Chapter 4: How Cells Obtain Energy

Energy Within The Cell I. Cells are little bags of chemical reactions A. reactions involve the rearrangement of matter B. atoms are neither created nor destroyed II. E is the capacity to cause or do work A. kinetic E is the E of motion 1. moving objects can perform work by transferring motion to other matter a. water moving through a dam to generate electricity b. legs pedaling a bicycle 2. thermal E is a type of kinetic E associated w/ the random movement of atoms or molecules a. heat is the transfer of thermal E from one object to another 3. light is another type of kinetic E

B. potential E is the E that matter possesses as a result of its location or position 1. chemical E is the E that can be transformed to power the work of a cell a. it is the most important type of E for living organisms III. Thermodynamics is the study of E transformations A. 1st law of thermodynamics 1. E in the universe is constant 2. E can be transferred/transformed but neither created nor destroyed

+ Oxygen CO2 + H2O

+ Oxygen CO2 + H2O

Fuel Waste Products

Heat & car moves

Heat & ATP

Energy Conversion

B. 2nd law of thermodynamics 1. during every E transfer/transformation, some E is converted to thermal E a. this E is unavailable to do work 1) low grade heat E 2. E conversions increase the disorder/randomness of the universe a. E conversions increase entropy

+ Oxygen CO2 + H2O

+ Oxygen CO2 + H2O

Fuel Waste Products

Heat & car moves

Heat & ATP

Energy Conversion

IV. Chemical reactions are of 2 types: they either release or store E A. exergonic reactions release E 1. reactant covalent bonds contain more PE than covalent bonds of the products a. reaction releases E to the environment = to the PE difference between reactants & products 1) burning of wood releases E of glucose as heat & light in 1 step 2) cellular respiration is release of E in many steps a) “slow burn” of glucose into CO2 & H2O

Reactants

Wood or Glucose

Products

CO2 & H2O

Energy Amount of Energy Released

Pote

nti

al E

ner

gy

B. endergonic reactions require a net input of E 1. reactants are PE poor relative to the products 2. E is absorbed during the reaction 3. products are relatively PE rich 4. CO2 & H2O w/ an input of E become PE rich sugar during photosynthesis C. living cells carry out thousands of exergonic & endergonic reactions 1. these reactions make up the metabolism of the organism 2. E released from exergonic reactions is used to drive endergonic reactions a. this is how cells do the work they need to do b. ATP is oftentimes the coupling mechanism between these reactions

Products

Glucose

Reactants

CO2 & H2O

Energy

Pote

nti

al E

ner

gy

Amount of Energy Required

V. ATP drives cellular work by coupling exergonic & endergonic reactions A. adenosine triphosphate 1. all 3 phosphates have a negative charge 2. clustered like charges make the ATP like a compressed spring 3. bonds among the phosphates are relatively unstable a. readily broken via hydrolysis 1) hydrolysis of terminal phosphate releases E a) exergonic

Hydrolysis H2O

ADP + P + Energy

B. ATP powers nearly all forms of cellular work 1. hydrolysis of ATP & phosphorylation event will provide E for endergonic reaction C. ATP is regenerated via cellular respiration 1. ~ 10 million ATP/second in a working muscle cell a. food we take in is digested/hydrolyzed 1) exergonic a) some of this E is used, w/ the help of O2, to add a phosphate back onto ADP converting it into ATP *endergonic *What changes occur as we “get into shape”?

ADP + P

ATP

Energy from exergonic reactions

Energy for endergonic reactions

Ph

osp

ho

ryla

tio

n

Hyd

rolysis

Enzymes Increase Chemical Reaction Rates By Lowering E Barriers I. Ordered structures tend to move toward disorder A. crumbling of the Roman Coliseum II. High E (unstable) systems tend to move toward low E (stable) states A. Sun is halfway through its life (loses E & particles) III. Proteins, DNA, carbohydrates & lipids are highly ordered, high E compounds A. why don’t they spontaneously breakdown into low E, disordered states 1. an E barrier exists that must be overcome before a reaction will proceed a. activation E 1) destabilization of the material b. this prevents our highly ordered cellular molecules from spontaneously breaking down

