Transcript Chapter 6

Chapter 6:
A Tour of the Cell
Observation
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Is the keystone of science.
Need: Techniques to observe cells.
Question ?
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Can cells be seen with the naked eye?
Yes, a few are large enough, but most
require the use of a microscope.
Microscope History
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1590 - Janseen Brothers invent the
compound microscope.
1665 - Robert Hooke “discovers” cells in
cork.
Early 1700’s - von Leeuwenhoek makes
many observations of cells including
bacteria.
Light Microscope - LM
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Uses visible light to illuminate the
object.
Relatively inexpensive type of
microscope.
Can examine live or dead objects.
Light Microscope
Occular Lens
Objective Lens
Stage with specimen
Light Source
Magnification
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Increase in diameter or size.
Resolution
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Ability to detect two discrete points as
separate from each other.
As Magnification increases, resolution
decreases.
LM working limits are 100 - 1000X.
Limitations - LM
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Miss many cell structures that are
beyond the magnification of the light
microscope.
Need other ways to make the
observations.
Light Microscope Variations
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Fluorescence: uses dyes to make parts of
cells “glow”.
Phase-contrast: enhances contrasts in
density.
Confocal: uses lasers and special optics to
focus only narrow slides of cells.
Electron Microscopes
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Use beams of electrons instead of
light.
Invented in 1939, but not used much
until after WWII.
TEM
SEM
Advantages
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Much higher magnifications.
Magnifications of 50,000X or higher
are possible.
Can get down to atomic level in some
cases.
Disadvantages
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Need a Vacuum.
Specimen must stop the electrons.
High cost of equipment.
Specimen preparation.
Transmission Electron Microscope - TEM
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Sends electrons through thinly sliced
and stained specimens.
Gives high magnification of interior
views. Many cells structures are now
visible.
TEM Limitations
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Specimen dead.
Specimen preparation uses extreme
chemicals so artifacts are always a
concern.
Scanning Electron Microscope - SEM
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Excellent views of surfaces.
Produces 3-D views.
Live specimens possible.
Limitations
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Lower magnifications than the TEM.
EM Variations
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High Voltage TEM
Tunnel SEM
Elemental Composition SEM
TEM - interior
SEM - surface
Cell Biology or Cytology
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Cyto = cell - ology = study of
Should use observations from several
types of microscopes to make a total
picture of how a cell is put together.
Other Tools for Cytology
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Cell Fractionation
Chromatography
Electrophoresis
Cell Fractionation
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Disrupt cells.
Separate parts by centrifugation at
different speeds.
Result - pure samples of cell structures
for study.
Cell Fractionation
Chromatography
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Technique for separating mixtures of
chemicals.
Separates chemicals by size or degree of
attraction to the materials in the medium.
Ex - paper, gas, column,
thin-layer
Electrophoresis
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Separates mixtures of chemicals by
their movement in an electrical field.
Used for proteins and DNA.
History of Cells
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Robert Hooke - Observed cells in cork.
Coined the term "cells” in 1665.
History of Cells
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1833 - Robert Brown, discovered
the nucleus.
1838 - M.J. Schleiden, all plants are
made of cells.
1839 - T. Schwann, all animals are
made of cells.
1840 - J.E. Purkinje, coined the term
“protoplasm”.
Cell Theory
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All living matter is composed of one or
more cells.
The cell is the structural and functional
unit of life.
R. Virchow
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“Omnis cellula e cellula”
All cells are from other cells.
Types of Cells
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Prokaryotic - lack a nucleus and other
membrane bounded structures.
Eukaryotic - have a nucleus and other
membrane bounded structures.
Prokaryotic
Eukaryotic
Nucleus
Eukaryotic
Prokaryotic
How small can a cell be?
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Mycoplasmas - bacteria that are .1 to
1.0 mm. (1/10 the size of regular
bacteria).
Why Are Cells So Small?
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Cell volume to surface area ratios
favor small size.
Nucleus to cytoplasm consideration
(control).
Metabolic requirements.
Basic Cell Organization
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Membrane
Nucleus
Cytoplasm
Organelles
Animal Cell
Plant Cell
Membrane
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Separates the cell from the
environment.
Boundary layer for regulating the
movement of materials in/out of a cell.
Cytoplasm
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Cell substance between the cell
membrane and the nucleus.
The “fluid” part of a cell. Exists in two
forms:
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gel - thick
sol - fluid
Organelle
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Term means "small organ” Formed
body in a cell with a specialized
function.
Important in organizational structure of
cells.
Organelles - function
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Way to form compartments in cells to
separate chemical reactions.
Keeps various enzymes separated in
space.
