Chapter Six A Tour of the Cell

CELLS A cell is the basic unit of a living thing that can perform all the processes associated with life Single cell or Unicellular: ex. Paramecium and bacteria Many cells or Multi-cellular: ex. Animals and plants Non-living things have no cells

The Microscope Types: Light microscope (LMs) visible light passes through the specimen and then through glass lenses. The lenses refract light such that the image is magnified into the eye or a video screen. Magnification is the ratio of an object’s image to its real size. Resolving power is a measure of image clarity LM cannot resolve the internal anatomy of organnels

Electron microscope (EM), focuses a beam of electrons through the specimen or onto its surface With shorter wavelengths than visible light therefore, finer resolution. Transmission electron microscopes (TEM) are used mainly to study the internal ultrastructure of cells. Scanning electron microscopes (SEM) are useful for studying surface structures. Microscopes are a major tool in cytology, the study of cell structures.

Study of cell functions Cells function can be studied by separating the major organelles The process used to separate the organelles is called Fractionation The process involved the centrifugation of cells to separate the different parts and studying the functions

Fractionation begins with homogenization, gently disrupting the cell Fractionation begins with homogenization, gently disrupting the cell. Then, the homogenate is spun in a centrifuge to separate heavier pieces into the pellet while lighter particles remain in the supernatant

Three major parts of the cell Nucleus: this is the control center for all cell’s activities PLASMA MEMBRANE: controls the entrance and exit of substances in and out of the cell Cytoplasm: this consists of all living matter in the cell except the nucleus Organelles float in the cytoplasm

A Composite Cell hypothetical cell major parts nucleus cytoplasm Plasma membrane 3-3

Cytoplasmic Organelles Endoplasmic Reticulum connected, membrane-bound sacs, canals, and vesicles transport system rough ER studded with ribosomes protein and lipid synthesis smooth ER lipid synthesis break down of drugs Ribosomes free floating or connected to ER site of protein synthesis 3-8

Cytoplasmic Organelles Golgi apparatus group of flattened, membranous sacs packages and modifies proteins Mitochondria membranous sacs with inner partitions generate energy 3-9

Cytoplasmic Organelles Lysosomes enzyme-containing sacs digest worn out cell parts or unwanted substances Centrosome two rod-like centrioles used to produce cilia distributes chromosomes during cell division Peroxisomes enzyme-containing sacs break down organic molecules 3-10

Cytoplasmic Organelles Cilia short hair-like projections propel substances on cell surface Flagellum long tail-like projection provides motility to sperm 3-11

Cytoplasmic Organelles Vesicles membranous sacs store substances Microfilaments and microtubules thin rods and tubules support cytoplasm allows for movement of organelles 3-12

Cell Nucleus control center of cell nuclear envelope nucleolus porous double membrane separates nucleoplasm from cytoplasm nucleolus dense collection of RNA and proteins site of ribosome production chromatin fibers of DNA and proteins stores information for synthesis of proteins 3-13

Vacuoles: this serves for the storage of food, water and wastes Chloroplast: found only in plants, contains chlorophyll which traps energy from the sun to produce glucose Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact. Plant cells are perforated with plasmodesmata, channels allowing cysotol to pass between cells.

1. Plant cells are encased by cell walls The cell wall, found in prokaryotes, fungi, and some protists, has multiple functions. In plants, the cell wall protects the cell, maintains its shape, and prevents excessive uptake of water. It also supports the plant against the force of gravity. The thickness and chemical composition of cell walls differs from species to species and among cell types.

Animal have 3 main types of intercellular links: tight junctions, desmosomes, and gap junctions. In tight junctions, membranes of adjacent cells are fused, forming continuous belts around cells. This prevents leakage of extracellular fluid.

Desmosomes (or anchoring junctions) fasten cells together into strong sheets, much like rivets. Intermediate filaments of keratin reinforce desmosomes. Gap junctions (or communicating junctions) provide cytoplasmic channels between adjacent cells. Special membrane proteins surround these pores. Salt ions, sugar, amino acids, and other small molecules can pass. In embryos, gap junctions facilitate chemical communication during development.

The cell theory Living things are composed on one or more cells Cell is the basic unit of organization of an organism All cells come from preexisting cells

Eukaryotes vs. Prokaryotes True nucleus No nucleus Membrane bound The genetic material DNA is concentrated in the nucleoid No membrane Examples: plants and animals Examples: Bacteria, virus and amoeba

Animals vs. Plant cells Animal Cells Plant cells Home work?