Cellular

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Cellular
Respiration
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Chemical energy used in cellular respiration is
created during photosynthesis
Heterotrophic organisms can then harvest this
chemical energy for their own needs
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These are the end products of photosynthesis
Glucose, water, and oxygen
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The product of photosynthesis we are concerned
with here is the glucose molecule
Traditionally, we learn the steps of cellular
respiration by tracking the degradation of the
glucose molecule
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Principles of Energy Harvest
Cellular respiration and fermentation are
catabolic, energy-yielding pathways
The products of photosynthesis are organic
compounds that store energy in the arrangement of
their atoms
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Catabolic pathways do not do any cellular work
Catabolism is linked to work by means of a
chemical drive-shaft
ATP
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As we study cellular respiration, we must always
keep in mind our main objective
Discovering how cells use the energy stored in
food molecules to make ATP!
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What is so important about ATP?
ATP is the central character in all
bioenergetics The triphosphate tail of ATP is the
chemical equivalent of a loaded spring The close
packing of the three negatively charged phosphate
groups is an unstable, energy-storing arrangement
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This chemical spring loses its terminal
phosphate, releasing energy The cells taps this
energy source by using enzymes to phosphorylate
other compounds Phosphorylation causes a molecule
to undergo some sort of change that causes it to
do work
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Once ATP loses its terminal phosphate, it becomes
ADP (adenosine diphosphate) To keep working, the
cell must regenerate its supply of ATP from ADP
inorganic phosphate
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To understand how a cell regenerates ATP, we need
to understand the fundamentals of the process of
cellular respiration
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Cellular respiration involves glycolysis, the
Krebs cycle, and electron transport

• Glycolysis and fermentation

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fermentation
And glycolysis
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Fermentation is the partial breakdown of sugars
that occurs in the cytoplasm of the cell
Fermentation occurs in the absence of oxygen as a
reactant
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Aerobic metabolism Oxygen Needed Anaerobic
metabolism Oxygen Not Needed Fermentation is an
anaerobic process!
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Step 1 Glucose is imported into the cell, where
glycolysis oxidizes one glucose molecule into two
pyruvate molecules
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C6H12O6
Glucose In
Gives two pyruvate
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Also from glycolysis
In addition to pyruvate, two ATP are produced
during glycolysis
This occurs by substrate-level phosphorylation,
the transfer of a phosphate from an organic
molecule to ADP
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SoGlycolysis has given us two pyruvate
molecules These can be used in alcohol
fermentation or lactic acid fermentation During
alcohol fermentation, pyruvate is converted to
ethanol in two steps
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Step 1 Carbon dioxide is released from the
pyruvate, which now becomes acetaldehyde
Step 2 Acetaldehyde is reduced (electrons added)
by NADH to ethanol
Dont forget This all occurs in the cytoplasm
of the cell!!
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Lactic Acid Fermentation
Pyruvate is reduced directly by NADH to form
lactate as a waste product (no carbon dioxide is
lost)
Human muscle cells make ATP by lactic acid
fermentation during strenuous exercise This
causes the burn you may feel
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Pyruvate is also used in the Krebs cycle, which
takes place in within the mitochondrial matrix
If molecular oxygen is present, pyruvate enters
the mitochondrion, where the enzymes of the Krebs
cycle complete the oxidation of the organic fuel
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Pyruvate is the junction between glycolysis and
the Krebs cycle
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Pyruvate is converted to Acetyl CoA in the
mitochondrion This is the junction between
glycolysis and the Krebs cycle
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The cycle generates 1 ATP per turn by
substrate-level phosphorylation, but most of the
chemical energy is transferred to electron
carriers (NAD and FAD). These electron carriers
(which get reduced to NADH and FADH2 shuttle
their high-energy electrons to the electron
transfer chain, which produces ATP by oxidative
phosphorylation
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The electron transport chain accepts electrons
from NADH and FADH2
As each complex in the chain accepts and in turn
donates electrons, the chemical energy harvested
from food is transformed into an H gradient
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The hydrogen ions flow back into the
mitochondrial matrix via ATP Synthase. This
complex harnesses the proton-motive force to
phosphorylate ADP, forming ATP. This is called
chemiosmosis Hydrogen ions that were driven out
of the mitochondrial matrix in the electron
transport chain (using energy) now drive
production of ATP
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The maximum output of cellular respiration is
about 38 ATP molecules
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6CO2 6H2O
C6H12O6 6O2
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Todays Lab
Exercise 5.1 Alcohol Fermentation This exercise
will demonstrate anaerobic respiration in yeast
cells (used in brewing and baking) Glucose is
broken down into alcohol and carbon dioxide
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We will be using four 50ml beakers, numbered 1
4.
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2
1
3
4
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Using a clean graduated cylinder, measure and
pour 20ml of the following solutions into
each beaker
Beaker 1 10 Glucose
Beaker 2 1 Starch
Beaker 3 1 Starch 5ml of 2 amylase
Beaker 4 10 Sugar substitute
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To each beaker we will now add 0.2 gram of yeast.
Stir each mixture with a clean glass stirring
rodDo not contaminate your beakers.
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Pour the contents of each beaker into four
different fermentation tubes, and number them.
Cover the opening (arrow) with your thumb and
invert each tube to remove air trapped in the
long (calibrated) part of the tubes.
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We will then incubate the tubes at 37 degrees C,
and check the solution levels every 20 minutes
for an hour
The gas produced will displace the solution in
the tube What is this gas?
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Scientific Method
Generate Hypotheses
What do you expect will happen in tube 1?
(glucose yeast)
If the yeast grows in tube 1, what should happen
in tube 2? (starch yeast)
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If yeast does not grow in tube 2, why not? Can
yeast utilize starch as a food source?
Tube 3 is identical to tube 2 except for the
addition of amylase What is amylase? Hint What
type of substance has ase as a suffix?
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Amylase This is a digestive enzyme, largely
produced by the pancreas and salivary gland, that
converts starches to sugar by hydrolysis.
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We will not be doing the bean respiration
experiment (exercise 5.2) Instead, we will be
blowing into a straw through a solution of
bromothymol blue
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Bromothymol blue is a dye used as an acid-base
indicator It will turn green in the presence of
CO2
Blow through the straw for about 30 seconds to
see an effect
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Homework Do all the summary questions at the end
of chapter 5