Download Ch.5-Cellular Respiration

Biology 20 Chapter 5
Cellular Respiration
McGraw - Hill Ryerson pgs. 182 - 199
Cellular Respiration

A process cells use to release energy needed for all
kinds of work

Example:


Muscular contraction
2 types of cellular respiration:
1.
2.
Aerobic respiration (O2 required)
Anaerobic respiration (O2 not required)
The Importance of Cellular Respiration
 Recall:
 Photosynthesis
converts light E into chemical E
Glucose can be:
Used immediately
Stored for a medium – term
Used 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 compounds
 Products 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
High
energy
ATP formation
reactants
oxidation -
energy
reduction
reaction
from
reaction
products
Low
energy
ADP + Pi
ATP
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
Role of ATP
requiring ATP
Examples
Motion
Chromosomes movements
during cell division
Movement of organelles
such as contractile vacuoles
emptying
Cytoplasmic streaming
Formation of pseudopods in
lymphocytes (WBCs) or
amoebas
Beating of cilia or flagella
such as in sperm cells or in
unicellular organisms
Various
specialized fibers
within cells contract
causing movement
of or within cell
Uses of ATP
Functions
Role of ATP
requiring ATP
Examples
Motion
Causes muscle
fibers to contract
Transport of
ions and
molecules
Powers active
transport of
molecules against
concentration
gradient across
membrane
Contraction of
skeletal, smooth, and
cardiac muscles
Sodium – potassium
pump
H+ ion pump
Uses of ATP
Functions
Role of ATP
requiring ATP
Building
molecules
Switching
reactions on
or off
Examples
Provides E
Joining amino acids
needed to build any in protein synthesis
large molecule
Building new strands
of DNA during DNA
replication
Alters shape of Switches certain
molecules, which enzymes on or off
alters function of
molecules
Uses of ATP
Functions
requiring ATP
Role of ATP
Examples
bioluminescence Reacts with a Produces light in
molecule called some light – generating
luciferin and
species
oxygen
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 stages
1. Glycolysis
2. Pyruvate oxidation.
3. Krebs cycle
4. 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 1
C6H12O6(s) + 2 ADP + 2 Pi  2 C2H5OH (l) + 2 CO2 (g) + 2
ATP
ethanol
 Anerobic cellular respiration type 2
C6H12O6(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
2
2
2 H2O
2
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 NADH
 Some 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
mitochondria
Mitochondrial matrix
Protein – rich liquid that fills innermost space of
mitochondria
Fluid – 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.
3.
4.
5.
2 carbons enter (as Acetyl co-A).
2 carbons leave as carbon dioxide- released as
waste.
(3) NAD+ are reduced to form NADH.
(1) FAD is reduced to form FADH2.
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
ETC
Dependent 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 cell
 Glycolysis is only 2.2 % efficient
However, aerobic respiration is 32 % efficient
Still, very good!
Links
Electron Transport and ATP Synthesis
http://bcs.whfreeman.com/thelifewire/content/chp
07/0702001.html
http://highered.mcgrawhill.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 pyruvate
 Enters 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