Transcript Can you describe the various methods of cell membrane transport?

Biology Review
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Cellular Respiration and Cellular Work
Note
Much of the text material is from, “Essential Biology with
Physiology” by Neil A. Campbell, Jane B. Reece, and Eric J.
Simon (2004 and 2008). I don’t claim authorship. Other
sources are noted when they are used.
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Outline
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Harvesting of chemical energy
Chemical cycle
ATP and ADP
Cellular respiration processes
Enzymes and enzyme inhibitors
Cell membrane transport
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http://www.nick-lane.net
Harvesting of Chemical Energy
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Chemical Energy
Food, gasoline, and other fuels are forms are sources of chemical
energy.
•
Carbohydrates and fats have carbon backbones that make them rich
in chemical energy.
http://www.bubblews.com
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Harvesting of Chemical Energy
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Cells and internal combustion engines use similar physical processes
to perform work.
•
A gasoline engine mixes oxygen with octane in an explosive chemical
reaction that breaks-down the covalent bonds in the carbon backbone
for rapid liberation of energy.
•
The reaction moves the pistons in the cylinders, which ultimately drives
the wheels.
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Harvesting of Chemical Energy (continued)
•
Cells use oxygen to harvest chemical energy from food molecules in a
more controlled process known as cellular respiration.
•
Aerobic cellular respiration, which requires oxygen, occurs in the mitochondria of eukaryotic cells.
•
Anaerobic respiration, which does not use oxygen, occurs in the cytosol
of prokaryotic and eukaryotic cells.
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The molecule ATP (adenosine triphosphate) is generated as a chemical
energy source for cellular work in both types of respiration.
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ATP Molecule
http://biology.clc.uc.edu
Adenosine triphosphate (ATP)
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Efficiencies
Automobile engines extract about 25 percent of the chemical energy
to produce kinetic energy to drive the wheels—the rest is converted to
heat.
• Cells extract about 40 percent of the chemical energy from food molecules to perform cellular work.
• The waste, or byproducts, of internal combustion engines and cellular
respiration are mostly CO2 and water.
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Cellular Work
The other 60 percent chemical energy generates body heat to maintain
the body at a constant temperature—about 98.6oF or 37oC.
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Sweating and other cooling mechanisms enable the body to lose excess
heat including in hot environments and physical exercise.
http://www.fitnessacademyhull.co.uk
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http://bioweb.uwlax.edu
Coco as a kitten (my cat)
http://www.isb.cnr.it
Life Requires Chemical Energy
http://www.americansingercanary.com
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Calories
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Calorie is a unit of chemical energy used in the physical and biological
sciences.
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A calorie (c) is the amount of energy required to raise the temperature
of one gram of water by one degree Celsius (oC).
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Calories (continued)
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The caloric content of food is measured by burning it completely to
ash under a container of water, and measuring the increase in the
water temperature.
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A handful of peanuts has enough chemical energy to boil more than
a quart of water if the peanuts could be completely converted to
heat.
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A calorimeter is used by food scientists to measure the caloric content of foods.
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Bomb Calorimeter
http://chemistry.umeche.maine.edu
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Kilocalories
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The use of calories (c) to express the energy content of food is not
practical since a calorie is a very small unit of measurement.
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The daily recommended diet for adults would be about 2.0 x 106, or
two million calories.
•
Instead, kilocalories (kcal or C) are used in which one kilocalorie is
equals to 1,000 calories (c).
Kilo- = 1,000.
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Kilocalories (continued)
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The daily recommended diet for adults is about 2,000 kilocalories (C).
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Gender, age, basal metabolic rate, physical activity, and other factors
determine recommended caloric intake.
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The calories listed on food labels are always expressed in kilocalories.
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A way to minimize confusion between c and C is to refer to kilocalories
as food calories.
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http://labelchoices.com
Food Label
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Have you compared food labels to determine nutritional
value and calories?
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Caloric Densities
Although certain foods may have
about equal food caloric content,
they can differ substantially in
caloric densities.
http://www.asymptotia.com
Each plate contains about
200 food calories.
http://www.wisegeek.com
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Caloric Accounting
Caloric accounting is based on a person’s food intake, basal metabolic
rate, and physical activity.
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Caloric imbalances between food intake, and basal metabolic rate and
physical activity can lead to weight gain or weight loss.
http://i.lv3.hbo.com
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http://www.thelastgreenvalley.org
http://www.dancinglondon.com
Calorie Expenditures
535 kcal (2 mph)
160 kcal (3 mph)
510 kcal (fast)•
170 kcal (slow)
http://briandesousa.com
http://www.morrisville.edu
600 kcal (fast), 200 kcal (slow)
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What are your favorite physical activities?
