Learning Objectives - Linn–Benton Community...
Transcript of Learning Objectives - Linn–Benton Community...
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Learning Objectives • Know the organization of a prokaryotic cell
• Learn the organelles of a eukaryotic cell
• Consider the properties of the cell membrane (aka plasma membrane)
• How does it restrict flow of molecules across the membrane?
• Visualize the flow of endomembrane trafficking through the cell
• Overview of eukaryotic organelles
• Consider how the organelles work together
• Know the difference between diffusion and osmosis
• Identify ways that cells transport molecules across membrane barriers
• Know the difference between diffusion and osmosis
• Understand the how the properties of the plasma membrane restrict diffusion across the
membrane
• The membrane is permeable to what types of molecules?
• Become familiar with the terminology of osmosis: hypotonic, hypertonic, and isotonic
solutions
• What happens to different cell types in these solutions?
• Identify ways that cells transport molecules across membrane barriers
• What is the difference between “active transport” and “facilitated diffusion”?
• Which one requires cells to expend energy?
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Cell Theory
1. All organisms are
composed of one or
more cells
2. Cells are the smallest
living things
3. Cells arise only by
division of previously
existing cells
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Cell size
• Smaller cells also have a greater surface area
a cell’s surface provides the interior’s only opportunity to interact
with the environment
as cell size increases, the volume grows more rapidly than
surface area (e.g., if surface area doubles, volume quadruples)
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Bacteria on the point of
a pin (!)
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Microscopy Resolution: minimum distance that two points can be apart and still
be distinguished as two separated points
• the limit of resolution of the human eye is about 100
micrometers (1/10 mm)
Compound light
microscopes use sets of
magnifying lenses to resolve
structures that are separated
by more than 200
nanometers
Electron microscopes have
1000 times the resolving
power of light microscopes
and can resolve objects as
close as 0.2 nanometers
apart
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Prokaryotic/Eukaryotic
There are two major types of cells
Prokaryotic
• lacks a nucleus and does not have an extensive
system of internal membranes
• all bacteria and archaea have this cell type
Eukaryotic
• has a nucleus and has internal membrane-
bounded compartments
• all organisms other than bacteria or archaea have
this cell type
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Prokaryotic
Cells
Prokaryotes are the simplest cellular organisms
have a plasma membrane surrounding a cytoplasm without interior compartments
• most bacteria have additional outer layers to the plasma membrane
– cell wall comprised of carbohydrates to confer rigid structure
– capsule may surround the cell wall
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Figure 4.5 Organization of a
prokaryotic cell
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Prokaryotic Cell Organization
• The interior of the prokaryotic cell shows simple organization
cytoplasm is uniform with little or no internal support framework
ribosomes (sites for protein synthesis) are scattered throughout the cytoplasm
nucleoid region (an area of the cell where DNA is localized)
• not membrane-bounded, so not a true nucleus
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Prokaryotic External Structures
Other structures sometimes found in prokaryotes relate to locomotion, feeding, or genetic exchange
a flagellum (plural, flagella) is a threadlike structure made of protein fibers that extends from the cell surface
• may be one or many
• aids in locomotion and feeding
pilus (plural, pili) is a short flagellum
• aids in attaching to substrates and in exchanging genetic information between cells
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Eukaryotic Cells
Eukaryotic cells are larger and more complex than prokaryotic cells Also have a plasma membrane
encasing the cytoplasm • internal membranes form
compartments called organelles
• the cytoplasm is semi-fluid and contains a network of protein fibers that form a scaffold called a cytoskeleton
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Eukaryotic cells have organelles
• Many organelles are immediately
conspicuous under the microscope
Nucleus
• a membrane-bounded compartment for DNA
Endomembrane system
• gives rise to the internal membranes found in the
cell
• each compartment can provide specific conditions
favoring a particular process
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Figure 4.6 Structure of an animal cell
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Inter-Kingdom Differences in
Eukaryotic Cells
The cells of plants, fungi, and many protists
have a cell wall beyond the plasma
membrane
All plants and many protists contain
organelles called chloroplasts
Plants contain a central vacuole
Only animal cells contain centrioles
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Figure 4.7 Structure of a plant cell
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Table 4.1 Be familiar with
the structures/
organelles in this
table
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The Plasma Membrane
• The plasma membrane is conceptualized
by the fluid mosaic model
a sheet of lipids with embedded proteins
• the lipid layer forms the foundation of the
membrane
• the fat molecules comprising the lipid layers are
called phospholipids
What makes it a “mosaic”?
