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Chapter 7
Cell Structure and Function
Ch 7-1 Life is Cellular
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•
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Goals:
Explain the Cell Theory
Describe how researchers explore living cells
Distinguish between eukaryotes and
prokaryotes
Discovery of the Cell
• Cells- basic units of life
• Robert Hooke (1665)- first to use the term cell while
looking at cork cells using compound microscope
• Anton van Leeuwenhoek (1674) uses single lens
microscope to see microorganisms
• Matthias Schleiden (1838) concludes all plants are
made of cells
• Theodor Schwann (1839) concludes all animals are
made of cells
• Rudolph Virchow (1855) proposes all cells come from
existing cells
Cell Theory
• These observations led to Cell Theory:
– All living things are composed of cells
– Cells are the basic unit of structure and function in
living things
– All cells come from existing cells
Improved Cell Exploration
• Compound light microscope- magnify up to
1000x
– Staining can improve visibility of organelles
– Fluorescent staining may also be used
• Confocal light microscope- scans cells with laser
beam to make 3-D images
• Electron microscopes- magnify up to 100,000x
and resolve biological structures as small as 2
nanometers and
– gave biologists the ability to see with great clarity the
structures that make up cells
Figure 4.1B
10 m
100 mm
(10 cm)
Length of
some nerve
and muscle
cells
Chicken
egg
10 mm
(1 cm)
Unaided eye
Human height
1m
Frog egg
10 m
1 m
100 nm
Most plant and
animal cells
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosome
10 nm
Proteins
Lipids
1 nm
0.1 nm
Small molecules
Atoms
Electron microscope
100 m
Paramecium
Human egg
Light microscope
1 mm
Figure 4.1B_2
Frog egg
10 m
1 m
100 nm
Most plant and
animal cells
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosome
10 nm
Proteins
Lipids
1 nm
0.1 nm
Small molecules
Atoms
Electron microscope
100 m
Paramecium
Human egg
Light microscope
1 mm
Figure 4.1B_3
Types of Electron Microscopes
• Transmission electron microscopes (TEMs)
pass a beam of electron through a thin
specimen
• Scanning electron microscopes (SEMs) scan a
beam of electrons over the surface of a
specimen
– Create excellent 3-D images
• Specimens from electron microscopy are
viewed in a vacuum, are preserved and
dehydrated, so living cells cannot be viewed
New Microscope Technology
• Scanning probe microscopes- trace surface of
specimens with fine probe while electronically
recording the position
Prokaryotes and Eukaryotes
Prokaryotes
• Cell membrane
• DNA (coiled into a region
called the nucleoid)
• Cytoplasm
• Ribosomes
• No true organelles
• Generally smaller than
eukaryotes
• Bacteria
Eukaryotes
• Cell membrane
• Nucleus (a membrane
surrounds the DNA)
• Cytoplasm
• Generally larger and more
complex
– Contain dozens of structures
(including ribosomes) and
internal membranes
• Highly specialized
– Single celled protists, RBC,
etc.
