Download 2 ATP - Hobbs High School

Chapter Eight
How Cells Harvest Energy
I. Introduction
– Equation for cellular respiration
– Review Terms:
•
•
•
•
•
Autotrophs vs Heterotrophs
Oxidation vs Reduction
Exergonic vs Endergonic
Substrate level phosphorylation vs Chemiosmotic (oxidative) phosphorylation
Aerobic vs anaerobic
II. Phases in Aerobic cellular respiration
– Major inputs/outputs of: Glycolysis, Preparatory (transition) reaction,
Krebs (Citric Acid) Cycle, ETS
– Where they occur in cell, if oxygen is required to be present, if oxygen
is used, # ATP’s generated
III. Anaerobic cellular respiration
– Types of anaerobic respiration
– Yeast vs animal cells
– Advantages vs Disadvantages
IV. Metabolic Pool (Terms: catabolism & anabolism)
• Introduction
• Autotrophs - “self feeders”; organisms that produce own organic
molecules – photosynthesis
• Heterotrophs - “fed by others”; organisms that consume molecules
produced by other organisms
• Cellular Respiration - Conversion of carbohydrates and other
metabolites (e.g. fats, proteins) to ATP
• ATP - Provides just the right amount of energy for cellular work with
no waste
• Glucose - Most common molecule used to generate ATP
• Conversion of glucose to ATP is about 39% efficient
• What happens to the rest of the energy?
– “lost” as heat [aka metabolic heat]
• Glucose is a type of Carbohydrate
• Why is ATP used for cell work and not glucose?
– Glucose releases too much energy atone time – wasteful
– ATP releases just right amount of energy
Fig. 7.2
• Chemical equation for cellular respiration:
Oxidation
(CH2O)n + O2
CO2 + H2O + energy
Reduction
• Oxidation - term used to indicate that a molecule
has lost hydrogen atoms
– Which reactant is being oxidized during cellular
respiration?
(CH2O)n
• Reduction - term used to indicate that a molecule
has gained hydrogen atoms
– Which reactant is being reduced during cellular
respiration?
O2
• Endergonic or Exergonic Reaction?
– C6H12O6 --------> CO2 + H2O
Exergonic
Energy released
drives the other
reaction
– ADP + P --------> ATP
Endergonic
• CONCEPT: Exergonic reactions are coupled
with endergonic reactions.
• During respiration, glucose is oxidized to CO2. However if electrons
were given directly to O2, the reaction would be Combustible and
cells would burst into flames.
• So cells transfer electrons to electron carriers:
1.
2.
3.
Soluble carriers that move electrons from one molecule to another
Membrane-bound carriers that form a redox chain
Carriers that move within membranes
• Example: Enzymes catalyze these redox reactions with the help of
cofactors such as nicotinamide adesosine dinucleotide (NAD+).
NAD+ accepts a pair of electrons (redox) from the substrate as well
as a proton. Another proton is donated to the solution. This forms
NADH which is an electron carrier. This reaction is reversible. Other
electron carriers include FAD+ and cytochromes.
Fig. 7.3
Fig. 7.1
• Aerobic - term used to denote “with oxygen”
• Anaerobic - term used to denote “without
oxygen”
• Does the chemical equation following reaction
represent aerobic or anaerobic cellular
respiration?
• C6H12O6 + O2 --------> CO2 + H2O + 36 ATPs
Aerobic
Low energy
products
• Does the chemical equation following reaction
represent aerobic or anaerobic cellular
respiration?
• C6H12O6 --------> C2H5OH + CO2 + 2 ATPs
Anaerobic
Still has high level of energy
• CONCEPT: Oxygen MUST be present for
glucose to be completely oxidized to CO2
– aerobic respiration: final e- acceptor oxygen (O2)
– anaerobic respiration: final e- acceptor inorganic
molecule (not O2)
– fermentation: final e- acceptor is an organic
molecule
• In the presence of oxygen, one (1) molecule of glucose
yields approximately 36-38 (net) molecules of ATP
• 4 (net) ATP’s are generated via substrate-level phosphorylation
• 32-34 ATP’s are generated via oxidative phosphorylation
(chemiosmosis/ETS driven by atoms supplied from hydrogen)
• Hydrogen atoms are supplied by Glucose
• Hydrogen atoms are carried to ETS of mitochondria by
coenzymes:
• NAD+ gains 1 hydrogen → NADH (each produces 2-3 ATPs)
• FAD gains 2 hydrogen → FADH2 (each produces 2 ATPs)
• When NAD/FAD pick up hydrogen atom(s), they are
Reduced
• Metabolism harvests energy in stages. The larger the
release of energy in any single step, the more of that
energy is released as heat.
• Cells make ATP by two different mechanisms.
1. Substrate-level phosphorylation (SLP)
– ATP formed by transferring a phosphate group directly
to ADP
– Occurs in the cytoplasm – all cells can perform this
type of phosphorylation
– Glycolysis
2. Oxidative phosphorylation (OP)
– ATP synthesized by the enzyme ATP Synthase by using
energy from a proton gradient
– Requires oxygen
– Occurs in the mitochondria
– Krebs Cycle (citric acid cycle) and Electron Transport
Chain (ETS)
Phases in Aerobic cellular respiration
Inputs/Outputs
Where Occurs
02 required /
02used
Net ATP
Glycolysis
glucose → pyruvate
Cytoplasm
No / ----
2 (SLP)
Preparatory Stage
pyruvate → acetyl
Mitochondria
Yes/ No
------
CoA
/ Matrix
oxaloacetate → citrate
Mitochondria
Yes / No
2 (SLP)
Yes / Yes
32 (OP)
Krebs Cycle
/ Matrix
ETS
Hydrogen → H20
Mitochondria/
Cristae
Fig. 7.5
• IMPORTANT: Aerobic cellular respiration
includes glycolysis (an anaerobic process).