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Phospholipids
• A phospholipid has a polar head and two non-polar tails
• The polar region contains a phosphate chemical group and is water-soluble (hydrophilic)
• The non-polar region is comprised of fatty acids and is water-insoluble (hydrophobic)
Figure. Phospholipid structure
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Lipid bilayer
• A lipid bilayer forms spontaneously whenever a
collection of phospholipids is placed in water Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Polar
(hydrophilic) region
Nonpolar (hydrophobic) region
(a)
(b)
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Chemistry of the plasma membrane
• The interior of the lipid bilayer
is completely nonpolar
no water-soluble molecules can
freely cross through it
cholesterol is also found in the
interior
• it affects the fluid nature of the
membrane
• its accumulation in the walls of
blood vessels can cause
plaques
• plaques lead to cardiovascular
disease
Do you think that cholesterol makes the plasma membrane
more or less fluid?
www.cytochemistry.net
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Membrane proteins
• Another major component of the membrane is a
collection of membrane proteins
Some proteins form channels that span the
membrane
• these are called transmembrane proteins
• What must be true about the region of the protein that
spans the membrane?
Other proteins are integrated into the structure of the
membrane
• for example, cell surface proteins are attached to the outer
surface of the membrane and act as markers
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Proteins are embedded within the
lipid bilayer
Polar
hydrophilic
heads
Polar
hydrophilic
heads
Nonpolar
hydrophobic
tails
Phospholipid
Cell identity
marker
Nonpolar
areas
of protein
Polar areas
of protein Phospholipids
Cholesterol
Cholesterol
Protein channel
Receptor protein
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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The Nucleus: The Cell’s Control
Center • The nucleus is the command
and control center of the cell
it also stores hereditary
information (in what molecule?
What theory does this relate
to?)
• The nuclear surface is
bounded by a double-
membrane called the nuclear
envelope (2 lipid bilayers!)
groups of proteins form
openings called nuclear pores
that permit proteins and RNA to
pass in and out of the nucleus
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The Nucleus: DNA
• The DNA of eukaryotes is packaged into
segments and associated with protein
this complex is called a chromosome
• the proteins enable the DNA to be wound tightly
and condense during cell division
• when the cell is not dividing, the chromosomes
exist as threadlike strands called chromatin
– protein synthesis occurs when the DNA is in the
chromatin form
http://www.wehi.edu.au/education/wehitv/molecular_visualisations_of_dna/
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The Nucleolus
• The cell builds proteins on structures called ribosomes
ribosomes consist of ribosomal RNA (rRNA) and several
different kinds of proteins
• Ribosomes are assembled in a region of the nucleus
called the nucleolus
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The Endomembrane System
• The endoplasmic reticulum (ER) is an
extensive system of internal membranes
some of the membranes form channels and
interconnections
other portions become isolated spaces
enclosed by membranes
• these spaces are known as vesicles
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The Endoplasmic Reticulum (ER)
• The portion of the ER dedicated to protein
synthesis is called the rough ER
the surface of this region looks pebbly
the rough spots are due to embedded ribosomes
• The portion of the ER that aids in the
manufacture of carbohydrates and lipids is
called the smooth ER
the surface of this region looks smooth because
embedded ribosomes are scarce
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Figure 4.9 The endoplasmic
reticulum (ER)
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The Golgi Complex
• After synthesis in the ER, the newly-made
molecules are passed to the Golgi bodies
Golgi bodies are flattened stacks of
membranes scattered through the cytoplasm
their numbers vary depending on the cell
their function is to collect, package, and
distribute molecules manufactured in the cell
the Golgi bodies of a cell are collectively
called the Golgi complex
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Figure 4.10 Golgi complex
http://molecularmovies.com/movies/berry_golgi.mov
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ER-Golgi trafficking
The ER and Golgi
complex function
together as a
transport system in
the cell
Figure 4.11 How the
endomembrane system
works
https://www.youtube.com/watch?
v=rvfvRgk0MfA
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Lysosomes
The Golgi complex also gives rise to
lysosomes
these membrane-bounded structures contain
enzymes that the cell uses to break down
macromolecules
• worn-out cell parts are broken down and their
components recycled to form new parts
• particles that the cell has ingested are also
digested
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Animation: Lysosome
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Inquiry & Analysis
How Does pH Affect a Protein’s Function?
1. Which of the three pH values
represents the highest
concentration (amount present
in a given volume) of H+ ions? Is
this value more acidic or more
basic than the other two?