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http://www.gosunstove.com
Chemical Cycle
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Solar Energy and Food
Food molecules represent the storage of solar energy in indirect form,
involving photosynthesis in plants.
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Animals rely on plants to convert energy from sunlight to the potential
energy of sugars and other organic molecules.
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Humans also depend on plant life for cotton, lumber, paper, and many
other products.
http://solar-center.stanford.edu
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Autotrophs and Heterotrophs
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Plants are autotrophs, or self-feeders, that synthesize organic matter
from inorganic molecules such as carbon dioxide, water, and minerals
from the soil.
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Animals are heterotrophs, or other-feeders, that are unable to synthesize organic matter from inorganic molecules—they must obtain nutrients from food.
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Heterotrophs depend on autotrophs for organic materials needed for
tissue growth and repair.
Autotrophs = also known as producers.
Heterotrophs = consumers.
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Food Web and Its Dependencies
Autotrophs
http://www.biologycorner.com
Heterotrophs
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Could you assemble a food web for human consumption
patterns?
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Chemical Cycle in Ecosystems
Sunlight
http://img.dailymail.co.uk
Photosynthesis
Chloroplasts in plants
http://pws.byu.edu
C6H12O6 (glucose)
+ O2 (oxygen)
CO2 (carbon dioxide)
+ H2O (water)
Cellular respiration
Mitochondria in animals and plants
http://www.soquel.org
ATP
Cellular work
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http://3.bp.blogspot.com
ATP and ADP
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Cellular Respiration
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The chemical equation for aerobic cellular respiration is shown on the
next slide.
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A key product of cellular respiration is adenosine triphosphate (ATP).
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The left- and right-hand sides of the equation are shown in a previous
slide, “chemical cycle in ecosystems.”
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The chemical equation represents what is known as a redox reaction.
Aerobic = requires oxygen.
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Chemical Equation
+
(glucose)
6O2
6CO2
Cellular
Respiration
+
6H2O
+
ATP
(chemical
energy)
ATP
molecule
Glucose
molecule
Up to 38 ATP
molecules are
produced for each
glucose molecule.
http://biology.clc.uc.edu
C6H12O6
http://eurekalert.org
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Redox Reaction
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The transfer of electrons from one molecule to another molecule is an
oxidation-reduction reaction.
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It is also called, more simply, a redox reaction.
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The loss of electrons is known as oxidation—glucose is oxidized, losing electrons to oxygen.
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Oxygen is reduced by accepting electrons and hydrogen atoms from
glucose.
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Energy is released when electrons and hydrogen atoms change partners from sugar to oxygen.
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Adenosine Triphosphate
The tail of adenosine triphosphate (ATP) contains potential energy
for cellular work.
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The three phosphate groups tend to repel each other because each
has a negative charge—they are held together by covalent bonds.
http://biology.clc.uc.edu
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ATP and ADP
The crowding of negative charges in the molecular tail of ATP is similar
to the storing of energy in a compressed spring.
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When released, a spring can perform useful work.
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The release of the third phosphate group from its molecular tail makes
the energy available for cellular work.
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The molecule, which now has two remaining phosphate groups, is called
ADP (adenosine diphosphate).
http://img.weiku.com
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Phosphate Transfer
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The third phosphate group released from ATP is transferred to other
molecules.
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The transfer enables cells to perform work—mechanical, chemical, or
transport.
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Examples of Cellular Work
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Mechanical—phosphate groups from ATP molecules are transferred
to motor proteins to enable muscle fibers to contract.
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Chemical—ATP provides energy for dehydration synthesis of macromolecules such as starches and proteins.
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Transport—ATP enables certain ions to be pumped across the plasma
membranes of neurons and other cells.
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ATP Cycle
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ATP is restored by adding a phosphate group to ADP using the chemical energy cellular respiration harvests from food molecules (such as
fats and carbohydrates).
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The process is called the ATP cycle.
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ATP Cycle (continued)
ATP
Potential energy from
food molecules
The circle
turns
clockwise
ADP +
Chemical energy for
cellular work
P
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http://www2.estrellamountain.edu
Cellular Respiration Processes
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Cellular Respiration
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Cellular respiration is a part of metabolism, the sum of all chemical
processes in cells of the body.
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Much, but not all, of cellular respiration occurs in the mitochondria.
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The potential energy in food is converted to chemical energy for use
by cells.
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More than two dozen chemical reactions are involved in cellular respiration.
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A specific enzyme catalyzes the chemical reaction in each metabolic
pathway.
