Microscopes provide windows to the world of the cell
Feb 25, 2016
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