Download PP Chapter 15 Text

Hewitt/Lyons/Suchocki/Yeh
Conceptual Integrated
Science
Chapter 15
THE BASIC UNIT OF LIFE—
THE CELL
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This lecture will help you
understand:
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Characteristics of Life
Macromolecules Needed for Life
Cell types
Tour of a Eukaryotic Cell
Cell Membrane Structure and Function
Transport Mechanisms: Diffusion, Facilitated Diffusion, Active Transport,
Endocytosis, Exocytosis
Cellular Communication
How Cells Reproduce
How Cells Use Energy
Chemical Reactions in Cells
Photosynthesis
Cellular Respiration: Glycolysis, Krebs Cycle, Electron Transport, Fermentation
Life Span of Cells
History of Science: Cell Theory
Math Connection: Diffusion
Science and Society: Stem Cells
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Characteristics of Life
All living things
• use energy
• develop and grow
• maintain themselves
• can reproduce
• are part of evolving populations
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Characteristics of Life
All living things use energy.
• Plants use electromagnetic energy from
sunlight.
• Animals convert food energy from plants
or other animals into chemical energy.
• 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 also maintain themselves.
• They build structures (bones, stems).
• They repair damage (immune system).
• They maintain an internal environment that
is consistent (body temperature, ion
balance).
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Characteristics of Life
All living things are capable of reproducing.
• Asexual reproduction occurs when an organism
reproduces by itself.
• Sexual reproduction occurs when organisms produce
sperm and eggs that join to form new individuals.
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Characteristics of Life
All living things are part of populations that
evolve.
• Populations do not remain constant.
• Populations change over time, across
generations.
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Macromolecules Needed for
Life
Proteins
Carbohydrates
Lipids
Nucleic acids
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Cell Types
Prokaryotic cells have no nucleus.
Prokaryotes are almost always single-celled
microscopic organisms. Their DNA is found in
a single circular chromosome. They usually
have an outer cell wall.
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Cell Types
Eukaryotic cells have a nucleus and may be single celled
or multicellular. They
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contain their DNA inside the nucleus
have linear chromosomes
contain organelles
are larger cells than prokaryotes
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Tour of a Eukaryotic Cell
Eukaryotic cells contain many parts, including
• cell membrane
• nucleus
• cytoplasm
• cytoskeleton
• organelles
All of the parts of the cell have specific functions.
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Tour of a Eukaryotic Cell
Plant cells also contain
• cell walls to make the cell rigid
• chloroplasts that perform photosynthesis
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CellMembrane Structure and
Function
The cell membrane
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defines the cell’s border.
controls what travels into and out of the cell.
functions in communicating with other cells.
consists of a phospholipid bilayer, membrane proteins,
and short carbohydrates.
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CellMembrane Structure and
Function
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 Mechanisms
Cells take in many materials, including water,
oxygen, and organic molecules, and discard
wastes such as carbon dioxide. Transport
occurs through
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Diffusion
Facilitated diffusion
Active transport
Endocytosis
Exocytosis
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Transport Mechanisms:
Diffusion
Diffusion is the tendency of molecules to move from
an area of high concentration to an area of low
concentration.
Diffusion results from the random motion of molecules
and requires no energy.
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Transport Mechanisms:
Diffusion
Diffusion occurs most efficiently (that is,
most rapidly and effectively) across small
distances, large surface areas, and thin
structures.
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Transport Mechanisms: Facilitated
Diffusion
Facilitated diffusion occurs when carrier proteins
bind to molecules and move them down a
concentration gradient, to an area of lower
concentration.
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Transport Mechanisms: Active
Transport
Active transport moves molecules against
a concentration gradient, in a direction
they would not go without an input of
energy.
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Transport Mechanisms:
Endocytosis
Cells use endocytosis when they capture material
in a section of cell membrane that pinches off to
form a vesicle. This is how some white blood
cells engulf invading bacteria.
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Transport Mechanisms: Exocytosis
In exocytosis, a vesicle fuses to the cell membrane and
dumps its contents outside of the cell.
The endocrine system releases some hormones into the
bloodstream using exocytosis.
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Cellular Communication
Cells communicate with each other via molecular
messengers.
Communication between adjacent cells occurs in animals
via gap junctions, which are like doorways between
cells. In plants, plasmodesmata serve as the doorways.
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Cellular Communication
Long-distance communication relies on message
molecules traveling through a medium such as
the bloodstream.
Like a key in a lock, the message molecule
eventually finds the right receptor. The key
fitting into the lock sets off a series of chemical
reactions that cause the target cell’s response.
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Cellular 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.
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How Cells Reproduce
Mitosis is part of the cell cycle. During the rest of
the cell cycle, called interphase, the cell grows,
copies its genetic material (DNA), and builds the
machinery necessary for division.
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How Cells Reproduce
• In prophase, the chromosomes condense, and
nuclear membranes break down.
• In metaphase, the chromosomes line up along
the equatorial plane.
• During anaphase, the sister chromatids are
pulled apart and move to opposite poles of the
cell.
• In telophase, new nuclear membranes form
around each set of chromosomes.
