McGraw - Hill Ryerson pgs. 182 - 199

Biology 20 Chapter 5Cellular Respiration

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)

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

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

•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

•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

ATP formation ATP

reactants

oxidation - energy

reduction from reaction reaction

products ADP + Pi

High energy

Low energy

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

•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+

•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

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

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

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

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

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

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

•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

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

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

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

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.

2

22

2

2 H2O

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

1 glucose + 2 ADP + 2 Pi + 2 NAD+ 2 pyruvate + 2 ATP + 2 NADH + 2 H+

•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

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

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

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.

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

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

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!

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).

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

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)

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

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

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

Energy needs

1 NADH pumps enough H+ ions to generate 3 ATPs

1 FADH2 pumps enough H+ ions to generate 2 ATPs

•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

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

Final step:

ATP is transported through both mitochondrial membranes into cytoplasm

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

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!

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

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

•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

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

•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

•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

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

•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

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

•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

•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

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)

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

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

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

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

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