Figure 4.3
Fimbriae
Ribosomes
Nucleoid
Plasma membrane
Cell wall
Bacterial
chromosome
A typical rod-shaped
bacterium
Capsule
Flagella
A TEM of the bacterium
Bacillus coagulans
Ch 7-2 Eukaryotic Cell Structure
• Goals:
– Describe the function of the nucleus
– Describe the function of major cell organelles
– Identify main roles of cytoskeleton
Eukaryotic Cell Structures
• The structures and organelles of eukaryotic cells
can be organized by their basic functions
Rough
Smooth
endoplasmic endoplasmic
reticulum
reticulum
NUCLEUS:
Nuclear
envelope
Chromatin
Nucleolus
NOT IN MOST
PLANT CELLS:
Centriole
Lysosome
Peroxisome
Ribosomes
Golgi
apparatus
CYTOSKELETON:
Microtubule
Intermediate
filament
Microfilament
Mitochondrion
Plasma membrane
Figure 4.4B
NUCLEUS:
Nuclear envelope
Chromatin
Nucleolus
Golgi
apparatus
NOT IN ANIMAL
CELLS:
Central vacuole
Chloroplast
Cell wall
Plasmodesma
Mitochondrion
Peroxisome
Plasma membrane
Cell wall of
adjacent cell
Rough
endoplasmic
reticulum
Ribosomes
Smooth
endoplasmic
reticulum
CYTOSKELETON:
Microtubule
Intermediate
filament
Microfilament
Cytoplasm
• Clear, gelatinous fluid inside of the cells
– Organelles are suspended in this jelly-like matrix
Nucleus
• Central, membrane-bound organelle that
contains DNA (in the form of chromatin) which
controls cellular functions
• Contains directions to make proteins
– Therefore controls activity of all other organelles
• Membrane is a porous, double-membrane
referred to as the nuclear envelope
Chromatin (in nucleus)
• Like a tangled ball of yarn in the nucleus
• Becomes organized into chromosomes just
before a cell divides
Nucleolus
• Prominent organelle within the nucleus
– Appears as a prominent dark area in the nucleus
• Assembly of ribosomes begins
Figure 4.5
Two membranes
of nuclear envelope
Chromatin
Nucleolus
Pore
Endoplasmic
reticulum
Ribosomes
Nucleus
Ribosomes (rRNA)
• Sites where the cell produces proteins
according to directions of DNA
• Simple structure made of RNA and protein
• Must leave the nucleus and enter cytoplasm
to make proteins
– A DNA copy with instructions for making proteins
is sent to a ribosome in the cytoplasm or one
attached to the ER
Figure 4.6
Ribosomes
ER
Cytoplasm
Endoplasmic
reticulum (ER)
Free ribosomes
Bound
ribosomes
Colorized TEM showing
ER and ribosomes
mRNA
Protein
Diagram of
a ribosome
Endoplasmic Reticulum (ER)
• Highly-folded membranes make up the ER
– Allows for lots of surface area for chemical reactions
to take place
– Fits into a compact space
• Rough ER has ribosomes imbedded in surface
– Newly made proteins leave the ribosome and are
inserted into the ER where they are chemically
modified
• Smooth ER has no ribosomes
– Produces enzymes responsible for the synthesis of
membrane lipids and detoxification of drugs (liver
cells)
Nuclear
envelope
Smooth ER
Ribosomes
Rough ER
Transport vesicle
buds off
4
Secretory
protein
inside transport vesicle
mRNA
Ribosome
3
Sugar
chain
1
2
Polypeptide
Glycoprotein
Rough ER
Golgi Apparatus
• Made of a series of tubular membranes
• Receives proteins synthesized on ribosomes of
the ER
• Modifies the proteins
• Then sorts and packs them into vesicles for
secretion or to be shipped to other parts of
the cell
Lysosomes
• Contain digestive enzymes
– Digest excess or worn out organelles, food
particles (lipids, carbohydrates, and proteins),
engulfed viruses, or bacteria
• Membrane prevents enzymes from leaking
out, but membrane can fuse with vacuole to
digest its contents
• Lysosomes can ingest the cell itself
Digestive
enzymes
Lysosome
Plasma membrane
Digestive
enzymes
Lysosome
Food vacuole
Plasma membrane
Digestive
enzymes
Lysosome
Food vacuole
Plasma membrane
Digestive
enzymes
Lysosome
Digestion
Food vacuole
Plasma membrane
Lysosome
Vesicle containing
damaged mitochondrion
Lysosome
Vesicle containing
damaged mitochondrion
Lysosome
Digestion
Vesicle containing
damaged mitochondrion
Vacuoles
• Vacuoles are large vesicles that have a variety of
functions.
– Can store water, salts, proteins, and carbohydrates
• Large, central vacuole in plants gives plant turgor pressure
– Some protists have contractile vacuoles that help to
eliminate water
– In plants, vacuoles may
• have digestive functions,
• contain pigments, or
• contain poisons that protect the plant.
Contractile
vacuole
Nucleus
Central vacuole
Chloroplast
Nucleus
Mitochondria
• Mitochondria are organelles that carry out
cellular respiration in nearly all eukaryotic cells.
• Cellular respiration converts the chemical energy
in foods to chemical energy in ATP (adenosine
triphosphate).
Mitochondria
• Mitochondria have two internal compartments.
1. The intermembrane space is the narrow region
between the inner and outer membranes.