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Components
Glycolysis
Electron micrograph of a human
lymphocyte cell—a number of
mitochondria are visible.
Krebs Cycle
Electron Transport Chain
The three processes involved
in cellular respiration.
http://www.sinauer.com
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Glycolysis
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The enzymes for glycolysis are in the cytosol of eukaryotic and prokaryotic cells.
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Glycolysis is anaerobic—it does not consume oxygen.
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The process breaks glucose molecules consisting of six carbons into
two, three-carbon molecules of pyruvic acid.
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For each molecule of glucose, four molecules of ATP are produced.
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Two electrons are also transferred to the molecule, NAD+ to produce
NADH for the electron transport chain.
NAD+ = an electron acceptor known as nicotine adenine
dinucleotide.
NADH = nicotine adenine dinucleotide, reduced.
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http://staff.jccc.net
Biochemistry of Glycolysis
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Glycolysis (continued)
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Pyruvic acid retains much of the energy of glucose that will be harvested in the Krebs cycle.
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Pyruvic acid is converted to a two-carbon compound called acetic acid.
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Acetic acid enters the Krebs cycle attached to a carrier molecule known
as coenzyme A (CoA) to form acetyl-CoA.
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ATP Output
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Glycolysis is not an especially efficient process since only four ATP
molecules are produced for every glucose molecule, along with two
electrons.
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In comparison, 36 ATP molecules (and many more electrons) are produced by the Krebs cycle.
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To sustain energy output in glycolysis, cells compensate by consuming
more glucose molecules if an adequate supply of carbohydrates is available.
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Anaerobic Effort
Cells can function for brief periods of time without oxygen through
the anaerobic conversion of glucose to pyruvic acid and ATP.
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Skeletal muscle fibers have sufficient amount of ATP molecules to
support anaerobic activity for about 5 seconds.
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These muscle fibers also have a secondary supply of the molecule
creatine phosphate to provide an additional 10 seconds of energy
reserve.
http://blog.beyou.tv
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Lactic Acid
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Lactic acid is a metabolic byproduct of pyruvic acid from the process of
glycolysis.
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During strenuous exercise, lactic acid accumulates in skeletal muscles,
which can produce muscle burning sensations and soreness.
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Skeletal muscles may temporarily shut down if lactic acid accumulates
in high concentrations.
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This is sometimes called, “hitting the wall.”
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http://www.abbagav.com
Hitting the Wall
Endurance runners must learn to stay within their
physiological limits until the final dash to the finish line.
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Lactic Acid (continued)
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Lactic acid is transported to the liver in the blood, where it is inactivated.
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The inactivation requires oxygen, which is one reason why a person
continues to breathe fast and heavy after vigorous exercise.
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Have you ever hit the wall, so to speak?
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Krebs Cycle
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The Krebs cycle occurs in mitochondria of eukaryotic (plant, animal,
and fungus) cells.
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It is also known by other names, and especially the citric acid cycle.
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The process is not found in prokaryotic cells because they lack mitochondria.
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http:/biology.unm.edu
Mitochondria
An electron micrograph of a mitochondrion.
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Krebs Cycle (continued)
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The Krebs cycle extracts chemical energy until CO2 is formed as a byproduct of aerobic cellular respiration.
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Each turn of the cycle produces two ATP molecules.
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Six electrons are donated to NAD+ molecules to produce NADH for the
electron transport chain.
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Two electrons are also donated to the molecule FADH2, for the electron
transport chain.
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Biochemistry of the Krebs Cycle
http://upload.wikimedia.org
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Electron Transport Chain
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The molecules of the electron transport chain are found in the inner
membrane of the mitochondria.
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Hydrogen ions (H+) “fall” toward oxygen molecules that entered the
mitochondria by passive diffusion along their concentration gradient.
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The process is aerobic—it requires a constant supply of oxygen molecules.
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The electron transport chain uses the electrons in NADH and FADH2
to pump hydrogen ions against their concentration gradient across the
mitochondrial membrane.
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Electron Transport Chain (continued)
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The hydrogen ions diffuse along their concentration gradient back into
the mitochondria.
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H+ inflow turns turbines of protein molecules, known as ATP synthases,
in the mitochondrial membrane.
ATP synthase
http://www.sparknotes.com
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Hoover Dam
Hoover Dam, Nevada and Arizona
http://www.mcnarybergeron.com
Turbines connected to generators
produce electrical energy from the
downhill flow of water.
Powerhouse turbines
http://www.bossanova.com
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ATP Regeneration
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Energy from the spinning of an ATP synthase attaches a phosphate
group to an ADP molecule to regenerate an ATP molecule.