2. What is the percent hemoglobin
bound to O2 for each of the
three pH concentrations at
saturation? At an oxygen level
of 20 mm Hg? At 40 mm Hg? At
60 mm Hg?
3. At an oxygen level of 40 mm
Hg, would hemoglobin bind
oxygen more tightly at a pH of
7.8 or 7.0?
4. How does pH affect the release
of oxygen from hemoglobin?
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Plant cell
wall
Vacuole
membrane
1.83 μm
Central
vacuole
Vacuoles
Vacuoles are membrane-
bounded storage compartments
• in plants, the central vacuole
stores water and dissolved
substances
• in some protists, the
contractile vacuole is found
near the cell surface and
accumulates excess water
from inside the cell that it then
pumps out
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Organelles That Harvest Energy
• Eukaryotic cells contain energy harvesting organelles that contain their own DNA
these organelles appear to have been derived from ancient bacteria that were taken up by eukaryotic cells (endosymbiosis)
these organelles include mitochondria and chloroplasts
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Mitochondria
• Mitochondria are cellular
powerhouses
• Sites for chemical
reactions called
oxidative metabolism
• The organelle is
surrounded by two
membranes
Figure 4.13(a) Mitochondria
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Chloroplasts
• Chloroplasts are the sites of photosynthesis
• The organelle is also surrounded by two membranes
Figure 4.14 A chloroplast
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Endosymbiosis
Both mitochondria and chloroplasts possess their own
molecule of circular DNA
• They cannot be grown free of the cell
they are totally dependent on the cells within which they occur
The theory of endosymbiosis
states that some organelles evolved from a symbiosis in which
one cell of a prokaryotic species was engulfed by and lived inside of a eukaryotic cell
the engulfed species provided their hosts with advantages because of special metabolic activities
What biological “theme” from Chapter 1 does this relate to?
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Support for Theory of Endosymbiosis
In addition to the double membranes and circular DNA found in mitochondria and chloroplasts, there is a lot of other evidence supporting endosymbiotic theory
mitochondria are about the same size as modern bacteria
the cristae in mitochondria resemble folded membranes in modern bacteria
mitochondrial ribosomes are similar to modern, bacterial ribosomes in size and structure
mitochondria divide by fission, just like modern bacteria
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The Cytoskeleton: Interior
Framework of the Cell
• The cytoskeleton is comprised of an internal framework of protein fibers that anchors organelles to fixed locations
supports the shape of the cell
helps organize ribosomes and enzymes needed for synthesis activities
• The cytoskeleton is dynamic and its components are continually being rearranged
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Three different types of protein fibers
comprise the cytoskeleton
Intermediate filaments
• thick ropes of intertwined protein
Microtubules
• hollow tubes made up of the protein tubulin
Actin filaments (microfilaments)
• long, slender microfilaments made up of the
protein actin
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Figure. The protein fibers of the cytoskeleton Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fibrous
protein
10 nm
Intermediate filament
25 nm
+ end
Microtubule
7 nm
Actin filament Actin
subunit
Tubulin
subunit
– end
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Figure 4.16 Centrioles
Centrioles are complex
structures that assemble
microtubules in animal cells and
the cells of most protists
they occur in pairs
they are found near the
nuclear envelope
they are composed of
microtubules
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Motility
Cellular motion is associated with the movement of actin microfilaments and/or microtubules
some cells “crawl” by coordinating the rearrangement of actin microfilaments
some cells swim by coordinating the beating of microtubules grouped together to form flagella or cilia
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Figure 4.17 Flagella and cilia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Microtubules
Plasma
membrane
Flagellum
Basal body
Microtubules (a)
(b)
© Manfred Kage/Peter Arnold/Photolibrary
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Diffusion and Osmosis
• Movement of water and nutrients into a cell or elimination of wastes out of cell is essential for survival
• This movement occurs across a biological membrane in one of three ways
• diffusion
• membrane folding
• transport through membrane proteins
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Diffusion
• Molecules move in a random fashion but there is a tendency to produce uniform mixtures
• The net movement of molecules from an area of higher concentration to an area of lower concentration is termed diffusion
• Molecules diffuse down a concentration gradient from higher to lower concentrations diffusion ends when equilibrium is reached
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Animation: How Diffusion Works
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Diffusion across the cell membrane
Only certain substances undergo diffusion across the plasma membrane—which ones? molecules like oxygen, carbon dioxide, and lipids
or
ions and polar molecules
• Water is able to diffuse freely across the plasma membrane aquaporins are selective
channels that permit water to cross
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Osmosis
Water moves down its concentration
gradient into or out of a cell through
osmosis What do we mean by “down its concentration
gradient?
the movement of water is dependent on the
concentration of other substances in a
solution
the greater the amount of solutes that are
dissolved in a solution, the lesser the amount
of water molecules that are free to move
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Essential Biological Process 4B: Osmosis
1 2 3
Diffusion then causes free water
molecules to move from the side where
their concentration is higher to the solute
side, where their concentration is lower.