2. The mitochondrial matrix contains
• the mitochondrial DNA,
• ribosomes, and
• many enzymes that catalyze some of the reactions of
cellular respiration.
Mitochondrion
Outer
membrane
Intermembrane
space
Inner
membrane
Cristae
Matrix
Chloroplasts
• Chloroplasts are the photosynthesizing
organelles of all photosynthesizing eukaryotes.
• Photosynthesis is the conversion of light energy
from the sun to the chemical energy of sugar
molecules (glucose).
Chloroplasts
• Chloroplasts are partitioned into compartments.
– Between the outer and inner membrane is a thin
intermembrane space.
– Inside the inner membrane is
• a thick fluid called stroma that contains the chloroplast
DNA, ribosomes, and many enzymes and
• a network of interconnected sacs called thylakoids.
• In some regions, thylakoids are stacked like poker chips.
Each stack is called a granum, where green chlorophyll
molecules trap solar energy.
Figure 4.14
Inner and
outer
membranes
Granum
Chloroplast
Stroma
Thylakoid
EVOLUTION CONNECTION: Mitochondria and
chloroplasts evolved by endosymbiosis
• Mitochondria and chloroplasts have
– DNA and
– ribosomes.
• The structure of this DNA and these ribosomes
is very similar to that found in prokaryotic cells.
• The endosymbiont theory proposes that
– mitochondria and chloroplasts were formerly small
prokaryotes and
– they began living within larger cells.
– Idea first suggested by biologist Lynn Margulis
Mitochondrion
Nucleus
Endoplasmic
reticulum
Some
cells
Engulfing
of oxygenusing
prokaryote
Engulfing of
photosynthetic
prokaryote
Chloroplast
Host cell
Mitochondrion
Host cell
Benefits of Membrane-bound Organelles
• Separates cell functions into distinct
compartments
– Allows chemical reactions to occur simultaneously
Cytoskeleton
• Network of tiny rods and filaments within the
cytoplasm that provides support and structure
for the cell
• Help anchor and support organelles
• Involved in movement
• Microtubules- thin hollow cylinders made of
protein
• Microfilaments- smaller, solid protein fibers
made of actin
Cytoskeleton
• Cells contain a network of protein fibers, called
the cytoskeleton, which functions in structural
support and motility.
• Scientists believe that motility and cellular
regulation result when the cytoskeleton
interacts with proteins called motor proteins.
Cytoskeleton
• The cytoskeleton is composed of three kinds of
fibers.
1. Microfilaments (actin filaments) support the cell’s
shape and are involved in motility.
2. Intermediate filaments reinforce cell shape and
anchor organelles.
3. Microtubules (made of tubulin) give the cell rigidity
and act as tracks for organelle movement.
Nucleus
Nucleus
Actin subunit
7 nm
Microfilament
Fibrous subunits
Tubulin subunits
10 nm
25 nm
Intermediate filament
Microtubule
Cilia and flagella move when microtubules bend
• While some protists have flagella and cilia that are
important in locomotion, some cells of multicellular
organisms have them for different reasons.
– Cells that sweep mucus out of our lungs have cilia.
– Animal sperm are flagellated.
Outer microtubule doublet
Central
microtubules
Radial spoke
Dynein proteins
Plasma membrane
Centrioles
• Play an important role in cell division
• Found in cells of animals and most protists
Ch 7-2 Cell Boundaries
• Goals:
• Identify the main functions of the cell
membrane and cell wall
• Describe what happens during diffusion
• Explain the processes of osmosis, facilitated
diffusion, and active transport
Cell Wall
• Fairly rigid structure located outside the
plasma membrane in some cells
– Plants, fungi, bacteria, and some protists
• Provides support and protection
• Composed of cellulose
• Very porous, so it is NOT selectively
permeable
– That is the job of the cell membrane
Cell Membrane
• Flexible phospholipid bilayer with proteins
responsible for maintaining homeostasis
• Surrounds all cells
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
phospholipid bilayer
Cell Membrane
•
•
•
•
Maintains homeostasis by:
Regulating what enters and leaves the cell
Also provides protection and support
Composed of a double-layered sheet called
the lipid bilayer which includes
– embedded and attached proteins in a structure
biologists call a fluid mosaic
Cell Membrane
• Fluid Mosaic Model
– Fluid: in motion
Outside
of cell
-Mosaic: “pattern” of
phospholipids and proteins
on cell surface
Carbohydrate
chains
Proteins
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
phospholipid bilayer
http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/bil.swf
Cell Membrane
• Many phospholipids are made from unsaturated
fatty acids that have kinks in their tails.
