fermentation
Lactic Acid Fermentation
• Converting pyruvic acid to Lactic
acid
– A.K.A. milk acid
• Bacteria are used to do this to get
cheese, yogurt, and sour cream
• Under heavy exercise you use up
Oxygen faster than you can
replace it
– Lactic Acid builds up and the acidity
causes fatigue, pain and cramps.
2 ADP+ 2
Glycolysis
2 NAD
2 NAD
Glucose
2 Pyruvic
acid
+ 2 H
2 Lactic
acid
(a) Lactic acid fermentation
Figure 6.15a
Alcoholic Fermentation
• Yeast convert pyruvic acid
into ethyl alcohol
• They break a CO2 off of
pyruvic acid
• The 2 carbon sugar left
behind forms ethyl alcohol
• Basis of wine and beer
industry, and bread making
2 ADP+ 2
2 CO2 released
2 ATP
Glycolysis
2 NAD
2 NAD
Glucose
2 Pyruvic
acid
+ 2 H
2 Ethyl
alcohol
(b) Alcoholic fermentation
Figure 6.15b
Efficiency of Glycolysis
• Compare the kilocalories of Glucose with
the kilocalories in the ATP that is made.
• The 2 ATP molecules made during
glycolysis receive only 2% of the energy in
glucose
– Where does the rest go?
• It’s still in pyruvic acid
• This small amount of energy is enough for
bacteria, but more complex organisms
need more of glucoses energy.
Objectives
• Define Cellular respiration
• Describe the major events in glycolysis
• Compare and contrast lactic acid
fermentation and alcoholic fermentation
• Calculate the efficiency of glycolysis
Stage 2: The Krebs Cycle
• The Krebs cycle completes the breakdown
of sugar
• Another kind of breakdown
• In the Krebs cycle, pyruvic acid from
glycolysis is first “prepped” into a usable
form, Acetyl-CoA
CoA
2
Acetic
acid
1
Pyruvic
acid
CO2
3
Acetyl-CoA
(acetyl-coenzyme A)
Coenzyme A
Figure 6.10
• The Krebs cycle extracts the energy of
sugar by breaking the acetic acid
molecules all the way down to CO2
– The cycle uses some of this energy to make
ATP
– The cycle also forms NADH and FADH2
Input
Output
2
1 Acetic acid
2 CO2
ADP
3
Krebs
Cycle
3 NAD
4
FAD
5
6
Figure 6.11
Electron Transport
Stage 3: Electron Transport
• Electron transport releases the energy your
cells need to make the most of their ATP
• The molecules of electron transport chains
are built into the inner membranes of
mitochondria
– The chain functions as a chemical machine that
uses energy released by the “fall” of electrons to
pump hydrogen ions across the inner
mitochondrial membrane
– These ions store potential energy
Protein
complex
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Electron transport chain
ATP synthase
Figure 6.12
The Versatility of Cellular Respiration
• Cellular respiration can “burn” other kinds of
molecules besides glucose
– Diverse types of carbohydrates
– Fats
– Proteins
Food
Polysaccharides
Sugars
Glycerol
Fats
Fatty acids
Proteins
Amino acids
Amino groups
Glycolysis
AcetylCoA
Krebs
Cycle
Electron
Transport
Figure 6.13
Adding Up the ATP from Cellular Respiration
Cytosol
Mitochondrion
Glycolysis
Glucose
2
Pyruvic
acid
2
AcetylCoA
Krebs
Cycle
Electron
Transport
Maximum
per
glucose:
by direct
synthesis
by
direct
synthesis
by
ATP
synthase
Figure 6.14