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CELL RESPIRATION
The Big Picture
This lesson meets the following DoE Specific Curriculum Outcomes for Biology 11: 314-2 and 314-9
MITOCHONDRIA
• Mitochondria (singular: mitochondrion)
are round or sausage-shaped organelles
that are usually scattered throughout
the cytoplasm of eukaryotic cells.
• Prokaryotic cells have no mitochondria they carry out cellular respiration
within the cytoplasm.
MITOCHONDRIA
• Mitochondria possess a double membrane
(referred to as an envelope) composed of a
smooth outer membrane and a highly
folded inner membrane.
• The folds of the inner membrane are
called cristae (singular: crista).
• The outer membrane plays a role similar
to that of the cell membrane
• The inner membrane is associated with
cell respiration.
MITOCHONDRIA
• The inner membrane creates two
compartments within the mitochondrion.
• The mitochondrial matrix is a proteinrich liquid that fills the innermost space
of a mitochondrion.
• A fluid-filled intermembrane space lies
between the inner and outer membrane.
• Both these compartments play a critical
role in aerobic respiration.
CELL RESPIRTION
• Def - the process in which a cell breaks down
sugar or other organic compounds to release
energy used for cellular work; may be anaerobic
or aerobic, depending on the availability of
oxygen.
• Aerobic can be summarized by the following
formula:
C6H12O6 + 6O2  6H20 + 6CO2 + energy (36 ATP)
GOALS of CELL RESPIRATION
C6H12O6 + 6O2  6CO2 + 6H2O + 36ATP
• Cell respiration has three goals:
1. Break the bonds between the six carbon
atoms of glucose, resulting in six carbon
dioxide molecules.
2. Move hydrogen atom electrons from
glucose to oxygen, forming six water
molecules.
3. Trap as much of the free energy released
in the process as possible in the form of
ATP.
STAGES of CELL RESPIRATION
• Stage 1: Glycolysis - a 10-step process
occurring in the cytoplasm.
• Stage 2: Pyruvate oxidation - a onestep process occurring in the
mitochondrial matrix.
STAGES of CELL RESPIRATION
• Stage 3: The Krebs cycle (also called the
tricarboxylic acid cycle, the TCA cycle, or
the citric acid cycle) - an eight-step cyclical
process occurring in the mitochondrial
matrix.
• Stage 4: Electron transport and
chemiosmosis (oxidative phosphorylation)
- a multistep process occurring in the
inner mitochondrial membrane.
Stage 1
Glycolysis
GLYCOLYSIS
• For each molecule of glucose,
glycolysis creates two molecules of
Pyruvate (Pyruvic Acid).
• All reactions (steps) take place in the
cytoplasm.
• The process is anaerobic - does not
require oxygen.
GLYCOLYSIS
• Two ATP molecules phosphorylates glucose
by adding phosphate groups to both ends of
the sugar molecule.
• The glucose molecule then splits into two
PGAL molecules.
• Each of the two PGAL molecules is oxidized
to BPG.
• The hydrogen each gives up is used to form
a NADH molecule.
GLYCOLYSIS
• Each of the BPG molecules is further
oxidized to form 3PG molecules.
• The phosphate groups they give up
are used to form ATP.
• Each 3PG molecule is finally oxidized
to form Pyruvate (Pyruvic Acid)
molecules and yield another ATP
molecule.
GLYCOLYSIS ENERGY YIELD
• In the process of converting one
glucose molecule to two Pyruvate
molecules…
• Four ATP are produced but two are
required resulting in a net gain of two
ATP.
• Two NADH are produced.
FERMENTATION
• Cells that contain mitochondria (Eukaryotes)
normally carry out Aerobic Cell Respiration.
• Pyruvate produced by Glycolysis enters the
mitochondria and is catabolised by the
Kreb’s Cycle and Electron Transport Chain.
• The latter process requires the presence of
free oxygen.
FERMENTATION
• Prokaryotic cells do not have mitochondria.
• Their cell respiration is anaerobic and takes
place in the cytoplasm.
• Unlike glycolysis that produces Pyruvate
molecules, anaerobic cell respiration
produces either ethyl alcohol or lactic acid.
• This process is called Fermentation.
ALCOHOL FERMENTATION
• In alcohol fermentation, glucose is split into
two Pyruvate molecules using two ATP’s.
• Each Pyruvate is then converted to ethanol
yielding two ATP’s (net) and releasing CO2.
• Alcohol fermentation takes in yeast and is
used to make beer, wine and bread.
LACTIC ACID FERMENTATION
• In lactic fermentation, pyruvate is converted
to lactic acid and two ATP’s (net).
• Takes place in bacteria cells.
• Can happen in eukaryotic cells during
periods of excess exercise.
• Muscle cells demands for ATP outstrips O2
supply (oxygen dept).
• Cell switches to anaerobic respiration and
produces lactic acid but reverses after rest.