Ene

rgy

Reactant

Products

Activation energy barrier

Enzyme

Ene

rgy

Reactant

Products

Activation energy barrier

Enzyme

Ene

rgy

Reactant

Products

Activation energy barrier

Enzyme helps reactant overcome activation energy barrier

c. how are we bags of chemical reactions if E barriers exist? 1) ENZYMES – proteins produced at the direction of DNA a) increase rate of reactions by lower the E barrier *contort bonds of the reactants into an unstable state *induced fit *position reactants for reaction to occur b) they are not consumed as they catalyze reactions *more than 1,000 reactions/sec c) they are specific for which substrate (reactant) they work on d) the site to which a substrate binds is the active site e) names end in “ase”

Ene

rgy

Reactant

Products

Activation energy barrier

Enzyme

Ene

rgy

Reactant

Products

Activation energy barrier

Enzyme helps reactant overcome activation energy barrier

Enzyme

Enzyme w/ empty active site

Enzyme

H2O

Substrate (sucrose)

Substrate binds to enzyme resulting in induced fit.

Water is added in this hydrolysis reaction

Glucose & fructose are separated into individual monomers

f) optimal temperature leads to highest rate of contact between enzyme & substrate *higher than optimal temperature can denature enzyme g) optimal pH enables native conformation of enzyme *non-optimal pH can denature enzyme *optimal pH for most enzymes is 6-8 *optimal pH for pepsin which digests proteins (stomach) is 2 *optimal pH for trypsin which digests proteins (small intestine) is 8

Enzyme

Enzyme w/ empty active site

Enzyme

H2O

Substrate (sucrose)

Substrate binds to enzyme resulting in induced fit.

Water is added in this hydrolysis reaction

Glucose & fructose are separated into individual monomers

h) many enzymes require binding of cofactors *ions of Z, Fe & Cu *many vitamins are organic cofactors & are called coenzymes *folic acid is a coenzyme for many enzymes involved in the synthesis of nucleic acids

Ene

rgy

Reactant

Products

Activation energy barrier

Enzyme

Ene

rgy

Reactant

Products

Activation energy barrier

Enzyme helps reactant overcome activation energy barrier

Enzyme

Enzyme w/ empty active site

Enzyme

H2O

Substrate (sucrose)

Substrate binds to enzyme resulting in induced fit.

Water is added in this hydrolysis reaction

Glucose & fructose are separated into individual monomers

i) enzymes are controlled through inhibitors j) competitive inhibitors bind to the active site of the enzyme & block the binding of the substrate k) noncompetitive inhibitors bind to a site other than the active site *changes the active site shape which prevents substrate binding l) feedback inhibition m) many drugs, pesticides & poisons are enzyme inhibitors

• Metabolic pathways are a series of reactions catalyzed by multiple enzymes. Feedback inhibition, where the end product of the pathway inhibits an upstream step, is an important regulatory mechanism in cells.

Active site of enzyme

Substrate

Enzyme

Competitive inhibitor

Allosteric site

Non-competitive inhibitor

Denatured enzyme

Photosynthesis & Cellular Respiration Transform E I. Cellular respiration uses O2 as sugar is broken down A. into CO2 & H2O B. E is released to convert ADP & Pi to ATP C. some E is lost as heat D. occurs in mitochondria of eukaryotic cells II. Photosynthesizers use LE to rearrange the atoms of CO2 & H2O A. into sugar & O2 III. Life on Earth is solar powered A. w/out photosynthesis, we don’t exist

Photosynthesis in chloroplasts Glucose + O2

ATP produced

CO2 + H2O

Breathing Supplies O2 For Use In Cellular Respiration & Removes CO2

I. Cellular respiration is the aerobic harvesting of E from food molecules A. carbohydrates, lipids & proteins II. Breathing involves the inhalation of O2 A. O2 diffuses from alveoli into blood B. heart pumps the oxygenated blood to cells C. O2 diffuses from blood into cells D. O2 diffuses throughout the cell into mitochondria E. mitochondria use O2 to extract E from sugars etc… F. this E is used to regenerate ATP 1. ATP is the E currency of cells G. CO2 is produced during this process a. waste product w/ little E value to cells b. diffuses from mitochondria into cytosol c. diffuses into blood – back to lungs - exhaled

