Download Cellular Respiration

Chapter 9
 Hunger
can present a variety of
different symptoms in different
people
• Ultimately, the cause is the same,
your body has a need for food
 Food
provides living things
with energy
• It is used as the chemical building
blocks needed for growth and
reproduction
 One
gram of sugar (C6H12O6)
when burned in the presence of
oxygen releases 3811 calories of
heat energy!
 Calorie
– the amount of energy
needed to raise the temperature
of 1 gram of water 1 degree
Celsius
• Is represented as kilocalories (C) on
food labels
 Cells
don’t actually “burn” the glucose
molecules
• Instead energy is gradually released
 The
releasing of energy starts with a
processes called Glycolysis
• In the presence of oxygen, glycolysis proceeds
to 2 other pathways
• In the absence of oxygen, glycolysis is followed
by another pathway
 Cells
don’t actually “burn” the glucose
molecules
• Instead energy is gradually released
 The
releasing of energy starts with a
processes called Glycolysis
• In the presence of oxygen, glycolysis proceeds to 2
other pathways
• In the absence of oxygen, glycolysis is followed by
another pathway
 In
the presence of oxygen, glycolysis is
followed by the Krebs Cycle and Electron
Transport Chan (ETC)
• They are included in the process of cellular
respiration
 Cellular
Respiration – the process that
releases energy by breaking down
glucose and other food molecules in the
presence of oxygen
 There
are 2 sites where cellular
respiration takes place
1.
2.
Glycolysis – in the cytoplasm
Krebs Cycle & ETC – in the mitochondria
6O2 + C6H12O6 -> 6CO2 + 6H2O + Energy
Oxygen + Glucose -> Carbon Dioxide + Water + Energy
 The
process requires oxygen and food and
gives off carbon dioxide, water and energy
 This
process occurs in multiple steps
• If there was only 1 step, all of the energy from
glucose would be released at once
• Cells need to control energy usage by storing it and
releasing it little bits at a time
 This is done by creating ATP
 Glycolysis
– the process in which one
molecule of glucose is broken in half,
producing 2 molecules of pyruvic acid, a
3 carbon compound
 is
the 1st set of reactions in cellular
respiration
 Even
though glycolysis is an energy releasing process, it requires energy to start
it
2
molecules of ATP are used to start
glycolysis, and ultimately when the process
is over, 4 ATP molecules are produced
*Glycolysis gives a net gain of 2 ATP molecules *
 One
reaction of glycolysis moves 4 high
energy electrons using an electron
carrier NAD+
• NAD+ + 4 electrons -> NADH
 With
the use of NAD+, energy can be
passed to other pathways of the cell
 Glycolysis
is so fast that thousands of
ATP’s can be produced in milliseconds!
 The
cell requires the use of NAD+ to pass
on the high energy electrons to keep
NAD+ free for more glycolysis to occur
1.
Created energized ATP molecules
2.
Passed on high energy electrons (w/
NADH)
3.
Created pyruvic acid (which gets used
in the Krebs Cycle)
 When
glycolysis occurs and there is no
oxygen present, it proceeds to the
pathway of fermentation
 Fermentation
– process that releases
energy from food molecules by producing
ATP in the absence of oxygen
 Anaerobic
– does not require oxygen
 During
fermentation, cells convert NADH
to NAD+ by passing the high energy
electrons back to pyruvic acid
• Keeps NAD+ free to accept more electrons
• Allows more ATP energy to be produced
1.
Alcoholic Fermentation
• Done by some yeasts and microorganisms to
produce alcohol and breads
pyruvic acid + NADH -> alcohol + CO2 + NAD+
2.
Lactic Acid Fermentation
• Occurs in muscles during rapid exercise when
the body cannot supply enough of oxygen to the
tissues
• Lactic Acid Fermentation can produce ATP to
supply muscles with additional energy
• Too much lactic acid buildup can cause a painful,
burning sensation which is associated with
muscle fatigue
pyruvic acid + NADH -> lactic acid + NAD+
 In
addition of supplying overused
muscles with energy, lactic acid
fermentation is also utilized for making
different food products
• Done with the use of bacteria
 Ex.)
cheeses, yogurts, pickles, sauerkraut
 At
the end of glycolysis, about 90% of the
chemical energy that was available in the
glucose is still unused
• It is trapped in high energy electrons and
pyruvic acid
 To
extract the rest of the energy, the cell
is going to use oxygen
• Because cellular respiration requires oxygen it is
an aerobic process
 In
the presence of oxygen, the pyruvic
acid produced in glycolysis is passed to
the second stage of cellular respiration,
the Krebs Cycle
 During
the Krebs Cycle, pyruvic acid is
broken down into carbon dioxide in a
series of energy extracting reactions
• Because a molecule called Citric Acid is one of
the first compounds formed, Krebs Cycle is also
referred to as the Citric Acid Cycle
 As
seen in glycolysis and photosynthesis,
the Krebs Cycle also produces high
energy electrons which require special
electron carriers
 Along
with carbon dioxide as a product,
the highly energized compounds NADH,
ATP and FADH2 are also produced
OR
 The
Krebs Cycle’s highly energized
electrons are passed to the ETC the
energized carrier molecules NADH and
FADH2
 The
purpose of the ETC
is to use the energized
electrons to convert
ADP into ATP
 How
much energy does cellular respiration
yield from 1 glucose molecule?
 Remember, glycolysis
had a net gain of 2 ATP
molecules
• Which is all that can be made in the absence of oxygen
(anaerobic)
 With
the addition of the Krebs Cycle and ETC,
the cell can make an additional 34 ATPs for a
grand total of 36 ATPs per glucose
 The
36 ATP molecules the cell makes per
glucose represents about 38% of the total
energy of glucose
• May not seen efficient, but the cell is more
efficient at using chemical fuel than the average
engine is at using gasoline fuel
 The
remaining 62% of glucose
energy is released as heat
• Which is why the body feels warmer after
vigorous exercise
 Quick
Energy
• Cells contain small amounts of ATP
made through glycolysis and cellular
respiration
 This ATP is enough to last about 90
seconds of intense activity
• After this small amount of ATP is used,
lactic acid fermentation starts, causing
lactic acid buildup in the muscles
 The only way to rid the body of this is with
oxygen, which is why heavy breathing
starts soon after activity
 Long-Term
Energy
• For exercise longer than 90 seconds,
cellular respiration is the only way to
generate a continuing supply of ATP
• Cellular respiration releases ATP more
slowly than fermentation does
 Why athletes have to pace themselves
• The body is also able to utilize
carbohydrate glycogen in muscles and
other tissues
 Can supply energy for 15 to 20 minutes of
activity