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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 6
A Tour of the Cell
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Cells: The Fundamental Units of Life
• first cell observed – Robert Hooke in
1665
•
•
thin slices of bottle cork
saw a network of “cells” that a monk would live
in
• first living cell (Spirogyra) observed by
Anton van Leeuwenhoek in 1674
•
also described bacteria he found in his mouth
(1676)
Cells: The Fundamental Units of Life
• the cell is the simplest collection of matter
that can be alive
• the Cell Theory:
• 1. all organisms are made of at least one
type of cell
• 2. all cells come from pre-existing cells
by this cell dividing in two
• 3. the cell is the basic, fundamental
unit of life
• attributed to: Theodor Schwann, Matthias
Jakob Schleiden, and Rudolf Virchow.
Anton van Leeuwenhoek
Cells: The Fundamental Units of Life
• modern interpretation added a
few more parameters
– 1. The activity of an organism depends
on the total activity of independent cells.
– 2. Energy flow (metabolism and
biochemistry) occurs within cells.
– 3. Cells contain hereditary
information (DNA) which is passed from
cell to cell during cell division.
– 4. All cells are basically the same in
chemical composition in organisms of
similar species.
Concept: Biologists use microscopes and the tools
of biochemistry to study cells
• first compound microscope – Zacharias
Jansen in 1590
• three important parameters of microscopy
– Magnification: the ratio of an
object’s image size to its real size
– Resolution: the measure of the
clarity of the image, or the minimum
distance of two distinguishable
points
• inversely related to the wavelength of
the radiation a microscope uses
– Contrast: visible differences in
parts of the sample
Human height
1m
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–
•
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Chicken egg
1 cm
Frog egg
1 mm
100 m
in compound microscopes – more than one lens
–
–
•
e.g. magnifying lens
0.1 m
ocular and objective lenses
improves resolution and allows for more than one
magnification
LMs can magnify effectively to about 1,000 times
the size of the actual specimen
this allows for individual cells within a tissue to be
visualized
Human egg
Most plant and
animal cells
10 m
1 m
100 nm
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
0.1 nm
Small molecules
Atoms
Superresolution
microscopy
Electron microscopy
•
in a light microscope (LM) - visible light is passed
through a specimen and then through glass lenses
the lenses refract (bend) the light - so that the
image is magnified
in a simple microscope - there is one lens for
magnification
Light microscopy
•
Length of some
nerve and
muscle cells
Unaided eye
Studying Cells: Microscopy
10 m
Light Microscopy (LM)
Brightfield
(unstained specimen)
50 m
50 m
Brightfield
(stained specimen)
Deconvolution
10 m
Phase-contrast
Differential-interferencecontrast (Nomarski)
Super-resolution
Fluorescence
10 m
1 m
• various techniques enhance
contrast of a LM and enable
cell components to be
stained or labeled
• BUT - most subcellular
structures, including
organelles, are too small to
be resolved by an LM
• LMs cannot resolve detail
finer than 0.2um - regardless
of magnification
Confocal
•
•
•
•
to improve resolution and magnification –
allowing for imaging of subcellular structure development of two other microscopes in the
1950s
called electron microscopes (EMs)- use a focused
beam of electrons rather than light
resolution increase – due to the shorter
wavelength of the electron beam
two types:
–
–
1. Transmission Electron Microscope (TEM)
2. Scanning Electron Microscope (SEM)
•
•
two types:
1. Scanning electron microscopes (SEMs) – electron
beam is focused onto the surface of a subject
–
–
–
providing images that look 3D
SEM electron beam excites the electrons of the gold on
the subject’s surface
several kinds of electrons are produced
•
–
–
–
Blood cells
e.g. secondary and back-scattered
these electrons are detected and projected onto a video
screen as a magnified image that appears 3D
can be colorized
other detectors can be used
•
e.g. to detect elemental composition
Pollen grains
•
2. Transmission electron microscopes (TEMs)
focus a beam of electrons through a specimen
–
–
–
–
–
–
subject is sectioned first into a very thin layer – with a
microtome
TEMs are used mainly to study the internal structure
of cells
subject is stained with heavy metals that adhere to
the internal structures of the cell
so some parts of the cell are more electron dense
than others
the electron beam passes through those less dense
and scattered by the more dense regions
