Two important factors in microscopy are:
1) Magnification: an increase in the object’s apparent size compared with its actual size. 2) Resolving Power: the ability of an optical instrument to show two objects are separate.
Three types of microscopes:
1) Light Microscope (LM) M: 1000x RP 0,2 micrometer (small bacterial cell) 2) Electron Microscope (EM) uses a beam of electrons to resolve electrons, better resolving powers than light microscope M:100,000x RP 0,2 nanometer
A) Scanning Electron Microscope (SEM) Surface
B) Transmission Electron Microscope (TEM) Internal Structure
Preparing specimen for electron microscope hard, light microscope still very useful as a window on living cells.
The Two Major Categories of Cells
Prokaryotic Cells (Bacteria and Archaea)
| Eukaryotic Cells (Protists, plants, fungi and animals)
| Older in Evolutionary Sense
| Younger in Evolutionary Sense
Simpler in structure
| Have organelles, membrane-enclosed structures that perform specific functions
| Nucleoid, not partitioned from the rest of cell.
| Most important organelle: nucleus, double membrane, hosts most of the DNA
| Circular DNA
| Linear DNA
1) All bounded by Plasma Membrane: regulates the traffic of molecules between the cell and its surroundings. 2) DNA
3) Ribosomes: tiny structures that build proteins according to instruction from the DNA
Overview of Eukaryotic Cells
Plant cells have:
1) Central vacuole
2) Cell Wall
Animal cells have:
The plasma membrane is the boundary that separates the living from its non-living environment The plasma membrane can regulate the traffic of chemical into and out of the cell.
Plasma membrane and others composed of mostly lipids and proteins. Lipids belong to special category phospholipids: two tails (water fearing) + phosphate group (+, water-loving) --> Phospholipid bilayer
Embed in the phospholipid bilayer of most membranes are proteins that help regulate traffic across the membrane and perform other functions.
The phospholipids and most of the proteins are free to drift about in the plane of the membrane: fluid mosaic.
Plant cells have a cell wall surrounding the plasma membrane made from cellulose fibers embedded in a matrix of other molecules. 1) Protect the cells
2) Maintain cell shape
3) Keep cells from absorbing so much water they burst
Plant cells are connected via channels that pass through the cell walls, joining the cytoplasm of each cell to that of its neighbors.
Animal cells have no cell way, but most of them have the extracellular matrix. 1) Hold cells together in tissues
2) Can have protective or supportive functions
Also most animals’ cells contain cell junctions, structures that connect to other cells. Cell junctions allow cells in a tissue to function in a coordinated way.
The Nucleus and Ribosomes: Genetic Control of the Cell
Nucleus is the executive boardroom of the cell.
Structure and Function of the Nucleus
Nucleus is bordered by a double membrane (similar to plasma membrane) called the nuclear envelope. Pores allow certain materials to pass between the nucleus and cytoplasm.
Within the nucleus, long DNA molecules and associated proteins form fibers called chromatin, each long chromatin fiber constitutes one chromosome.
Chromosomes are made of chromatin.
Chromatin is a combination of DNA and proteins.
Number of Chromosomes depends on species.
The nucleolus, is where ribosomes are made.
Ribosomes are responsible for protein synthesis. Components of ribosomes are made in the nucleus, then transported through the pores into the cytoplasm. There they begin their work: 1) Some are suspended in the fluid of the cytoplasm, making proteins that remain in the fluid. 2) Others are attached to the outside of...
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