McGraw - Hill Ryerson pgs. 182 - 199 Biology 20 Chapter 5 Cellular Respiration.
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Transcript of McGraw - Hill Ryerson pgs. 182 - 199 Biology 20 Chapter 5 Cellular Respiration.
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McGraw - Hill Ryerson pgs. 182 - 199
Biology 20 Chapter 5Cellular Respiration
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Cellular Respiration
A process cells use to release energy needed for all kinds of work
Example: Muscular contraction
2 types of cellular respiration:1. Aerobic respiration (O2 required)
2. Anaerobic respiration (O2 not required)
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The Importance of Cellular Respiration
Recall:Photosynthesis converts light E into chemical E Glucose can be:
Used immediatelyStored for a medium – termUsed to synthesize molecules that can store E for long term •Plants: glucose starch•Animal and fungal cells: glucose glycogen
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The Importance of Cellular Respiration
glucose + oxygen carbon dioxide + water + energy
C6H12O6(s) + 6 O2 6 CO2(g) + 6 H2O(l) + energy
Glucose is converted into energy molecule, ATP (adenosine triphosphate)
Intermediate products include: NADH, FADH2, ATP
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•Intermediate products
NADH is reduced form of NAD+ (nicotinamide adenine dinucleotide)
FADH2 is reduced form of FAD+ (flavin adenine dinucleotide) Electron carriers
Transfer e- through oxidation – reduction reactions LEO, GER
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•Transfer of e -
Releases E Produces more stable ions or compoundsProducts have less E than reactants
Thus, E is released during oxidation Can be used to make ATP
e – transport chains (ETC) Shuttle e – from one molecule to another
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ATP formation ATP
reactants
oxidation - energy
reduction from reaction reaction
products ADP + Pi
High energy
Low energy
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I.) Energy, Cells, and ATP
1 human cell contains about 1 billion ATP molecules
Active transport Movement of substances through a membrane against a concentration gradient
Requires a membrane – bound carrier protein and ATP
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•Active transport
Carrier proteins are “pumps” Ex:
sodium – potassium pump Without pump, nerve and muscle cells could not function
Other pumps move: Vitamins, amino acids, and H+
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•ATP
Another use is large – scale motion Muscular contraction
Requires movement of 2 different protein molecules sliding past one another ATP supplies E to change shape of one of the molecules• Result: movement of contractile fibers
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Uses of ATP
Functions requiring ATP
Role of ATP Examples
Motion Various specialized fibers within cells contract causing movement of or within cell
Chromosomes movements during cell divisionMovement of organelles such as contractile vacuoles emptyingCytoplasmic streamingFormation of pseudopods in lymphocytes (WBCs) or amoebasBeating of cilia or flagella such as in sperm cells or in unicellular organisms
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Uses of ATP
Functions requiring ATP
Role of ATP Examples
Motion Causes muscle fibers to contract
Contraction of skeletal, smooth, and cardiac muscles
Transport of ions and molecules
Powers active transport of molecules against concentration gradient across membrane
Sodium – potassium pumpH+ ion pump
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Uses of ATP
Functions requiring ATP
Role of ATP Examples
Building molecules
Provides E needed to build any large molecule
Joining amino acids in protein synthesisBuilding new strands of DNA during DNA replication
Switching reactions on or off
Alters shape of molecules, which alters function of molecules
Switches certain enzymes on or off
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Uses of ATP
Functions requiring ATP
Role of ATP Examples
bioluminescence Reacts with a molecule called luciferin and oxygen
Produces light in some light – generating species
oExample: glow worms and fireflies
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II.) Glucose and ATP
Glucose is our “blood sugar” High E content Small Highly soluble
Thus, ideal for transportation within and between cells, and throughout body
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III.) Releasing Energy
During respiration: Chemical bonds of reactant food molecules are broken
New bonds are formed in resulting chemical products E is required to break bonds E is released when new bonds form
Respiration is an E releasing process because: More E is released during formation of product molecules than is consumed to break apart reactant molecules
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•Cellular respiration is not 100 % efficient
36 % of E content of 1 glucose molecule is converted into ATP Thus, 64 % is released as heat
Used to maintain body temperature in birds and mammals
Cell is quite efficient compared to automobiles (25 – 30 % efficient)
Cell resp
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1. Aerobic Cellular Respiration
Occurs in presence of O2 (g) and involves complete oxidation of glucose
Involves 4 stages1. Glycolysis2. Pyruvate oxidation.3. Krebs cycle4. Electron transport chain and
chemiosmosis. Overall aerobic respiration equation:C6H12O6(s) + 6 O2 + 36 ADP + 36 Pi 6 CO2(g) + 6
H2O(l) + 36 ATP
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2. Anaerobic cellular respiration
Occurs in absence of O2 (g) and glucose is not completely oxidized
2 types of anaerobic cellular respiration
Both types have two stages that occur in cytoplasm of cells Stage 1: glycolysis Stage 2: fermentation
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Anaerobic respiration
Anerobic cellular respiration type 1C6H12O6(s) + 2 ADP + 2 Pi 2 C2H5OH (l) + 2 CO2 (g) + 2 ATP
ethanol
Anerobic cellular respiration type 2C6H12O6(s) + 2 ADP + 2 Pi 2 C3H6O3 (l) + 2 ATP
lactic acid
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Stage 1- Glycolysis
Aerobic respiration produces more ATP molecules than either type of anaerobic cellular respiration.
