cell respiration revised09
TRANSCRIPT
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An Introduction To Metabolism
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Metabolism
• The totality of an organism’s chemical processes.
• Concerned with managing the material and energy resources of the cell.
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Catabolic Pathways
• Pathways that break down complex molecules into smaller ones, releasing energy.
• Example: Respiration
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Anabolic Pathways
• Pathways that consume energy, building complex molecules from smaller ones.
• Example: Photosynthesis
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Energy
• Ability to do work.• The ability to rearrange a collection of matter.• Forms of energy:– Kinetic– Potential– Activation
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Kinetic Energy
• Energy of action or motion.
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Potential Energy
• Stored energy or the capacity to do work.
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Activation Energy
• Energy needed to convert potential energy into kinetic energy.
Potential Energy
Activation Energy
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Energy Transformation
• Governed by the Laws of Thermodynamics.
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1st Law of Thermodynamics
• Energy can be transferred and transformed, but it cannot be created or destroyed.
• Also known as the law of Conservation of Energy.
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2nd Law of Thermodynamics
• Each energy transfer or transformation increases the entropy of the universe.
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Entropy
• Measure of disorder.
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Free Energy
• The portion of a system's energy that can perform work.
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Chemical Reactions
• Are the source of energy for living systems.
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Cell - Types of Work
• Mechanical - muscle contractions• Transport - pumping across membranes• Chemical - making polymers
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ATP
• Adenosine Triphosphate• Made of: - Adenine (nitrogenous base) - Ribose (pentose sugar) - 3 phosphate groups
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Adenine
Ribose
Phosphates
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Key to ATP
• Is in the three phosphate groups.• Negative charges repel each other and makes
the phosphates unstable.
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ATP
• Works by energizing other molecules by transferring phosphate groups.
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ATP vs Food
• ATP: – Renewable energy resource.– Unstable bonds
• Food:– Long term energy storage– Stable bonds
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ATP Cycle
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ATP in Cells
• A cell's ATP content is recycled every minute.• Humans use close to their body weight in ATP
daily.• No ATP production equals quick death.
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Enzymes
• Biological catalysts made of protein.• Cause the rate of a chemical reaction to
increase.
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Chemical Reaction
AB + CD AC + BD
AB and CD are “reactants”AC and BD are “products”
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Enzymes
• Lower the activation energy for a chemical reaction to take place.
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Enzyme Terms
• Substrate - the material and enzyme works on.• Enzyme names: Ex. Sucrase - ase name of an enzyme 1st part tells what the substrate is. (Sucrose)
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Enzyme Name
• Some older known enzymes don't fit this naming pattern.
• Examples: pepsin, trypsin
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Active Site
• The area of an enzyme that binds to the substrate.
• Structure is designed to fit the molecular shape of the substrate.
• Therefore, each enzyme is substrate specific.
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Enzymes
• Usually specific to one substrate. • Each chemical reaction in a cell requires its
own enzyme.
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Factors that Affect Enzymes
• Environment• Cofactors• Coenzymes• Inhibitors• Allosteric Sites
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Environment
• Factors that change protein structure will affect an enzyme.
• Examples:– pH shifts– temperature– salt concentrations
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Enzyme Inhibitors
• Competitive - mimic the substrate and bind to the active site.
• Noncompetitive - bind to some other part of the enzyme.
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Control of Metabolism
• Is necessary if life is to function.• Controlled by switching enzyme activity "off"
or "on” or separating the enzymes in time or space.
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Process of Cellular Respiration
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Process of Cellular Respiration
• The process by which food molecules are broken down to release energy is respiration.
• Respiration that occurs in the presence of oxygen is called aerobic respiration.
• Respiration that occurs without oxygen is called anaerobic respiration.
• The energy payoff is much greater when molecules are broken down aerobically.
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Glycolysis• 1st step of respiration• Glycolysis is the breakdown of glucose (6-carbon
molecule to pyruvic acid (3-carbon molecule).• Glycolysis occurs in the cytoplasm and is anaerobic.• Glycolosis produces hydrogen ions and electrons,
which combine with carrier ions called NAD+ (nicotanamide dinucleotide) to form NADH.