Addition of solute molecules that cannot
cross the membrane reduces the
number of free water molecules on that
side, as they bind to the solute.
Diffusion causes water molecules to
distribute themselves equally on both
sides of a semipermeable membrane.
Water
molecules
Hypotonic Hypertonic
Urea
Isotonic
Semipermeable
membrane
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Animation: How Osmosis Works
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Animation: Osmosis
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Osmotic concentration
The concentration of all molecules dissolved in a solution
if the osmotic concentrations of two solutions is equal,
the solutions are each called isotonic
if two solutions have unequal osmotic concentration, the solution with the higher solute concentration is said to be hypertonic, and the solution with the lower solute concentration is said to be hypotonic
Hyper = more, Hypo = less; Tonic = solute (dissolved substance)
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Osmotic pressure
Movement of water by osmosis into a cell
causes pressure called osmotic pressure
enough pressure may cause a cell to swell
and burst
osmotic pressure explains why so many cell
types are reinforced by cell walls
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Figure 4.18 Osmotic pressure in
plants and animal cells
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Animation: Hemolysis and
Crenation
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Bulk Passage into and out of Cells
• Bulky substances are contained within
vesicles as they are moved into and out of
a cell
endocytosis is the engulfing of substances
outside of the cell in order to form a vesicle
that is brought inside the cell
exocytosis is the discharge of substances
from vesicles at the inner surface of the cell
Endo = In, Exo = Out
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4.10 Bulk Passage into and out
of Cells Forms of endocytosis
• Phagocytosis is
endocytosis of
particulate (solid)
matter
• Pinocytosis is
endocytosis of liquid
matter
Figure 4.19 Endocytosis
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Copyright © 2011 Pearson Education, Inc.
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Figure 4.20 Exocytosis
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Animation: Endocytosis and
Exocytosis
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Selective Permeability
Selective permeability allows cells to
control specifically what enters and leaves
involves using proteins in the membrane for
transporting substances across
transport can be down a concentration
gradient (i.e., diffusion) or against a
concentration gradient (i.e., active transport)
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Selective
Permeability-Diffusion Selective diffusion
• proteins act as open channels for whatever is small enough to fit inside the channel
• this form of diffusion is common in ion transport
Facilitated diffusion • proteins act as carriers that can bind only
to specific molecules and transport them
• transport is limited by the availability of carriers
• when all the carriers are in use, then the transport is saturated
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Animation: How Facilitated
Diffusion Works
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Active transport
Active transport utilizes protein channels that open only when energy is supplied
energy is used to pump substances against or up their concentration gradients
allows cells to maintain high or low concentration of certain molecules
• recall that diffusion always ends in equilibrium
Most of the active transport in cells is carried out by the sodium-potassium pump
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The Sodium-Potassium pump
Sodium-potassium (Na+-K+) pump
uses energy, in the form of ATP, to pump
three Na+ out of the cell and to pump two K+
into the cell
nearly 1/3 of the energy expended by the
body’s cells is given over to driving these
pumps
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Essential Biological Process 4D:
The Sodium-Potassium Pump
P
P
The splitting of ATP provides energy to change the shape of the
transport protein. The sodium ions are driven through the pump.
The sodium ions are released to the outside of the membrane,
and the new shape of the pump allows two potassium ions to
bind.
Release of the phosphate allows the sodium-potassium
pump’s transport protein to revert to its original form,
releasing the potassium ions on the inside of the membrane.
3 4
The sodium-potassium pump utilizes a transport protein that
binds three sodium ions and a molecule of ATP.
