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CONCEPTS IN BIOLOGY
TWELFTH EDITION
Enger • Ross • Bailey
CHAPTER 4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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4.1 The cell theory


All living things are made of cells.
A cell
–
2
The basic unit of all living things.
The historical context of the cell
theory

Robert Hooke coined the
term “cell”.
–

Anton van Leeuwenhoek
–
–
3
Look at cork cells under a
simple microscope.
Made better microscopes
Used them to look at a variety
of substances and identified
animalcules (i.e., little
animals).
The historical context of the cell
theory

Mathias Jakob Schleiden (1838, German)
–

Theodor Schwann (1839, German)
–
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Concluded that all plants were made of cells
Concluded that all animals were made of cells
Initial observations of cells


Cell wall
– Outer non-living part of
plant cells
Protoplasm
– Interior living portion of
the cell
– Nucleus
 Contains the genetic
information of the cell
– Cytoplasm
 Fluid part of the
protoplasm
– Organelles
 “Little organs” within
the protoplasm
Different kinds of cells


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Prokaryotic
– Structurally simple cells
– Lack a nucleus
– Lack most other organelles
– Bacteria
Eukaryotic cells
– More complex
– Have a nucleus
– Have a variety of organelles
– Plants, animals, fungi, protozoa and algae
Major cell types
4.2 Cell size

Prokaryotic cells
–

1-2 micrometers in
diameter
Eukaryotic cells
–
10-200 micrometers in
diameter
Surface area to volume ratio

Cell size is limited.
–
–
–
Cells must get all of their nutrients from their environment
through their cell membranes.
Volume increases more quickly than surface area.
Surface area-to-volume ratio must remain small (because
metabolic and nutrition requirements). A few exceptions,
please see page 72.
4.3 The structure of cell membranes

Cell membranes
–

Thin sheets composed of phospholipids and
proteins
Fluid-mosaic model
–
Two layers of phospholipids

Fluid
–
–

Mosaic
–
12
Has an oily consistency
Things can move laterally within the bilayer.
Proteins embedded within the phospholipid bilayer
The phospholipid bilayer

Phospholipid structure
–
–

Bilayer
–
–

Hydrophobic tails of each
layer associate with each
other.
Hydrophilic heads on the
surface of the bilayer
Cholesterol
–
–
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Hydrophobic tails
Hydrophilic heads
–
Hydrophobic
Found within the
hydrophobic tails
Keeps the membrane
flexible
Membrane proteins


Some are on the surface.
Some are partially
embedded.
–

Some are completely
embedded.
–

Protrude from both sides
Functions
–
–
14
Protrude from one side
–
Transport molecules across
the membrane
Attachment points for other
cells
Identity tags for cells
4.4 Organelles composed of
membranes







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Plasma membrane (cell membrane)
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Peroxisomes
Vacuoles and vesicles
Nuclear membrane
The plasma membrane



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Composed of a single phospholipid bilayer
Separates the contents of the cell from the external
environment
Important features
– Metabolic activities (See p. 73)
– Moving molecules across the membrane (p. 73)
– Structurally different inside and outside (p. 73)
– Identification: Self vs. nonself (p. 73-74)
– Attachment sites (p. 74)
– Signal transduction (p. 75)
The endoplasmic reticulum


A set of folded membranes and tubes throughout the
cell.
Provides a large surface area for important chemical
reactions.
–

Because it is folded, it fits into a small space.
Two types of ER
–
–
Rough
 Has ribosomes on its surface
– Sites of protein synthesis (Proteinmanufacturing machine, e.g. pancreas cell, p.
75)
Smooth
 Lacks ribosomes
 Metabolizes fats
 Detoxifies damaging chemicals
e.g. Human liver (p. 75)
Figure 4.9
The Golgi apparatus


Stacks of flattened
membrane sacs.
Functions
–
–
–
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Modifies molecules that
were made in other
places.
Manufactures some
polysaccharides and
lipids.
Packages and ships
molecules.
Traffic through the Golgi
–
–
–
Vesicles bring molecules from the ER that contain
proteins.
Vesicles fuse with the Golgi apparatus.
The Golgi finishes the molecules and ships them
out in other vesicles.



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Some are transported to other membrane structures.
Some are transported to the plasma membrane.
Some vesicles become lysosomes. (p. 77)
Lysosomes

Vesicles containing enzymes that digest
macromolecules.
–
–
–
–

Carbohydrates
Proteins
Lipids
Nucleic acids
Interior contains low pH
– These enzymes only work at pH=5.
– The cytoplasm is pH=7.

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If the lysosome breaks open, these enzymes will
inactivate and will not damage the cell.
Functions of lysosomes


Digestion
– of food taken into
the cell
Destruction
– Disease-causing
organisms (p. 77)
– Old organelles
Peroxisomes

Contain the enzyme catalase
–
–
–
–
24
Breaks down hydrogen peroxide (H2O2)
Breaks down long-chain fatty acids
Synthesizes cholesterol and bile salts
Synthesizes some lipids
Vacuoles and vesicles



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Membrane-enclosed sacs
Vacuoles
– Larger sacs
– Contractile vacuoles
 Forcefully expel excess water from the
cytoplasm
Vesicles
– Smaller vesicles
The nuclear membrane




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Separates the genetic
material from the rest of
the cell
Filled with nucleoplasm
Composed of two
bilayers
Contains holes called
nuclear pore complexes
– Allow large
molecules like RNA
to pass through the
membrane into the
cytoplasm
Interconversion of membranes