Breathing

O2 CO2

Muscle cells carry out cellular respiration where glucose + O2 are converted to CO2 + H2O + ATP

O2 CO2

Summary Equation For Cellular Respiration

I. Glucose is the fuel used most often in cellular respiration A. glucose & O2 atoms are rearranged into CO2, H2O 1. some of the E from this exergonic process is stored/banked in the regeneration of ATP a. ~ 34% of the PE of glucose 1) the rest is released as heat (~ 66%) *Why do you do get so hot & sweat so much when exercising? 2. consists of many steps B. can produce up to 32 ATP/glucose molecule

C6H12O6 6O2 + 6CO2 6H2O 30-32 ATP Heat + + +

The Human Body Uses E From ATP For All Its Activities

I. Your brain cells burn ~ ¼ lb. of glucose/day A. uses ~ 15% of the O2 consumed on a daily basis II. Calories on food packages are actually kcal (kilocalories) III. Walking at 3 mph, how far would you have to travel to burn off the equivalent of an extra slice of pizza, which has about 475 kcal? How much time would this take? A. ~ 6 miles B. ~ 2 hours of walking time

Running (8-9 mph)

Dancing-fast

Bicycling (10mph)

Swimming (2 mph)

Walking (4 mph)

Dancing-slow

Driving a car

Walking (3 mph)

~980

~510

~490

~408

~341

~245

~205

~60

Number of kcal consumed/hour (on average)

Electrons Release E As They Move From Food to Oxygen

I. Oxidation-Reduction reactions involve the movement of e- from one molecule to another A. in the equation below, the movement of e- is in the form of a H 1. Is glucose oxidized or reduced? a. To what compound? 2. What about the O2 we inhale? Oxidized or reduced? a. To what compound? B. a.k.a. redox reactions C. oxidation is loss of e- D. reduction is gain of e- 1. just remember OIL RIG

C6H12O6 6O2 + 6CO2 6H2O 30-32 ATP Heat + + +

Loss of H atoms (is oxidized)

Gains H atoms (is reduced)

E. nicotinamide adenine dinucleotide is made from niacin & is a taxi cab for e- 1. NAD+ (oxidized form) 2. NADH is the reduced form 3. can carry 2 e- & 1 H+ a. deliver e- to electron transport chain (ETC) 1) embedded in mitochondrial cristae a) folded inner mitochondrial membrane 2) e- release E as they move “down” the ETC toward oxygen a) used to make ATP *What role does oxygen’s electronegativity play in this process?

H OH O + 2H Becomes oxidized

NAD+ + 2H

2H+ + 2 e-

NADH

e- e-

Carrying 2 electrons

+ H+ Becomes reduced

+ 2H+ +1/2 O2 = H2O

NAD+

+ H+

NADH

e- e-

e-

e-

e- e-

As electrons move down the electron transport chain they lose energy that is used to make ATP

ATP

Stages Of Cellular Respiration: 4 Stages I. Glycolysis: occurs in the cytosol A. E-Investment phase 1. glucose is phosphorylated twice a. 2 ATP are used b. this traps the glucose in the cell c. destabilizes sugar & so sugar splits 1) 2 molecules of Glyceraldehyde 3-phosphate (G3P)

Pyruvate Oxidation

Glycolysis: Glucose to Pyruvate

ATP net gain of 2 via

substrate-level phosphorylation

NADH

e- e-

NADH

e- e-

NADH

e- e-

Citric Acid Cycle

FADH2

e- e-

Oxidative phosphorylation (electron transport + chemiosmosis)

ATP ATP

Glucose

ATP

ADP P

ATP

ADP

P P

Glucose 6-Phosphate

Fructose 1,6-biphosphate

P P

Glyceraldehyde 3-phosphate (G3P)

ENERGY INVESTMENT PHASE

2 ATP

2 ADP

e- e-

NADH

NAD+

2 Pyruvate

2

2

Glucose

B. E-Payoff phase 1. 2 G3P are oxidized so that 2 NAD+ are reduced to 2 NADH a. view NADH’s as carriers of high E e- 2. a phosphate is added to each 3 carbon compound a. now each is a biphosphorylated compound 1) 1,3-Biphosphoglycerate 3. each 1,3-Biphosphoglycerate loses a phosphate to an ADP a. this produces 2 ATP via substrate-level phosphorylation

