The Building Blocks of Life Cells & Cell Organelles The Building Blocks of Life 2008-2009

Cell Theory Cells first described by Hooke – 1665 First LIVING cells described by Leeuwenhoek Schleiden – all plants made of cells Schwann – all animals made of cells Virchow – all cells come from pre-existing cells Principles of Cell Theory cells are the basic units of life all living things are composed of cells cells come only from other cells

animal cells plant cells bacteria cells Types of cells Prokaryote - no organelles Eukaryotes - organelles animal cells plant cells

Cell size comparison most bacteria eukaryotic cells 1-10 microns Bacterial cell Animal cell most bacteria 1-10 microns eukaryotic cells 10-100 microns Animation micron = micrometer = 1/1,000,000 meter diameter of human hair = ~20 microns

Prokaryote/Eukaryote DNA comparison Prokaryotes lack internal organization – NO organelles Prokaryote DNA shaped as a closed ring floating in cytoplasm Nucleoid region Eukaryote DNA in linear chromosomes enclosed in a nucleus

Prokaryote/Eukaryote Cell Wall Comparison Prokaryotes all have cell walls Unique composition - peptidoglycan Eukaryotes may or may not have cell walls Animal cells – none Plant cells – cell walls made of cellulose Fungal cells – cell walls made of chitin

Prokaryote vs. Eukaryote Cell Wall of peptidoglycan No membrane bound organelles Ribosomes are present DNA in a ring, floating in the cytoplasm May or may not have cell walls Membrane bound organelles DNA enclosed in a nucleus and arranged in linear chromosomes

Plant Cell vs. Animal Cell Cell Wall of cellulose Large Central Vacuole Chloroplasts No cell wall Vacuoles are small and transient No chloroplasts

Observing Cells – How We Know What We Know… Light Microscopes Remember Hooke and Van Leeuwenhoek Magnification Size of image Resolving power Clarity of image Observing Organelles Too small for light microscope Electron Microscope Scanning EM External views Transmission EM Thin sections of specimen – internal views

TEM vs SEM – both are images of cells from a rabbit trachea (windpipe) TEM vs SEM – both are images of cells from a rabbit trachea (windpipe). Cilia are visible.

Why are cells small? With size increase, volume grows more than surface area. Small objects have larger surface area:volume ratio Cell/Plasma membrane functions as selective barrier Enough oxygen, nutrients, wastes must pass in to service entire volume of the cell Only so much “stuff” can pass through at a time. Need a surface large enough to accommodate volume, thus cells have to be small.

Eukaryotic Cells and Complex Internal Membranes Membranes create ORGANELLES Partition cells into compartments Provide separate “little rooms” so that incompatible processes can go on at the same time in the cell Internal membranes of cells participate directly in metabolism Enzymes are often built directly into membranes Chemical reactions occur at such sites All membranes are similar, but different All made of phospholipid bilayer But suited to specific functions due to embedded enzymes, etc.

Why study cells? Cells  Tissues  Organs  Bodies bodies are made up of cells cells do all the work of life!

The Work of Life What jobs do cells have to do for an organism to live… “breathe” gas exchange: CO2 vs. O2 eat take in & digest food make energy ATP build molecules proteins, carbohydrates, fats, nucleic acids remove wastes control internal conditions respond to external environment build more cells growth, repair, reproduction & development ATP

Stay Tuned for an in depth Tour of the Eukaryotic Cell! 2008-2009