Nucleus
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Most conspicuous organelle.
usually spherical, but can be lobed or
irregular in shape.
Structure
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Nuclear membrane
Nuclear pores
Nucleolus
Chromatin
Nuclear Membrane
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Double membrane separated by a 2040 nm space.
Inner membrane supported by a
protein matrix which gives the shape to
the nucleus.
Nuclear Pores
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Regular “holes” through both
membranes.
100 nm in diameter.
Protein complex gives shape.
Allows materials in/out of nucleus.
Nucleolus
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Dark staining area in the nucleus.
0 - 4 per nucleus.
Storage area for ribosomes.
Chromatin
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Chrom: colored
- tin: threads
DNA and Protein in a “loose” format.
Will form the cell’s chromosomes.
Nucleus - Function
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Control center for the cell.
Contains the genetic instructions.
Ribosomes
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Structure: 2 subunits made of protein
and rRNA. No membrane.
Function: protein synthesis.
Subunits
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Large:
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45 proteins
3 rRNA molecules
Small:
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23 proteins
1 rRNA molecule
Locations
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Free in the cytoplasm - make proteins
for use in cytosol.
Membrane bound - make proteins that
are exported from the cell.
Endomembrane System
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Membranes that are related through
direct physical continuity or by the
transfer of membrane segments called
vesicles.
Endomembrane System
Endoplasmic Reticulum
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Often referred to as ER.
Makes up to 1/2 of the total membrane
in cells.
Often continuous with the nuclear
membrane.
Structure of ER
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Folded sheets or tubes of membranes.
Very “fluid” in structure with the
membranes constantly changing size
and shape.
Types of ER
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Smooth ER: no ribosomes.
Used for lipid synthesis, carbohydrate
storage, detoxification of poisons.
Rough ER: with ribosomes.
Makes secretory proteins.
Golgi Apparatus or Dictyosomes
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Structure: parallel array of flattened
cisternae. (looks like a stack of Pita
bread)
3 to 20 per cell.
Likely an outgrowth of the ER system.
Structure Has 2 Faces
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Cis face - side toward the nucleus.
Receiving side.
Trans face - side away from the
nucleus. Shipping side.
Function of Golgi Bodies
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Processing - modification of ER
products.
Distribution - packaging of ER
products for transport.
Golgi Vesicles
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Small sacs of membranes that bud off
the Golgi Body.
Transportation vehicle for the modified
ER products.
Movie
Lysosome
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Single membrane.
Made from the Trans face of the Golgi
apparatus.
Movie
Function
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Breakdown and degradation of cellular
materials.
Contains enzymes for fats, proteins,
polysaccharides, and nucleic acids.
Over 40 types known.
Lysosomes
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Important in cell death.
Missing enzymes may cause various
genetic enzyme diseases.
Examples: Tay-Sachs, Pompe’s
Disease
Vacuoles
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Structure - single membrane, usually
larger than the Golgi vesicles.
Function - depends on the organism.
Protists
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Contractile vacuoles - pump out
excess water.
Food vacuoles - store newly ingested
food until the lysosomes can digest it.
Plants
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Large single vacuole when mature
making up to 90% of the cell's volume.
Tonoplast - the name for the vacuole
membrane.
Function
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Water regulation.
Storage of ions.
Storage of hydrophilic pigments.
(e.g. red and blues in flower petals).
Function: Plant vacuole
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Used to enlarge cells and create turgor
pressure.
Enzymes (various types).
Store toxins.
Coloration.
Microbodies
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Structure: single membrane.
Often have a granular or crystalline
core of enzymes.
Function
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Specialized enzymes for specific
reactions.
Peroxisomes: use up hydrogen
peroxide.
Glyoxysomes: lipid digestion.
Enzymes in a
crystal
Mitochondria
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Structure: 2 membranes. The inner
membrane has more surface area than
the outer membrane.
Matrix: inner space.
Intermembrane space: area between
the membranes.
Inner Membrane
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Folded into cristae.
Amount of folding depends on the level
of cell activity.
Contains many enzymes.
ATP generated here.
Function
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Cell Respiration - the release of
energy from food.
Major location of ATP generation.
“Powerhouse” of the cell.
Mitochondria
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Have ribosomes.
Have their own DNA.
Can reproduce themselves.
May have been independent cells at
one time.
Chloroplasts
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Structure - two outer membranes.
Complex internal membrane.
Fluid-like stroma is around the internal
membranes.
Inner or Thylakoid Membranes
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Arranged into flattened sacs called
thylakoids.
Some regions stacked into layers
called grana.
Contain the green pigment chlorophyll.
Function
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Photosynthesis - the use of light
energy to make food.
Chloroplasts
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Contain ribosomes.
Contain DNA.
