Transcript The Basic Unit of Life—The Cell

Chapter 15 Lecture
Conceptual
Integrated Science
Second Edition
The Basic Unit of
Life—The Cell
© 2013 Pearson Education, Inc.
This lecture will help you understand:
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Characteristics of Life
Macromolecules Needed for Life
Cell Types: Prokaryotic and Eukaryotic
The Microscope
Tour of a Eukaryotic Cell
The Cell Membrane
Transport into and out of Cells
Cell Communication
How Cells Reproduce
How Cells Use Energy
ATP and Chemical Reactions in Cells
Photosynthesis
Cellular Respiration and Fermentation
History of Science: Cell Theory
Math Connection: Why Does Diffusion Limit the Size of Cells?
Science and Society: Stem Cells
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Characteristics of Life
• All living things
– use energy.
– develop and grow.
– maintain themselves.
– have the capacity to reproduce.
– are parts of populations that evolve.
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Characteristics of Life
• All living things use energy.
– Plants take electromagnetic energy from
sunlight and convert it to chemical energy.
– Animals convert energy from food into
chemical energy.
– Living things use this chemical energy to build
structures and fuel their activities.
– How living things use energy is consistent
with the laws of physics.
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Characteristics of Life
• All living things develop and grow, changing
over time.
• Living things maintain themselves.
– They build structures (bones, stems).
– They repair damage (heal wounds).
– They maintain their internal environments
(body temperature, water balance).
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Characteristics of Life
• All living things have the capacity to reproduce.
– Asexual reproduction occurs when an organism
reproduces by itself.
– Sexual reproduction occurs when organisms produce
sperm and eggs that join to develop into new
individuals.
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Characteristics of Life
• All living things are parts of populations that
evolve.
– Populations do not remain constant.
– Populations change over time, across
generations.
– Populations may evolve in response to their
environments.
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Macromolecules Needed for Life
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Proteins
Carbohydrates
Lipids
Nucleic acids
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Cell Types: Prokaryotic and Eukaryotic
• Prokaryotic cells have no nucleus.
• Prokaryotes are almost always
single-celled, microscopic
organisms. Their DNA is
found in a single circular
structure. They usually
have an outer cell wall.
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Cell Types: Prokaryotic and Eukaryotic
• Eukaryotic cells have a nucleus and may be
single-celled or multicellular. They
– have their DNA inside the nucleus.
– have linear chromosomes.
– have various organelles.
– are larger than prokaryotic cells.
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The Microscope
• Light microscopes allow people to view cells and
make out the larger features within them.
• Electron microscopes allow people to view even
smaller structures within cells.
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The Microscope
Light microscope
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The Microscope
Electron microscope
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Tour of a Eukaryotic Cell
• Eukaryotic cells contain many parts, including:
– Cell membrane
– Nucleus
– Cytoplasm
– Cytoskeleton
– Organelles
• All the parts of the
cell have specific
functions.
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Tour of a Eukaryotic Cell
• Plant cells also contain
– a cell wall to make the cell rigid.
– chloroplasts that perform photosynthesis.
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Eukaryotic Cell Structures
Eukaryotic Cell Structures
Structures within a eukaryotic cell that perform
important cellular functions are known as organelles.
Cell biologists divide the eukaryotic cell into two major
parts: the nucleus and the cytoplasm.
The Cytoplasm is the portion of the cell outside the
nucleus.
Eukaryotic Cell Structures
Plant Cell
Nucleolus
Nucleus
Smooth
endoplasmic
reticulum
Nuclear envelope
Ribosome (free)
Rough endoplasmic
reticulum
Ribosome
(attached)
Golgi
apparatus
Cell wall
Cell membrane
Chloroplast
Mitochondrion
Vacuole
Eukaryotic Cell Structures
Animal Cell
Nucleolus
Smooth endoplasmic
reticulum
Nucleus
Nuclear envelope
Rough
endoplasmic
reticulum
Ribosome (free)
Cell membrane
Ribosome
(attached)
Centrioles
Mitochondrion
Golgi
apparatus
Nucleus
What is the function of the nucleus?
Nucleus
Nucleus
The nucleus is the control center of the cell.
The nucleus contains nearly all the cell's DNA
and with it the coded instructions for making
proteins and other important molecules.
