Clothespins and Muscle Fatigue
Introduction: Automobiles and machines must be supplied
with gasoline or electricity as a source of energy before they
can move. Your muscles require energy in the form of ATP to
contract.
Muscles can produce ATP by using oxygen (aerobic
respiration) or not using it (anaerobic respiration). Anaerobic
respiration in muscle cells produces lactic acid. When
muscles do a lot of work quickly, the buildup of lactic acid
reduces their ability to contract until exhaustion eventually
sets in and contraction stops altogether. This is called muscle
fatigue.
Materials: clothespin, timer
Procedure:
•Hold a clothespin in the thumb and index finger of your
dominant hand.
•Count the number of times you can open and close the
clothespin in a 20-s period while holding the other fingers of
the hand straight out. Make sure to squeeze quickly and
completely to get the maximum number of squeezes for each
trial.
•Repeat this process for nine more 20-s periods, recording the
result for each trial in a suitable table. Do not rest your fingers
between trials.
•Repeat the procedure for the non-dominant hand.
Right Hand
Trial 1
Trial 2
Trial 3
Etc….
Left Hand
Trial 1
Trial 2
Trial 3
Etc….
Number of squeezes
Sample table:
Questions:
•Prepare a suitable graph of the data you collected.
•What happened to your strength as you progressed through each trial?
•Describe how your hand and fingers felt during the end of your trials.
•What factors might cause you to get more squeezes (to have less fatigue)?
•Were your results different for the dominant and the nondominant hand? Explain why
they would be different.
•Your muscles would probably recover after 10 min of rest to operate at the original
squeeze rate. Explain why.
Click here
then… click here…
Cellular respiration
8-year-old Sarah suddenly felt pins and needles in the muscles of her legs as she
walked. Within a year, she couldn’t walk without experiencing muscle pain,
shortness of breath, and a racing heart. When Sarah engaged in light physical
activity, her muscles generated as much lactic acid as would normally be
produced during prolonged strenuous exercise. The lactic acid buildup was
responsible for the muscle pain, but why was it accumulating abnormally?
Sarah’s problem was narrowed down to her energy production system. But
where?
The trouble could lie within one of the three components of cellular respiration:
glycolysis, the Krebs cycle, or the electron transport system???
Cellular respiration
Biochemists traced Sarah’s problem to the electron transport
system in her mitochondria. This chain of proteins allows for the
efficient production of ATP, and in Sarah’s case, one of the
proteins, cytochrome a3, was defective. Her muscles could not
make sufficient amounts of ATP and, instead, produced excess
lactic acid. Observations showed that Sarah’s muscle cells had
produced huge numbers of mitochondria to make up for the low
energy yield.
Cellular respiration
Researchers found a substitute for the faulty protein: a simple
mixture of vitamin C and a modified form of vitamin K. Sarah
began feeling better almost instantly. By the age of 20, she no
longer used a wheelchair and was completely free of symptoms.
The mixture did not cure Sarah’s it simply filled the gap caused
by the defective protein. Without a team of investigators who
understood cellular respiration, she would have been denied
the opportunity to lead a normal life.
Cellular respiration
We are going to start by focusing on how to get energy from glucose….
Photoautotrophs – make glucose from sunlight
(photosynthesis)
Heterotrophs – get glucose from eating photoautotrophs or
heterotrophs.
REDOX Reactions revisited….
Cellular respiration
Cells have developed several different mechanisms to extract
the energy they need from available nutrients. In each case,
redox reactions are involved.
In one method, the redox reactions result in the transfer of
electrons from glucose to oxygen. Glucose is oxidized to carbon
dioxide and oxygen is reduced to water. The overall reaction is
as follows:
C6H12O6 (aq) + 6 O2(g)  6 CO2(g) + 6 H2O (l) + energy via heat and ATP
Cellular respiration
Aerobic respiration is accomplished through a series of
about 20 reactions in which the product of one reaction is
the reactant of the next, with each step catalyzed by a
specific enzyme.
