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A Tour of the Cell
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History of the Cell
¾ Cells were first discovered in 1665 by
Robert Hooke
From Micrographia
¾ The accumulation of scientific evidence led
to the ‘cell theory’
(1) All living things are composed of cells
(2) All cells form from previously existing cells
• Cells are the building blocks of all life forms
• Organisms are either:
¾ Single-celled, such as most bacteria and protists
¾ Multicelled, such as plants, animals, and most
fungi
Cells are made up of MACROMOLECULES:
(1) Nucleic Acids
(2) Proteins
(3) Lipids
(4) Carbohydrates
The Two Major Categories of Cells
¾ Prokaryotic cells
¾ Eukaryotic cells
Prokaryotes Vs. Eukaryotes
Prokaryotic cell
Eukaryotic cell
Nucleoid region
Nucleus
Organelles
Figure 4.4
Prokaryotic cells:
¾Are much smaller than eukaryotic cells
¾Lack internal structures surrounded by
membranes
¾ Lack a nucleus
A Detailed View of Prokaryotic Cells
Prokaryotic
flagella
Nucleoid region (DNA)
Ribosomes
Plasma
membrane
Cell wall
Capsule
Pili
Figure 4.5
A Detailed View of Eukaryotic Cells
¾ An idealized animal cell
Ribosomes
Cytoskeleton
Centriole
Lysosome
Flagellum
Not in most
plant cells
Plasma
membrane
Nucleus
Mitochondrion
Rough
endoplasmic
reticulum (ER)
Golgi
apparatus
Smooth
endoplasmic
reticulum (ER)
Figure 4.6A
A Detailed View of Eukaryotic Cells
¾ An idealized plant cell
Not in animal cells
Cytoskeleton
Mitochondrion
Central
vacuole
Nucleus
Cell wall
Rough endoplamsic
reticulum (ER)
Chloroplast
Ribosomes
Plasma
membrane
Smooth
endoplasmic
reticulum (ER)
Plasmodesmata
Golgi apparatus
Figure 4.6B
Antony van Leeuwenhoek (1632-1723):
Microscope Maker
¾ Identified and termed ‘animalcules’
Microscopes as Windows to Cells
¾ The light microscope is used by many scientists
(1) Light passes through
the specimen
(2) Lenses enlarge, or
magnify, the image
(a) Light micrograph (LM) of a white blood cell
(stained purple) surrounded by red blood cells
Figure 4.2A
Microscope Terminology
Magnification: An increase in the specimen’s
apparent size
Resolving power: The ability of an optical
instrument to show two objects as separate
The Electron Microscope:
¾ Uses a beam of electrons instead of light
¾ Has a higher resolving power than light microscopes
(can magnify up to 100,000X)
¾ The power of electron microscopy reveals
many details of cellular components
Scanning Electron Microscopy
(b) Scanning electron micrograph (SEM) of a white
blood cell
Figure 4.2B
¾ for studying external cellular structures
Transmission Electron Microscopy
(c) Transmission electron micrograph (TEM) of a white blood cell
¾ for studying internal cellular structures
Figure 4.2C
Power and Scale of Microscopy
Length of some
nerve and
muscle cells
Chicken
egg
Unaided eye
Human height
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
Proteins
Electron microscope
Plant and
animal
cells
Light microscope
Frog
eggs
Lipids
Small
molecules
Atoms
Figure 4.3
MEMBRANE STRUCTURE AND FUNCTION
The plasma membrane separates the living
cell from its nonliving surroundings and
regulates what goes in and out.
Organelles are surrounded by membranes
to separate them as distinct compartments
of the cell with specialized functions.
