- The document discusses energy, metabolic pathways, enzymes, and their roles in cells. It covers the following key points: - ATP acts as the "energy currency" of cells, storing and transporting chemical energy within cells to power metabolic reactions. ATP is regenerated through coupled reactions with energy-releasing steps like ATP breakdown. - Enzymes catalyze metabolic pathways, speeding up biochemical reactions without being used up. They have specific active sites that facilitate reactions on substrates. Feedback inhibition regulates pathways by shutting them down when products accumulate. - Energy from the sun powers photosynthesis, producing carbohydrates that are broken down through cellular respiration to regenerate ATP. This cycling of energy between organisms maintains the flow

1. 5-1
Chapter 5
The Dynamic Cell
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McGraw-Hill Education.

2. • In this section, the following objective will be covered:
• Summarize the laws of thermodynamics and how they relate to
living organisms.
5.1What Is Energy?

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5-3
What Is Energy?
•Energy is the capacity to do work.
•Our biosphere gets its energy from the sun.
•Two basic forms of energy
• Potential energy—stored energy
• Kinetic energy—energy of motion
• Two forms are converted back and forth
• During conversions, some lost as heat

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5-4
Potential Energy Versus Kinetic Energy
(left and center): © Patrik Giardino/Corbis;(right):© Joe McBride/Corbis

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5-5
Calorie and
Kilocalorie
•Measuring energy
• Food energy measured in calories
• Calorie—amount of heat required to raise
temperature of 1 gram of water by 1°C
• Kilocalorie or Calorie = 1,000 calories
• Value listed on food packages

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5-6
Energy Laws
•Two energy laws
• First law—conservation of energy
• Energy cannot be created or destroyed, but it
can be changed from one form to another.
• Second law
• Energy cannot be changed from one form to
another without a loss of usable energy.
• Heat is the least usable form of energy.

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5-7
Entropy
• Every energy transformation leads to an increase in
the amount of disorganization or disorder.
• Entropy—relative amount of disorganization
• Only way to maintain or bring about order is to add
energy
• Our universe is a closed system.
• All energy transformations increase the total
entropy of the universe.
• Energy provided by the sun allows plants to make
glucose from the more disorganized water and
carbon dioxide.
• Some of sun’s energy is lost as heat

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5-8
Cells and Entropy
Unequal distribution
of hydrogen ions
• more organized
• more potential energy
• less stable
• less entropy
Equal distribution
of hydrogen ions
• less organized
• less potential energy
• more stable
• more entropy

9. • In this section, the following objective will be covered:
• Explain the role of adenosine triphosphate (ATP) in a
cell.
• Describe the flow of energy between photosynthesis and
cellular respiration.
5.2 ATP: Energy for Cells

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5-10
ATP: Energy for Cells
• Adenosine triphosphate
• Energy currency of cells
• Cells use ATP to carry out nearly all activities.
• One nucleotide along with 3 phosphate groups
makes it unstable.
• Easily loses a phosphate group to become ADP
(adenosine diphosphate)
• Continual cycle of breakdown and regeneration

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5-11
ATP

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5-12
The ATP Cycle
• ATP releases energy
quickly.
• Amount of energy
released is usually just
enough for a biological
purpose
• Breakdown can be easily
coupled to an energy-
requiring reaction.

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5-13
Coupled
Reactions
• Energy-releasing reaction can
drive an energy-requiring
reaction
• Usually energy-releasing
reaction is ATP breakdown

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5-14
Coupled Reaction
ATP breakdown provides the energy for muscle
movement.
• Myosin combines with ATP.
• ATP breaks down.
• Release of ADP + P causes myosin to change shape and pull
on the actin filament.
(photo): © CNRI/ScienceSource

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5-15
The Flow of
Energy
• Activities of chloroplasts and
mitochondria enable energy to flow
from the sun through all living things.
• Photosynthesis—solar energy used
to convert water and carbon dioxide
into carbohydrates
• Food for plants and other
organisms
• Cellular respiration—carbohydrates
broken down and energy used to
build ATP
• Useful energy is lost with each
transformation.
• Living things dependent on constant
in/out of solar energy

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5-16
Flow of Energy
(leaves): © Comstock/PunchStock RF; (woman): © Karl Weatherly/Getty RF

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5-17
Humans and Energy
•Humans are also involved in the cycling of
molecules between plants and animals and
in the flow of energy from the sun.
• Inhale oxygen, eat plants and animals
• Energy rich foods allow us to produce the ATP
required to maintain our bodies and carry on
activities.

18. • In this section, the following objective will be covered:
• Identify the role that enzymes play in metabolic pathways and the
ways they can be inhibited.
5.3 Metabolic Pathways and Enzymes

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5-19
Metabolic Pathways and Enzymes
Metabolic pathway—series of linked reactions
• The letters E1–E6 represent enzymes.
• Protein molecules that function as organic catalysts speed up reactions.
• Can only speed up possible reactions
a. Active enzyme and active pathway
b. Feedback inhibition
c. Inactive enzyme and inactive pathway

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5-20
Enzymatic
Action
• Enzymes act on substrates
• May facilitate breakdown or synthesis
reactions

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5-21
Enzyme’s
Active Site
• Accommodates substrate
• Like a lock and key—specific to one
substrate
• Induced fit model—undergoes slight
shape change to accommodate substrate
• Change in shape facilitates reaction
• Active site returns to original shape after
releasing product(s)
• Enzymes are not used up by the reaction.