27
Membranes are converted from one membranous
organelle to another.
Energy converting organelles

28
Mitochondrion(See p.78)
– A small bag with a large
bag stuffed inside.
– Larger internal bag is
folded into cristae.
 Cristae contain
proteins for cellular
respiration.
– Releases the
energy from food
– Requires oxygen
– Uses the energy
to make ATP
(See Ch.6)
Energy converting organelles

Chloroplasts
–
–
–
–
–
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Saclike organelle
Contain chlorophyll
Perform photosynthesis
 Uses the energy in light
to make sugar
Contain folded membranes
called thylakoids
 Thylakoids stacked into
grana
 Thylakoids contain
chlorophyll and other
photosynthetic proteins.
Thylakoids surrounded by
stroma (See p. ch.7)
Nonmembranous organelles





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Ribosomes
Cytoskeleton
Centrioles
Cilia flagella
Inclusions
Ribosomes


Made of RNA and proteins
(p.79)
Composed of two subunits
–
–


Are the sites of protein
production (p.80)
Found in two places
–
–
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Large
Small (p.79-80)
Free floating in the
cytoplasm (p.80)
Attached to endoplasmic
reticulum (p.80)
Cytoskeleton


Provides shape,
support and
movement
Made up of
–
–
–
Microtubules (p.81)
Microfilaments
(p.81)
Intermediate
filaments (p.81)
Centrioles



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Two sets of microtubules
arranged at right angles to
each other.
Located in a region called
the centrosome.
– Microtubule-organizing
center near nucleus.
Organize microtubules
into spindles used in
cell division.
Cilia and Flagella (See p.82)


Hair-like projections extending from the cell.
Flagella
–
–

Cilia
–
–

34
Long and few in number
Move the cell through its environment
Small and numerous
Move the environment past the cell
9 + 2 arrangement of microtubules
Inclusions

Collections of miscellaneous materials
–

35
Can be called granules (p. 82)
Temporary sites for the storage of nutrients and
waste (p. 82)
Nuclear components (p. 82-84)

Contains chromatin
–
–


Surrounded by nuclear
membrane
Contains one or more
nucleoli
–

Site of ribosome synthesis
Contains nucleoplasm
–
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DNA + proteins
Becomes condensed during
cell division into
chromosomes.
Water, nucleic acids, etc.
Getting through membranes (p. 84)






37
Diffusion
Facilitated diffusion
Osmosis
Active transport
Endocytosis
Exocytosis
Diffusion


Molecules are in constant,
random motion.
Molecules move from
where they are most
concentrated to where
they are less
concentrated.
–
–
38
This is called diffusion.
Involves a concentration
gradient (diffusion
gradient)
 No concentration
gradient=dynamic
equilibrium
The rate of diffusion

39
Depends on
– The size of the molecule
 Smaller molecules diffuse faster.
– The size of the concentration
gradient
 The greater the concentration
difference, the faster the diffusion.
Diffusion across membranes


Diffusion can only happen if there is no
barrier to the movement of molecules.
Can only happen across a membrane if the
membrane is permeable to the molecule
–
–
40
Membranes are semi-permeable; they only allow
certain molecules through.
Membrane permeability depends on the
molecules size, charge and solubility.
The direction of diffusion



41
Determined solely by
the concentration
gradient.
Diffusion is passive that
does not require energy
input.
Example:
– Oxygen diffusion
(p. 85)
Osmosis



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The diffusion of water
through a selectivelypermeable membrane.
Occurs when there is a
difference in water
concentration on
opposite sides of the
membrane.
Water will move to the
side where there is less
water
–
Or more solute
Hypertonic vs. hypotonic (p. 86)

If a cell has less water (more solute) than its
environment
–

If a cell has more water (less solute) than its
environment
–

It is hypotonic to its surroundings.
If a cell has equal amounts of water (and solute) as
its environment
–
43
It is hypertonic to its surroundings.
It is isotonic to its surroundings.
Physiological relevance of osmosis
44
Osmosis in animal and plant cells
45
Facilitated diffusion

Some molecules have
to be carried across the
membrane.
–

Still involves diffusion
–
–
–
46
Accomplished by carrier
proteins
Follows a concentration
gradient
Is passive transport
Example (glucose, p.88)
Active transport





Opposite of diffusion
Moves molecules across a
membrane UP their
concentration gradient
Uses transport proteins in
the membrane
– Specific proteins pump
specific molecules
Requires the input of energy
Example (Na and K ion, p.
88)
Endocytosis

Moves large molecules or sets of molecules into the
cell
–
–
–
48
Phagocytosis
 Cell eating
 Food engulfed by the membrane
 Material enters the cell in a vacuole.
Pinocytosis
 Cell drinking
 Just brings fluid into the cell
Receptor-mediated endocytosis
 Molecules entering the cell bind to receptor proteins first
Exocytosis


Moves large molecules or sets of molecules
out of the cell.
Vesicles containing the molecules to be
secreted fuse with the plasma membrane.
–
49
Contents are dumped outside the cell.
Endocytosis and exocytosis
50
Prokaryotic cells

51
Two different types of
prokaryotes
– Domain eubacteria
 Contains bacteria
– Domain archaea
 Contains
prokaryotes that
live in extreme
environments
Prokaryotic cell structure

Contain DNA and enzymes
–
–

Able to reproduce
Engage in metabolism
Surrounded by a plasma membrane
–
Plasma membrane surrounded by a cell wall

–
Cell wall surrounded by a capsule




52
Maintains the shape of the cell
Helps them adhere to hosts
Protects them from destruction
Contain ribosomes (Example p. 90 of Antibiotics)
May contain flagella
–
Facilitates movement
Different types of eukaryotic cells
53
Summary of cell organelles and their
functions
54