Microscopes provide windows to the world
of the cell
Cellular Diversity• The average adult has
nearly 100 trillion cells• There are about 200
different types of cells• Cells come in a variety
of shapes and sizes• Cellular diversity
permits organization of cells into more complex tissues and organs
History of the Microscope• 1665, Robert Hooke described cells using
a light microscope• Magnification vs resolution• Highest magnification of l.m. = 1000x• 1950, Electron microscope allowed
researchers to clearly identify organelles• There are 2 types:
– Transmission– Scanning
Transmission Electron Microscope
(TEM)• e- transmitted through
specimen are focused • image magnified by
electromagnetic lenses to bend trajectories of charged e- – Used to study internal cell
structure – Image is focused onto a viewing
screen/film
Scanning Electron Microscope
(SEM)• e- beam scans surface of
specimen that is coated with a thin film of gold
• Beam excites secondary e- on sample’s surface
• Secondary e- are collected & focused on viewing screen– Useful for studying surface of
specimen– SEM has great depth of field &
produces 3D image
SEM images
Disadvantages of Electron microscopes
• Can usually only view dead cells because of the elaborate preparation required
• May introduce structural artifacts
Cell Fractionation
• Technique that enables researchers to isolate organelles without destroying their function– Disrupted cells are
centrifuged to isolate components of different sizes, densities, and shapes
Surface area: volume ratio
Place in order depending on which will dissolve fastest slowest•granulated sugar•Powdered sugar•Sugar cube•Fine sugar
Why do you cut up potatoes to boil them?
Cells
• Prokaryotic vs Eukaryotic• Cell sizes (0.1-100um)
– What limits a cell from being too large?– Too small?
• Eukaryotic cells have 1000x volume of prokaryotic cells, but only 100x the surface area. How can they compensate for the small surface area to volume ratio?
Prokaryote“before nucleus”
Eukaryote“true nucleus”
A Generalized CellCytoplasm
- all the cellular contents between the plasma membrane and the nucleus- cytosol - the fluid portion, mostly water*site of many chem. Rx.- organelles - subcellular structures having characteristic shapes and specific functions
The cytoskeleton - network of protein filaments throughout the cytosol-provides structural support for the cell-three types according to increasing size: microfilaments (cables), intermediate filaments (cables), and microtubules (support beams)
Resist tension
Bearingtension
Resistcompression
Organelles• Centrosome -
located near the nucleus, consists of two centrioles
Cilia and Flagella Cilia - short, hair-like projections from the cell surface, move fluids along a cell surface
Flagella - longer than cilia, move an entire cell; ex. sperm cell’s tail
Internal Membranes• Partitions cell into compartments• Have unique lipid & protein compositions
depending upon their specific fx.• Participate in metabolic reactions
(enzymes)
• 1. Nuclear envelope - a double membrane that separates the nucleus from the cytoplasm
– Nuclear pores - numerous openings in the nuclear envelope, control movement of substances between nucleus and cytoplasm
– Nucleolus - spherical body that produces ribosomes
Class I: membrane derived
2. Endoplasmic reticulum - network of membranes in the shape of flattened sacs or tubules
- Rough ER - connected to the nuclear envelope, a series of flattened sacs, surface is studded with ribosomes, produces various proteins
-Smooth ER - a network of membrane tubules, does not have ribosomes, synthesizes fatty acids and steroids, detoxifies certain drugs
•3. Golgi complex - consists of 3-20 flattened, membranous sacs called cisternae - modify, sort, and package proteins for transport to different destinations- proteins are transported by various vesicles
4. Vesicles
• Sacs made of membrane
• Transport substances throughout cell and to/fro membrane
5. Vacuoles
• Food vacuole formed by phagocytosis (protists & macrophages)
• Contractile vacuole pumps excess water from cell (protozoans)
• Central vacuole enclosed by membrane (tonoplast); stores organic compounds, ions, poisons, provides turgor pressure (plants)
6. Lysosomes• Sequesters destructive enzymes from cytosol• Maintains optimum acidic environment for enzyme
function
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Peroxisome• Bound by a single
membrane derived from lipids w/i cell
• Contains enzymes that transfer Hydrogen atoms from various substrates to oxygen (H2O2).
• Contains catalase that converts H2O2 to water.
• Breaks down fatty acids • Detoxification of alcohol &
other poisons (liver)
Class II: bacteria like organelles (energy production)
Mitochondria - the “powerhouses” of the cell– Generate ATP– More prevalent in
physiologically active cells: muscles, liver and kidneys
– Inner and outer mitochondrial membranes
– Cristae - the series of folds of the inner membrane
– Matrix - the large central fluid-filled cavity
– Self-replicate during times of increased cellular demand or before cell division
Class III: Involved in Gene Expression