ATP

P

Product

Enzyme

P

P

Substrate

ADP

Enzyme

Substrate-level phosphorylation

P P

Pyruvate

Energy Payoff Phase

P

ADP

NAD+

e- e-

NADH P P

ATP

P

ADP

ATP

P

ADP

NAD+

e- e-

NADH P P

ATP

P

ADP

ATP

G3P G3P

1,3-Biphosphoglycerate

4. each 3-phosphoglycerate will eventually become a PEP a. phosphoenolpyruvate 5. each PEP will lose a phosphate to an ADP a. this produces 2 ATP via substrate-level phosphorylation b. 2 molecules of 3 carbon pyruvates are produced 6. 4 ATP are produced via substrate-level phosphorylation 7. What is the net E gain by the end of glycolysis? a. 2 ATP b. 2 NADH

P P

Pyruvate

Energy Payoff Phase

P

ADP

NAD+

e- e-

NADH P P

ATP

P

ADP

ATP

P

ADP

NAD+

e- e-

NADH P P

ATP

P

ADP

ATP

G3P G3P

1,3-Biphosphoglycerate

ATP

P

Product

Enzyme

P

P

Substrate

ADP

Enzyme

Substrate-level phosphorylation

2 ATP

2 ADP

e- e-

NADH

NAD+

2 Pyruvate

2

2

Glucose

II. Pyruvate Oxidation A. each pyruvate enters the mitochondrial matrix B. each pyruvate loses a carboxyl as a CO2 1) removed via breathing 2) 2 carbon compound is all that remains C. 2 carbon compound is oxidized 1) 2 NAD+ are reduced to 2 NADH 2) 2 carbon compound is an acetyl group a) each acetyl group is picked up by a taxi cab *coenzyme A (derived from a B vitamin) *together they are called acetyl CoA

Pyruvate Oxidation

Glycolysis: Glucose to Pyruvate

ATP net gain of 2 via

substrate-level phosphorylation

NADH

e- e-

NADH

e- e-

NADH

e- e-

Citric Acid Cycle

FADH2

e- e-

Oxidative phosphorylation (electron transport + chemiosmosis)

ATP ATP

Acetyl coenzyme A 2-Pyruvate

NAD+

e- e-

NADH

CO2

#1

#3

#2

Coenzyme A

CoA

III. Citric Acid Cycle (Kreb’s Cycle/Tricarboxylic Acid Cycle) A. occurs in mitochondrial matrix B. at the beginning of the Citric Acid Cycle, enzymes strip each 2 carbon acetyl group from each AcetylCoA 1. each Coenzyme A is recycled C. 2 carbon acetyl group is added to a 4 carbon oxaloacetate D. 6 carbon citrate forms

Citric Acid Cycle NAD+

e- e-

NADH

Acetyl coA CoA

Oxaloacetate

Citrate

NAD+

e- e-

NADH

CO2

NAD+

e- e-

NADH

ADP + P ATP

FAD

e- e-

FADH2 CO2

E. redox reactions lead to 6 NADH’s being produced/2 acetyl groups F. redox reactions lead to 2 FADH2’s being produced/2 acetyl groups G. substrate-level phosphorylation leads to 2 ATP being produced/2 acetyl groups H. 4 carbon oxaloacetate is regenerated by the end of the cycle I. produces most of our CO2

Citric Acid Cycle NAD+

e- e-

NADH

Acetyl coA CoA

Oxaloacetate

Citrate

NAD+

e- e-

NADH

CO2

NAD+

e- e-

NADH

ADP + P ATP

FAD

e- e-

FADH2 CO2

Pyruvate Oxidation

Glycolysis: Glucose to Pyruvate

ATP net gain of 2 via

substrate-level phosphorylation

NADH

e- e-

NADH

e- e-

NADH

e- e-

Citric Acid Cycle

FADH2

e- e-

Oxidative phosphorylation (electron transport + chemiosmosis)

ATP ATP

IV. Oxidative Phosphorylation – mitochondrial cristae A. up to this point there has been a net gain of 4 ATP B. this stage produces the greatest number of ATP C. utilizes electron transport chain proteins

NAD+ e- e-

NADH

e- 2

e- 2 + ½ O2 + 2 H+ = H2O

Electron movement along the ETC provides energy to make

ATP

Molecular oxygen we breath in is split into 2 oxygen atoms – each of which picks up 2 electrons from the ETC and 2 H+ to form water.