Glycolysis: Occurs in both aerobic and anaerobic cellular respiration
Occurs in cytoplasm of all cells An anaerobic process 10 reactions, each is catalyzed by enzyme 2 ATP molecules are used, 4 ATP molecules and 2 NADH+ ions produced
Converts a 6-Carbon glucose to 2 3-C pyruvate molecules.
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2
22
2
2 H2O
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Reactants and products of glycolysis
Reactants Products
Glucose 2 pyruvate (2 C3H4O3)
2 NAD+ 2 NADH
2 ATP 2 ADP
4 ADP 4 ATP*note: net 2 ATP since 2 ATP are required to replenish the 2 used in step 1 of glycolysis
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1 glucose + 2 ADP + 2 Pi + 2 NAD+ 2 pyruvate + 2 ATP + 2 NADH + 2 H+
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•Glycolysis is not efficient
Transfers 2.2 % of available energy in glucose to ATP Some is released as heat
Most E remains in 2 pyruvate and 2 NADHSome unicellular microorganisms use glycolysis for their E needs
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Aerobic Cellular Respiration
End products are: CO2 (g) , H2O (l) , ATP
Uses mitochondria: Eukaryotic organelle in cell cytoplasm Specialize in production of ATP Consists of double membrane: Smooth outer membrane
Semi - permeable Highly folded inner membrane
Associated with cellular respiration
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Inner membrane- Creates 2 compartments within mitochondriaMitochondrial matrix
Protein – rich liquid that fills innermost space of mitochondriaFluid – filled intermembrane space
Lies between inner and outer membrane
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Stage 2: Pyruvate Oxidation
Connects glycolysis in cytoplasm with Krebs cycle in mitochondrial matrix.
2 pyruvate molecules are transported through 2 outer mitochondrial membranes into matrix.
3 steps: Carbon dioxide removed. Acetic acid forms Co-enzyme A attaches to acetic acid = acetyl co-A.
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Steps
Step 1: CO2 is removed from each pyruvate Pyruvate is decarboxylated 1/3 of CO2 breathed out as a waste product
Step 2: Acetic Acid forms Remaining 2 carbon portions are oxidized by NAD+.
Each NAD+ gains 2 H+ ions (2 protons and 2 electrons) from pyruvate
2 NADH proceed to stage 4 of aerobic respiration Remaining 2 C compound becomes acetic acid (acetyl group)
Step 3: Acetyl co-A forms. Coenzyme A (CoA) becomes attached to acetic acid group
Forms 2 acetyl CoA Enters next stage of aerobic cellular respiration
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Stage 3: The Krebs Cycle
Occurs 2 times for every glucose molecule.Cyclic because one of the products of step 8 becomes a reactant in step 1.
Begins when acetyl – CoA (2 per glucose) condenses with oxaloacetate to form citric acid.
In 1 turn of the cycle, the 2 C atoms that were originally in glucose are removed as CO2.
Pyruvate is oxidized, NAD+ and FAD are reduced.
