Cellular Respiration
Glycolysis
Preparatory reaction
Citric acid (krebs) cycle
Electron transport chain
Glycolysis
Occurs outside mitochondria
Breaks down glucose into two
pyruvate molecules
Evolutionary speaking, glycolysis
occurs in all organisms, meaning it
probably evolved before the citric
acid cycle and the electron transport
chain
Steps in Glycolysis
1.
2.
3.
4.
5.
6.
Begins when glucose is activated with two ATP molecules,
the glucose splits into two C molecules known as G3P.
G3P is then oxidized, removing electrons and H ions.
The lost electrons and H ions are then accepted by NAD+
resulting in two NADH.
G3P oxidation results in the production of 4 high-energy
phosphate groups which make 4 ATP molecules, called
substrate-level phosphorylation.
There is a net gain of only 2 ATP molecules in glycolysis
because 2 of the ATP molecules are used in supplying
energy for the reaction
What happens next depends on if O2 is available or not.
If it is available, pyruvate enters and C.R. ensues. If not,
fermentation occurs, and pyruvate is reduced.
Preparatory Reaction
Connects glycolysis to the citric acid
cycle
converts pyruvate to a 2-carbon
acetyl group and attaches it to
coenzyme A resulting in acetly-CoA
through a redox reaction.
The reaction occurs twice for each
glucose molecule
Citric Acid (krebs) cycle
Occurs in the matrix of the mitochondia
Sometimes called the krebs cycle because it was named for sir
Hans Krebs who described the reaction in the 1930s.
Begins by the addition of a 2-carbon acetyl group to a 4-carbon
molecule forming a 6-carbon citric acid molecule
In the reactions that follow, at three different times, two electrons
and one H ion are accepted by NAD+ , forming NADH
At one time in the cycle, two electrons and one H ion are accepted
by FAD, forming FADH2
Some energy is released and is used to make ATP by substratelevel phosphorylation,
One high-energy metabolite accepts a phosphate group and ADP
to ATP in the reaction.
For each glucose molecule that goes in, the citric acid cycle turns
twice.
The products of the cycle are 4 CO2, 2 ATP, 6 NADH and 2 FADH2
The electron transport chain
Takes place in the cristae of the mitochondria, in which
electrons are passed from carrier to carrier
Some carriers are cytochrome molecules(complex carbon
rings with iron in the center)
NADH and FADH2 carry the electrons through the system
Each time the electrons are passed on, NADH gives up its
electrons and becomes NAD+ then picks up electrons,
therefore they are reduced.
ATP is released at each redox (reduction) reaction
Oxygen must be present for this to work, therefore this
process is also called oxidative phosphorylation
Oxygen accepts electrons in the reaction and combines with
hydrogen ions to form water.
The electrons are being delivered to the system by FADH2,
at this time two ATP molecules are formed
Coenzymes and ATP in the system undergo recycling.
For Monday Nov. 10
Study for a 20-point quiz (credit)
Beginning lab on CR
Study session after school TH 11/13
TEST will be on Monday 11/17
Lab Report for CR will also be due on
that day
Homework: complete/review the rest
of the notes online at
kauscience.k12.hi.us