• These kinks prevent phospholipids from packing
tightly together, keeping them in liquid form.
• In animal cell membranes, cholesterol helps
stabilize the membranes
– prevent the fatty acid tails from sticking together
Cell Membranes
• Membranes may exhibit selective permeability,
allowing some substances to cross more easily than
others.
Diffusion
• Brownian motion- random movement of atoms and
molecules
– caused by their collisions with one another
• Diffusion is the net movement of molecules across a
concentration gradient
– Move from an area of high concentration to and area of
low concentration
– http://www.biosci.ohiou.edu/introbioslab/Bios170/diffusi
on/Diffusion.html
– Slow process because it relies on random motion of atoms
and molecules
• Diffusion does not require energy so it is referred to as
passive transport
• Eventually, the particles reach equilibrium where the
concentration of particles is the same throughout
Figure 5.3A
Molecules of dye
Membrane
Pores
Net diffusion
Net diffusion
Dynamic Equilibrium
Osmosis
• Diffusion of water across a membrane
Osmosis
• High concentration of water to low
concentration of water
• Fresh water to salt water
• http://www.stolaf.edu/people/giannini/flasha
nimat/transport/osmosis.swf
Hypotonic Solution
• ‘Hypo-’ means less
• Concentration of solute
(dissolved solids) is less
outside of cell than
inside
• Therefore a higher
concentration of water
outside the cell
• Water will enter cell
• Cell may lyse (burst)
• Cell wall prevents lysis in
plant cells
Hypertonic Solution
• ‘Hyper-’ means more
• Concentration of solute
is higher outside of cell
• Therefore a lower
concentration of water
outside the cell
• Water leaves the cell
• Results in plasmolysis in
plant cells
Isotonic Solution
• ‘Iso-’ means equal
• Solute concentration is
the same outside and
inside the cell
• Water moves in and out
of the cell but in equal
amounts
• No change in cell size
• Animals prefer this
When molecules don’t diffuse
• Some molecules diffuse easily
• Others do not because of their size, shape, or
polarity
Phospholipids
• Fatty acid tails are nonpolar
• Heads are polar
• Tails don’t want to be
near water because
water is polar
• Polar ♥ Polar
• Non-polar ≠ Polar
Proteins
• Transport Proteins- needed for the movement
of certain substances and waste materials
across the plasma membrane
• Channel or carrier
Facilitated Diffusion
• Hydrophobic substances easily diffuse across a
cell membrane.
• However, polar or charged substances do not
easily cross cell membranes and, instead, move
across membranes with the help of specific
transport proteins
• Process is called facilitated diffusion, which
– does not require energy and
– relies on the concentration gradient.
Active Transport
• Requires energy (ATP)
• Used for large molecules or substances
moving against their concentration gradient
(low to high)
Endocytosis and Exocytosis
• Endocytosis- taking materials
into the cell by means of
infolding of membrane to form
a vacuole
• 2 types:
– phagocytosis- cytoplasmic
extensions surround food
particle and package it in a
vacuole
• Cell then engulfs it
– pinocytosis- formation of tiny
pockets in cell membrane to
take in liquids
Endocytosis and Exocytosis
• Exocytosis- membrane of a vacuole fuses with
cell membrane and releases contents out of
cell
Functions of Membrane Proteins
CYTOPLASM
Enzymatic
activity
Fibers of
extracellular
matrix (ECM)
Phospholipid
Cholesterol
Cell-cell
recognition
Receptor
Signaling
molecule
Transport
Attachment to the cytoskeleton
and extracellular matrix (ECM)
Signal
transduction
ATP
Intercellular
junctions
Glycoprotein
Microfilaments
of cytoskeleton
CYTOPLASM
Other Protein Functions
• Other proteins
– serve as tags on the surface to ID chemical signals
and other cells
– On inner surface help anchor membrane to cell’s
internal support structure