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Cell Structure and Function

Bio 100

Tri-County Tec. College

Pendleton, S. C.

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Tools to observe cells--

Microscopes– light– transmission electron– scanning electron

Each has a unique value to the person studying cells.

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The Light Microscope

uses visible light for illumination magnifies to 1000x (some to 2000x) good for looking at most cells living cells can be observed not good for looking at cell parts

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Two important concepts Magnification defined as “how much

larger/bigger the object appears” Calculated by multiplying the objective

by the ocular (40X objective x 10X ocular = 400 X magnification)

Resolution is the ability of a microscope to show two objects as distinct or separate from each other

Catch 22 to be sure Chalk talk time on resolution

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Transmission Electron Micros.

electron beam for illumination magnifies 100,000x or more specimen has to be dead and cut into

thin sections good for observing cell parts

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Scanning Electron Micros.

electron beam for illumination can visualize 3D surfaces of whole

specimens specimen must be dead good for looking a surface architecture

of cells

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Let’s Review Cell Theory The cell is the structural and functional

unit of life Whatever “life” is, it begins at the

cellular level All living things are composed of one or

more cells Cells can only come from preexisting

cells Another Catch 22 is spontaneous

generation versus biogenesis

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The Cell Membrane

Composed of a phospholipid bi-layer with proteins embedded in it

fluid-mosaic model– proteins are randomly distributed in the

membrane (mosaic)– proteins are not static in position (fluid)

membrane contains pores

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Cell Membrane, ctd.

movement of materials through pores– if smaller than the pores

lipid soluble substances– dissolve in the membrane and move in on

the other side the membrane is selectively permeable carrier proteins

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Organelles of the cell

“little organs” that carry out the functions of the cell

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Endoplasmic Reticulum

Looks like a maize in the cytoplasm smooth endoplasmic reticulum (SER)

– does not contain ribosomes rough endoplasmic reticulum (RER)

– contains ribosomes system of channels for internal cellular

transport

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Golgi Apparatus

Looks like a stack of pancakes usually near the ER packages cellular secretions for export

from the cell In some cells, hormones are produced

in the ER and the Golgi Apparatus packages these for export.

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Ribosomes

Some are located in ER others float free in cytoplasm both kinds are the places where

proteins are synthesized composed of RNA (ribosomal-RNA) protein synthesis takes place in the

cytoplasm

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Mitochondria

Sites of energy production (ATP synthesis via cellular respiration)

use oxygen to produce ATP shaped somewhat like a peanut reactions of energy production take

place on numerous membranes that form the inside of the mitochondrion

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Centrioles

form the structures that are involved in pulling the chromosomes apart during cell division.

each cell has two line up at opposite ends of a dividing

cell and establish the direction at which division will take place

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Nuclear Organelles

located in or associated with the nucleus– nuclear membrane– chromatin– nucleolus– chromosomes

nuclear membrane– controls what enters and exits the nucleus

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Nuclear Organelles--2

Chromatin– stretched out chromosomes– long, thin strands of DNA

Nucleolus– looks like a small nucleus inside the

nucleus– synthesizes ribosomes

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Nuclear Organelles--3

chromosomes– before cell division chromatin condenses

into chromosomes– composed of DNA– genes are locations on a chromosome that

contain directions for making a specific human protein

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Cytoskeletal Elements

Microtubules and microfilaments microtubules

– hollow cytoskeletal elements microfilaments

– solid cytoskeletal elements support the cell from the inside

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Organelles of Locomotion

Cilia and flagella flagella

– long, whiplike structures that cause certain cells to move

– human sperm cell has a flagellum cilia

– short structures that move materials over the surfaces of certain human tissues

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Inclusions

storage areas in the cell somewhat like closets surrounded by a membrane usually spherical in shape like a beach

ball plant cells usually have more inclusions

than do animal cells

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Lysosomes

Lysosomes

–membranous sacs of powerful digestive enzymes

–digest worn out cell parts and foreign matter in the cytoplasm

–“garbage collectors” of the cell

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Peroxisomes

membranous sacs of oxidizing enzymes detoxify poisons by oxidation cells produce hydrogen peroxide which

is a poison peroxisomes destroy hydrogen peroxide “detox” centers

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Chloroplasts

Found only in plant cells location for photosynthesis

– production of glucose from carbon dioxide and water

contain chlorophyll (a and b) Also contain carotenoids and

phycobilins

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Meanwhile, back at the ranch..

Plant cells joined together into tissues by cell junctions

Sticky middle lamella cements adjacent cells together

Each plant cell connected to adjoining cells by plasmodesmata

Tiny channels that allow cytoplasm to be continuous between the cells

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Extracellular Matrix

Animal cells have elaborate ECM composed mostly of glycoproteins

Tight junctions=continuous belts around cells (membranes of neighboring cells fused at tight junctions)

Anchoring junctions (desmosomes)=rivets fastening cells together into strong sheets

Communicating junctions (gap)=provide cytoplasmic channels between adjacent cells

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Eucaryotic vs. Procaryotic

One is complex, the other is simple.

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Procaryotic Cell

simple, unorganized cell no membrane-bound organelles no nuclear membrane

– no nucleus division by binary fission r/t mitosis small simple ribosomes examples: bacteria (K. Procaryotae)

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Eucaryotic Cell

complex, well organized cell membrane-bound organelles nuclear membrane division involves mitosis the kind of cell we are composed of and

that we have been discussing members of all other kingdoms

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The End

The language of the cell is a key to understanding the science of Biology.