The Fluid Mosaic Model of Membranes:
¾ Membranes are composed of lipids AND
proteins and are highly dynamic (fluid)
¾ Membranes of the cell have selective
permeability (04-07a-MembraneStructure.mov):
(1) They allow some substances to cross more easily than
others
(2) They block passage of some substances altogether
(3) The traffic of some substances can only occur through
transport proteins (like glucose)
The LIPID Component
¾ The lipids belong to a special category called
phospholipids
¾ Phospholipids form a two-layered membrane, the
phospholipid bilayer
Outside cell
Hydrophilic
head
Hydrophobic
tail
Cytoplasm
(inside cell)
(a) Phospholipid bilayer of membrane
Figure 4.7A
Phospholipids in Membranes
The PROTEIN Component
¾ Most membranes have specific proteins
embedded in the phospholipid bilayer
Hydrophilic
region of
protein
Phospholipid
bilayer
Hydrophobic
region of protein
(b) Fluid mosaic model of membrane
Figure 4.7B
FUNCTIONS of Membrane Proteins
Cytoplasm
Fibers of
extracellular
matrix
c Enzymatic activity
b Cell signaling
a Attachment to
cytoskeleton and
extracellular
matrix
e Intercellular
joining
d Transport
Cytoskeleton
f Cell-cell
recognition
Cytoplasm
Figure 4.8
04-08-ReceptorProtAnim.mov
EVOLUTION CONNECTION:
The Origin of Membranes
¾ Phospholipids were probably among the
organic molecules on the early Earth
¾ When mixed with
water, phospholipids
spontaneously form
membranes
THE NUCLEUS:
GENETIC CONTROL OF THE CELL
¾ The nucleus is the ‘manager’ of the cell
Genes in the nucleus store the information necessary to
produce proteins, which perform cellular functions
Structure and Function of the Nucleus
¾ The nucleus is bordered by a double
membrane called the nuclear envelope
¾The nucleus contains chromatin and
the nucleolus
Ribosomes
Chromatic
Nuclear
envelope
Nucleolus
Pore
Figure 4.9
How DNA Controls the Cell
n Genes encoded by DNA
are copied to another
molecule, mRNA
omRNA molecules
representing genes are
exported from the nucleus
into the cytoplasm
p Ribosomes in the
cytoplasm ‘read’ the
mRNA and use the info to
make a protein
Figure 4.10
DNA
1 Synthesis of
mRNA in the
nucleus
mRNA
Nucleus
Cytoplasm
2 Movement of
mRNA into
cytoplasm via
nuclear pore
3 Synthesis of
protein in the
cytoplasm
mRNA
Ribosome
Protein
The Central Dogma of Molecular Biology
DNA
n
RNA
o
nTranscription
oTranslation
Protein
Exceptions to the Central Dogma
DNA
n
RNA
Retroviruses
o
Protein
Chloroplasts and Mitochondria:
Energy Conversion
¾ Cells require a constant energy supply to do
all the work of life
Chloroplasts
¾ Chloroplasts are
the sites of
photosynthesis:
the conversion of
light energy to
chemical energy
Figure 4.17
Inner and outer
membranes of
envelope
Space between
membranes
Granum
Stroma (fluid in
chloroplast)
Mitochondria
¾ Mitochondria are the sites of cellular
respiration, the process of producing ATP
from food molecules
Outer
membrane
Inner
membrane
Cristae
Matrix
Space between
membranes
Figure 4.18
EVOLUTION CONNECTION:
The Origin of Organelles
¾ The Endosymbiont
Theory: eukaryotic
organelles evolved
from prokaryotes that
were engulfed by other
cells
The Cytoskeleton:
Cell Shape and Movement
¾ The cytoskeleton is an infrastructure of the
cell consisting of a network of fibers:
(1) Actin Fibers (structure & movement OF the cell)
(2) Microtubules (structure & movement WITHIN the cell)
Functions of the Cytoskeleton:
¾ Provide mechanical
support and structure
to the cell to give it
shape
Figure 4.19A
Functions of the Cytoskeleton:
¾ The cytoskeleton can
change the shape of a
cell for movement
Figure 4.19B
Motile Appendages
¾ Flagella propel the cell in
a whiplike motion
¾ Cilia move in a
coordinated back-and-forth
motion
Figure 4.20A, B
Non-moving cells have cilia and flagella, too
¾ The human windpipe
is lined with cilia
Figure 4.20C
The universal architecture of eukaryotic cilia
(a) Paramecium
(b) Cells from
fallopian
tube
(c) Cross section of cilium
Figure 1.9
CELL SURFACES:
Protection, Support, and Cell-Cell
Interactions
¾ Most cells secrete materials that are external
to the plasma membrane (except those that
have cell walls!)