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5-22
Enzyme
Inhibition
• Occurs when an active enzyme is prevented
from combining with its substrate
• Cyanide is a poison because it binds to and
inhibits cytochrome c oxidase.
• Penicillin interferes with a bacterial enzyme that
kills the bacteria.
• Feedback inhibition
• When a product is in abundance, it competes
with substrate for active site
• An end product of a pathway can inhibit the
first enzyme in the pathway—binds to site
other than active site to cause shape
change—which shuts the entire pathway
down

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5-23
Active Enzyme and Active Pathway
a. Active enzyme and active pathway

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5-24
Feedback Inhibition
When a product builds up—the body doesn’t
need more
• Product binds to enzyme and changes its shape
• Loss of shape = loss of function
b. Feedback inhibition

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5-25
Feedback Inhibition, Concluded
Now the substrate can’t bind to enzyme and the reaction
stops
• When the product gets low, enzyme will go back to original
shape
• Enzyme starts working again
c. Inactive enzyme and inactive pathway

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5-26
Energy of Activation
• Molecules frequently do not react with each other unless activated.
• Energy of activation (Ea)—energy needed to cause molecules to react
with one another
• Enzymes lower the amount of energy required.
• Enzymes bring substrates into contact and even sometimes
participate in the reaction.

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5-27
Energy of
Activation (𝐄 𝐚)
• A LOWER hurdle is
easier/ faster to
get over
• A LOWER energy
of activation
makes a reaction
easier/ faster

28. • In this section, the following objective will be covered:
• Compare and contrast passive versus active transport, and list the
types of each.
• Explain osmosis and the effect it has on cells in environments of
varying tonicity.
5.4 CellTransport

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5-29
Cell
Transport
•Plasma membrane regulates traffic in and
out of cell.
•Selectively permeable—some substances
pass freely, some transported, some
prohibited
•3 ways to enter
• Passive transport—substances move
from higher to lower concentration, no
additional energy required
• Active transport—substances move from
lower to higher concentration, additional
energy is required
• Bulk transport—movement independent
of gradients, additional energy required

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5-30
PassiveTransport
• No energy required for simple diffusion
• Molecules move down their concentration gradient
until equilibrium is reached.
• Cell does not expend additional energy—molecules
already in motion
• Some molecules slip between phospholipids.
• Facilitated diffusion—others use transport protein
specific to molecule
• Water uses aquaporins—this explains faster than expected
transport rate

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5-31
Simple Diffusion Demonstration
a.Crystal of dye is placed in the water b. Diffusion of water and dye molecules c. Equal distribution of molecules results

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Facilitated
Diffusion

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5-33
Osmosis Demonstration

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5-34
Osmosis in Animal and Plant
Cells – Isotonic Environment
• Isotonic solution
• No net gain or loss of water
• Concentration of water same on both sides of
the membrane
• 0.9% saline isotonic to red blood cells

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5-35
Osmosis in Animal and Plant
Cells – Hypotonic Environment
•Hypotonic solution
• Concentration of water outside cell greater than
inside cell
• Cell gains water
• Animal cells may lyse or burst
• Plant cells use this to remain turgid

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5-36
Osmosis in Animal and Plant
Cells – Hypertonic Environment
•Hypertonic solution
• Concentration of water outside cell less than
inside cell
• Cell loses water
• Animal cells shrink
• Plant cells undergo plasmolysis and may wilt.

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5-37
Active
Transport
• Cells expend energy to move molecules
against a concentration gradient.
• Requires transport protein
• Sodium-potassium pump important in
maintaining gradient of ions used in nerve
impulse conduction

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5-38
Bulk
Transport
• Macromolecules are often too large
to be moved by transport proteins.
• Vesicle formation takes them in or
out of cell.
• Exocytosis—movement out of cell
• Endocytosis—movement into cell
• Phagocytosis—cell surrounds, engulfs, and
digests particle
• Pinocytosis—vesicle forms around liquid or
small particles
• Receptor-mediated endocytosis—
receptors for particular substances found in
coated pit—selective and more efficient

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5-39
BulkTransport –
Exocytosis

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BulkTransport –
Endocytosis

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5-41
Receptor-Mediated
Endocytosis

42. Chapter 5
Objective
Summary
• You should now be able to:
• Summarize the laws of thermodynamics
and how they relate to living organisms.
• Explain the role of adenosine
triphosphate (ATP) in a cell.
• Describe the flow of energy between
photosynthesis and cellular respiration.
• Identify the role that enzymes play in
metabolic pathways and the ways they can
be inhibited.
• Compare and contrast passive versus
active transport, and list the types of each.
• Explain osmosis and the effect it has on
cells in environments of varying tonicity.