Prokaryotes Part I

Introduction to Cells Compound Light Microscope: Allows light to pass through a specimen and magnifies the image with lenses Ch. 7

Electron microscopes: Use beams of electrons to produce images. Scanning EM: Produces three-dimensional images Transmission EM: Produces images that look almost like light microscope images (but much more magnified)

Anton van Leeuwenhoek First to create glass of a high enough quality to be useful in microscopes. First person to observe single celled organisms (which he called animalcules - “little animals”) Observed bacteria, spermatozoa, muscle

Robert Hooke Used a crude compound microscope First to see and identify cork cells. Coined the term “cells.”

The Cell Theory All living things are made of cells Cells are the basic structural and functional unit of life New cells arise from pre-existing cells

Amoeba Sea Urchin Embryo Corn Leaf Cell

Why are cells so small? Cells are small for two possible reasons: Increase surface area Cells need nutrients Cells need to get rid of waste materials These nutrients/wastes must move out of the cell – if the cell were large it would have to move large distances to exit the cell Permit specialization Having a large number of cells allows there to be different types of cells doing different things

Cell Types Cells are classified based on internal structures (or lack thereof) Eukaryotic (eu-: true; -kary-:nucleus): Animals Plants Fungi Protists Prokaryotic (pro-: before; -kary-: nucleus): Bacteria

Animal Eukaryotic Cells Very complicated cells Contain little membrane-bound structures that have specific functions (organelles: “little organs”) Nucleus is well defined – contains DNA Nucleus was discovered by Robert Brown Organelles are suspended in a jelly-like substance called the cytoplasm Everything is held inside of the cell by a membrane called a cell membrane

Animal Cell

Plant Eukaryotic Cells Almost identical to animal cells except they have three more organelles than animals cells Cell wall: allows plants to stand upright Chloroplast: where photosynthesis takes place Large Central Vacuole: storage compartment

Plant Cell

Bacterial Prokaryotic Cells Simplest cells The first forms of life were probably bacterial cells (or something like it) Lack membrane-bound organelles Contain cytoplasm (cell jelly) All prokaryotes are unicellular

Characteristics of Prokaryotes con't Do not possess a distinct nucleus Nucleoid: Ill-defined region of the cell where the DNA is usually located. DNA Loop: DNA is a long single fiber that contains almost all of the genetic material of the cell. Plasmid: Small circular loop of DNA that contains the rest of the genetic material Can be transferred between bacterial cells Can contain genes for antibiotic resistance

Characteristics con't Have ribosomes floating freely in the cytoplasm The ribosome is where proteins are made Certain antibiotics (tetracycline and streptomycin) prevent prokaryotic ribosomes from working Most prokaryotes have a cell wall Some can develop a capsule Many prokaryotes have a flagellum (or multiple flagella, plural) for movement

Cell Wall Functions: Give the cell shape Protects the cell from hostile environmental conditions Made up of peptidoglycans (mesh of sugars and proteins) Two types Gram-positive cell wall Gram-negative cell wall Penicillin and Lysozyme

Capsule Jelly-like coating that surrounds the cell wall Composed of carbohydrates More common in gram-negative bacteria Four functions: Prevent dessication (drying out) Help bacterial cells stick to each other or to other surfaces (e.g., tissues of other organisms) Protect bacteria from antibiotics Prevent bacteria from being phagocytized.

Capsule con't Capsule Bacterial Cell

Flagellum Provides movement Proteins that stick out through holes in the cell membrane Spin like propellers