the electrons that pass through hit a piece of film
negative or hit a detector for displaying the image
Studying Cells: Cell Fractionation
TECHNIQUE
• another way to study cells is to study
their individual components
• subcellular fractionation takes cells
apart and separates the major
organelles from one another
• centrifuges fractionate cells into their
component parts
– separates based on the density of the
organelle within a separating solution –
like sugar
• cell fractionation enables scientists
to determine the functions of
organelles by being able to isolate
them
Homogenization
Tissue
cells
Homogenate
Centrifuged at
1,000 g
(1,000 times the
force of gravity)
for 10 min Supernatant
poured into
next tube
20,000 g
20 min
Pellet rich in
nuclei and
cellular debris
Centrifugation
Differential
centrifugation
80,000 g
60 min
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a plant)
Pellet rich in
“microsomes”
(pieces of plasma
membranes and
cells’ internal
Pellet rich in
membranes)
ribosomes
Concept: Eukaryotic cells have internal membranes that
compartmentalize their functions
• the basic structural and functional unit of every organism is
the cell
• two types of cells: prokaryotic or eukaryotic
• prokaryotic cells: domains Bacteria and Archaea consist of
prokaryotic cells
• protists, fungi, animals, and plants all consist of eukaryotic
cells
Comparing Prokaryotic and Eukaryotic
Cells
• Basic features of all cells
– Plasma membrane
– Semifluid substance called cytosol
– DNA in the form of Chromosomes (carry genes)
– Ribosomes (make proteins)
• Prokaryotic cells:
– no nucleus
– DNA in an unbound region
called the nucleoid
– no membrane-bound
organelles
– a Cytoplasm bound by the
plasma membrane
• Eukaryotic cells
– membrane – bound
nucleus containing DNA
(nuclear envelope)
– membrane-bound
organelles
– a Cytoplasm in the region
between the plasma
membrane and nucleus
The Plasma Membrane
• the plasma membrane is a semipermeable barrier
– allows sufficient passage of oxygen,
nutrients, and waste to service the
volume of every cell
• the general structure of a
biological membrane is a double
layer of phospholipids
– known as a phospholipid bilayer
– membrane proteins embedded within
it or found attached to one layer
Outside of cell
Inside of cell
0.1 m
(a) TEM of a plasma
membrane
Carbohydrate side chains
Hydrophilic
region
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
The Cytosol
• also known as the intracellular fluid or ICF
• made up of multiple levels of organization:
– concentration gradients of ions and small molecules
– larger complexes of enzymes for metabolic pathways
– large complexes of proteins
• e.g. proteasomes in eukaryotes – protein degradation
• e.g. carboxysomes in prokaryotes – carbon fixation (Calvin cycle –
synthesis of sugar from CO2)
• prokaryotic cells – site of the cell’s metabolic reactions
The Cytosol – Eukaryotic Cells
• eukaryotic cells – part of the cytoplasm
– about 55% of the cell’s volume
– about 70-90% water PLUS
•
•
•
•
•
ions
dissolved nutrients – e.g. glucose
soluble and insoluble proteins
waste products
macromolecules and their components - amino acids, fatty
acids
• ATP
• unique composition with respect to
extracellular fluid (ECF)
•
-fluid found outside of a cell
Cytosol
•higher K+
•lower Na+
•higher concentration
of dissolved and
suspended proteins
(enzymes, organelles)
•lower concentration
of carbohydrates
(due to catabolism)
•larger reserves of amino
acids (anabolism)
ECF
•lower K+
•higher Na+
•lower concentration
of dissolved and
suspended proteins
•higher concentration
of carbohydrates
•smaller reserves of amino
acids
DNA & Chromosomes
• one type of organizational unit of DNA= chromosomes
•
in eukaryotes each chromosome is composed of a single DNA molecule
associated with proteins (histones)
• prokaryotic chromosome = genophore
– found in the nucleoid region of the cell
– multiple copies may exist
– usually just one circular piece of double-stranded DNA
• means there is no need for telomeres
– length varies – several hundred thousand to a few million base pairs
• still significantly smaller than a eukaryotic chromosome
– not really a chromosome – no chromatin
• not found associated with histones proteins
• can associated with nucleoid-associated proteins (NAPs) – play a role in spatially organizing
the genophore within the nucleoid region
• DNA is looped and supercoiled rather than compacted by histones
Extrachromosomal DNA - Plasmids
•
•
•
•
pieces of DNA not part of the genophore/chromosome
replicate independently of the genophore
substantially smaller – usually only a few thousand base pairs
can be found in all three domains: Bacteria, Archaea and