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Up to 34 ATP molecules are produced by a ATP synthase—compare
this number with the much smaller ATP output from glycolysis.
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Versatility of Cellular Respiration
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So far, we have focused on glucose as a fuel source for cellular respiration.
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Cellular respiration also uses other carbohydrates, fats, and proteins.
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The digestive process hydrolyzes large food molecules into monomers
that can be absorbed by the small intestine for glycolysis and the Krebs
cycle.
http://www.borderfoodsinc.com
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http://safety.more4kids.com
Carbon Monoxide and Cyanide
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Carbon monoxide (CO) and cyanide block the transfer of electrons to
oxygen in the electron transport chain.
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The mitochondria cannot harvest food energy to convert ADP to ATP.
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The cells stop working and the organism can die, usually very rapidly.
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Enzymes and Enzyme Inhibitors
http://www.unc.edu
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Enzymes
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The sum of all chemical reactions in an organism is its metabolism.
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Enzymes are specialized proteins that lower activation thresholds and
speed-up many types of chemical reactions.
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The covalent bonds in molecules must be broken to initiate a chemical
reaction.
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Covalent bond breakage occurs, for example, when a disaccharide (a
double sugar) is hydrolyzed into two monosaccharides (single sugars).
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Enzymes (continued)
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Energy, usually in the form of heat, is needed for a chemical reaction
to occur—the threshold amount of heat is called its activation energy.
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Adding substantial amounts of heat is often not possible or desirable
with living cells.
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Enzymes enable metabolism to occur at lower temperatures by reducing the amount of activation energy required to break molecular bonds.
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Enzymes are catalysts that lower the barriers for chemical reactions to
occur.
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Induced Fit
An enzyme is specific in the chemical reaction it catalyzes although
thousands of different chemical reactions occur in the human body.
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The active site of an enzyme has a shape that fits a portion of the
substrate molecule, much like the correct key readily opens a door
lock.
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As an enzyme attaches to the substrate, it changes its shape slightly
to enable a physical embrace between the molecules in what is called
induced fit.
http:/www.carefreeenzyme.com
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Induced Fit (continued)
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The enzyme places the substrate under physical or chemical stress,
making it easier to break the covalent bonds and initiate the chemical
reaction.
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Once the covalent bonds are broken, the enzyme molecule can bind
with another substrate molecule to begin the process again.
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Enzyme Inhibitors
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Certain types of molecules can inhibit metabolic reactions by binding
to enzymes and disrupting their functions.
•
Enzyme inhibitors are specific to the enzymes they target.
•
Some inhibitors are imposters of substrates that bind to enzymes.
•
Other inhibitors bind to a different part of the enzyme and change the
shape of the active site so that it can no longer bind to the substrate.
•
Organisms produce enzyme inhibitors to control the overproduction of
enzymes.
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Enzyme Inhibitors (continued)
Enzymes inhibitors are manufactured for many medical and biological
purposes.
•
Malathion, an insecticide, inhibits an enzyme for the functioning of insect
nervous systems.
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Aerial spraying of malathion has been used to control Mediterranean fruit
fly infestations in southern California—it turned-out to be a controversial
program.
http://www.cpaphils.org
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American Civil War
http://nmhm.washingtondc.museum
http://www.a2zcds.com
During the American Civil War, many soldiers died from bacterial
infections in the treatment of their wounds—possibly as many as
died in battle.
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Antibiotics
Antibiotics are derived from microorganisms that disable or kill bacteria.
• In the 1920s, Alexander Fleming discovered penicillin when he found a
mold prevented the growth of bacteria that he was trying to cultivate in
bread.
• Penicillin, the first antibiotic to be developed, inhibits an enzyme needed
to form the cell walls in bacteria.
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The death rates from diseases such as bacterial pneumonia and surgical infections dropped substantially once antibiotics were widely available.•
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Antibiotics (continued)
Ampicillin and bacitracin—bacterial cell walls.
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Erythromycin, streptomycin, and tetracycline—bacterial ribosomes.
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Ciprofloxacin—bacterial chromosomal structure.
http://textbookofbacteriology.net
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What types of conditions can be treated with antibiotics?
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Cell Membrane Transport
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Cell Membrane Transport
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Cells can control the flow of materials across their plasma membranes.
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A major function of the plasma membrane, in addition to providing the
cell boundary, is regulating the movement of molecules into and out of
the cell.
•
Three forms of transport are: diffusion, osmosis, and active transport—
the first two are passive processes that do not require chemical energy.
http://upload.wikimedia.org
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Diffusion
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The heat energy of molecules causes them vibrate and this move randomly in what is called Brownian motion.
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A result of the motion is diffusion, the tendency of molecules to spread
into the available space.