Na+ P
P P
A
1
Na+
K+
P P
A A D P
P
2
Na+
Na+
Na+
K+
Na+
Na+
Na+
K+
K+
K+
K+
ATP
ADP
P P
A
Na+
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Animation: How the Sodium
Potassium Pump Works
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Ion gradient
• The result of the Na+-K+ pump is to generate a concentration gradient with more Na+ outside of the cell than inside
• Cells exploit this gradient in key ways
for the conduction of signals along nerve cells
for the transportation of important molecules into the cell against their concentration gradient
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Coupled Transport
• The cell membrane has many facilitated diffusion channels for Na+ but it is only transported if partnered with another substance this is called coupled transport
• The concentration gradient favoring the entry of Na+ into the cell is so strong that a coupled substance will be transported even if it is against the concentration gradient coupled transport is a common way for cells to
accumulate sugars and amino acids
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Animation: The Sodium
Potassium Exchange Pump
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The Flow of Energy in Living
Things
• Energy is the ability to do work [ W = F • s ]
• Energy is considered to exist in two states kinetic energy
• the energy of motion
potential energy • stored energy that can be used for motion
• All the work carried out by living organisms involves the transformation of potential energy to kinetic energy
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Figure 5.1 Potential and kinetic energy
(a) Potential energy
(b) Potential energy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a: © Nice One Productions/Corbis RF
(c) Kinetic energy
Question from the reading:
• Is the energy in a “high-
energy” food bar kinetic or
potential?
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Solar Chemical
Energy from the sun is captured by some organisms and used to make molecules
these molecules then contain potential energy due to the arrangement of their atoms
the potential energy in molecules is a form of chemical energy that can be used to do work in cells
chemical reactions involve making and breaking bonds between atoms
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Heat Energy
• Heat energy is the
most convenient form
of energy to measure
• Thermodynamics is
the study of energy or
heat changes
There are many forms of energy but all of them
can be converted to heat
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The Laws of Thermodynamics
Laws of thermodynamics govern the energy changes of the universe, including those involved with any activity of an organism
• 1st Law of Thermodynamics the total amount of energy in the universe remains constant
energy can change from one state to another but it can never be created nor destroyed
during the energy conversions, some of the energy is lost as heat energy
• 2nd Law of Thermodynamics the amount of disorder, or entropy, in the universe is increasing
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Figure 5.3 Entropy in action
• What process did
we experiment
with in lab 2 that
exemplifies
entropy?
• What is an
example of a
cellular
mechanism that
uses energy to
reverse entropy?
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Chemical Reactions
• The starting molecules of a chemical reaction are called
the reactants or substrates
• The output molecules from the reaction are called
products
What are the substrates?
What are the products?
Where is the energy?
Is the energy kinetic or potential?
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Endergonic vs. Exergonic
There are two kinds of chemical reactions
endergonic reactions have products with more energy than the
reactants
• these reactions require an input of energy
exergonic reactions have products with less energy than the
reactants
• these reactions tend to occur spontaneously
Is polysaccharide
formation endergonic
or exergonic?
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Exergonic Reactions
Question:
• If exergonic reactions tend to occur
spontaneously, why haven’t they all done so?
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Activation Energy
• All chemical reactions require an initial input of
energy called activation energy
the activation energy initiates a chemical reaction by
destabilizing existing chemical bonds
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Catalysis .
Reactions become more
likely to happen if their
activation energy is lowered
this process is called
catalysis
catalyzed reactions proceed
much faster than non-
catalyzed reactions
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Enzymes
Enzymes are the catalysts used by cells to
perform particular reactions
enzymes bind specifically to a molecule and
stress the bonds to make the reaction more
likely to proceed
the active site is the site on the enzyme that
binds to a reactant
the site on the reactant where the enzyme
binds is called the binding site
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Figure 5.5 An enzyme’s shape
determines its activity
Induced fit
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How Enzymes Work
• The binding of a reactant to an enzyme causes the enzyme’s shape to change slightly
this leads to an “induced fit” where the enzyme and substrate fit tightly together as a complex
the enzyme lowers the activation energy for the reaction
the enzyme is unaffected by the chemical reaction and be re-used
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Essential Biological Process 5A:
How Enzymes Work
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Animation: How Enzymes Work
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Animation: Enzyme Action and the
Hydrolysis of Sucrose
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Biochemical Pathways
• Catalyzed reactions
may occur together in
sequence
the product of one
reaction is the
substrate for the next
reaction until a final
product is made
the series of reactions
is called a
biochemical pathway
Figure 5.6 A biochemical pathway
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Animation: A Biochemical Pathway
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Factors Affecting Enzymes
• Temperature and pH affect enzyme activity
enzymes function within an optimum temperature
range
• when temperature increases, the shape of the enzyme
changes due to denaturing of the protein chains
enzymes function within an optimal pH range
• the shape of enzymes is also affected by pH
• most human enzymes work best within a pH range of 6 - 8
– exceptions are stomach enzymes that function in acidic ranges
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Figure 5.7 Enzymes are
sensitive to their environment
Why might a human
enzyme need to
function at low pH?