– See Aerobic cellular respiration flow chart.
• Interesting Facts about ATP production
– In men, have enough to sustain life for one minute
– Some poisons inhibit ATP synthase
– Some tissues have more mitochondria
• Chicken: dark - legs (more myoglobin) vs. light – breasts
(less myoglobin)
– Rigor mortis due to lack of ATP (which is required
for muscle relaxation.
• Glycolysis
A. Glucose priming – 3 reactions that prime glucose
to be cleaved and requires energy (2 ATP)
B. Cleavage and rearrangement – split glucose into
G3P
C. Oxidation – 2e- and 1 proton are transferred
from G3P to NAD+ forming NADH
D. ATP generation – produces a pyruvate and 2 ATP
molecules from each G3P ( 2 pyruvate and 4 ATP
made)
• 4 ATP formed but 2 ATP used which results in 2 ATP
gained.
Glycolysis
• Preparatory stage
– Occurs if oxygen is present
– Location – mitochondria
– Pyruvate + NAD+ + CoA → acetyl – CoA + NADH +
CO2 + H+
• NADH used later
• Acetyl group enters the next step – Krebs (citric acid)
cycle
• Krebs Cycle - Has Three segments
1. Acetyl-CoA + oxaloacetate → 6-carbon citrate molecule
2. Citrate rearrangement and decarboxylation
• reduces citrate to a 5-carbon intermediate and then to a 4-carbon
succinate
• produces 2 NADH and 1 ATP
3. Regeneration of oxaloacetate
• Succinate undergoes a series of reactions to return back to
oxaloacetate so it can reenter the cycle
• Producing one NADH and one FADH2
• NOTE: Through a series of 9 reactions the Krebs cycle
extracts electrons and synthesizes 1 ATP each cycle.
The Krebs cycle turns twice with each glucose
molecule.
Krebs Cycle
• Electron Transport Chain and Chemiosmosis
– ETC produces a proton gradient
• Gradient is formed as electrons move through electron
carriers located in the mitochondrial membrane.
• Each electron attracts a proton and transfers them into the
intermembrane space of the mitochondria.
– Chemiosmosis utilizes the electrochemical gradient to
produce ATP
• The mitochondrial matrix is negative compared to the
intermembrane space
• The positive protons are attracted to the negative matrix and
want to diffuse from high concentration to low
concentration
• The protons can only pass through a protein channel created
by ATP Synthase
• As protons pass through ATP synthase the protein rotates
taking kinetic energy and storing it as potential energy in
newly formed ATP.
http://vcell.ndsu.nodak.edu/animations/etc/
movie-flash.htm
http://vcell.ndsu.nodak.edu/animations/atp
gradient/movie-flash.htm
Fig. 7.16
• Anaerobic cellular respiration = FERMENTATION (pg. 140)
• Pyruvate is the pivotal metabolite in cellular respiration.
• In man, the major driving force affecting the fate of
pyruvate is the presence or absence of oxygen!!!
• If oxygen is present, pyruvate enters into the preparatory
stage and aerobic cellular respiration occurs.
• If oxygen is not present:
• fermentation occurs
• oxygen is NOT used as a final electron acceptor
• water is not formed
FERMENTATION
Glycolysis
Glucose

net 2 ATP
pyruvate
PRODUCTS
Yeast Cells
CO2 + C2H5OH
Carbon dioxide + ethanol
Alcoholic Fermentation
Animal Cells
C2H5 COOH (lactic acid)  pH causes
muscle fatigue
In liver cells some lactic acid is converted
back to pyruvate and reprocesses it via
aerobic respiration (O2 recovery)
NOTE: Fermentation includes glycolysis. The NADH created during glycolysis must be
recycled to continue respiration. The NADH reduces the organic compound present
(ethanol or lactic acid) in order to regenerate NAD+.
Advantages
Disadvantages
Rapid burst of energy
short lived
Economic Benefits: (pg. 141)
Low ATP yield
Yeast: making of beers, wines and
2% efficiency
bread.
Anaerobic bacteria: making of cheese,
yogurt, ect. And Isopropanol, acetic
acid, ect.
Products are toxic
• Some organisms use inorganic molecules to
regenerate NAD+ from NADH
– Methanogens
• CO2 reduced to CH4
• Methanobacterium
– Sulfur Bacteria
• SO4 reduced to H2S
• Archaeon - Thermoproteus tenax
Metabolic Pool
Anabolism
Metabolism =
+
Catabolism
Synthetic
Degradative
Building up
Breaking down
Catabolic reactions release (produce) energy which may be used
to drive Anabolic reactions
• Other types of molecules (metabolites) may be used for the
generation of ATP such as Proteins & Fats.
• Proteins remove amino groups
–
–
–
–
First the protein is broken into individual amino acids
Amno group is then removed in a process called deamination
Carbon chains that remain enter glycolysis and the Krebs cycle
Non-essential (11) vs. Essential (9) amino acids
• 11 can be synthesized (non-essential)
• 9 can not be synthesized – supplied by diet (essential due to lack of
enzymes)
• Fats
– Broken into fatty acids and glycerol
– Produce acetyl group that then enters the Krebs cycle
Fig. 7.20