•
Although each molecule moves randomly, the overall movement is in
one direction, from high- to low-concentration, along its concentration
gradient.
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Diffusion and Directional Movement
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The directional movement can be shown with movement of dye across
a semi-permeable membrane in a container of water
•
The membrane has pores large enough to pass the dye molecules but
not the water.
•
An equilibrium exists once the dye is evenly diffused—the number of
molecules moving across the membrane is now about the same in both
directions.
•
Two different dyes will diffuse along their own concentration gradients
as if the other molecule did not exist.
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Concentration Gradients
Passage
of time
Concentration gradient
Passage
of time
Red
Green
Individual concentration gradients
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Passive Transport
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Diffusion across a semi-permeable membrane is a form of passive
transport since it does not require expenditure of chemical energy.
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A cell’s plasma membrane is selectively permeable to some molecules.
•
The membrane allows certain small ions to pass (such as Na+ and
K+), but not large molecules such as proteins and phosphate groups.
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Passive Transport (continued)
•
Passive transport is an important process for maintaining all living
cells.
•
For example, O2 enters the hemoglobin of red blood cells through
passive diffusion to be transported in blood to meet the metabolic
needs of the body’s tissues.
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Osmosis
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The passive transport of water across a semi-permeable membrane is
called osmosis.
•
Consider a membrane separating two compartments that is permeable
to H2O but not to C6H12O6 (glucose), a larger molecule.
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Osmosis (continued)
•
The solution with a higher concentration of solute (in this case, glucose)
is hypertonic and the solution with a lower solute concentration is hypotonic.
•
H2O will diffuse across the membrane from the hypotonic solution to the
hypertonic solution until equilibrium is established.
•
The solutions are isotonic once they reach equal concentrations of glucose.
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http://schools.moe.edu.sg
Water Movement
H2O molecules are small enough to pass through the semipermeable membrane, but the glucose molecules cannot pass
because they are much larger.
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Water Regulation
The survival of cells depends on the body’s ability to regulate water
uptake and loss.
•
When red blood cells are immersed in an isotonic solution, the volume
of the cells remains constant.
•
Hypotonic and hypertonic environments can cause a cell to expand and
burst or shrivel and die.
http://www.mce.k12th.net
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Red Blood Cells
http://www.ccs.k12.in.us
Distilled water = hypotonic solution.
Salt water = hypertonic solution.
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Active Transport
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Active transport requires the expenditure of chemical energy to move
molecules across a cell’s plasma membrane.
•
A transport protein in the plasma membrane, using ATP as its energy
source, pumps the solute across the membrane against its concentration gradient.
•
Active transport enables cells to maintain intracellular concentrations of
molecules that differ from the extracellular environment.
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Active Transport (continued)
•
A cell generally has a higher concentration of potassium (K+) ions and
lower concentration of sodium (Na+) ions in the intracellular space.
•
The concentration differences are regulated by the sodium-potassium
pump of transport proteins.
•
This pump is vital in enabling neurons to generate nerve impulses—or
action potentials—as we will discuss in an upcoming lecture.
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Exocytosis
Large molecules, including many proteins, are too large to fit through
the plasma membrane.
•
Transport vesicles carry proteins manufactured by the ribosomes, and
fuse with the plasma membrane to empty their contents outside of the
cell.
•
The process is known as exocytosis.
http://www.linkpublishing.com
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Endocytosis
The opposite process is endocytosis—cells take in materials such as
food molecules and water in vesicles that bud inward from the plasma
membrane.
•
Endocytosis and exocytosis both require chemical energy, and thus are
active processes.
http://www.pigur.co.il
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Can you describe the various methods of cell membrane
transport?
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Receptor-Mediated Endocytosis
•
Another type of endocytosis is when certain external molecules bind
with receptor proteins in the plasma membrane to be transported
into the cell.
•
This process is called receptor-mediated endocytosis.
•
In a genetic disorder, plasma membranes of cells cannot take-up
sufficient amounts of cholesterol bound to low density lipoproteins
(LDL).
•
High LDL levels result, which can lead to cardiovascular problems if
left untreated or inadequately treated.
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Cell Signaling
•
Many types of cells can communicate with each other across their
plasma membranes.
•
A signal from outside of the cell—such as a water-soluble hormone—is
received by receptor proteins in the plasma membrane or cytoplasm.
•
The signal triggers a chemical chain reaction inside the cell, in what is
known as a signal transduction pathway.
•
The signal can lead to responses such as metabolic changes in the cell
or rearrangement of the cytoskeleton.
•
Cell signaling is a key mechanism for many hormones of the endocrine
system.
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