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Cellular Respiration
CELLULAR RESPIRATION
Introduction
• Nearly all the cells in our body break down
sugars to provide the energy to make ATP
• Most cells of most organisms obtain energy
aerobically using oxygen
– The aerobic processing of energy from sugar is called
cellular respiration
– Cellular respiration yields CO2, H2O, and a large
amount of ATP
Differences in how cells break down glucose - aerobic vs.
anaerobic respiration
• Aerobic respiration requires O2 vs. Anaerobic
respiration which doesn’t use O2
• Some cells only use anaerobic respiration
• Some cells use aerobic respiration
• Some cells usually use aerobic but may resort to
anaerobic respiration if necessary
The process of cellular respiration takes place in the
mitochondria of eukaryote cells
Structure of the Mitochondrion
In Our Body:
• Breathing and cellular respiration are closely
related.
• Breathing supplies oxygen to our cells for cellular
respiration and removes carbon dioxide from our
cells which is a waste product of cellular respiration
O2
CO2
Lungs
CO2
BREATHING
O2
Bloodstream
Muscle cells carrying out
CELLULAR RESPIRATION
Sugar + O2  ATP + CO2 + H2O
Figure 6.1
• Cellular respiration breaks down glucose
molecules and stores their energy in ATP
(adenosine triphosphate: ADENOSINE –P—P--P)
– The process uses O2 and releases CO2 and H2O
Chemical equation for cellular respiration
Glucose
Figure 6.2A
Oxygen gas
Carbon
dioxide
Water
Energy
STAGES OF CELLULAR RESPIRATION AND
FERMENTATION
Respiration occurs in three main stages
• Cellular respiration oxidizes sugar and produces
ATP in three main stages
– Glycolysis occurs in the cytoplasm
– The Krebs cycle and
– The electron transport chain occur in the
mitochondria
Important Molecules Involved
NAD+ Electron and hydrogen ion
FAD++ carrier molecules
NAD+ carries 2 electrons and one hydrogen
ion/ molecule
FAD++ carries 4 electrons and two hydrogen
ions/ molecule
Glycolysis – In cytoplasm
6 carbon sugar (1 molecule)
ATP needed to break
molecule apart
NAD+ collects
electrons and
hydrogen and
forms ATP
3 carbon molecule ( 2 molecules)
Kreb Cycle – matrix of mitochondrion
A multi-step process involving many enzymes that uses oxygen to break down
the pyruvic acid molecules to CO2, captures energy as ATP, and collects
energized electrons and hydrogen to send to cristae membranes of
mitochondrion
ELT & Chemiosmosis – cristae of
mitochondrion
Chemiosmosis involves the pumping of protons through special channels
in the membranes of mitochondria from the inner to the outer
compartment. The pumping establishes a proton gradient that flows
through ATP synthase to make 32-34 ATP
The 3 stages of aerobic cellular respiration
• For each glucose molecule that enters cellular
respiration, chemiosmosis produces 36 - 38 ATP
molecules
Cytoplasmic
fluid
Mitochondrion
Electron shuttle
across
membranes
GLYCOLYSIS
2
Glucose
Pyruvic
acid
by substrate-level
phosphorylation
2
Acetyl
CoA
used for shuttling electrons
from NADH made in glycolysis
KREBS
CYCLE
by substrate-level
phosphorylation
KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
by chemiosmotic
phosphorylation
Maximum per glucose:
Figure 6.14
Animal Cells use many kinds of organic
molecules as fuel for cellular respiration
• Polysaccharides can be broken down to
monosaccharides and then converted to glucose
for glycolysis
• Proteins can be digested to amino acids, which
are chemically altered and then used in the
Krebs cycle
• Fats are broken up and fed into glycolysis and
the Krebs cycle
Fermentation is an anaerobic alternative
to aerobic respiration
• Under anaerobic conditions (no oxygen), many
kinds of cells can use glycolysis alone to produce
small amounts of ATP
– But a cell must have a way of replenishing or
regenerating NAD+ (NADH  NAD+)
Alcoholic Fermentation
• In alcoholic fermentation, pyruvic acid (pyruvate) is
converted to CO2 and ethanol
– This recycles NAD+ to keep glycolysis working
released
GLYCOLYSIS
Glucose
Figure 6.15A
XO
2 Pyruvic
acid
2 Ethanol
Figure 6.15C
Lactic Acid Fermentation
• In lactic acid fermentation, pyruvic acid (pyruvate)
is converted to lactic acid (lactate)
– As in alcoholic fermentation, NAD+ is recycled
• Lactic acid fermentation is used to make cheese
and yogurt
GLYCOLYSIS
Glucose
Figure 6.15B
2 Pyruvic
acid
2 Lactic acid
Food molecules provide raw materials for
biosynthesis
• In addition to energy, cells need raw materials
for growth and repair
– Some are obtained directly from food
– Others are made from intermediates in glycolysis
and the Krebs cycle
• Biosynthesis (making cell parts and organic
compounds) uses ATP
The fuel for respiration ultimately comes
from photosynthesis
• All organisms have the
ability to harvest energy
from organic molecules
– Plants, but not animals,
can also make these
molecules from inorganic
sources by the process of
photosynthesis
Figure 6.18