Transcript lecture 4, tour of the cell, 030309c

Tour of the Cell
Lecture 4
http://www.steve.gb.com
Much of the text material in the lecture notes is from our textbook,
“Essential Biology with Physiology” by Neil A. Campbell, Jane B.
Reece, and Eric J. Simon (2004 and 2008). I don’t claim authorship.
Other sources were sometimes used, and are noted.
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Outline
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Drugs that target cells
Microscopic world of cells
Microscopy
Cell types
Cell components and functions
Origin of membranes
Words and terms to know
Possible test items
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American Civil War
http://nmhm.washingtondc.museum
http://www.a2zcds.com
During the American Civil War, many soldiers died from infections in the
treatment of their wounds (possibly as many as actually died on the
battlefield).
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Penicillin
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Antibiotics derived from microorganisms disable or kill bacteria.
In the 1920s, Alexander Fleming discovered penicillin when he observed
that mold prevented the growth of bacteria that he was trying to cultivate in
bread.
Fleming recognized the value of an agent that inhibits bacterial growth,
and the age of antibiotics was born.
The death rates from diseases such as bacterial pneumonia and surgical
infection dropped substantially once antibiotics were introduced and then
widely used.•
The discovery of penicillin is a famous case of ‘serendipity.’
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Bread Mold
http://www.sciencemore.com
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Antibiotic Actions
Antibiotics destroy bacteria or inhibit their growth.
• Penicillin works by disrupting the synthesis of the cell walls in bacteria.
• Erythromycin binds to a structure that synthesizes proteins found only in
bacterial cells.
• Ciprofloxacin, used in treating anthrax infections, targets an enzyme that
helps maintain the genetic structure of bacteria.
http://web.edu
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Cell Theory
Cells were first described in 1665 by the British scientist, Robert Hooke,
while examining a thin slice of cork through a microscope.
• Over the next two centuries, cells were found in all organisms examined
under a microscope.
• By the mid-1800s the accumulation of evidence (through the process of
inductive reasoning) led to the cell theory: all organisms are composed
of cells.
• The theory was later expanded to
include observations that new cells
arise from previously existing cells.
Microscopic view of commercial
cork obtained from Cork Oak
http://instruct1.cit.cornell.edu
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Cellular Structure of Cork
http://farm1.static.flickr.com
Robert Hooke’s drawing
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Grove of Cork Oak
http://www.isa.utl.pt
http://cache.eb.com
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Microscopic World of Cells
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Each cell in a living organism is very complex.
Cells must be very small for materials to move in and out of the cell to
meet its needs.
A modern jet aircraft, if it was reduced to the size of a cell, would seem
simple in comparison.
Organisms are single-cellular, such as bacteria and protista, and multicellular as animals, plants, and most fungi.
The human body has many trillions of cells that work together to perform
specific functions.
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http:www.semaphorin.com
A Few Types of Neurons
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Light Microscope
A portable microscope
similar to the one Darwin
used on the H.M.S Beagle
http://www.meijitechno.com
Modern lab and
classroom version
http://www.hps.cam.ac.uk
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LM Operation
Light microscopes (LMs) were first developed during the Renaissance
period.
• Visible light passes through the specimen—the lens enlarges the image
and projects it onto the human eye or camera.
• Modern light microscopes have compound lenses to reduce chromatic
(color) aberration and spherical aberration for improving the quality of
the viewed image.
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Magnification and Resolving Power
Two key aspects of microscopes are magnification and resolving power.
• Magnification is the increase in an object’s apparent size compared to
its actual size.
• Resolving power is the ability to show two or more objects as distinct
entities.
• Due to limitations in resolving power, the maximum useful magnification
is about 1000 times.
The Big Dipper—an ancient
eye test
http://nightglories.com
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LM Micrograph
http://www.steve.gb.com
Cross-section of bamboo showing its internal
vasculature.
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LM Micrograph
http://marby.online.com
Cell structure in an elodea leaf
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LM Micrograph
http://www7.ocn.ne.jp
Cross section through a buttercup stem
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LM Micrograph
http://www.uwash.edu
Red blood cells and a stained white blood cell
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LM Micrograph
http://www.emsdiasum.com
Coronal cross-section of a rat brain
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Electron Microscope
http://www.usaft.af.mil
An electron microscopy lab
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EM Operation
The study of the structure of cells continued to advance once electron
microscopes (EMs) were developed in the 1950s.
• Electron microscopes use beams of electrons rather than light to explore
the very small world.
• The resolving power is much higher than for light microscopes, allowing
for much higher useful magnifications.
