Download chapter 9 cellular respiration

CHAPTER 9
CELLULAR RESPIRATION
9-1 Chemical Pathways
FOOD:
• Food is the main energy source of
living things.
• One gram of the sugar glucose, when
burned in the presence of oxygen,
releases 3811 calories of heat energy.
• A calorie is the amount of energy
needed to raise the temperature of 1
gram water up one Celsius degree.
• A food Calorie (capital C) is not the same
as a calorie (lowercase c).
- A food Calorie is a kilocalorie, which
equals 1000 calories.
• Glucose (food) is gradually broken
down, and energy is released within
cells.
- Glycolysis starts the process.
- When oxygen is present, glycolysis
is followed by the Krebs cycle and the
electron transport chain. If oxygen is not
present, a different pathway is taken.
Cellular Respiration
• Cellular Respiration is the process that
releases energy by breaking down
food molecules in the presence of
oxygen.
• Glycolysis, the Krebs cycle and the
electron transport chain make up the
process of cellular respiration.
Equation:
Oxygen + glucose  carbon dioxide +
water + energy
Glycolysis
• Glycolysis takes place in the cytoplasm
of a cell.
• When oxygen is present, Glycolysis is
followed by the Krebs cycle and the
Electron Transport Chain. They take
place inside the mitochondria.
• Glycolysis is the process in which one
molecule of glucose is broken in half.
This produces 2 molecules of pyruvic
acid and a 3-carbon compound.
• Glycolysis starts by using the energy of 2
ATP molecules. At the end of glycolysis,
4 ATP molecules have been produced. It
has a net gain of 2 ATP molecules.
• NAD+ is present during glycolysis. It is
the electron carrier nicotinamide
adenine dinucleotide.
• NAD+ main function in glycolysis is to
carry high-energy electrons which
becomes NADH and holds the electrons
until they can be transferred to other
molecules (to the electron transport
chain)
• The process of glycolysis does not
require oxygen to occur, therefore it
can supply energy to the cells when
oxygen is not present.
• If oxygen is not present, glycolysis is
followed by fermentation (anaerobic
reaction).
Fermentation
• Fermentation is the process in which
cells convert NADH and NAD+ by
passing high-energy electrons back to
pyruvic acid.
• It produces a steady supply of ATP.
• There are 2 main types:
– Alcoholic
– Lactic acid
• Yeasts and some microorganisms use
alcoholic fermentation.
• The equation:
pyruvic acid + NADH  alcohol +
carbon dioxide + NAD+
• Lactic acid fermentation converts glucose
into lactic acid.
• The equation:
pyruvic acid + NADH  lactic acid +
NAD+
• During excessive exercise, your muscles
produce ATP by lactic acid fermentation.
This occurs AFTER they have used up all of
the ATP produced by cellular respiration.
Ch 9 Section 2
The Krebs Cycle and
Electron Transport
An Overview:
• The pathways of cellular respiration are
said to be aerobic because they require
oxygen.
• At the end of glycolysis, 90% of the
energy in glucose is still unused.
• The cell wants to use all of the energy, so
it uses oxygen to accept the high energy
electrons.
• Krebs Cycle and Electron Transport Chain
MUST HAVE oxygen to complete these
final steps of cellular respiration.
Psst…don’t write
this, let’s just
think a little bit!
Rolling and Folding???
• Some of the steps in cellular
respiration take place in the
membrane inside the cell structure
called the mitochondrion, which has a
folded inner membrane. What
purpose do these folds serve?
Cellular Respiration
Glucose
(C6H1206)
+
Oxygen
(02)
Glycolysis
Krebs
Cycle
Electron
Transport
Chain
Carbon
Dioxide
(CO2)
+
Water
(H2O)
The Krebs Cycle
• Discovered in 1937 by
British biochemist
Hans Kreb.
• Hans Kreb won the
Nobel Prize in 1953 for
his discovery of the
Krebs cycle.
• Krebs cycle is also
known as the citric
acid cycle.
• It is the second stage
of cellular respiration.
• The pyruvic acid
produced in glycolysis
is passed to the
second stage of
cellular respiration,
Krebs cycle.
• Pyruvic acid is broken
down into carbon
dioxide in a series of
reactions.
• Citric acid is the first
compound formed in
the reactions.
(AKA…citric acid cycle)
Stages of Krebs Cycle:
STAGE 1 – Citric Acid Production
• Pyruvic Acid enters the mitochondria (where
the rest of cellular respiration occurs)
• A carbon is removed, forming carbon dioxide
• Electrons are removed, changing NAD+ to
NADH
• Coenzyme A joins the 2-carbon molecule to
form acetyl-CoA
• Acetyl-CoA then adds the 2-carbon acetyl
group to a 4-carbon compound, forming
citric acid
STAGE 2 – Energy Extraction
• Citric Acid (from stage 1) is broken down
into a 5-carbon compound, then into a
4-carbon compound.
• 2 molecules of carbon dioxide are
released
• Electrons join NAD+ and FAD to form
NADH and FADH2
• One molecule of ATP is generated
• THE TALLY from one molecule of pyruvic
acid = 4 NADH, 1 FADH2 and one
molecule of ATP.
What happens to the Krebs
Cycle products?
• CO2 released is
the source of
CO2 in your
breath
• Each exhale you
expel the CO2
produced by the
Krebs cycle
• ATP produced
during the Krebs
Cycle can be used
for cellular
activities
• NADH (electron
carriers) can be
used to generate
huge amounts of
ATP.
Electron Transport
• Electrons produced in the Krebs Cycle are passed
to the electron transport chain by the electron
carrier molecules NADH and FADH2.
• The electron transport chain uses the highenergy electrons from the Krebs Cycle to convert
ADP to ATP.
• This couples the movement of high-energy
electrons with the production of ATP.
• Three stages:
– Electron transport
– Hydrogen Ion Movement
– ATP production (ATP synthase uses energy from H+
ions to convert ADP to ATP.
Totals:
• The complete breakdown of glucose
through cellular respiration, including
glycolysis, results in the production of
36 molecules of ATP.
Quick Energy vs. Long-Term
Energy
• Energy and Exercise: At the start of a
race, your muscles contain ATP to last
only a few seconds. By the 50 meter
mark, most of the ATP is produced by
lactic acid fermentation. At the end
of the race, you are breathing deeply.
Why? To resupply your body with
oxygen!!!
• If you exercise for more than 90
seconds, ATP is produced through
cellular respiration. This process
releases energy more slowly so you
can “pace yourself”.
• Your body stores energy in muscle in a
carbohydrate called glycogen.
Glycogen is broken down during the
first 15 minutes of activity, then your
body breaks down fat for energy.
A SUMMARY 
• Photosynthesis: deposits energy and
occurs in plants, algae, and bacteria
• Cellular Respiration: withdraws
energy and takes place in all
eukaryotes and some prokaryotes