Transcript A Tour of the Cell

A Tour of the Cell
Basics of Cells
Plasma Membrane
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Forms external border
Distinguishes cell from surroundings
Cytoplasm
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Everything between plasma membrane and nucleus
Typically known as fluid
Organelles
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Play specific key roles in the lifecycle of cells
Basics of Microscopes
Light Microscope (LM) passes light through a
specimen
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Typically is compound (two lenses) or simple (one
lens)
Electron Microscopes (EM) replaces the beam of
light with one of electrons
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Specimen must be dead
Held within a veritable vacuum
Much more detailed- can see within cells, and under
certain conditions individual atoms
Types of Electron Microsopes
Scanning (SEM) studies cell surfaces by
passing electrons over the surface of a cell
that has been coated with metal

3D images
Transmission (TEM) studies the internal
structures of cells by aiming electrons
through a section of the cell
Different Types
of Microscopes
Are Necessary for
Different Sized
Cells
How they work
Magnification: increase in the apparent
size of an object
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Ocular is typically 10x
Objectives are typically 4x, 10x, 40x, and
100x
Total Magnification is ocular x objective
Resolution: the measure of the clarity
of an image
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Increases with the sophistication of the
microscope
Cell Theory
ALL living things are composed of cells
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Schleiden and Schwann
ALL cells come from other cells
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Biogenesis
Virchow
Cells are the most basic unit of life
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Cell Size versus function
Smallest are mycoplasmas (.1 to 1.0
micrometers)
Muscle and nerve cells are longest (almost
1 meter in length!)
Many fall somewhere between
The Ratio of cell surface to cell volume
that imposes upper limits on cell size
Cell Size Regulation
Prokaryotic Cells
Bacteria and Archaea
Cannot be seen with a low power
microscope
Lacks a nucleus  instead compacts DNA
into a nucleoid region
Ribosomes in the cytoplasm detect
messages from the DNA and assemble
amino acids into polypeptides accordingly
Surrounding those bacteria!
Plasma Membrane encloses the cytoplasm
Outside of the plasma membrane is a
bacterial cell wall
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Protects
Maintains shape
Very Complex!
Some have a capsule that surrounds the cell
wall
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Help with attachment to surfaces/substrates
Pili assist with attachment and sharing of
genetic information
Flagella assist with movement
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Not the same as eukaryotic flagella!
Eukaryotic Cells are
Compartmentalized!
Endomembrane System
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Nucleus, Endoplasmic reticulum (ER), Golgi
Apparatus (GA), Lysosomes, Peroxisomes, Vacuoles
Work in the synthesis, storage, and export of
important molecules
Energy Converting Organelles
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Chloroplasts, Mitochondria
Cytoskeleton
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Cilia, flagella
Nucleus
Genetic Control Center
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DNA fibers form into
fibers of chromatin
Each fiber contains a
chromosome
Surrounded by a
nuclear envelope,
perforated by nuclear
pores
Nucleolus in the center
is responsible for
producing ribosomes
ER “network within the cell”
ROUGH (RER) is dotted with ribosomes
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Produces membrane for use within the cell
Produces proteins for export out of the cell
Antibodies are a good example
Releases these secretory proteins via transport
vesicles for protection
ER “network within the cell”
SMOOTH (SER) is continuous with the RER,
but lacks ribosomes
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Activity is a result of enzymes that are
embedded within the membrane
Synthesizes lipids, phospholipids and steroids
in specific cells
In the liver, SER assists with the breakdown of
harmful substances and the regulation of
blood sugar
Can also store calcium ions- necessary for
musculature
ROUGH
SMOOTH
GA (The UPS of the Cell)
Non-interconnected
sacs of “pancakes”
A varied resume:
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Molecular warehouse/finishing factory
Receives and modifies products from the ER
Ships out the secretory proteins from there
Incorporates products that are made within the
cell into the membranes and organelles that they
are destined to become a part of
Lysosomes and Peroxisomes
Lysosomes contain digestive enzymes
(produced in ER and GA)
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Protect cell by being enclosed in a membrane
Engulf nutrients into food vacuoles- then fuse and digest
them
Destroy bacteria or other invaders
Recycling center for damaged organelles
Embryonic development… why we don’t have webbing
Peroxisomes produce hydrogen peroxide and
break it down into water and oxygen; also assist
in the breakdown of various products
Peroxisomes are
SImilar
Lysosomal Storage Diseases
Missing a hydrolytic enzyme that is normally
found in the lysosome
Pompe’s disease: too much glycogen
accumulates in the liver cells
Tay-Sachs: lack a lipid digesting enzyme which
allows the nervous system to be damaged due
to an accumulation of lipids on the cells
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Deadly, though carriers can be detected
Vacuoles
Membranous sacs
Central Vacuole in plants can contain a
large lysosome, or help the cell to grow
by absorbing water
Typically store food, water and waste for
the cell
The Endomembrane System
Chloroplasts
Only found in photosynthetic organisms
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Plants and some protists
Contain an inner and outer membrane
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Intermembrane space in between
Fluid within the inner membrane is known as
stroma
Contain stacks of thylakoid disks, known as
grana
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These are the actual sites where the chlorophyll
traps solar energy
Mitochondria
Convert energy from one chemical form into
another
Carry out cellular respiration
Food/Sugar  ATP, the cell’s energy currency
Also has an outer and an inner membrane
Interior is a fluid area known as the
mitochondrial matrix
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Where the chemical reactions of cellular respiration
occur
Heavily folded (folds = cristae)
Folds
increase
surface
area for
C.R.
Endosymbiosis
Mitochondria and Chloroplasts resemble
their own cells
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Double membranes
Contain their own DNA
Implication is that they were “cannibalized”
by other cells
Cytoskeleton
Supportive network of fibers
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Microfilaments: mainly composed of actin
Often assist with muscle contraction
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Microtubules: composed of tubulins
Elongate(stretch)
Provide anchorage for organelles
A network of “railroad” tracks?
Cilia and Flagella
Cilia: short, numerous appendages
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Paramecium
Flagella: longer, less numerous
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Euglena
Both assist with movement
Similar in physical structure to centrioles
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Involved with cellular division
Comparing the
2
Cell Surfaces and Junctions
Mostly for Support
Cell junctions allow them to connect to each
other
Plasmodesmata form channels between cells so
that they can interact appropriately as tissue
Extracellular matrix holds the “tissue” together
Tight junctions make a “leak-proof surface” <think
stomach acid..>
Anchoring Junctions hold cells loosely together
so that substance scan still flow between them
Communicating Junctions allow for cells to share
necessary substances
Connections
Forming
channels
Thus, there are four main
functional categories
Manufacture:
Breakdown:
Energy Processing
Support, Movement, and Communication
Thus, there are four main
functional categories
Manufacture:
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Nucleus, Ribosomes, RER, SER, GA
Breakdown:
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Lysosomes, Peroxisomes, Vacuoles
Energy Processing
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Chloroplasts, Mitochondria
Support, Movement, and Communication
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Cytoskeleton, Cell Walls, Extracellular Matrix,
Cell Junctions
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