Can reproduce themselves.
Often contain starch.
May have been independent cells at
one time.
Plastids
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Group of plant organelles.
Structure - single membrane.
Function - store various materials.
Examples
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Amyloplasts/ Leucoplasts - store
starch.
Chromoplasts - store hydrophobic
plant pigments such as carotene.
Ergastic Materials
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General term for other substances
produced or stored by plant cells.
Examples:
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Crystals
Tannins
Latex
Resins
Cytoskeleton
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Network of rods and filaments in the
cytoplasm.
Functions
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Cell structure and shape.
Cell movement.
Cell division - helps build cell walls and
move the chromosomes apart.
Components
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Microtubules
Microfilaments
Intermediate Filaments
Microtubules
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Structure - small hollow tubes made of
repeating units of a protein dimer.
Size - 25 nm diameter with a 15 nm
lumen. Can be 200 nm to 25 mm in
length.
Tubulin
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Protein in microtubules.
Dimer - a and b tubulin.
Microtubules
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Regulate cell shape.
Coordinate direction of cellulose fibers
in cell wall formation.
Tracks for motor molecules.
Microtubules
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Form cilia and flagella.
Internal cellular movement.
Make up centioles, basal bodies and
spindle fibers.
Cilia and Flagella
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Cilia - short, but numerous.
Flagella - long, but few.
Function - to move cells or to sweep
materials past a cell.
Movie
Cilia and Flagella
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Structure - 9+2 arrangement of
microtubules, covered by the cell
membrane.
Dynein - motor protein that connects
the tubules.
Dynein Protein
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A contractile protein.
Uses ATP.
Creates a twisting motion between the
microtubules causing the structure to
bend or move.
Centrioles
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Usually one pair per cell, located close
to the nucleus.
Found in animal cells.
9 sets of triplet microtubules.
Help in cell division.
Basal Bodies
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Same structure as a centriole.
Anchor cilia and flagella.
Basal Body
MTOCs
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Microtubule Organizing Centers - sites that
microtubules grow from.
Assist in cell division by anchoring spindle
fibers.
May be anchored by centrioles.
Microfilaments
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5 to 7 nm in diameter.
Structure - two intertwined strands of
actin protein.
Microfilaments
are stained green.
Functions
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Muscle contraction.
Cytoplasmic streaming.
Pseudopodia.
Cleavage furrow formation.
Maintenance and changes in cell
shape.
Movie
Intermediate Filaments
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Fibrous proteins that are super coiled
into thicker cables and filaments
8 - 12 nm in diameter.
Made from several different types of
protein.
Functions
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Maintenance of cell shape.
Hold organelles in place.
Cytoskeleton
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Very dynamic; changing in composition
and shape frequently.
Cell is not just a "bag" of cytoplasm
within a cell membrane.
Cell Wall
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Nonliving jacket that surrounds some
cells.
Found in:
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Plants
Prokaryotes
Fungi
Some Protists
Plant Cell Walls
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All plant cells have a Primary Cell Wall.
Some cells will develop a Secondary
Cell Wall.
Primary Wall
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Thin and flexible.
Cellulose fibers placed at right angles
to expansion.
Placement of fibers guided by
microtubules.
Secondary Wall
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Thick and rigid.
Added between the cell membrane
and the primary cell wall in laminated
layers.
May cover only part of the cell; giving
spirals.
Makes up "wood”.
Middle Lamella
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Thin layer rich in pectin found between
adjacent plant cells.
Glues cells together.
Cell Walls
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May be made of other types of
polysaccharides and/or silica.
Function as the cell's exoskeleton for
support and protection.
Extracellular Matrix - ECM
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Fuzzy coat on animal cells.
Helps glue cells together.
Made of glycoproteins and collagen.
Evidence suggests ECM is involved
with cell behavior and cell
communication.
Intercellular Juctions
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Plants-Plasmodesmata
Plasmodesmata
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Channels between cells through
adjacent cell walls.
Allows communication between cells.
Also allows viruses to travel rapidly
between cells.
Intercellular Juctions
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Animals:
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Tight junctions
Desmosomes
Gap junctions
Tight Junctions
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Very tight fusion of the membranes of
adjacent cells.
Seals off areas between the cells.
Prevents movement of materials
around cells.
Movie
Desmosomes
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Bundles of filaments which anchor
junctions between cells.
Does not close off the area between
adjacent cells.
Coordination of movement between
groups of cells.
Gap Junctions
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Open channels between cells, similar
to plasmodesmata.
Allows “communication” between cells.
Movie
Summary
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Answer: Why is Life cellular and what
are the factors that affect cell size?
Be able to identify cellular parts, their
structure, and their functions.