Bacteria and Viruses

Chapter 20

20.1 - Bacteria

Prokaryotes – single-celled organisms that do not have membrane bound organelles

Has three shapes: Bacillus – rod-shaped Coccus – sphere-shaped Spirillum – spiral-shaped

Bacterial Structures

Plasmid – a circular DNA molecule in bacteria

Ribosome – site of protein synthesis

Cell wall Cell membrane

Plasmid

Bacterial Structures

Flagella – long whiplike projection that moves side to side

Cytoplasm – gel-like substance found inside the cell

Ring of DNA

Obtaining Energy and Nutrients Photoautotrophs – organisms that get their

energy from sunlight through photosynthesis Ex. – cyanobacteria

Chemoautothrophs – the only organisms that can get their energy from inorganic sources Inorganic – does not contain carbon atoms

Heterotrophs

Reproduction

Binary fission – reproduce by asexual reproduction A single cell divides into two identical cells

Conjugation – occurs when two bacteria exchange genetic material

20.2 - Viruses

Viruses are not considered living because they can’t reproduce on their own, and they can’t grow

Viral Structures

Nucleic acid – The genetic material of a virus can be either DNA or RNA

Capsid – the protein coat

Envelope – a membrane surrounding the capsid

Envelope

Viral Structures

Tail fibers – function like a tiny syringe which injects the viral DNA into its bacterial host Bacteriophage – viruses

that infect bacteria

Bacteriophage

Reproduction

Lytic cycle – viral replication that results in the destruction of a host cell and the release of many new virus particles

Reproduction

Lysogenic cycle – viral replication in which viral genetic information is made without immediately destroying the host cell Viruses undergo lysogentic cycles can remain

dormant

Viroids and Prions

Viroid – a single strand of RNA that has no capsid

Viroids cause abnormal development and stunted growth in plants

Viroids and Prions

Prions – misshapen versions of proteins that are found in the brain They attach to normal proteins and cause them to

take on the shape of the prion

20.3 – Bacteria, Viruses, and Humans

Bacteria and the Environment Bacteria produce oxygen, make nitrogen

available to other organisms, and help decompose dead organisms.

Bacteria and Industry

Foods, such as pickles, soy sauce, and sourdough bread, are made by using bacteria

Bacteria is used in cleaning up oil spills and in sewage treatment plants

Koch’s Postulates

Robert Koch, a German physician, developed a technique for diagnosing a pathogen Pathogen – an organism or virus that causes

disease

Bacterial Diseases

Bacteria can cause disease by producing toxins and by destroying body tissues Toxins – poisonous chemicals

Ex. of toxins – Foods contaminated with bacteria can cause food poisoning.

Ex. of destroying body tissues – necrotizing fasciitis

Antibiotic Resistance

Antibiotics – chemicals that inhibit the growth of or kill bacteria

Antibiotic resistance – the ability of bacteria to tolerate antibiotics

Antibiotic Resistance

Penicillin was used for most bacterial infections

Do not overuse antibiotics Ex. of resistance – hand sanitizer

Viral Diseases

Because viruses enter the host cells to reproduce, it’s difficult to develop a drug that kills the virus without harming the living cell.

Antibiotics are not designed to kill viruses Vaccine – a weakened form of a pathogen

that prepares the immune system to recognize and destroy the pathogen Ex. – flu shot