Nucleus
The Nucleus
Chromatin
Nucleolus
Nuclear envelope
Nuclear pores
Ribosomes
What is the function of the ribosomes?
Ribosomes
Ribosomes
One of the most important jobs carried out in the
cell is making proteins.
Proteins are assembled on ribosomes.
Ribosomes are small particles of RNA and protein
found throughout the cytoplasm.
Endoplasmic Reticulum
What is the function of the endoplasmic
reticulum?
Endoplasmic Reticulum
There are two types of ER—rough and smooth.
Endoplasmic Reticulum
Ribosomes
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Golgi Apparatus
What is the function of the Golgi apparatus?
Golgi Apparatus
The Golgi apparatus appears as a stack of closely
apposed membranes.
Golgi Apparatus
What is the function of lysosomes?
Vacuoles
What is the function of vacuoles?
Vacuoles
In many plant cells there
is a single, large central
vacuole filled with liquid.
Vacuole
Vacuoles
Vacuoles are also found
in some unicellular
organisms and in some
animals.
The paramecium contains
a contractile vacuole
that pumps excess water
out of the cell.
Contractile vacuole
Mitochondria and Chloroplasts
What is the function of the mitochondria?
Mitochondria and Chloroplasts
Mitochondria
Nearly all eukaryotic cells
contain mitochondria.
Mitochondria convert the
chemical energy stored in
food into compounds that
are more convenient for the
cell to use.
Mitochondrion
Mitochondria and Chloroplasts
What is the function of chloroplasts?
Mitochondria and Chloroplasts
Chloroplasts
Chloroplast
Plants and some other
organisms contain
chloroplasts.
Chloroplasts capture
energy from sunlight and
convert it into chemical
energy in a process
called photosynthesis.
Cytoskeleton
What are the functions of the cytoskeleton?
Cytoskeleton
The cytoskeleton is a network of protein
filaments that helps the cell to maintain its
shape. The cytoskeleton is also involved in
movement.
The cytoskeleton is made up of:
• microfilaments
• microtubules
Cytoskeleton
Cytoskeleton
Cell membrane
Endoplasmic
reticulum
Microtubule
Microfilament
Ribosomes
Mitochondrion
Cytoskeleton
Centrioles are located near the nucleus and help
to organize cell division.
The Cell Membrane
• The cell membrane
– defines a cell's boundary.
– controls what moves into and out of the cell.
– consists of a phospholipid bilayer, membrane
proteins, and short carbohydrates.
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Cell Membrane
Cell Membrane
Outside of
cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside of cell
(cytoplasm)
Protein
channel
Lipid bilayer
The Cell Membrane
• The fluid mosaic model describes the structure
of the cell membrane, a mosaic of proteins and
phospholipids, almost all of which can move
fluidly around the membrane.
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Transport into and out of cells
• Cells take in many resources, including water,
oxygen, and organic molecules.
• Cells also discard wastes.
• Transport occurs through:
– Diffusion
– Facilitated diffusion
– Active transport
– Endocytosis and exocytosis
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Transport into and out of cells
• Diffusion is the tendency of molecules to move
from an area of high concentration to an area of
low concentration.
– Molecules diffuse
across the phospholipid
bilayer of the cell
membrane.
– Diffusion requires no
energy from the cell.
It is a form of passive
transport.
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Diffusion Through Cell Boundaries
Diffusion
Particles in a solution tend to move from an area
where they are more concentrated to an area
where they are less concentrated.
This process is called diffusion.
When the concentration of the solute is the same
throughout a system, the system has reached
equilibrium.
Diffusion Through Cell Boundaries
Osmosis
Osmosis
Osmosis is the diffusion of water through a selectively
permeable membrane.
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Osmosis
How Osmosis Works
Dilute sugar
solution
(Water more
concentrated)
Concentrated
sugar solution
(Water less
concentrated)
Sugar
molecules
Selectively
permeable
membrane
Movement of
water
Osmosis
Water tends to diffuse from a highly concentrated
region to a less concentrated region.
If you compare two solutions, three terms can be
used to describe the concentrations:
hypertonic (“above strength”).
hypotonic (“below strength”).
isotonic (”same strength”)
Osmosis
Osmotic Pressure
Osmosis exerts a pressure known as osmotic
pressure on the hypertonic side of a selectively
permeable membrane.