• Electron micrographs can be produced at magnifications of 100,000 or
higher.
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Types of Electron Microscopes
Scanning electron microscopes are used for studying the surfaces of
cells.
• Transmission electron microscopes are used for exploring the internal
structure of cells.
• Light microscopes can be used with live or prepared (dead) specimens,
while electron microscopes can only be used with prepared specimens.
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EM Micrograph
http://www.allergy-details.com
A ‘potpourri’ of pollens
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EM Micrograph
http://www.microscopy-uk.org
Blood—neutrophils and lymphocytes
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EM Micrograph
http:www3.niaid.nih.gov
Escherichia coli (E. coli)
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EM Micrograph
http://www.spaceref.com
Microbes—specifically archaea
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We now examine cells and their organelles
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Cell Types
Prokaryotic cells—evolutionary much older cells, and much simpler in
structure than eukaryotic cells. Bacteria, for example, are prokaryotes.
• Eukaryotic cells—much more complex internal structure. All animal and
plant cells are eukaryotes.
• Prokaryotic cells are much smaller than eukaryotic cells and do not have
a true nucleus—they have a nucleoid region containing genetic material.
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Prokaryotic Cell
The bacteria E. coli dividing
http://www.cod.edu
A highly-stylized representation
http://www.bio.mtu.edu
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Eukaryotic Cell
Electron micrograph—the
nucleus and endoplasmic
reticulum are prominent
http://www.cod.edu
A highly-stylized representation
http://www.steve.gb.com
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First Appearances
The age of the Earth based on scientific evidence is about 4.3 billion
years.
• Prokaryotic cells appeared about 3.5 billion years before present (bp).
• The first eukaryotic cells evolved about 1.7 billion years bp.
http://www.web.utah.edu
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Components of Eukaryotic Cells
Component
Cytoplasm
Plasma membrane
Nucleus
Chromosomes
Ribosomes
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Mitochondria
Cytoskeleton
Vacuoles
Flagella and cilia
Centrioles
Cell wall
Chloroplasts
Central vacuole
Animal Cell
Plant Cell
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Cytoplasm
Electron micrograph
http://www.danforthcenter.org
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Cytoplasm
The cytoplasm is the region of the cell between the nucleus and plasma
membrane.
• It contains various organelles suspended in a fluid known as the cytosol.
• Each organelle is adapted to perform specific functions, as we will discuss.
• Most organelles in eukaryotic cells are enclosed by their own membranes.
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Plasma Membrane
Computer-generated graphic
http://www.sci-design.com
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Plasma Membrane
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Cells have a plasma membrane separating the interior and exterior of the
cell—they are also known as the intracellular and extracellular spaces.
The membrane consists primarily of phospholipids and proteins in a ‘fluid
mosaic.’
The plasma membrane regulates the traffic of molecules moving into and
out of the cell.
It is selectively permeable—that is, the membrane allows some molecules
to pass through while preventing the passage of others.
Transport proteins embedded in the plasma membrane allow the passage
of other molecules such as glucose molecules.
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Nucleus
Electron micrograph
http:.//www.science.org.au
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Nucleus
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The nucleus has a double membrane known as the nuclear envelope.
The double membrane is similar in structure to the plasma membrane.
Pores in the membrane allow the passage of material between nucleus
and cytoplasm.
DNA molecules and associated proteins form long fibers in the nucleus
called chromatin.
The nucleus also contains a ball-like mass (the nucleolus) that produces
the component parts of ribosomes.
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Chromatin and DNA
Packed
Unpacked
Computer-generated graphics
Both images from http://www.cgl.ucsf.edu
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Ribosomes
Computer-generated graphic
http://rna.ucsc.edu
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Ribosomes
Ribosomes are located in the cytoplasm, near the cell nucleus, where
they synthesize proteins.
• Some ribosomes make proteins that will be dissolved in the cytoplasm,
while others make proteins for the plasma membrane or secretion by the
cell.
• DNA transfers genetic information via messenger RNA to the ribosomes
to synthesize proteins.
• We will discuss DNA and RNA in future lectures on the genetic basis of
life.
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Endoplasmic Reticulum
Electron micrograph
http://www.bu.edu
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Endoplasmic Reticulum
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The endoplasmic reticulum (ER) produces many types of molecules of life.
It is a complex system of tubes and sacs running through the cytoplasm.
Rough ER has the visual appearance of roughness due to ribosomes that
stud its exterior surface.
The products of ribosomes are modified in the rough ER and sent on their
way in transport vesicles.
Cells that secrete substantial amounts of protein, such as salivary glands,
are rich in rough ER.