Definition of aerobic :
aer·o·bic/əˈrōbik/
Adjective: Relating to, involving, or requiring free oxygen: "simple aerobic
bacteria".
Relating to or denoting exercise that improves the efficiency of the body's
cardiovascular system in absorbing and transporting oxygen.
Cellular respiration
The overall equation for aerobic respiration tells us that 12 hydrogen atoms
break away from glucose and attach to six oxygen atoms from the six oxygen
(O2) molecules to become six water (H2O) molecules.
This is called oxidation because hydrogen atoms carry electrons away from
carbon atoms in glucose to oxygen atoms.
Cellular respiration
When the hydrogen atoms form covalent bonds with oxygen, the shared
electron pairs occupy positions closer to the oxygen nuclei than they did when
they were part of the glucose molecule.
This happens because oxygen is much more electronegative than carbon. An
electron occupying an energy level closer to a nucleus is equivalent to a
skydiver occupying a position closer to the ground—both possess less free
energy.
The decrease in potential energy coupled with an increase in entropy causes a
decrease in free energy and an overall exergonic process.
Cellular respiration
This change also constitutes an oxidation because, once
bound to carbon atoms, the highly electronegative oxygen
atoms draw the shared electron pairs to themselves. This
results in a change that is considered equivalent to carbon
losing electrons
Cellular respiration
In a living cell, the free energy released
from the combustion of glucose would
also dissipate as heat and light, but cells
have evolved methods to trap some of
the energy (about 34% of it).
By moving the positions of electrons in certain molecules to higher
free energy states (such as in ATP).
Cellular respiration
Activation energy prevents spontaneous combustion and allows
living things to control the oxidation process.
Specific enzymes catalyze every step in the aerobic respiration
process. They lower the activation energy and allow the reactions
to occur at a rate that is consistent with the needs of the cell.
Cellular respiration
Oxygen is not the only possible electron acceptor in the oxidation
of glucose in a cell.
Some microorganisms use NO2, SO4, CO2, and even Fe3 as final
electron acceptors. These organisms are known as obligate
anaerobes and include such notable bacteria (and their associated
disorders) as:
Clostridium tetani (tetanus)
Clostridium botulinum (food poisoning)
Clostridium perfringens (gas gangrene).
Have you been paying attention???
What is a photoautotroph?
An organism that produces energy by photosynthesis
What is the equation for cellular respiration for a heterotroph?
C6H12O6 (aq) + 6 O2(g)  6 CO2(g) + 6 H2O (l) + energy via heat and ATP
What type of proteins are required for Aerobic respiration ?
Enzymes
What does OIL RIG stand for ?
Oxidation is loss, reduction is gain
In cellular respiration is glucose oxidized or reduced?
oxidized
When the hydrogen atoms form covalent bonds with oxygen,
the shared electron pairs occupy positions closer to the oxygen
nuclei than they did when they were part of the glucose
molecule. Why??
Oxygen is more electronegative than carbon
How much of the free energy released is actually traped by the cell?
34%
The first law of thermodynamics tells us that energy cannot
be created or destroyed—it can only be changed from one
form into another or transferred from one object to another.
The ultimate goal is to capture as much of the available free
energy as possible in the form of ATP.
This goal is accomplished through two distinctly different energytransfer mechanisms called:
1. substrate-level phosphorylation
2. oxidative phosphorylation.
Substrate-level phosphorylation
In substrate-level phosphorylation, ATP is formed directly in an
enzyme-catalyzed reaction.
In the process, a phosphate-containing compound transfers a
phosphate group directly to ADP, forming ATP
Oxidative Phosphorylation
ATP is formed indirectly. This process is oxidative because it
involves a number of sequential redox reactions, with oxygen
being the final electron acceptor.
It yields many more ATP molecules for each glucose molecule
processed.
Cellular respiration - homework
Read pages 114 – 120.
Answer “Learning check” 1 – 6.
Write a paragraph that describes a coupled reaction.