Transport into and out of cells
• Facilitated diffusion occurs when a transport
protein binds to a molecule and moves it down a
concentration gradient.
– Facilitated diffusion requires no energy from
the cell. It is a form of passive transport.
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Facilitated Diffusion
Glucose
molecules
Facilitated Diffusion
Protein
channel
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Transport into and out of cells
• Active transport occurs when a transport protein
moves a molecule against its concentration
gradient.
– Active transport requires energy from the cell.
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Active Transport
Active Transport
Sometimes cells move materials in the opposite
direction from which the materials would normally
move—that is against a concentration difference.
This process is known as active transport.
Active transport requires energy.
Active Transport
Molecular Transport
In active transport, small molecules and ions are
carried across membranes by proteins in the
membrane.
Energy use in these systems enables cells to
concentrate substances in a particular location,
even when diffusion might move them in the
opposite direction.
Active Transport
Molecular Transport
Molecule to be carried
Active
Transport
Transport into and out of cells
• Larger amounts of material can be transported
into and out of cells through endocytosis and
exocytosis.
– In endocytosis, a vesicle pinches off from the cell
membrane.
– In exocytosis, a vesicle fuses with the cell membrane.
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Active Transport
Endocytosis and Exocytosis
Endocytosis is the process of taking material into the
cell.
Two examples of endocytosis are:
– phagocytosis
– pinocytosis
During exocytosis, materials are forced out of the cell.
Cell Communication
• Cells communicate with one another using special
molecules.
• Communication between adjacent cells occurs when
molecules move from one cell to another through special
"doorways."
– Animal cells have gap junctions.
– Plant cells have plasmodesmata.
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Cell Communication
• Long-distance communication relies on
message molecules traveling through the
bloodstream.
– Receptors are membrane proteins.
– A receptor binds a message molecule with a
lock-and-key fit.
– The binding of the receptor to a message
molecule initiates a series of chemical
reactions that results in the target cell's
response to the message.
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Cell Communication
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How Cells Reproduce
• In mitosis, one parent cell divides
into two daughter cells that have
the same genetic information as
the parent cell.
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How Cells Reproduce
• A dividing cell goes through the stages of the
cell cycle: gap 1, synthesis, gap 2, and mitosis
and cytokinesis.
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The Cell Cycle
Cell Cycle
The cell cycle is the series of events that cells go
through as they grow and divide.
Interphase is the period of growth that occurs
between cell divisions.
The Cell Cycle
During the cell cycle:
• a cell grows
• prepares for division
• divides to form two daughter cells, each of
which begins the cycle again
The Cell Cycle
The cell cycle consists of four phases:
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G1 (First Gap Phase)
S Phase
G2 (Second Gap Phase)
M Phase
Events of the Cell Cycle
Events of the Cell Cycle
During G1, the cell
– increases in size
– synthesizes new proteins and organelles
Events of the Cell Cycle
During the S phase,
• chromosomes are replicated
• DNA synthesis takes place
Once a cell enters the S phase, it usually
completes the rest of the cell cycle.
Events of the Cell Cycle
The G2 Phase (Second Gap Phase)
• organelles and molecules required for cell division
are produced
• Once G2 is complete, the cell is ready to start the
M phase—Mitosis
Events of the Cell Cycle
Cell Cycle
How Cells Reproduce
• The phases of mitosis:
– Prophase: Chromosomes condense, and
nuclear membranes break down.
– Metaphase: Chromosomes line up along the
equatorial plane.
– Anaphase: Sister chromatids are pulled apart
and move to opposite poles of the cell.
– Telophase: New nuclear membranes form
around each set of chromosomes.
• After mitosis, cytokinesis occurs: The cytoplasm
divides, completing cell division.
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How Cells Reproduce
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How Cells Use Energy
• Two things are necessary for a chemical
reaction to occur:
– Must be consistent with the law of
conservation of energy.
• Exothermic (energy-releasing) reactions occur
spontaneously.
• For all other reactions, cells rely on usable energy
stored in molecules of ATP.
– Activation energy needed for initial breaking
of bonds.
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How Cells Use Energy
• ATP provides energy for chemical reactions in
cells.
• Cells obtain energy from ATP when one
phosphate group is removed, leaving ADP.