Eukaryota
• carry genes that confer antibiotic resistance to prokaryotes
• used in the laboratory for manipulation of genes
The Eukaryotic Nucleus: Information Central
• the nucleus contains most of the eukaryotic cell’s genes and is usually the most
conspicuous organelle
• the nuclear envelope encloses the nucleus, separating it from the cytoplasm
– not found in prokaryotic cells – so NO nucleus in prokaryotic cells
• the nuclear envelope is comprised of two phospholipid bilayers
– each membrane is a lipid bilayer
– often connected to the endoplasmic reticulum
• the nucleolus is located within the nucleus and is the site of ribosomal RNA
(rRNA) synthesis
– more synthetic the cell is – the greater number of nucleoli
Nucleus
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Rough ER
Pore
complex
Ribosome
Close-up
of nuclear
envelope
Chromatin
Ribosomes: Protein Factories
• Ribosomes are particles made of ribosomal RNA (rRNA) and protein
• comprised of two subunits
– large
– small
• ribosomes carry out protein synthesis in two locations
– in the cytosol (free ribosomes) – both prokaryotes & eukaryotes
– in eukaryotes - on the outside of the endoplasmic reticulum or the
nuclear envelope (bound ribosomes)
• can also be found in chloroplasts and mitochondria
0.25 m
Free ribosomes in cytosol
Endoplasmic reticulum (ER)
Ribosomes bound to ER
Large
subunit
Small
subunit
TEM showing ER and
ribosomes
Diagram of a ribosome
Prokaryotic Cells
• usually smaller and less complex than eukaryotic cells
• first cells to evolve
• single-celled organisms
– 0.5 to 5um in diameter (eukaryotes 10-100um)
– some species exist as aggregates called colonies
• e.g. cyanobacteria
• some prokaryotes can be multi-cellular at points in their life-cycle
• defined as having no nuclear membrane, no mitochondria or
other organelles
• divided into two domains:
– Bacteria
– Archaea
Prokaryotic Cells
• Bacteria:
– collective biomass – 10x of all
eukaryotes
– vast genetic diversity among
members
– physical diversity
• shapes: spheres (coccus), rods
(bacilli) and spirals
1 µm
Spherical
(cocci)
2 µm
Rod-shaped
(bacilli)
5 µm
Spiral
Prokaryotic Cells
Fimbriae
Nucleoid
• made up of numerous components:
– cell capsule
– cell wall
– plasma membrane
– fimbrae
– flagella(e)
– cytoplasm
– nucleoid region
– ribosomes
Ribosomes
Plasma
membrane
Bacterial
chromosome
Cell wall
Capsule
Flagella
(a) A typical
rod-shaped
bacterium
cell wall
capsule
plasma membrane
genophore
cytoplasmic
granules
plasmid
poly-ribosomes
ribosome
subunits
Prokaryotic Cells
Fimbriae
Nucleoid
• Bacterial cell components:
– nucleoid region – nonmembranous region where the
DNA is located
•
•
•
•
60% DNA
40% protein and RNA (mRNA)
DNA is a circular chromosome
other smaller pieces of circular
DNA are located here – plasmids
(house genes for antibiotic
resistance)
– ribosomes - for protein synthesis
Ribosomes
Plasma
membrane
Bacterial
chromosome
Cell wall
Capsule
(a) A typical
rod-shaped
bacterium
Flagella
Prokaryotic Cells
Fimbriae
Nucleoid
• Bacterial cell components:
– plasma membrane – phospholipid
bilayer similar to that of eukaryotes
– cell wall – rigid structure outside the
PM
• composed of a peptidoglycan layer (crosslinked sugars)
• for protection, structural support &
reproduction
• gram negative bacteria have an additional
layer outside the cell wall – called a
lipopolysaccharide layer
• this layer is responsible for the toxicity of
these bacteria
– capsule - also called the glycocalyx or
“slime layer”
• for adherence
Ribosomes
Plasma
membrane
Bacterial
chromosome
Cell wall
Capsule
(a) A typical
rod-shaped
bacterium
Flagella
Prokaryotic Cells
Fimbriae
Nucleoid
• Bacterial cell components:
– fimbrae – structures involved in
attachment
• shorter ones involved in reproduction = pilus
Ribosomes
Plasma
membrane
Bacterial
chromosome
– flagella – made of protein filaments
• for locomotion
– cytoplasm – intracellular fluid of the
prokaryote
• bound by the plasma membrane
• no membrane-bound organelles
Cell wall
Capsule
(a) A typical
rod-shaped
bacterium
Flagella
The Eukaryotic Cell
• cells of the Domain Eukaryota
• a eukaryotic cell has internal membranes that
partition the cell into organelles
– known as the endomembrane system
• single eukaryotic cells found in the Kingdom
Protista
• remaining Phyla in the domain contain mainly
multicellular organisms
– fungus, plants and animals
• plant and animal cells have most of the same
organelles
The Eukaryotic cell
• 1. Plasma membrane
• 2. Nucleus
• 3. Cytoplasm
– a. cytosol
– b. cytoskeleton
• 4. Cytoplasmic organelles
– endomembrane system
Outside of the plasma membrane will be a Cell Wall
in plants and fungus
– not the same composition