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Smooth ER
Smooth ER synthesizes lipids, among other biological molecules.
• It lacks the embedded ribosomes found in the membrane of rough ER.
• Cells in the ovaries and testes are rich in smooth ER, and produce the
steroids, estrogen and testosterone.
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Detoxification
Smooth ER in the cells of the liver produce enzymes for the detoxification
of drugs and poisons in the blood.
• Smooth ER increases in liver cells when exposed to the chemicals in some
drugs.
• As a result, the body increases its tolerance to a chemical, requiring higher
dosages to achieve the same effect.
• An increase in tolerance to some drugs is a hallmark of addiction—it has a
firm biological basis.
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Golgi Apparatus
Electron micrograph
http://www.bu.edu
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Golgi Apparatus
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The Golgi apparatus is named for its discover, the Italian scientist, Camillo
Golgi.
It works with the ER to refine, store, and distribute molecules synthesized
in the cell.
Products manufactured in the ER reach the Golgi apparatus via transport
vesicles.
Enzymes in the Golgi apparatus modify many of the products from the ER.
The Golgi apparatus tags proteins with ‘addresses’ for their destinations
within the cell.
Containers known as vesicles budding from the Golgi apparatus distribute
molecules to other organelles.
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Lysosomes
Electron micrograph
http://biology.unm.edu
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Lysosomes
A lysosome is a membrane-enclosed sac of enzymes needed for cellular
digestion.
• Lysosomes provide a compartment for chemical digestion to prevent selfdestruction of the cell.
• Enzymes breakdown macromolecules including proteins, glycogen, fats,
and nucleic acids.
• The molecules produced from the cellular digestive process nourish the
cell.
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Other Functions
Other lysosomes serve as recycling centers by engulfing and digesting
damaged organelles and making the molecules available for forming new
organelles.
• Lysosomes in white blood cells ingest bacteria—the enzymes destroy the
bacterial cell walls.
• Another type destroys the webbing joining the fingers in human embryos.
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Mitochondria
Electron micrograph
http://is2.okcupid.com
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Mitochondria
Mitochondria are responsible for cellular respiration in harvesting energy
to perform cellular work.
• Sugars and other food molecules are converted to a form of energy known
as ATP.
• The inner membrane of mitochondria contains many folds to increase the
surface area and maximize ATP output.
• We will discuss harvesting of chemical energy when we discuss the Krebs
cycle.
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Mitochondria—plural; mitochondrion—singular
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Cytoskeleton
Color-enhanced electron micrograph
http://www.bcsb.org
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Cytoskeleton
Microtubules in the cytoplasm form a network of fibers known as the cell’s
cytoskeleton
• They provides structural support and means for specialized movements.
• Microtubules are constructed of proteins to provide structural support,
which is important in animal cells that don’t have semi-rigid cell walls.
• The microtubules hold the organelles in place in the cytoplasm and guide
the movement of vesicles.
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Additional Functions
Microtubules also guide the movement of chromosomes when cells divide.
• Unlike a bony skeleton, the cytoskeleton can be dismantled in one part of
the cell to reform in a new location.
• This process occurs through the removal and replacement of its units of
proteins.
• It contributes to the crawling motion of amoeba and the movement of white
blood cells.
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Vacuoles
Synaptic vesicles (a type of
vacuole) in a neuron
Electron micrograph
http://www.pharmacology.com
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Vacuoles
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Vacuoles are membrane-enclosed sacs that bud from the Golgi apparatus
endoplasmic reticulum, and plasma membrane.
They differ in size depending on their functions.
The synaptic vesicles in the end buttons of neurons contain transmitter
substances released in response to nerve impulses that signal to other
neurons.
Other vacuoles form in the plasma membrane to engulf food so it can be
transported to the lysosomes.
Plant cells often have a large central vacuole as we will discuss later in the
lecture.
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Flagella
Electron micrograph
http://www2.sunysuffolck.edu
Human sperm
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Flagella
The microtubules found in some eukaryotic cells have appendages that
can move.
• Flagella propel cells through an undulating, whip-like motion.
• Flagella generally occur singly—for example, in sperm which must travel
the female reproductive tract to fertilize the ovum (or egg).
• Problems with flagella can result in male infertility, as we will discuss in the
lecture on sexual reproduction.
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Flagella—plural; flagellum—singular
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Cilia
Electron micrograph
http://www.talbotcentral.ucr.edu
Human oviduct
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Cilia
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Cilia, usually shorter and more numerous than flagella, promote movement through rhythmic back-and-forth movements (think, ancient galley
ship).