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How Cells Use Energy
• Cells eventually turn ADP back into ATP by
adding a phosphate group during cellular
respiration.
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How Cells Use Energy
• The sodium-potassium pump uses active
transport to control the levels of sodium ions
(Na+) and potassium ions (K+) in cells. This
process uses one molecule of ATP.
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How Cells Use Energy
• Reacting molecules must collide with an
activation energy that is needed for the initial
breaking of bonds.
• The activation energy for many essential
chemical reactions is very high.
• A catalyst is a substance that lowers the
activation energy, allowing a reaction to happen
more quickly.
• The catalysts in cells are enzymes—large,
complex proteins.
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How Cells Use Energy
• An enzyme binds the reactants at its active site
and releases the products.
• In the process, the enzyme is not altered or
destroyed; it can be used again and again.
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How Cells Use Energy
• Cells regulate enzymes
– Cells control the synthesis and degradation of
enzymes.
– Enzyme function depends on temperature,
pH, and other features of the environment.
– Inhibitors can block the function of enzymes.
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How Cells Use Energy
• Two types of enzyme inhibition
– In competitive
inhibition, the
inhibitor binds
to the active site
of an enzyme so
that the enzyme
cannot bind its
substrate.
– Noncompetitive inhibition occurs when an inhibitor
binds to a different part of the enzyme, changing the
active site so that the enzyme can no longer bind to
its substrate.
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Photosynthesis
• The process organisms use to convert light energy from
the Sun into chemical energy.
• Conducted in the chloroplasts of plants.
• Occurs in two stages: the light-dependent reactions and
the light-independent reactions.
• Photosynthesis is the ultimate source of (practically) all
organic molecules on Earth.
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The Photosynthesis Equation
The Photosynthesis Equation
The equation for photosynthesis is:
6CO2 + 6H2O
C6H12O6 + 6O2
Light
carbon dioxide + water
sugars + oxygen
Light
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The Photosynthesis Equation
Photosynthesis uses the energy of sunlight to
convert water and carbon dioxide into highenergy sugars and oxygen.
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The Photosynthesis Equation
Light energy
Light-Dependent
Reactions
(thylakoids)
H2O
ADP
+
NADP
Sugar
O2
ATP
NADPH
Calvin Cycle
(stroma)
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CO2
+
H20
Light and Pigments
What is the role of light and chlorophyll in
photosynthesis?
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Light and Pigments
Light and Pigments
How do plants capture the energy of sunlight?
In addition to water and carbon dioxide,
photosynthesis requires light and chlorophyll.
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Light and Pigments
Plants gather the sun's energy with light-absorbing
molecules called pigments.
The main pigment in plants is chlorophyll.
There are two main types of chlorophyll:
– chlorophyll a
– chlorophyll b
– Caratnoid
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Light and Pigments
Chlorophyll absorbs light well in the blue-violet and
red regions of the visible spectrum.
Estimated Absorption (%)
100
80
60
Chlorophyll b
Chlorophyll a
40
20
0
(nm)
400 450 Wavelength
500 550 600
650 700 750
Wavelength (nm)
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Light and Pigments
Chlorophyll does not absorb light will in the green
region of the spectrum. Green light is reflected by
leaves, which is why plants look green.
Estimated Absorption (%)
100
80
60
Chlorophyll b
Chlorophyll a
40
20
0
400 450 500 550 600 650 700 750
Wavelength (nm)
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Light and Pigments
Light is a form of energy, so any compound that
absorbs light also absorbs energy from that light.
When chlorophyll absorbs light, much of the energy
is transferred directly to electrons in the chlorophyll
molecule, raising the energy levels of these
electrons.
These high-energy electrons are what make
photosynthesis work.
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Photosynthesis
Light-dependent reactions
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Photosynthesis
• Light-independent reactions
– The light-independent reactions make use of
stored energy from the light-dependent
reactions.
– Carbon is fixed, moved from atmospheric CO2
to the sugar glucose.
– The molecules produced during
photosynthesis are used as a starting point for
building all of the macromolecules of life.
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Inside a Chloroplast
H2O
CO2
Light
NADP+
ADP + P
Lightdependent
reactions
Calvin
Calvin
cycle
Cycle
Chloroplast
O2
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Sugars