bacteria and viruses- microbiology

what are pathogens

microorganisms that cause disease

how do prokaryotic cells differ from eukaryotic cells

• much smaller

• A cytoplasm that lacks membrane-bound organelles

• Ribosomes that are smaller (70 S) than those found in eukaryotic cells (80 S)

• No nucleus, instead having a single circular bacterial chromosome that is free in the cytoplasm and is not associated with proteins

• A cell wall that contains the glycoprotein murein 

  • Murein is sometimes known as peptidoglycan

what do all bacteria have

• a bacterial cell wall containing peptidoglycan murein

• a cell surface membrane similar to those in eukaryotic cells

• a nucleoid ( a single, circular stran of DNA that is the genetic material of the bacterium)- no nucleus

• 70S ribosomes which are the site of protein synthesis

• A cytoplasm that lacks membrane-bound organelles

what do some bacteria have

• pili- thread-like projections from the surface of the cell wall that enable the bacteria to attach to other cells or surfaces

  • Involved in gene transfer during sexual reproduction

• flagella- long rapidly rotating whip-like structures which can mvoe the bacteria about. Some prokaryotes have more than one

• a capsule or slime layer- a thick slippery substance around the outside of the cell wall. It helps to protect bacteria from drying out and from attack by cells of the immune system of the host organism

• mesosomes- internal extensions of the membrane which fold into the cytoplasm and may be the site of cellular respiration

• plasmids- small circles of additional DNA that code for specific characteristics

role of viruses

• all act as pathogens

• scientists use viruses to produce genetically modified organisms and they hope to use viruses to attack some of the bacteria that cause disease

what are viruses

viruses are the smallest of the microorganisms ranging from 0.02-0.3 micrometers.

non cellular infectious particles

not cells- arrangement of genetic material and protein that invade living cells and take control of the cellular biochemistry to make more viruses

this reproduction and the fact that they change and evolve in an adaptive way means they are classed as living organisms

what are obligate intracellular parasites?

• viruses classed as obligate intracellular parasites

• can only exist and reporduce as aparasites only in the cells of other livign organisms

• cause some kind of damage and disease as they take control of living cells to reproduce

• they can resist drying and long periods of storage and still maintian their ability to infect cells

• very few drugs have effect on viruses

what do all viruses have

All have:

• a protein coat or capsid which consists of simple repeating protein units known as capsomers arranged in diff ways. The amount of genetic material needed to code for coat production is minimised by using these repeating units. These units also make assembling the protein coat in teh host cell as simple as possible

• nucleic acids actign as genetic material- either DNA or RNA.

• VAPS (viral attachment particles) which target proteins in the host cell surface membrane. Specific in tissue they attack and molecules they respond to and how viruses attach to cells they infect. They stick out from the capsid or envelope

• They do not possess a plasma membrane, cytoplasm, or ribosomes

what do only some viruses have

• a lipid envelope which is produced from the host cell membrane and which covers the genetic material and protein coat. The prescence of the envelope makes it easier for the viruses to pass from cell to cell, but makes them vulnerable to substances such as ether which will dissole the lipid membrane

• Some contain proteins inside the capsid which perform a variety of functions

  • E.g. HIV contains the enzyme reverse transcriptase which converts its RNA into DNA once it has infected a cell

how viruses reproduce

• Viruses can only reproduce by infecting living cells and using the protein-building machinery of their host cells to produce new viral particles

how are viruses classified

classifies by their genome and their mode of replication

the form of genetic material influences how the virus makes new viruses in the host cell

what are DNA viruses

• have DNA as their genetic material

• the DNA acts directly as a template for both the viral DNA and for the mRNAs needed to induce synthesis of viral proteins.

• Examples: smallpox, adenoviruses, and bacteriophages

  • Bacteriophages are viruses that infect bacteria, such as the λ (lambda) phage

what are RNA viruses

• have RNA as their genetic material

  -Most have a single strand of RNA

  -They do not produce DNA at all

• much more likely to mutate than DNA viruses

• RNA viruses don’t produce DNA as part of their life cycle. Majority of RNA virus contian a single strand of RNA

• eg plant and animal disease caused by RNA virus influde tobacco mosaic virus, ebola fever. polio, influenza and measles

what is retrovirus

• a special type of RNA virus that does produce DNA

• They contain a single strand of RNA surrounded by a protein capsid and lipid envelope

• the single strand of viral RNA controles the syntehsis of reverse transcriptase which is responsible for makign DNA molecules from the single strand of RNA

• This DNA is then incorporated into the host cell DNA using integrase enzymes and is used as a template for new viral proteins and ultimately a new viral RNA genome

• HIV is retrovirus and some forms of leukemia also caused by retrovirus