Bacteria and Viruses Chapter 19 Bacteria Viruses 19

Bacteria and Viruses Chapter 19

Bacteria & Viruses

19. 1 Bacteria l Come in many shapes and sizes l Most common microorganisms are prokaryotes l Average size of 1 -5 micrometers – Compared to eukaryotic cells that are 10 -100 micrometers in diameter

2 Branches of Bacteria (Domains) l Archebacteria (similar to early Earth) – Confined to extreme environments Methanogens - reduce CO 2 to CH 4 Extreme halophiles - salt loving – Thermoacidophiles – Similar to early earth More closely related to eukaryotes than to modern bacteria – – – l Eubacteria (most modern) – very diverse

Bacterial Classification

Prokaryotic Phylogeny

Prokaryotic & Eukaryotic Cells

Classifying Prokaryotes l Eubacteria – – – Largest prokaryote Domain Lack nuclei Cell wall of a carbohydrate- Peptidoglycan Cell membrane around cytoplasm Some have an extra cell wall on the outside to resist damage

Classifying Prokaryotes l Archaebacteria – – Lack nuclei Have cell walls without peptidoglycan Are chemically different from Eubacteria Many live in extremely harsh environments

Bacteria Shapes

Identifying Prokaryotes l Shapes – – – Bacilli- Rod shaped Cocci- Spherical shaped Sprilla- spiral shaped Colorized SEM 9, 000 Colorized SEM 12, 000

Identifying Prokaryotes l Cell walls – Gram staining used to tell them apart – Gram+ bacteria look purple – Gram- bacteria look pink

The Bacterial Cell Wall l Instead of cellulose, contain peptidoglycan – l l A polymer of modified sugars cross-linked with amino acids The gram stain distinguishes many disease causing bacteria based on the type of cell wall Many antibiotics work by attacking the bacterial cell wall

The Gram Stain l Gram (+) Purple – – l accept gram stain have simpler cell walls with large amounts of peptidoglycan Gram (-) Pink – – – do not stain have more complex cell walls with less peptidoglycan cell walls contain lipopolysaccharides are more likely to be pathogenic (cause disease) more resistant to antibiotics

Cell Wall & Gram Stain

Gram (+) & Gram (-) Gram (+)Purple & Gram (-)Pink

Identifying Prokaryotes l Movement – Flagella – Lash, snake or spiral forward – They do not move at all

Motility (movement) l l About half are capable of directional movement. 3 mechanisms: – – – l flagella - different from eukaryotes spiral shaped bacteria (spirochetes) have a filament that spirals around the cell under the outer sheath some bacteria secrete slimy chemicals & glide Taxis – – movement toward or away from a stimulus many bacteria exhibit this form of movement

Structures of Movement

Structure of Prokaryotic Flagella

Metabolic Diversity l Heterotrophs – Chemoheterotrophs: must take in organic molecules for energy and carbon – Photoheterotrophs: Use sunlight for energy but need organic compounds for a carbon source

Metabolic Diversity l Autotrophs – Chemoautotrophs: perform chemosynthesis to make carbon from carbon dioxide. Does not require sunlight – Photoautotrophs: use light to convert carbon dioxide and water into carbon compounds and oxygen gas.

Getting Energy l Bacteria need a constant supply of energy l Obligate aerobes- require constant supply of oxygen l Obligate anaerobes- need no oxygen, for some oxygen will kill it l Facultative anaerobes- survive with or with out oxygen

Growth and Reproduction l Binary fission (to split) l Conjugation l Spore formation

Binary Fission

Bacterial Conjugation

Endospores (example: Anthrax) l Some bacteria form resistant cells called l Resist extremes of temperature, p. H, etc. endospores (11, 000 year old spores found)

Importance of Bacteria l l l Only a minority cause disease Many are essential to life on earth Decomposers – l Nitrogen Fixers – l l Break down dead matter Converts nitrogen into a form plants can use Humans use Bacteria Often live in symbiotic relationships with other organisms

19. 2 Viruses What is a virus? – Particles of nucleic acid and proteins – Core made up of DNA or RNA surrounded by a capsid Head – Need to infect a living host to reproduce Tail fiber DNA 300, 000 l

Viral Structure

Bacteriophage

Are Viruses Alive? l l l Viruses contain nucleic acids & proteins Viruses, by themselves, cannot make or use food, grow or reproduce Some scientists believe viruses were never independently living organisms Others believe viruses evolved from simple bacteria like mycoplasmas & rickettsiae Another hypothesis: viruses are genes that have escaped from the genomes of living cells Not much evidence to support any one of these