Intermembrane space

H+

H+ H+ H+

H+ H+ H+

H+ H+

H+ H+

Mitochondrial Matrix

Mitochondrial crista

H+

H+

H+ H+

H+ H+

III

H+

IV

Q

II

I

ADP + Pi

ATP

NADH NAD+ FADH2 FAD+

e- 2

½ O2 + 2H+

H2O

e- 2 e- 2

e- 2

e- 2

rotor

rod

catalytic knob

1. embedded in mitochondrial cristae 2. receives e- from all NADH & FADH2

a. Glycolysis: 2 NADH b. Pyruvate Oxidation: 2 NADH c. Citric Acid Cycle: 6 NADH & 2 FADH2

NAD+ e- e-

NADH

e- 2

e- 2 + ½ O2 + 2 H+ = H2O

Electron movement along the ETC provides energy to make

ATP

Molecular oxygen we breath in is split into 2 oxygen atoms – each of which picks up 2 electrons from the ETC and 2 H+ to form water.

Intermembrane space

H+

H+ H+ H+

H+ H+ H+

H+ H+

H+ H+

Mitochondrial Matrix

Mitochondrial crista

H+

H+

H+ H+

H+ H+

III

H+

IV

Q

II

I

ADP + Pi

ATP

NADH NAD+ FADH2 FAD+

e- 2

½ O2 + 2H+

H2O

e- 2 e- 2

e- 2

e- 2

rotor

rod

catalytic knob

D. each NADH is oxidized by PC-I (protein complex I) 1. the e- lose E as they move across PC-I a. this E is used to pump H+ from the mitochondrial matrix into the intermembrane space E. Ubiquinone (Q), a mobile e- carrier, oxidizes PC-I

Intermembrane space

H+

H+ H+ H+

H+ H+ H+

H+ H+

H+ H+

Mitochondrial Matrix

Mitochondrial crista

H+

H+

H+ H+

H+ H+

III

H+

IV

Q

II

I

ADP + Pi

ATP

NADH NAD+ FADH2 FAD+

e- 2

½ O2 + 2H+

H2O

e- 2 e- 2

e- 2

e- 2

rotor

rod

catalytic knob

F. Ubiquinone is oxidized by PC-III (protein complex III) 1. the e- skip PC-II G. e- lose E as they move across PC-III 1. this E is used to pump H+ from the mitochondrial matrix into the intermembrane space

Intermembrane space

H+

H+ H+ H+

H+ H+ H+

H+ H+

H+ H+

Mitochondrial Matrix

Mitochondrial crista

H+

H+

H+ H+

H+ H+

III

H+

IV

Q

II

I

ADP + Pi

ATP

NADH NAD+ FADH2 FAD+

e- 2

½ O2 + 2H+

H2O

e- 2 e- 2

e- 2

e- 2

rotor

rod

catalytic knob

H. Cytochrome c (Cyt c), a mobile e- carrier, oxidizes PCIII I. Cyt c is oxidized by PC-IV (protein complex IV) 1. e- lose E as they move across PC-IV a. this E is used to pump H+ from the mitochondrial matrix into the intermembrane space

Intermembrane space

H+

H+ H+ H+

H+ H+ H+

H+ H+

H+ H+

Mitochondrial Matrix

Mitochondrial crista

H+

H+

H+ H+

H+ H+

III

H+

IV

Q

II

I

ADP + Pi

ATP

NADH NAD+ FADH2 FAD+

e- 2

½ O2 + 2H+

H2O

e- 2 e- 2

e- 2

e- 2

rotor

rod

catalytic knob

J. the e- have lost much of their PE (potential energy) & are being held onto by PC-IV K. the oxygen we breath in is used to remove e- from PC-IV 1. ½ O2 combines w/ 2 e- from PC-IV & 2 H+ to form H2O L. there is now a concentration gradient of H+ across the inner mitochondrial membrane 1. like water stored behind a dam

