Bacteria Chapter 20 Sections 1

What Are Prokaryotes?  Single-celled organisms that do not have membrane-bound organelles  Found in 3 shapes:  Bacillus – rod shaped  Coccus – sphere shaped  Spirillum – spiral shaped  Divided into 2 major groups:  Archaea Bacteria – found in extremely harsh environments such as salt lakes and hot springs  Eubacteria – called “true bacteria”; found everywhere; generally the type of bacteria that causes sickness in humans

BACTERIAL SHAPES

Bacterial Structure  Bacteria have genetic information in the form of DNA  Bacterial DNA is a single chromosome clustered in a mass called a NUCLEOID  Bacteria often have small extra loops of DNA called plasmids  PLASMID- a circular DNA molecule in bacteria  Bacterial cell membranes are lipid bilayers (like animal cells)  Bacteria have a rigid cell wall that is made of a protein- carbohydrate compound called PEPTIDOGYLCAN

GRAM STAINING  The presence or lack of a membrane covering the peptidoglycan cell wall determines if a bacteria is considered “gram-positive” or “gram- negative”.  Gram-Positive Bacteria  Have a thick layer of peptidoglycan and NO outer membrane  Appear purple after staining because their peptidoglycan layer traps the purple dye and so when the pink dye is absorbed it cannot be seen because the purple dye is so much darker  Gram-Negative Bacteria  Have a thin layer of peptidoglycan and DO HAVE an outer membrane  Appear pink after staining because the purple dye is not trapped, therefore the pink dye can be absorbed by the cell and seen

Gram Staining Illustrations

Structure of Bacteria

Grouping Bacteria  Bacteria are divided into 3 groups based on how they obtain energy and nutrients  Photoautotrophs – organisms that get their energy from sunlight through photosynthesis  Ex: Cyanobacteria  Chemoautotrophs – organisms that get their energy from inorganic sources (sulfur and nitrogen-containing substances)  Heterotrophs – organisms that both get their energy and nutrients from other organisms  Most absorb energy from dead organisms or are parasites/pathogens

Reproduction in Bacteria  There are 3 types of reproduction that prokaryotes may use:  Binary Fission  Genetic Recombination  Endospore Formation

Binary Fission  Prokaryotes usually reproduce asexually by binary fission  Binary Fission occurs when a single cell divides into two identical new cells  Mutations do occur during prokaryotic reproduction, and new forms emerge frequently

Genetic Recombination  There are 3 ways that prokaryotes can form new genetic combinations:  Conjugation – when 2 bacteria exchange genetic material  Transformation – when bacteria take up DNA fragments from their environment  Transduction – when genetic material, such as a plasmid, is transferred by a virus

Endospore Formation  Some bacteria survive harsh conditions by forming thick-walled structures called ENDOSPORES  Endospores form inside the bacteria and surround the DNA and a small bit of cytoplasm  Endospores survive boiling, radiation, and acid  The bacteria show no signs of life but can be revived after hundreds of years