Free E is transferred to ATP, NADH, and FADH2
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The process.
1. 2 carbons enter (as Acetyl co-A).2. 2 carbons leave as carbon dioxide-
released as waste.3. (3) NAD+ are reduced to form NADH.4. (1) FAD is reduced to form FADH2.5. 1 ATP is produced.
* Remember this happens 2 times for every glucose!
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Stage 4: Electron Transport and Chemiosmosis
2 Parts: ETC and Chemiosmosis.NADH and FADH2 eventually transfer H atom electrons to a a series of protein compounds Associated with inner mitochrondrial membrane called electron transport chain (ETC).
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Part I: Electron Transport Chain Process
1. 1 NADH gives up 2 e- at beginning of ETC H+ ion is also released into matrix
2. e- shuttles through ETC As e – move from carrier to carrier, they release E E is used to force H+ from within matrix across inner membrane
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3. Each H+ ion gains potential E, as they move through protein pumps into intermembrane space
4. e – reach last components of ETC and now have low E E used to pump H+ ions
5. O2 (g) strips 2 e- from final energy carrier With 2 H+ ions, forms H2O (l)
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6. Both NADH and FADH2 deliver e – to ETC-Differences between NADH and FADH2 FADH2 has a lower E content
Thus, E released is not sufficient to pump as many H+ ions
FADH2 enters ETC at a different location
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ETC mechanism
Converts chemical E, in e-, into electrochemical potential H+ ion gradient across inner mitochondrial membrane Analogy: stored E possessed by a charged battery
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Part 2: Chemiosmosis and Oxidative ATP Synthesis
1. H+ ions accumulate in intermembrane space create an electrochemical gradient that stores E
2. Higher positive charge in intermembrane space than in matrix Creates a potential difference (voltage) across inner mitochondrial membrane
3. Inner mitochondrial membrane is impermeable to H+ ions H+ ions move through proton channels associated with ATP synthase (ATPase) enzyme As H+ ions move through ATPase complex, E that is released drives the synthesis of ATP from ADP and Pi in matrix
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Energy needs
1 NADH pumps enough H+ ions to generate 3 ATPs
1 FADH2 pumps enough H+ ions to generate 2 ATPs
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•Review:
ETC followed by chemiosmosis is last stage of oxidative phosphorylation.Began with reduction of NAD+ and FAD with H atoms from glucose
Continual production of ATP is dependent on maintenance of H+ reservoir Depends on continual movement of e- through ETCDependent on availability of oxygen as final e - acceptor
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Review:
e- are pulled down ETC E released keeps H+ ions moving into H+ reservoir Fall back into matrix
Drive synthesis of ATP• Oxidative ATP synthesis
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Final step:
ATP is transported through both mitochondrial membranes into cytoplasm
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Energy tally
Step NADH FADH2 ATP
Glycolysis 2 0 2
Pyruvate oxidation 2 0 0
Krebs cycle 6 2 2
ETC/Chemiosmosis 0 0 32
Total = 36 ATP
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Aerobic Respiration Energy Balance Sheet
# of ATP varies according to type of cell and various environmental conditions
Theoretical yield:36 ATP per glucose per cell
Actual yield:30 ATP per glucose per cellGlycolysis is only 2.2 % efficient
However, aerobic respiration is 32 % efficientStill, very good!
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Links
Electron Transport and ATP Synthesis
http://bcs.whfreeman.com/thelifewire/content/chp07/0702001.html
http://highered.mcgraw-hill.com/olc/dl/120071/bio11.swf
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Anaerobic Cellular Respiration
Glycolysis is 1st step Conversion of NAD+ to NADH is crucial, otherwise, glycolysis will halt
Anaerobic organisms transfer H atoms from NADH to organic molecules instead of ETC, used by aerobic organisms Fermentation
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•Fermentation
2 types: Alcohol fermentation- plants. Lactic acid fermentation- animals.