Intermembrane space

H+

H+ H+ H+

H+ H+ H+

H+ H+

H+ H+

Mitochondrial Matrix

Mitochondrial crista

H+

H+

H+ H+

H+ H+

III

H+

IV

Q

II

I

ADP + Pi

ATP

NADH NAD+ FADH2 FAD+

e- 2

½ O2 + 2H+

H2O

e- 2 e- 2

e- 2

e- 2

rotor

rod

catalytic knob

M. H+ can move back into the matrix via ATP synthase 1. H+ moves through 1st half channel of stator & binds to rotor a. this causes rotor & attached rod to spin inside catalytic knob 1) after 1 rotation, H+ passes through 2nd half channel into matrix

Intermembrane space

H+

H+ H+ H+

H+ H+ H+

H+ H+

H+ H+

Mitochondrial Matrix

Mitochondrial crista

H+

H+

H+ H+

H+ H+

III

H+

IV

Q

II

I

ADP + Pi

ATP

NADH NAD+ FADH2 FAD+

e- 2

½ O2 + 2H+

H2O

e- 2 e- 2

e- 2

e- 2

rotor

rod

catalytic knob

Stator

1st half channel

2nd half channel

2. another H+ follows this same path 3. spinning rod activates sites in catalytic knob that phosphorylates ADP to ATP

Intermembrane space

H+

H+ H+ H+

H+ H+ H+

H+ H+

H+ H+

Mitochondrial Matrix

Mitochondrial crista

H+

H+

H+ H+

H+ H+

III

H+

IV

Q

II

I

ADP + Pi

ATP

NADH NAD+ FADH2 FAD+

e- 2

½ O2 + 2H+

H2O

e- 2 e- 2

e- 2

e- 2

rotor

rod

catalytic knob

Stator

1st half channel

2nd half channel

N. the e- of each NADH can generate about 2.5 ATP O. the e- of each FADH2 can generate about 1.5 ATP P. Why the difference? 1. NADH are oxidized at PC-I a. these e- drive 3 proton pumps 1) PC-I, PC-III, & PC-IV 2. FADH2 are oxidized at PC-II (not a proton pump) a. these e- drive only 2 proton pumps 1) PC-III & PC-IV 2) therefore, fewer H+ will be pumped into intermembrane space a) fewer H+ will move through ATP synthase *fewer ATP will be produced

Q. Why are ~32 ATP expected to be produced from a molecule of glucose? R. In which of the 4 stages of cellular respiration is O2 required? S. Where & how many NADH’s are produced w/in each stage? T. FADH2’s? U. Where & how many ATP’s are produced w/in each stage? 1. What is the name of the mechanism used to produce ATP in each case?

Fermentation: Harvesting Of E Anaerobically I. Cells can produce ATP w/out O2

A. this pathway is glycolysis 1. provides a net gain of 2 ATP a. as long as NAD+ is available b. can help keep your muscles contracting for a short period of time II. Lactic Acid Fermentation A. NADH is oxidized back to NAD+ as pyruvate is reduced to lactate 1. lactate is carried by the blood to the liver where it can be converted back to pyruvate & used by liver cells B. bacteria carry out this process in the making of cheese, yogurt & sauerkraut

2 ATP

2 ADP

e- e-

NADH

NAD+

2 Pyruvate

2

2

Glucose

Gly

coly

sis

e- e-

NADH

NAD+

2 Lactate

2

2

III. Alcohol Fermentation A. NADH is oxidized back to NAD+ as pyruvate is converted to CO2 & ethanol 1. CO2: bubbles in beer & champagne 2. alcohol: kills confined yeast in wine vat at a 14% concentration level

2 ATP

2 ADP

e- e-

NADH

NAD+

2 Pyruvate

2

2

Glucose

Gly

coly

sis

e- e-

NADH

NAD+

2 Ethanol

2

2

CO2 2