Download CR Glycolysis – September 24th

Cellular Respiration:
Glycolysis
Monday September 24th, 2012
Review of Oxidation and
Reduction
 Oxidation: Losing electrons. Called
oxidation because you tend to lose
electrons to oxygen. Oxygen is
electronegative (likes to hog electrons)
 Reduction: Gaining electrons
How do Cells Convert
Chemical Energy from one
Form to Another?
We will be looking at 2 energy-transfer
mechanisms:
 Substrate-level Phosphorylation
 Oxidative Phosphorylation
Substrate-Level
Phosphorylation
 Substrate-level
phosphorylation is a type of
metabolism that results in the
formation and creation of
Adenosine Triphosphate
(ATP)
 Phosphate group is
transferred to ADP from
substrate
 Example of
phosphoenolpyruvate as
substrate
 For each glucose molecule
created = 4 ATP molecules
are generated in Glycolysis
(step 1) and 2 in Krebs Cycle
(step 3)
Oxidative Phosphorylation
 As electrons are transferred from one carrier to
another, energy is released and used to form
ATP. Because oxygen must be present to
accept the electrons at the end of the ETC, the
process of forming ATP is called oxidative
phosphorylation
 Oxidative phosphorylation can produce more
ATP molecules per glucose molecule than
substrate-level phosphorylation
What you should know
about Glycolysis!
 Anaerobic process  does not require
oxygen
 Takes place in the cytoplasm (the liquid
stuff that organelles swim around in)
 Makes up the first 10 steps of cellular
respiration
Glycolysis!  Splitting
Sugars
 Glycolysis is the process of breaking down
glucose
 Glucose (6-carbon sugar) is split into 2
molecules of pyruvic acid (3-carbon sugars)
 Catabolic process
 Results in 2 molecules of ATP, 2 molecules
of pyruvic acid, 2 molecules of water and 2
NADH (an enzyme that helps transport
electrons)
Two Main Stages of
Glycolysis:
 Glycolysis 1: The activation phase,
which uses ATP molecules; and
 Glycolysis 2: Oxidation and
phosphorylation reactions, which not only
reduce glucose to pyruvate but also
produce ATP molecules
Glycolysis 1
 In it’s most simplest form, glucose can be
thought of as a 6-carbon molecule (also
contains some Hydrogen and Oxygen:
OOOOOO – Glucose
 First step in glycolysis: substrate-level
phosphorylation  when a phosphate
group is added to the glucose molecule
by ATP:
OOOOOOOO
 This makes Fructose-6-phosphate
Glycolysis 1, continued…
 Another ATP molecule must
phosphorylate the fructose-6-phosphate,
producing fructose-1,6-diphosphate
 This molecule is split into two PGAL
(glyceraldehyde-3-phosphate)
 ** Glycolysis 1 uses up two molecules of
ATP
Glycolysis 1
Glycolysis II
 Each PGAL is oxidized  the electrons
that are removed are picked by the
coenzyme NAD+
 Remember, when these electrons are
picked up, so is a hydrogen ion, thus
NAD+ is reduced to NADH
 NADH carries the H atom to another
electron carrier where 2 electrons and a
hydrogen are removed, once again
forming NAD+
Glycolysis II, continued…
 In the meanwhile PGAL that was
oxidized, gets phosphorylated and
becomes PGAP  2 molecules of PGAP
are created
 ADP molecules remove the phosphate
groups from PGAP  2 molecules of
ATP and PGA produced!
 PGA is then oxidized to make two water
molecules and two PEP
(phosphoenolpyruvate) molecules
Glycolysis II, continued …
 Another substrate-level phosphorylation
occurs – 2 ADP molecules remove the
phosphate groups from the PEP
molecules  results in 2 ATP molecules
and 2 pyruvate molecules
 The energy stored in these ATP can now
be used for aerobic cellular respiration in
mitochondria
Summary
 The process of Glycolysis results in 2 ATP
molecules
 We started with 1, 6-carbon molecule of glucose
 We added 2 phosphorous molecules to Glucose
and converted the Glucose to Fructose  2 ATP
molecules are used
 Enzyme breaks down fructose into 2, 3-carbon
sugar isomers
 The 2, 3-carbon sugars were changed by NAD+,
which left us with NAD+ with some H+ electrons
The End Results are:
 4 ATP molecules, 2 H2O, 2 pyruvic acids
and 2 NADH molecules
 2 molecules of ATP were used during the
process  2 ATP molecules result as net
 The 2 pyruvic molecules are either passed
along and used in the Krebs Cycle to create
more ATP or are converted to lactic acid