METABOLISM
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METABOLISM
METABOLISM
What is metabolism?
Total of all chemical reactions occurring within the
body
Categories of metabolic reactions
Catabolic reactions
Degradation pathways
Anabolic reactions
Synthesis pathways
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METABOLISM
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ENERGY
What is energy?
No mass; does not take up space
Has the capacity to do work (potential energy) or to
put matter into motion (kinetic energy)
Can be converted into different forms but is not
created or destroyed
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ENERGY
What types of energy are there?
Chemical
Energy stored in chemical bonds
Electrical
Involves movement of charged particles
Mechanical
Involves movement of matter
Electromagnetic (radiant)
Energy traveling in waves
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Quick Quiz: Potential energy can be
“stored” in all of the following forms
except…
A) Electromagnetic energy
B) Electrical energy
C) Mechanical energy
D) Chemical energy
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ENERGY
Where does our energy for metabolism come from?
Chemical energy
Nutrients (food)
Electromagnetic energy
Heat (thermal)
Sun or geothermal sources
Visible light
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ENERGY
Energy for cellular metabolism must be “refined”, or converted to useful types of energy
Photosynthesis
Electromagnetic energy (sunlight) chemical energy
Aerobic respiration
Chemical energy (chemical bonds of certain molecules) chemical energy (more usable form for cells)
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ATP (adenosine triphosphate)
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Quick Quiz: ATP is an example of
which of the following energy forms?
A) Electromagnetic energy
B) Thermal energy
C) Mechanical energy
D) Chemical energy
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Energy Flow & Nutrient Cycling
in Biological Systems
Energy
1-way flow
Ultimately lost as
heat
Nutrients
Cycled
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Nutrients
What are nutrients?
Chemical substances needed for normal metabolism &
growth
O C H N
Ca P K S Na Cl Mg I Fe
Organic vs. inorganic nutrients
Macronutrients
Proteins
Carbohydrates
Lipids
Nucleic acids
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Quick Quiz: Which of the following is
NOT recycled in an ecosystem?
A) Carbon
B) Electromagnetic energy
C) Water
D) Nitrogen
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ENZYMES
Chemical reactions
Reactants are converted into products
Atoms become combined in new forms
O2 + 2 H2 2 H2O
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ENZYMES
Reaction rates
Typically too slow to sustain life
Need help to speed up
Enzymes are biological catalysts
Catalysts speed up reactions
They do not make a reaction happen that wouldn’t
have happened otherwise
Enzymes are usually made out of protein
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ENZYMES
Reaction rates
Typically too slow to sustain life
Need help to speed up
Enzymes are biological catalysts
Catalysts speed up reactions
They do not make a reaction happen that wouldn’t
have happened otherwise
Enzymes are usually made out of protein
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ENZYMES
In order to react, molecules go through awkward
transitions
Unstable, high-energy states: Transition states
Enzymes help to speed up reactions by stabilizing
transition states
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Reactants:
2H2 O2
Activation energy
Difference between free energy
of reactants and products
Products: 2H2O
Time
Fre
e e
nerg
y
ENZYMES
Quick Quiz: True or false: An enzyme
makes a reaction that wouldn’t have
happened
A) True
B) False
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Quick Quiz: The difference between
the amount of energy in reactants and
the maximal amount of energy in the
transition state is called…
A) Activation energy
B) Free energy
C) Catalyst
D) Potential energy
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Photosynthesis
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C6H12O6
Photosynthesis
Occurs in chloroplasts
Outer membranes (2)
Thylakoid membrane system
Stroma
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Photosynthesis
Two distinct events
Light-dependent reactions (light reactions)
Occurs in thylakoids of chloroplasts
Energy from sunlight used to generate ATP &
NADPH
Splits H2O, releasing O2 as a byproduct
Light-independent reactions (dark reactions)
Occurs in stroma of chloroplasts
Uses CO2, ATP &
NADPH to synthesize
glucose
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Photosynthesis
Process summary
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Photosynthesis
How is light energy actually captured and
converted into chemical energy?
Photopigments capture photons of light
Chlorophylls (a, b)
Accessory pigments (carotenoids, phycobilins)
Electron carriers transfer energy to form ATP &
NADPH
Calvin-Benson cycle uses the ATP & NADPH to “fix”
CO2 into sugars (glucose)
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Quick Quiz: Which stage of
photosynthesis requires carbon
dioxide?
A) Light-dependent reactions
B) Light-independent reactions
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Quick Quiz: True or false: the goal of
photosynthesis is to produce oxygen.
A) True
B) False
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Light-Dependent Reactions
Photopigments & the Electromagnetic Spectrum
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Photopigments & the Electromagnetic Spectrum
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Englemann’s Experiment
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Light Capture & Energy Transport
Two photosystems for capturing light energy
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Quick Quiz: In a plant cell, which of the
following is NOT where you would find
chlorophyll?
A) Photosystem I
B) Photosystem II
C) ATP synthase
D) Thylakoid membrane
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Quick Quiz: What is the final product
of the “light reactions”?
A) glucose
B) starch
C) ATP
D) NADPH
E) C and D only
F) All of the above
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Light-Independent Reactions
Calvin-Benson cycle
Occurs in stroma of chloroplast
Use ATP & NADPH generated during light-dependent
reactions
Carbon fixation
6 CO2 + 6 RuBP 1 glucose
Rubisco (enzyme)
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RuBP = ribulose bisphosphate
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Photosynthesis
Process summary
ATP + NADPH
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C6H12O6
Quick Quiz: How many carbon atoms
does RuBP have?
(Just press the number on your
keypad that corresponds with your
answer.)
