Download Cell Respiration Basics

The Basics of Cellular
Respiration (H. Biology)
Cell metabolism involves all
chemical reactions
Cell Respiration: Overall Equation
The cell cannot use the amount of energy
in a glucose molecule all at once.
The cell uses energy in the smaller
“packets” contained in ATP molecules.
• Cell respiration also provides “carbon skeletons”
used in biosynthesis of other organic
compounds.
• It takes place in both plant and animal cells.
There are 3 major stages of Cell
respiration
• Glycolysis (sometimes listed separately from cell
respiration because it happens outside the mitochondrion.)
• Krebs cycle
(Citric Acid Cycle)
• Electron Transport
System (chain)
& Oxidative phosphorylation
(E.T.O.P.)
mitochondrion
I) Glycolysis
• It occurs in the cytosol of the cytoplasm.
cytosol
• It is anaerobic so it requires no oxygen.
Glycolysis In Depth
• 1) Glucose is converted to glucose-6-phosphate.
(This takes 1 ATP to supply the phosphate)
• 2) Glucose-6-phosphate splits into 2 3C phosphate
compounds: PGALs (This takes another ATP)
• 3) Through a series of reactions the 3C phosphates
(PGALs) are chemically rearranged into 2 3C pyruvic
acid molecules
• 4) Also – 4 ATP are produced all together, and 2 NADH
molecules. (This leaves a net production of 2 ATPs
from glycolysis.)
Prior to Krebs Cycle (AKA Citric Acid Cycle)
Pyruvic Acid is converted into Acetyl
Coenzyme A (Acetyl CoA) This is called
oxidative decarboxylation.
If there is enough O2, the pyruvic acid produced
during glycolysis is transported to the
mitochondrion.
• A complex system of enzymes converts the
pyruvic acid to acetate, and NADH is produced.
• A carrier molecule picks up the acetate to form
Acetyl-Coenzyme A (acetyl CoA).
The Acetyl CoA is
the compound that
delivers the acetate
to the Krebs
Cycle.
Note the carbon
dioxide given off
in this process.
Also – see the
NADH produced.
II) Krebs cycle (Citric Acid Cycle)
It is named for Hans Krebs who
discovered it in 1953. (It is also called the
citric acid cycle” because citric acid is formed
at the start of the cycle.)
During the Krebs cycle Acetyl CoA molecules
formed from pyruvic acid molecules, are broken
down.
CO2 is given off, and ATP is produced. (1 ATP
per each pyruvic acid or each turn of the
cycle.)
This happens in the matrix of the mitochondrion.
(Aerobic respiration in the mitochondron)
Inner folds called cristae increase surface area
for chemical reactions involved in cell
respiration.
High energy electrons are carried by special
compounds (NADH & FADH2) from Krebs
cycle to the Electron Transport Chain.
Krebs Cycle (Citric Acid Cycle) in Depth
1) 2C “Acetyl group” (acetate)
from Acetyl CoA combines
with a 4C acid (oxaloacetate)
to 6C Citrate (citric acid).
Black balls are carbon atoms
2) After several steps:
6C citric acid is converted
to 5C acid (ketoglutarate)
Carbon Dioxide is
given off, and
NADH is formed.
• 3) 5C acid is converted to a 4C acid. Carbon Dioxide is
given off, and NADH is formed
• 4) 4C acid is “rearranged” 1ATP, and FADH2 is formed.
• 5) 4C acid becomes oxaloacetate, and NADH is
formed, The oxaloacetate
is involved in
a series of reactions
and the cycle begins
again. Since each
molecule of C6H12O6
produces 2 pyruvic
acid molecules in
glycolysis, the Krebs
cycle completes
two turns.
and the cycle begins again
Summary of Products from Krebs
• NADH
(needed for the last part of Cell RespirationE.T. & O.P.)
• FADH2
(needed for the last part of Cell Respiration(E.T. & O.P.)
• 2 ATP molecules
(1 for each pyruvic acid converted to Acetyl CoA)
III) The Electron Transport System (chain)
(Let’s call it E.T.) & Oxidative Phosphorylation.
E.T. provides
energy to
produce the
most ATPs
of cell
respiration
It takes place in the mitochondrion’s inner
membrane. Electrons are carried and ATPs are
produced. It is an aerobic process.
All of this for the E.T. & O.P..
oxidative phosphorylation
What Happens During E.T….
• 1) NADH and FADH2 carry Hydrogen atoms
(energy rich electrons and protons) to the E.T.
system.
• 2) E.T. consists of a series of electron carriers
(proteins called cytochromes) embedded in
the mitochondrion cristae (folds of inner
membrane).
cristae
3) H atoms separate into protons (H+) and
electrons (e-).
4) Electrons are passed from one carrier
(cytochrome proteins) to the next in E.T. (This
is accomplished through a series of oxidationreduction reactions.)
5) The terminal cytochrome combines
electron, protons & oxygen to form water
O2 to form water.
6) Some of the free energy of the E.T. carried
electrons is used to transport protons from the
mitochondrial matrix, across the cristae, to the
inter-membrane space.
Due to the proton concentration gradient produced, the
protons diffuse back across the membrane to the
matrix, through ATP synthase enzyme complex.
• This is called chemiosmosis.
• Grand total of ATPS from Glycolysis, Krebs, and ET
system = 38 (34 from E.T.).
Chemiosmosis
Energy given off from diffusing protons permits
the enzyme known as ATP synthase, located on
the inner mitochondrial membrane, to produce
ATP molecules.
ATP synthase
ATP Final Tally from 1 glucose broken
down through cell respiration.
• Glycolysis
= 2 ATPs
• Krebs Cycle (Citric Acid Cycle) = 2 ATPs
• Electron Transport System & Oxidative
Phosphorylation (E.T.O.P.)
= 34 ATPs
Total =
38 ATPs