• After mitosis, the cytoplasm divides
(cytokinesis), and cell division is complete.
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How Cells Reproduce
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How Cells Use Energy
• Energy-releasing reactions occur
spontaneously. This is consistent with the
laws of physics.
• For all other reactions, cells rely on the
energy of ATP to power them.
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How Cells Use Energy
Even energy-releasing reactions have an
activation energy that is necessary for
them to happen. A catalyst is a substance
that lowers this 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 to a specific reactant at the
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 control enzyme function by synthesizing and
degrading enzymes as necessary.
In addition, inhibitors can block the function of
enzymes.
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How Cells Use Energy
• 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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Chemical Reactions in Cells
• ATP is the energy currency of the cell.
• In the ATP reaction, one phosphate group is
removed, leaving ADP. Removing the phosphate
group releases energy.
• Organisms use some of the energy they take in
through food to make more ATP.
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Chemical Reactions in Cells
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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Photosynthesis
• Is the process organisms use to convert light energy
from the sun into chemical energy
• Is conducted in the chloroplasts of plants
• Occurs in two stages: the light-dependent reactions
and the light-independent reactions
• Is the ultimate source of all food on Earth
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Photosynthesis
The light-dependent reactions of
photosynthesis
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Photosynthesis
In the light-independent reactions:
• The light-independent reactions use the
stored energy from ATP and NADPH.
• Carbon is fixed, moved from atmospheric
CO2 to the sugar glucose.
• These materials are the basis for all of the
macromolecules of life.
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Cellular Respiration
Cells break down glucose to produce ATP.
This process is aerobic (uses oxygen).
This process yields 38 molecules of ATP
from every molecule of glucose.
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Cellular Respiration
Cellular respiration occurs in three steps:
• Glycolysis
• The Krebs cycle
• Electron transport
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Cellular Respiration: Glycolysis
Glycolysis takes place in the cytoplasm of
cells.
The glucose molecule is split into two
molecules of pyruvic acid, releasing two
molecules of ATP.
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Cellular Respiration: Krebs
Cycle
The Krebs cycle occurs in the cell’s mitochondria.
In the Krebs cycle, pyruvic acid is converted to
acetic acid and bound to a molecule of
coenzyme A. The result—acetyl-CoA—is broken
down into CO2.
Two molecules of ATP are harvested. Additional
energy is stored in the molecules NADH and
FADH2.
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Cellular Respiration: Electron
Transport
• Electrons carried by NADH and FADH2 are sent
down electron transport chains.
• In the process, the electrons lose energy, which
is used to pump hydrogen ions across a
membrane inside the mitochondria.
• At the end of the chain, the electrons combine
with O2 to make water.
• The concentration gradient generated by
pumping hydrogen ions is used to make ATP.
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Cellular Respiration:
Fermentation
In certain cells, under certain conditions, glycolysis is
followed by fermentation. Fermentation uses no oxygen
and generates no ATP. But, it regenerates the molecules
necessary to keep glycolysis going, so cells can continue
to obtain energy through glycolysis.
Lactic acid fermentation occurs in muscle cells when there
is not enough oxygen for cellular respiration to continue.
Alcoholic fermentation by yeast is used to make beer and
wine.
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Life Span of Cells
• Most eukaryotic cells can live for a certain
number of cell divisions, not a specific
length of time.
• Telomeres, lengths of DNA at the ends of
chromosomes, get shorter with every cell
division.
• Eventually, the cell can no longer divide
without losing critical genetic information.
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Life Span of Cells
• Some cells contain a special enzyme—
telomerase—that lengthens telomeres.
• These cells can divide indefinitely.
• Germ cells—those that produce eggs and
sperm—contain telomerase and are
immortal.
• Some tumor cells also contain a lot of
telomerase and can divide indefinitely.
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History of Science: Cell Theory
• In 1665, Hooke found chambers (actually
dried cell walls) in cork and named them
cells.
• Van Leeuwenhoek was the first to
describe many types of living cells.
• The central importance of cells was not
established until the late 1800s.
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History of Science: Cell Theory
The cell theory states:
• All living things are made up of one or
more cells.
• All cells come from other cells.
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Math Connection: Diffusion
For a cell with a radius of 1 micrometer,
Surface area
4πr2
4 π(1)2
4π
=3
=
=
=
3
3
Volume
4/3 π r
4/3 π(1)
4/3 π
For a cell with a radius of 2 micrometers,
Surface area
4 π r2
4 π(2) 2
4 π (4)
=
=
=
= 1.5
3
3
Volume
4/3 π r
4/3 π(2)
4/3 π (8)
For a cell with a radius of 3 micrometers,
Surface area
4 π r2
4 π(3) 2
4 π (9)
=1
=
=
=
3
3
Volume
4/3 π r
4/3 π(3)
4/3 π (27)
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Science and Society: Stem Cells
Embryonic stem cells come from human
embryos that have yet to differentiate into
distinct types of cells. These cells have the
capacity to develop into all of the kinds of
cells in the body.
Although stem cells have great promise for
treating many conditions, the use of
human embryos is controversial.
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