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Cell Energy
ATP and Enzymes
Respiration
Photosynthesis
Energy
• Energy – the ability to do work
• ATP – molecule that stores energy in
which organisms use; adenosine
triphosphate
• Calorie – the unit used to measure the
amount of energy food contains
• Metabolism – the collection of the
chemical reactions that occur in a cell;
anabolism and catabolism
Energy
• Potential energy – stored energy, energy
that results from position
– Food has potential, stored, energy
• Kinetic energy – energy of motion
– Our bodies convert food into kinetic energy
ATP and ADP
• ADP – adenosine diphosphate turns into
ATP through the process of
phosphorylation, addition of a phosphate
group to a molecule
Energy from
food
Synthesis of
ATP
ADP + P
ATP
Energy used by cell
Hydrolysis
of ATP
Role of Enzymes
• Proteins that help chemical reactions in
living organisms and help control the
chemical environment at cell’s level
• Catalyst – a chemical that helps a
chemical reaction, but is not consumed or
changed in the reaction
– Enzymes act as a catalyst in biochemical
reactions
Role of Enzymes
Role of Enzymes
• Reactant – the reactant molecule in which the
enzyme reacts
• Substrate – the area on the enzyme where the
substrate fits in shape and chemistry
• Active site – where substrate fits
• Product – the molecule produced in the enzyme
reaction
• Pepsin – an enzyme produced by the stomach
for digestion of proteins
• Amylase – an enzyme produced in the salivary
glands for the digestion of carbohydrates
Role of Enzymes
• Enzymes lower the activation energy
required for chemical reactions to take
place
Cellular Respiration
• The process by which living things release
energy from food
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
glucose + oxygen carbon + water + energy
dioxide
Cellular Respiration
• Redox reaction – a chemical reaction in
which electrons are transferred between
atoms
• Reduction – a chemical reaction that
results in a gain of electrons
– Glucose loses electrons and hydrogen
• Oxidation – a chemical reaction that
results in a loss of electrons
– Oxygen gains electrons and hydrogen
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
Cellular Respiration
• Electron carriers – special molecules that
carry electrons from one set of reactions to
another
• NADH (nicotinamide adenine dinucleotide)
– the main electron carrier involved in
cellular respiration
Stages of cellular respiration
• Glycolysis
– Glucose is split
• Kreb’s Cycle
– Produces ATP, NADH, and FADH2
• Electron Transport Chain
– Produces ATP
Glycolysis
• Uses 2 ATP molecules to split glucose into
two 3-carbon compounds.
• Bonds rearrange and produce NADH from
NAD+, along with two 3-carbon compounds.
• Two 3-carbon compounds are converted into
pyruvic acid, along with 4 ATP.
• In order to move into the mitochondria, pyruvic
acid is converted into acetic acid, which bonds
to coenzyme A to create acetyl CoA. It
releases acetic acid into mitochondria
Glycolysis
NADH
3-carbon NAD+
compound
3-carbon
compound
2 ATP
Pyruvic Acid
2 ATP
Glucose
3-carbon
compound
3-carbon
compound
Pyruvic Acid
NAD+
NADH
2 ATP
Kreb’s Cycle
• Acetic acid enters the matrix of
mitochondria.
• The cycle also uses 3 NAD+ and 1 FAD
molecule through a series of chemical
reactions.
• The products are 2 CO2, 1 ATP, 3 NADH,
and FADH2 molecules.
Kreb’s Cycle
Electron Transport Chain
• NADH transfers electrons to first electron
carrier. High energy electrons passed
down chain.
• Energy is released each time electrons are
moved down the chain, which pumps H+
across the membrane. Water is also
formed.
• The energy released, with ATP synthase,
produces ATP by adding phosphate to ADP
Fermentation
• Anaerobic – not requiring oxygen
• Fermentation – process for making ATP not
requiring oxygen
• Lactic acid – an organic waste produced by
anaerobic fermentation
– Occurs during periods of intense exercise “side ache)
• Ethyl alcohol – a liquid waste produced by
anaerobic fermentation
– Occurs in yeasts when making bread and alcoholic
beverages.
Controlling Respiration
• Feedback inhibition – process used by
cells to control metabolic pathways
– Too much of a substance creates a pathway
to stop the production of the substance
– Too little of a substance creates a pathway to
increase production of a substance
– Ex. - Hyperventilate, Hunger, Increased
respiration during exercise
Photosynthesis
• Heterotrophs – organisms that cannot make
their won food and must obtain energy from
the foods they eat
• Autotrophs – a self-nourishing organism that
makes its own food
• Photosynthesis – process by which autotrophs
harvest energy to make glucose
6CO2 + 12H2O + light  C6H12O6 + 6O2 + 6H2O
Leaf Anatomy
• Stoma – an opening on the underside of a
leaf for gas exchange
• Vascular bundle – a vein in a leaf that
transports water and food
• Mesophyll – the green tissue inside a leaf
• Chlorophyll – the pigment that absorbs
light in autotrophs
Leaf Anatomy
Top Layer
Mesophyll
Vascular
Bundle
Stoma
Light Absorption
Light Absorption
• The first step in photosynthesis is the
absorption of light energy
• Plant cells convert energy from light to
chemical energy; called the light reaction
• Produces ATP and NADPH
Light Reaction
Light Reaction
• Electrons gain energy when light strikes
chlorophyll.
• Excited electrons transferred to a reaction
center and enter an electron transport
chain.
• An assembly of proteins and pigments
through which electrons are transferred to
reaction centers is called a photosystem
Light Reaction
• Photosystem I – chlorophyll absorbs red
light and produces ATP; electrons return
to reaction center
• Photosystem II – chlorophyll absorbs red
light and moves electrons to Photosystem
I; electrons are replaced by the splitting of
water and oxygen is released
• Energy enriched electrons produce ATP
by adding a phosphate to ADP
• No glucose is produced after the light
reaction.
Dark Reaction (Calvin Cycle)
• The first step of the Calvin cycle, CO2
molecules combine with the sugar RuBP
(ribulose bisphosphate) to make PGA
(phophosglycerate).
– The source of carbon in photosynthesis is
CO2 in the air.
• The second step of the Calvin cycle,
energy from ATP combines with electrons
from NADPH to form G3P, and energy rich
sugar molecule.
Dark Reaction (Calvin Cycle)
• The third step of the Calvin cycle, G3P
produces glucose and other compounds
needed for growth and metabolism.
• The fourth step of the Calvin cycle, energy
from ATP is added to G3P to make RuBP.
The cycle is complete and begins again.
Dark Reaction (Calvin Cycle)
Making Glucose in Difficult
Conditions
• C4 plants – a plant that photosynthesizes
in hot, dry weather
– Special enzymes convert CO2 into a fourcarbon compound
– Ex. corn and crabgrass
• CAM plants – a plant that takes in CO2
only during the night.
– Open stomata at night and store CO2 for use
in the day
– Ex. Cacti and pineapple