Plant Cell Walls and Cell Junctions
¾ Plant cells are encased by cell walls
Walls of two adjacent
plant cells
Vacuole
Plasmodesmata
(channels between cells)
Figure 4.21
Animal Cell Surfaces and Cell Junctions
¾ Animal cells lack cell walls:
(1) They secrete a sticky covering called the
extracellular matrix
(2) This layer helps hold cells together to form
tissues and organs and so on.
Connections Between Animal Cells:
Extracellular matrix
(a) Tight junctions
(b) Anchoring
junctions
(c) Communicating
junctions
Plasma membranes
of adjacent cells
Extracellular matrix
Figure 4.22
The Secretory System: Manufacturing
and Distributing Cellular Products
¾ Many of the membranous organelles in the cell
belong to the secretory, or endomembrane, system
The Endoplasmic Reticulum
¾ The endoplasmic
reticulum (ER):
Nuclear
envelope
(1) Produces an enormous
variety of molecules
Ribosomes
(2) Is composed of smooth
and rough ER
Rough ER
Smooth ER
Figure 4.11
Rough ER
¾ The “roughness” of the rough ER is due to
ribosomes that stud the outside of the ER
membrane
¾ The functions of the rough ER include:
(1) Producing proteins
(2) Producing new membrane
After the rough ER synthesizes a molecule it
packages the molecule into transport vesicles
4
Transport vesicle
buds off
Ribosome
3
1
Protein
2
Secretory
protein inside
transport
vesicle
Rough ER
Polypeptide
Figure 4.12
Smooth ER
¾ The smooth ER lacks the surface ribosomes
of ER and produces lipids, including steroids
The Golgi Apparatus
¾ Works in partnership with the ER
¾ Refines, stores, and distributes the products of cells
Transport
vesicle
from ER
“Receiving” side of
Golgi apparatus
Golgi apparatus
New vesicle forming
Transport vesicle
from the Golgi
“Shipping” side of
Golgi apparatus
Plasma membrane
Figure 4.13
Lysosomes
¾ A lysosome is a membrane-enclosed sac:
(1) It contains digestive enzymes
(2) The enzymes break down macromolecules
Digestive Functions of the lysosome:
To fuse with food vacuoles to digest the food
Lysosome
Digestive enzymes
Plasma
membrane
Digestion
Food
Food vacuole
(a) Lysosome digesting food
Figure 4.14a
Digestive Functions of the lysosome:
To break down damaged organelles
Lysosome
Digestion
Damaged
organelle
(b) Lysosome breaking down damaged organelle
Figure 4.14b
Vacuoles: Membranous Sacs
¾ Two types are the contractile vacuoles of
protists and the central vacuoles of plants
Central
vacuole
Contractile
vacuoles
(a) Contractile vacuoles in a protist
(b) Central vacuole in a plant cell
Figure 4.15
Summary of the Endomembrane System
Rough ER
Transport
vesicle from ER
Golgi
apparatus
Secretory
vesicle from Golgi
Secretory
protein
Vacuole
Lysosome
Plasma membrane
Figure 4.16
04-16-EndomembraneSysAnim.mov
BIOLOGY AND SOCIETY:
Drugs That Target CELLS
¾ Antibiotics are one of the great marvels
of modern medicine:
(1)Treatment with
these drugs will kill
invading bacteria
(2)The drugs don’t
harm the human
cells of the host
Figure 4.1
BIOLOGY AND SOCIETY:
Drugs That Target CELLS
¾ Chemotherapy and Cancer:
(1) Targets cells that
are growing rapidly
(2) The drugs don’t
affect most human
cells, but…