Viral Infection l Lytic Cycle – – – Virus attaches to host cell Injects its DNA Host makes RNA from viral DNA Cell begins to make copies of virus New viruses form Host cell bursts

Lytic Cycle of the T 4 Phage

Viral Infection l Lysogenic Cycle – – – Virus attaches to host cell Injects DNA Viral DNA incorporates itself into the host DNA Viral DNA can be dormant Once it becomes active, it follows the 4 processes in the lytic cycle

Lytic and Lysogenic Cycle (video) l http: //www. youtube. com/watch? v=g. U 8 Xeq. I 7 yts &feature=related

Phage Lytic and Lysogenic Cycles

Viral Infection l Retrovirus: Genetic information is RNA – Produces DNA copy and creates a prophage Envelope – Example: HIV/AIDS Glycoprotein Protein coat RNA (two identical strands) Reverse transcriptase

19. 3 Diseases Caused by Bacteria and Viruses l Pathogens- disease causing agents l Bacterial Disease l Viral Diseases

Diseases Caused By Bacteria l How does bacteria produce disease? – Damage the cells and tissues by breaking down the cells for food – Releasing toxins (poisons into the body)

Preventing Diseases l Vaccines l Immunity l Antibiotics

Controlling Bacteria l Sterilization l Disinfectants l Proper food storage

Diseases Caused by Viruses l Viruses disrupt the body’s normal equilibrium l Cannot be treated with antibiotics l Viruses can infect humans and plants

Virus-like Particles (Viroids) l Viroids- single stranded RNA molecule with no capsid – They cause diseases in plants – Infect cell and produce more viroids by disrupting the plant metabolism

Virus-like Particles (Prions) l Prions- contain only protein; no DNA or RNA – They cause diseases in animals and humans – Prions clump and cause normal protein to clump with it- creating new prions

Prion Action

Chapter 19 Viruses and Bacteria Multiple Choice Practice Questions

19– 1 –Which characteristic distinguishes eubacteria from archaebacteria? l l Eubacteria lack peptidoglycan in their cell walls. Eubacteria contain peptidoglycan in their cell walls. Eubacteria lack a nucleus. Eubacteria do not possess mitochondria.

19– 1 – Rod-shaped prokaryotes are called l l bacilli. cocci. spirilla. streptococci.

19– 1 – Bacteria that must live without oxygen are called l l obligate aerobes. facultative anaerobes. obligate anaerobes. facultative aerobes.

19– 1 – Prokaryotes that make their own food molecules from carbon dioxide and water but live where there is no light are called l l photoautotrophs. photoheterotrophs. chemoautotrophs. chemoheterotrophs.

19– 1 – Bacteria that attack and digest the tissue of dead organisms are called l l decomposers. nitrogen fixers. chemoautotrophs. archaebacteria.

19– 2 – Viruses that contain RNA as their genetic information are known as l l prions. oncoviruses. retroviruses. bacteriophage.

19– 2 – The first type of virus to be studied was the l l bacteriophage. tobacco mosaic virus. influenza virus. AIDS virus.

19– 2 –Which l l of the following statements about viruses is true? Viruses appear similar to bacteria when studied with a light microscope. Viruses display the essential characteristics of living things. Viruses can reproduce independently if they contain DNA. Viruses cannot reproduce unless they infect a living cell.

19– 2 – A virus integrates its DNA into the DNA of the host cell but remains inactive for a while in l l a lytic infection. a lysogenic infection. neither a lytic nor a lysogenic infection. retroviral infection.

19– 2 – Retroviruses are considered unique because l l they have RNA in their capsid and not DNA. they have DNA in their capsid and not RNA. after infection of a host cell, their RNA makes DNA. after infection of a host cell, their DNA makes RNA.

19– 3 –Biologists l l know that bacteria can cause human disease by entering cells and using the cell to make new bacteria. producing toxic substances that interfere with normal cell functi decomposing the remains of dead organisms. changing atmospheric nitrogen into nitrogen compounds.

19– 3 –Biologists l l know that bacteria can cause human disease by entering cells and using the cell to make new bacteria. producing toxic substances that interfere with normal cell functio decomposing the remains of dead organisms. changing atmospheric nitrogen into nitrogen compounds.

19– 3 – A process that destroys bacteria by subjecting them to great heat is known as l l refrigeration. sterilization. pickling. boiling.

19– 3 – Which of the following diseases is transmitted by a mosquito bite? l l influenza measles West Nile virus chickenpox

19– 3 – Which of the following diseases is thought to be caused by prions? l l diphtheria mad cow disease tuberculosis smallpox

19– 3 – The best way to combat viral diseases is l l to use antibiotics. to treat individual symptoms. to use preventive vaccines. to let the disease “cure itself. ”