Chapter 5: The Working Cell
All chemical reactions involve the
transfer of energy
• Metabolism – All chemical reactions of a cell
• Energy has two forms:
• Potential Energy – stored energy (i.e. chemical
bonds)
• Kinetic Energy – energy of movement
Potential and Kinetic Energy (5-1)
Laws of Energy
• Conservation of energy
– Energy cannot be created; only changed
– Total energy in a closed system remains constant
• Entropy
– Available energy is lost when changes occurs
– All processes cause increases in disorder as energy
is lost
Fig. 5-2
Energy is carried by molecules
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A.T.P. Adenosine TriPhosphate
Energy molecule found in all living organisms
Adenine Base with three Phosphate groups
Breaking the phosphate-phosphate bond
releases stored energy to be used by to the
cell
ATP is rechargeable (Fig. 5-9)
ATP in action
ATP Synthase
• Turns ADP + Pi into ATP
• Energy comes from H+ that are
pumped across a membrane then
move through a channel in ATP
synthase
Reactions Require Energy
• Activation Energy increases the kinetic energy of
molecules
• More movement increases the likelihood of
collisions.
• Enzymes lower the activation energy of a reaction
Enzymes are Protein Catalysts
• Catalysts are not used up in the reaction
• Each enzyme performs a specific reaction.
• Enzymes end in “ase” (ex: catalase)
How do enzymes work?
• Reactants (Substrate) bind to enzyme’s active
site
• “Induced Fit” Hypothesis
Induced Fit (5.9)
Multiple enzymes create metabolic
pathways which can produce a
variety of products (NIB)
Enzyme Regulation
• Enzymes can be inhibited by molecules
blocking the active site
• Allosteric regulation: secondary site regulates
enzyme
• Enzymes can be inhibited by negative
feedback
Enzyme control (5.10)
If an enzyme changes, substrates
are unable to bind.
• The enzyme is denatured
– Increased Heat
– Change pH
• Enzymes perform within a narrow
temperature and pH range.
Diffusion
• Molecules move randomly through a fluid
because of their kinetic energy.
• Net movement is from areas of high
concentration to areas of low concentration
• This high -> low movement occurs until the
concentration is equal throughout
(equilibrium).
Membrane proteins (5.11)
Transport Across Membranes
• Diffusion - movement of molecules from high
concentration to low concentration.
• Equilibrium is reached and the concentration
on both sides remain constant
• In cells transport can be
– Simple – move straight through membrane
– Facilitated – passes through channel or carrier
proteins
Diffusion Through a Membrane
Osmosis
• Diffusion of free water across membrane
• Moves from low concentration of salts to high
concentration – think slugs
• Osmosis controlled to maintain cell size and
shape
Free water molecules diffuse
through a membrane
Isotonic solution
• Salt concentration is the same
inside and outside of a cell.
• Net movement of water is zero.
Hypertonic solution
• Salt concentration is higher outside
the cell.
• Net movement of water is out of
the cell.
Hypotonic solution
• Salt concentration is lower outside
the cell.
• Net movement of water is into the
cell.
Active Transport (5.16)
• Maintains high concentration.
• Requires energy (ATP) to move molecules.
Endocytosis
• Cell membrane engulfs molecules/
microorganisms
• Vesicles carry material where they are broken
down
Exocytosis –5.18
Vesicles release molecules
Receptor Proteins Play a Role in
Cell Communication
Exam 1
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50 questions - multiple choice
Bring Scantron
Number 2 pencil
Extra credit assignments – 10 points
Sample questions