Cellular Respiration
Chapter 6
Autotrophs
• Autotrophs are organisms that can use basic
energy sources (i.e. sunlight) to make energy
containing organic molecules from inorganic
raw materials.
• 2 Types
– Photosynthetic autotrophs
– Chemosynthetic autotrophs
Chemosynthesis
• Chemosynthesis is a process used by
prokaryotic organisms to use inorganic
chemical reactions as a source of energy to
make larger organic molecules.
Heterotrophs
• Heterotrophs require organic molecules as
food.
• They get their energy from the chemical
bonds in food molecules such as
carbohydrates, fats, and proteins.
Prokaryotic Cells
Prokaryotic Cells
• Prokaryotic cells have no nuclei.
• Prokaryotic cells lack mitochondria and
chloroplasts.
• They carry out photosynthesis and cellular
respiration within the cytoplasm or on the
inner surfaces of the membranes.
Eukaryotic Cells
Eukaryotic Cells
• Eukaryotic cells contain nuclei, mitochondria,
and in the case of plant cells chloroplasts.
• Plant cells, animal cells, fungi and protists are
all eukaryotic.
Cellular Respiration
• Cellular respiration is the controlled release of
chemical-bond energy from large, organic
molecules.
• This energy is utilized for many activities to
sustain life.
• Both autotrophs and heterotrophs carry out
cellular respiration.
Aerobic Vs. Anaerobic
• Aerobic respiration requires oxygen.
• Anaerobic respiration does not require
oxygen.
Aerobic Respiration
• Aerobic cellular respiration is a specific series
of enzyme controlled chemical reactions in
which oxygen is involved in the breakdown of
glucose into carbon-dioxide and water.
• The chemical-bond energy is released in the
form of ATP.
• Sugar + Oxygen  carbon dioxide + water +
energy (ATP)
Aerobic Respiration
• Simplified Reaction:
• C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) ΔHc 2880 kJ
• Covalent bonds in glucose contain large
amounts of chemical potential energy.
• The potential energy is released and utilized
to create ATP.
Glycolysis
• Glycolysis is a series of enzyme controlled
anaerobic reactions that result in the breakdown
of glucose and the formation of ATP.
• A 6-carbon sugar glucose molecule is split into
two smaller 3-carbon molecules which are
further broken down into pyruvic acid or
pyruvate.
• 2 ATP molecules are created during glycolysis and
electrons are released during the process.
Krebs Cycle
• The Krebs cycle is a series of enzymecontrolled reactions that take place inside the
mitochondrion.
• Pyruvic acid formed during glycolysis is broken
down further.
• Carbon dioxide, electrons, and 2 molecules of
ATP are produced in this reaction.
Electron Transport System
• The electrons released from glycolysis and the
Krebs cycle are carried to the electrontransport system (ETS) by NADH and FADH2.
• The electrons are transferred through a series
of oxidation-reduction reactions until they are
ultimately accepted by oxygen atoms forming
oxygen ions.
• 32 molecules of ATP are produced.
Aerobic Respiration Summary
• Glucose enters glycolysis.
– Broken down into pyruvic acid.
• Pyruvic acid enters the Krebs cycle.
– Pyruvic acid is further broken down and carbon-dioxide is
released.
• Electrons and hydrogen ions from glycolysis and the
Krebs cycle are transferred by NADH and FADH2 to the
ETS.
– Electrons are transferred to oxygen to form oxygen ions.
– Hydrogen ions and oxygen ions combine to form water.
Anaerobic Cellular Respiration
• Anaerobic respiration does not require oxygen
as the final electron acceptor.
• Some organisms do not have the necessary
enzymes to carry out the Krebs cycle and ETS.
• Many prokaryotic organisms fall into this
category.
• Yeast is a eukaryotic organism that performs
anaerobic respiration.
Fermentation
• Fermentation describes anaerobic pathways
that oxidize glucose to produce ATP.
• An organic molecule is the ultimate electron
acceptor as opposed to oxygen.
• Fermentation often begins with glycolysis to
produce pyruvic acid.
Alcoholic Fermentation
• Alcoholic fermentation is the anaerobic
pathway followed by yeast cells when oxygen
is not present
• Pyruvic acid is converted to ethanol and
carbon-dioxide.
• 4 ATPS are generated from this process, but
glycolysis costs 2 ATPs yielding a net gain of 2
ATPs.
Lactic Acid Fermentation
• In Lactic acid fermentation, the pyruvic acid
from glycolysis is converted to lactic acid.
• The entire process yields a net gain of 2 ATP
molecules per glucose molecule.
• The lactic acid waste products from these
types of anaerobic bacteria are used to make
fermented dairy products such as yogurt, sour
cream, and cheese.
Lactic Acid Fermentation
• Lactic acid fermentation occurs in the human
body in RBCs and muscle cells.
• Muscle cells will function aerobically as long as
oxygen is available, but will function
anaerobically once the oxygen runs out.
• Nerve cells always require oxygen for respiration.
• RBCs lack a nucleus and mitochondria and
therefore must always perform anaerobic, lactic
acid fermentation.
Fat Respiration
• A triglyceride (neutral fat) consists of a
glycerol molecule with 3 fatty acids attached
to it.
• A molecule of fat stores several times the
amount of energy as a molecule of glucose.
• Fat is an excellent long-term energy storage
material.
• Other molecules such as glucose can be
converted to fat for storage.
Protein Respiration
• Protein molecules must first be broken down
into amino acids.
• The amino acids must then have their amino
group (-NH2) removed (deamination).
• The amino group is then converted to
ammonia. In the human body ammonia is
converted to urea or uric acid which can then
be excreted.