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Quick Quiz: Which of these is a
product of the Calvin-Benson cycle
(aka the “dark-reactions” or “light-
independent reactions”)
A) ATP
B) glucose
C) NADPH
D) CO2
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Variations to Photosynthetic Systems in Plants
Differences in environments (light intensity,
temperature, rainfall, soil conditions, etc) can
affect how photosynthesis proceeds in plants
How to deal with hot, dry conditions
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Stomata
Allow gas exchange through leaves (O2, CO2,
H2O)
Close in hot dry weather to prevent excess water loss
Causes increase in O2 levels; decrease in CO2 levels
Triggers photorespiration (bad news!)
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C3 Plants
E.g., evergreen trees (temperate zones)
With stomata closed…
Rubisco fixes O2 when CO2 levels drop
Efficiency reduced
by 1/2
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C4 Plants
E.g., grasses, corn, tropical plants
Two carbon fixation steps
Each fixed in different types of cells
Maintain higher internal
CO2 levels in the cells that
make sugar than C3’s
Lose less water, make more glucose than C3 plants during hot/dry conditions
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CAM Plants
E.g., cactus, desert plants
Stomata close during the day and open at night
Carbon fixation occurs at night
Most efficient under
hot/dry conditions
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Quick Quiz: Which of the following
plants uses a 4-carbon molecule in the
Calvin cycle?
A) Corn
B) Douglas fir
C) Saguaro cactus
D) A and B
E) A and C
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“The Circle of Life”
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“The Circle of Life”
36 ATP
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Aerobic Respiration
C6H12O6 + 6 O2 6 CO2 + 6 H2O + 36 ATP
glucose oxygen carbon dioxide water
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Aerobic Respiration
Involves 3 linked processes
Glycolysis
Citric acid cycle
TCA (tricarboxylic acid cycle) / Krebs cycle
Oxidative phosphorylation
Respiratory transport chain / electron transport
chain
ATP synthase
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Aerobic Respiration
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Glycolysis
“Sugar splitting”
Occurs in cytoplasm
Net reaction:
1 glucose 2 pyruvate + 2 ATP + 2 NADH
C6H12O6 C3H3O3
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Glycolysis (part 1)
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Glycolysis (part 2)
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Glycolysis
Bottom line…
1 glucose 2 pyruvate + 2 ATP + 2 NADH
Glucose (6 C) split into 2 molecules of pyruvate (3C)
To TCA cycle
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Glycolysis
Bottom line…
1 glucose 2 pyruvate + 2 ATP + 2 NADH
Glucose (6 C) split into 2 molecules of pyruvate (3C)
Uses 2 ATP, produces 4 ATP net yield of 2 ATP
Available for immediate energy needs
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Glycolysis
Bottom line…
1 glucose 2 pyruvate + 2 ATP + 2 NADH
Glucose (6 C) split into 2 molecules of pyruvate (3C)
Uses 2 ATP, produces 4 ATP net 2 ATP
Produce reducing potential (NADH)
To electron transport (oxidative phosphorylation)
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Quick Quiz: The end result of
glycolysis is 2 molecules of ________.
A) Carbon dioxide
B) Oxygen
C) Glucose
D) Pyruvate
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Quick Quiz: True or false: Plant cells
have mitochondria.
A) True
B) False
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TCA Cycle
Occurs in mitochondria
Matrix (inner compartment)
Net reaction:
2 pyruvate 6 CO2 + 2 “ATP” + 8 NADH + 2 FADH2
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TCA Cycle
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TCA Cycle
Bottom line…
2 pyruvate 6 CO2 + 2 “ATP” + 8 NADH + 2 FADH2
Glucose now completely oxidized to CO2
Diffuses from cell
Generates lots of reducing potential (NADH, FADH2)
To electron transport chain (ETC)
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Quick Quiz: Which of the following is
NOT a product (or byproduct) of the
TCA cycle?
A) NADH
B) FADH2
C) ATP
D) Pyruvate
E) CO2
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Oxidative Phosphorylation
Occurs in mitochondria (inner membrane)
Most efficient system for ATP generation
Net reaction:
10 NADH + 2 FADH2 + 6 O2 32 ATP + 6 H2O
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Oxidative Phosphorylation
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ATP
ADP + Pi
INNER
COMPARTMENT
Oxidative Phosphorylation
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Oxidative Phosphorylation
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Oxidative Phosphorylation
Bottom line…
10 NADH & 2 FADH2 + 6 O2 32 ATP + 6 H2O
Use “energy carriers” (NADH, FADH2) from glycolysis and
TCA cycle to generate ATP
O2 is the terminal acceptor for the transferred electrons
Involves ATP synthase
Uses H+ concentration gradient
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Aerobic Respiration
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Quick Quiz: Where is the electron
transport chain located?
A) Cytoplasm
B) Mitochondrial matrix
C) Outer mitochondrial membrane
D) Inner mitochondrial membrane
E) Intermembrane space (outer compartment)
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Quick Quiz: What would happen to
oxidative phosphorylation if oxygen
were not available?
A) Oxidative phosphorylation would cease
B) Oxidative phosphorylation would increase
C) Oxidative phosphorylation would occur at
the same rate
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Anaerobic Respiration
ATP generation in the absence of O2
Involve terminal electron acceptors other than
oxygen
E.g., O-containing salts (nitrates, nitrites, sulfates,
sulfites)
Anaerobic bacteria
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Anaerobic Respiration
ATP generation in the absence of O2
ATP produced through glycolysis with lactic acid
and/or ethanol and CO2 as end products
Fermentation
Lactic fermentation
Alcoholic fermentation
Decreased efficiency; have to deal with by-products
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Lactic Fermentation
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Alcoholic Fermentation
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Alternate
Energy
Sources &
Biosynthesis
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Quick Quiz: True or False – The TCA
cycle can only be used to oxidize
(process) pyruvate.
A) True
B) False
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