Similarities: Both occur in 2 stages Both occur in cytoplasm of cell Both require glycolysis as 1st step
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I.) Alcohol Fermentation
NADHs produced during glycolysis pass H atoms to acetaldehyde 2 Acetaldehyde forms when 2 CO2 is removed from 2 pyruvate Enzyme pyruvate decarboxylase is used
2 Ethanol is produced
Process recycles NAD+ and allows glycolysis to continue C6H12O6(s) + 2 ADP + 2 Pi 2 C2H5OH (l) + 2 CO2
(g) + 2 ATP
ethanol
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•Applications of Alcohol Fermentation
Carried out by yeast cells Breads, pastries, wine, beer, liquor, soy sauce
Bread Leavened by mixing yeast cells with flour and H2O
Yeast cells ferment glucose in starch Release CO2
Cause bread to rise
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•Beer and wine making
Yeast cells ferment sugars found in fruit juices
Mixture bubbles as yeast cells release CO2 and ethanol Wine making
Fermentation ends when concentration of ethanol is 12 % Yeast cells die due to alcohol accumulation
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Food products dependent on microbial fermentation
Food Raw material
Bread Flour
Soy sauce Soya bean
Vinegar Alcohol (from fruit or grain fermentation)
Chocolate Cacao bean
Sauerkraut Cabbage
Wine and beer Grapes and barley
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•Louis Pasteur
Provided experimental evidence that yeast was responsible for alcohol fermentation
Further work led him to discover that many diseases were caused by microbes
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II.) Lactic Acid Fermentation
Under normal conditions, animals obtain E from glucose by aerobic respiration
Strenuous exercise: Muscle cells demand more ATP than can be supplied by aerobic respiration alone
Additional ATP supplied by lactic acid fermentation
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•Lactic Acid Fermentation Process
NADH produced during glycolysis transfers H atoms to pyruvate in cytoplasm Regenerates NAD+
Allows glycolysis to continue Pyruvate lactic acid
C6H12O6(s) + 2 ADP + 2 Pi 2 C3H6O3 (l) + 2 ATP
lactic acid
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•Accumulation of lactic acid consequences
Causes muscle stiffness, soreness, and fatigue
Lactic acid is transported from muscles to liver
When vigorous exercise ceases:Lactic acid is converted back to pyruvateEnters remaining stages of aerobic respiration Extra O2 is required to chemically process lactic acid “Oxygen debt” - panting
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Exercise Physiology: VO2 max and Lactic Acid Threshold
Exercise physiology Branch of biology dealing with body’s biological responses
Most common question: shortage of energy by athletes
Athletic fitness Measure of ability of heart, lungs, and bloodstream to supply O2 to cells of body
Other factors to athletic fitness: Muscular strength, muscular endurance, flexibility, body composition (ratio of fat to bone to muscle)
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Maximum oxygen consumption (VO2 max)
A measure of body’s capacity to generate E required for physical activity
Treadmill exercise test is used to measure VO2 max 10 – 15 minute test Animal is forced to move faster and faster on a treadmill
Expired air is collected and measured by a computer
VO2 max measures: Volume of O2 (mL) that cells of body can remove from bloodstream in 1 minute per kg of body mass While body experiences maximum exertion
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Values
VO2 max values: Average: 35 mL/kg/min. Athletes: 70 mL/kg/min.
VO2 max Can be increased with more exercise Genetic variation is also a factor Decreases with age
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Lactic acid threshold
Value of exercise intensity at which blood lactic acid concentration begins to increase sharply Exercising beyond threshold may limit duration of exercise Due to pain, muscle stiffness, and fatigue
Athletic training improves blood circulation and efficiency of O2 delivery to body cells Result:
Decrease in lactic acid production Increase in lactic acid threshold
Untrained individuals reach a lactic acid threshold at 60 % VO2 max
Elite athletes reach threshold at or above 80 % VO2 max
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Supplements and toxins
Creatine phosphate May serve as an E source by donating its phosphate to ADP
Occurs naturally in body and many foods Athletes consume compound to produce more ATP in muscles
Compound may also buffer muscle cells and delay onset of lactic acid fermentation
Potential harmful side – effects are possible
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Chemical toxicity
Cyanide and hydrogen sulfide directly act on specific reactions within respiration pathway
Carbon Monoxide Poisoning: CO competes for protein binding sites on RBC
Hemoglobin proteins carry O2 throughout body Severe drop in blood’s oxygen carrying capacity Possible death by asphyxiation
Without O2, immediate halt to ETC and pumping of H+ ions across inner mitochondrial membrane•Cell death