HOW CELLS HARVEST CHEMICAL ENERGY
I.
Breathing supplies oxygen to our cells and removes carbon dioxide
a. Respiration is synonymous with breathing; an exchange of
gases
b. Cellular respiration is the aerobic harvesting of energy from
food molecules by cells
II.
Cellular respiration banks energy in ATP molecules
a. Glucose + Oxygen gas  Carbon Dioxide + Water + Energy
b. C6H12O6 + 6O2  6CO2 + 6 H2O + ATPs
c. Stores about 40 % of glucose’s chemical energy in ATP
d. Efficient energy conversion system (gas engine only coverts 25
% gasoline to energy)
III.
The human body uses energy from ATP for all its activities
a. As much as 75 % of the energy a person takes in during the day
is used for life sustaining activities
IV.
Cells tap energy from electrons transferred from organic fuels to
oxygen
a. Cellular respiration dismantles glucose in a series of energy
releasing steps, storing this released energy as ATP
V.
Hydrogen carriers such as NAD+ shuttle electrons in redox
reactions
a. REDOX REACTION  the movement of electrons from one
molecule to another
b. OXIDATION  loss of an electron
c. REDUCTION  gaining an electron
d. NAD+ (Nicotinamide Adenine Dinucleotide)  made from the
vitamin niacin and shuttles electrons in redox reactions
VI.
Redox reactions release energy when electrons “fall” from a
hydrogen carrier to oxygen
a. ELECTRON CARRIERS  molecules that pick up electrons
b. ELECTRON TRANSPORT CHAINS  electrons are passed
along these chains, releasing small amounts of usable energy
VII. Two mechanisms generate ATP
a. CHEMIOSMOSIS  use the potential energy in concentration
gradients to synthesize a molecule
b. ATP SYNTHASES  protein complexes that reside in the
membrane that synthesize ATP
c. SUBSTRATE-LEVEL PHOSPHORYLATION  an enzyme
transfers a phosphate group from an organic substrate molecule
to ADP
VIII. Overview: Respiration occurs in three main stages
a. Three stages
i. GLYCOLYSIS
ii. KREBS CYCLE
iii. ELECTRON TRANSPORT CHAIN (ETC)
IX.
Glycolysis harvests chemical energy by oxidizing glucose to
pyruvic acid
a. GLYCOLYSIS  “splitting of sugar”
b. Glucose is changed to pyruvic acid in a series of 9 steps
c.
d.
e.
f.
i. During this two molecules of ATP are produced and two
molecules of NADH are also produced
ii. ATP energy is usable, NADH must be sent to the ETC
Glycolysis is universal, happening in every living cell
INTERMEDIATES  the chemicals formed between glucose
and pyruvic acid
Steps 1-4 of glycolysis are part of the first preparatory phase
Steps 5-9 of glycolysis are the second energy yielding phase
i. IT TAKES 2 ATP TO START GLYCOLYSIS WHICH
MAKES 4 ATP MOLECULES; NET GAIN OF 2 ATP
MOLECULES
g. GLUCOSE  2 PYRUVIC ACID
h. C6H12O6  3-CARBON COMPOUND
i. Yeasts and bacteria can survive on only glycolysis; most
organisms however require more energy
X.
Pyruvic acid is chemically groomed for the Krebs Cycle
a. Pyruvic acid is diffused from the cytoplasm into the
mitochondria
b. Pyruvic acid must be “groomed” to enter the Krebs cycle
i. It is oxidized while a molecule of NAD+ is reduced to
NADH
ii. A carbon atom is removed and released in CO2
iii. A compound called coenzyme A binds with 2-Carbon
molecule to form acetyl coenzyme A (ACETYL CoA)
c. Acetyl CoA is a high-energy molecule for the Krebs Cycle
XI.
The Krebs cycle completes the oxidation of organic fuel,
generating many NADH and FADH2 molecules
a. Named after German-British researcher Hans Krebs
b. Cycle disassembles acetyl CoA and energy storing molecules
and CO2
c. Each turn produces 1 ATP; 3 NADH molecules; and 1 FADH2
d. Since there are two acetyl CoA’s, go through cycle 2x
e. Final products (NET) 2 ATP, 6 NADH; 2 FADH2
f. So far, with glycolysis and Krebs we are at 4 ATP; 10 NADH;
and 2 FADH2
g. Now energy in NADH and FADH2 must be released
XII. Chemiosmosis powers most ATP production
XIII. Certain poisons interrupt critical events in cellular respiration
a. Cyanide and carbon monoxide block the electron flow thus
inhibit an H+ gradient; stopping ATP production
XIV. Review Each molecule of glucose yields many molecules of ATP
a. 3 Steps
i. Glycolysis (Net 2 ATPs)
ii. Krebs Cycle (Net 2 ATPs)
iii. ETC (about 34 ATPs)
b. Total net yield is 38 ATP per glucose molecule
c. About 40% of glucose potential energy is utilized
XV. Fermentation is an anaerobic alternative to aerobic respiration
a. ALCOHOLIC FERMENTATION  the production of ethanol
from glucose
i. Done to release the NADH that results from glycolysis
b. LACTIC ACID FERMENTATION  the production of lactic
acid from glucose
c. STRICT ANAEROBES  require anaerobic conditions
d. FACULTATIVE ANAEROBES  can make ATP by
fermentation or chemiosmosis depending on O2 availability
XVI. Cells use many kinds of organic molecules as fuel for cellular
respiration
XVII. Food molecules provide raw materials for biosynthesis
a. Food may not only be used for energy; it is also used to create
macromolecules for repair and growth
XVIII. The fuel for respiration ultimately comes from photosynthesis
a. Animals cells can only harvest energy from organic compounds
but plant cells can produce organic compounds from inorganic
ones using the energy of sunlight