• End product is 2 ATP’s
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Breakdown of Pyruvic Acid
• The 2nd step that takes place in respiration is the breakdown of pyruvic acid, and aerobic process.
• Pyruvic acid (3-carbon molecule) is changed to acetic acid (2-carbon molecule). The carbon that comes off makes CO2. Acetic acid combines with a substance called coenzyme A (CoA), forming acetyl-CoA.
• This process takes place in the mitochondria.
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Citric Acid Cycle
• The 3rd step of aerobic respiration is the citric acid cycle.• Acetyl-CoA combines with a 4-carbon molecule to form a 6-
carbon molecule, citric acid. Citric acid is broken down 1st to a 5-carbon molecule and then to a 4-carbon molecule, releasing CO2 at each step.
• This cycle of chemical reactions produces more ATP and releases additional electrons.
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Electron Transport Chain
• The 4th part of aerobic respiration is the electron transport chain (ETC).
• The ETC is a series of molecules along which electrons are transferred, releasing energy.
• Carrier molecules bring the electrons released during glycolysis and the citric acid cycle to the ETC.
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ETC (con’t)
• The molecules of the ETC are located on the inner membranes of the mitochondria.
• This is an aerobic process, because oxygen combines with two hydrogen ions to produce with water.
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What happens if no oxygen is present?
If the final electron acceptor, oxygen, is used up, the chain becomes jammed. The reactions of the ETC can’t take place without oxygen.
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Anaerobic Respiration
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Anaerobic Respiration
• If oxygen isn’t present, there’s no electron acceptor to accept the electrons at the end of the ETC.
• If this occurs, then NADH accumulates.• Once all the NAD+ has been converted to
NADH, the Krebs cycle and glycolysis both stop (both need NAD+ to accept electrons).
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• Once this happens, no new ATP is produced, and the cell soon dies. Cells have derived a method to escape dying – ANAEROBIC RESPIRATION.
• The main objective of anaerobic respiration is to replenish NAD+ so that glycolysis can proceed once again. It occurs in the cytoplasm right along with glycolysis.
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• There are two forms of anaerobic respiration:– Alcoholic fermentation– Lactic acid fermentation
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Alcoholic Fermentation
• Alcoholic fermentation occurs in plants, fungi (yeast), and bacteria.
• There are 2 steps to alcoholic fermentation:– The conversion of pyruvic acid to acetaldehyde
• 1 CO2 and 1 acetaldehyde is produced
– The conversion of acetaldehyde to ethanol• NADH is used to drive the reaction, releasing NAD+
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• The goal of this reaction is not to produce ethanol, but it is to free the NAD+, which allows glycolysis to continue.
• The reward is 2 ATP from glycolysis for each 2 converted pyruvate. This is better than the alternative, which is 0 ATP.
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Lactic Acid Fermentation
• Lactic acid can occur in some bacteria and plants, but it is mostly found in animals, including humans.
• Anytime your muscle cells require energy at a faster rate than it can be supplied by aerobic respiration, they begin to carry out lactic acid fermentation.
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• There is only one step in lactic acid fermentation:
• Now, NAD+ can be used for glycolysis.• When O2 becomes available again, lactic acid
can be broken down and its store of energy can be retrieved.
• Because O2 is required to do this, lactic acid fermentation creates what is often called an oxygen debt.
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Lactic Acid Fermentation
• Uses only Glycolysis.• An incomplete oxidation - energy is still left in
the products (lactic acid). • Does NOT require O2
• Produces ATP when O2 is not available.
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Lactic Acid Fermentation
• Done by human muscle cells under oxygen debt.
• Lactic Acid is a toxin and causes soreness and stiffness in muscles.
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Fermentation - Summary
• Way of using up NADH so Glycolysis can still run.
• Provides ATP to a cell even when O2 is absent.
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Aerobic vs Anaerobic
• Aerobic - Rs with O2
• Anaerobic - Rs without O2
• Aerobic - All three Rs steps.• Anaerobic - Glycolysis only.