Cilia in the oviducts sweep the fertilized egg along the reproductive path
for implantation in the uterus.
Cilia in the respiratory tract sweep mucus with trapped debris out of the
lungs.
Tobacco smoke can damage or
destroy the cilia, which interferes
with the body’s normal cleansing
mechanism.
Smoker’s cough is the body’s
attempt to cleanse the respiratory
system.
http://www.gibinquirer.net
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Extracellular Matrix
Most animal cells secrete a thick, sticky coat known as the extracellular
matrix.
• The coat helps hold cells together in tissues, and provides protective and
supportive functions.
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Cell Junctions
Adjacent cells in many animal tissues are connected by cell junctions.
• Tight junctions bind cells together to form a leak-proof sheet of tissue (such
as in the intestines).
• Anchoring junctions bind cells together, but allow some molecules to pass
among the extracellular spaces.
• Communicating junctions are channels that enable H2O and other small
molecules to flow among neighboring cells.
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Centrioles
Computer-generated graphic
http://www.sparkleberrysprings.com
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Centrioles
Centrioles are canned-shaped structures made of microtubules that
support cell division.
• We will discuss their function when we cover mitosis and meiosis in
later lectures.
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Plant-Specific Cell Components
Silver Maple Tree, Queens, New York
http://graphics8.nytimes.com
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Cell Wall
Electron micrograph
http://www.aber.ac.uk
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Cell Wall
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A plant cell is encased by a semi-rigid wall on the exterior of the plasma
membrane.
The wall protects the cell, maintains its shape, and keeps it from absorbing
too much water.
Cell walls are collectively strong enough to hold up even the tallest of trees
against the force of gravity.
They are formed from cellulose embedded in a matrix of lignin and other
molecules.
This arrangement is similar to the construction of steel-reinforced concrete
and fiberglass.
Plant cells have junctions and channels that enable water and other small
molecules to pass among cells.
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Central Vacuole
Electron micrograph
http://fig.cox.miami.edu
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Central Vacuole
Plant cells may have a large central vacuole to store nourishment,
water, and even poisons that protect against plant-eating animals.
• Some central vacuoles contain pigments to provide color that can
attract pollinating insects.
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Chloroplasts
Electron micrograph
http:/www.bio.ic.ac.uk
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Photosynthesis
Most of the living world requires energy provided by photosynthesis.
• Photosynthesis involves the conversion of sunlight to sugars and other
energy-rich molecules.
• Oxygen (O2) is produced as a by-product and released into the atmosphere.
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Chloroplasts
Chloroplasts are the organelles in plants and protists that perform photosynthesis.
• The flat, disk-shaped objects in the electron micrograph are grana, where
photosynthesis takes place.
• We will discuss photosynthesis when we cover the Calvin cycle in a later
lecture.
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Venus Fly Trap
http://www.mooseyscountrygarden.com
One of the few types of plants to contain lysosomes
and digestive enzymes.
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http://naturalscientist.blogspot.com
Origin of Cell Membranes
Oil-in-vinegar analogy
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Membrane Formation
The plasma membrane is the cell boundary—without a membrane a cell
would not be a separate unit.
• The formation of membranes was probably one of the earliest events in
the evolution of life.
• Phospholipids, found in membranes, were likely among the first organic
molecules to be formed through chemical reactions on Earth before life
originated.
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Phospholipids
Phospholipids spontaneously assemble into membrane-like structures
when mixed with water.
• Assembly requires no genetic instructions—the organization depends only
on their hydrophobic and hydrophilic characteristics of phospholipids.
• The membranes provided a package for new organelles as they developed
early on.
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Words and Terms to Know
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Antibiotic
Cell junction
Cell theory
Cell wall
Central vacuole
Chloroplast
Chromatin
Cilia
Cytoplasm
Cytoskeleton
Cytosol
Electron microscope
Endoplasmic reticulum
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Flagellum
Golgi apparatus
Light microscope
Lysosome
Mitochondrion
Nucleoid region
Nucleus
Organelle
Phospholipid
Plasma membrane
Ribosome
Vacuole
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Possible Test Items
1. Describe the biological mechanisms and effects of antibiotics such as
penicillin and erythromycin.
2. What is the cell theory? What implications does it have for modern
biology?
3. Describe the light microscope and electron microscope. What are
three major differences?
4. List and describe four similarities or differences between prokaryotic
and eukaryotic cells.
5. Describe the locations and functions of five organelles found in most
eukaryotic cells.
6. Describe the locations and function of three features of plant cells not
found in animal cells.
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