bio - bacteria + viruses

good sources: https://www.khanacademy.org/science/biology/biology-of-viruses/virus-biology/a/intro-to-viruses https://www.khanacademy.org/science/biology/biology-of-viruses/virus-biology/a/bacteriophages

pathogen

pathogen

something that spreads disease

characteristics of a virus

• no nucleus or cell membane

• non-living

• Made only of a strand of DNA or RNA

• contains a protein code (capsid) and at times a lipid envelope (protective outer coat)

characteristics of bacteria

• prokaryote (single-celled)

• no nucleus

• causes illness

viroid

• a circle of RNA

• specifically infects plants (stops it from producing protein)

prion

• only made of protein

• causes misfolding of proteins in host

  • results in diseases related to the brain

bacteriophages

how bacteria inject DNA into host (pierce host cells)

endocytosis

the method by which viruses of eukaryotes enter and fuse with the membrane

• uses the host’s enzymes to produce proteins and copies of itself

2 main types of infections:

1) Lytic infection: a type of viral infection in which the virus enters a host cell, hijacks the cells to replicate itself, and then causes the host cell to burst (lyse), releasing newly formed virus particles to infect neighboring cells.

2) Lysogenic: involves the integration of viral DNA (or RNA in some cases) into the host cell's genome. Instead of immediately hijacking the cells to replicate and cause cell lysis, the viral genetic material becomes part of the host's DNA and is replicated along with it as the cell divides.

vaccine

contains form of weakened pathogen so body learns to produce correct antibodies in response to a viral disease

examples of viral infections

• cold

• flu

• SARS

• HIV

characteristics of HIV

• composed of RNA

  • retrovirus

• infects eukaryotic hosts

• injects DNA through endocytosis

• infects immune cells specifically

similarities between bacteria and archaea?

• single-celled

• prokaryotes

• (no nucleus)

• reproduce through binary fission

• both considered pathogens

  • cause disease

what do (bad) bacteria do?

produce toxins that infect cells and dismantle their proper functions

major characteristic of prokaryotes

grouped by need for oxygen (obligate aerobe)

obligate aerobe

need oxygen

obligate anaerobe

oxygen = toxic

facultative aerobe

can live with or without oxygen

bacteria and archaea are _______ similar but have different ________ characteristics

structurally, molecular

3 forms of bacteria:

• bacili

  • rod-shaped

• spirilla

  • spiral

• cocci

  • spherical

why do they sound like types of pasta

3 main parts of bacteria:

• plasmid

• flagellum (tail)

• pili (hair-like structure)

molecular differences between bacteria and archaea?

the amount of peptidoglycan within a cell wall differ between B and A

archaea have entirely different lipids present in their cell membrane

*peptidoglycan is also the specific trait identified and targeted by antibiotics

Why is it hard to say whether viruses are alive or not?

Viruses cannot reproduce if they are alone — they need living cells to help them.

describe virus (again)

• Made only of a single strand of DNA or RNA surrounded by a protein coat.

• Need living cells in order to reproduce and to make copies.

• Much smaller than most cells.

• Not classified by Linneaus.

composed of:

1. A protective protein shell, or capsid

2. A nucleic acid genome made of DNA or RNA, tucked inside of the capsid

3. A layer of membrane called the envelope (some but not all viruses)

describe viroid

• Has less in common with living things than viruses do.

• Cause disease in plants.

• Made of a single strand of RNA.

• Unlike viruses, they do not have a protein coat.

describe prion

• Made only of proteins that can cause other proteins to fold incorrectly.

• Contain no genetic material.

• Cause brain diseases such as Alzheimer’s/dementia.

Does not have genes

prion

Includes infectious bacteria

pathogen

Made of only RNA

viroid

Any living thing or particle that can cause infectious disease

pathogen

Made only of protein

prion

Infects plants

viroid

Made of genetic material surrounded by a protein coat

virus

Can contain RNA or DNA but is not living

virus

What is the protein shell around each viral particle called?

capsid

What must viruses do before they can reproduce?

infect the host cell

A virus cannot infect a host cell unless…

its surface proteins fit receptor molecules on the host cell’s surface

How do the structures of bacteriophages help them infect host cells?

they contain spikes that help attach them to the cells of the host organism

why do they look like the cookie robots from despicable me

Lytic infection

• Attachment: Proteins in the "tail" of the phage bind to a specific receptor (in this case, a sugar transporter) on the surface of the bacterial cell.

• Entry: The phage injects its double-stranded DNA genome into the cytoplasm of the bacterium. DNA copying and protein synthesis: Phage DNA is copied, and phage genes are expressed to make proteins, such as capsid proteins.

• Assembly of new phage: Capsids assemble from the capsid proteins and are stuffed with DNA to make lots of new phage particles.

• Lysis: Late in the lytic cycle, the phage expresses genes for proteins that poke holes in the plasma membrane and cell wall. The holes let water flow in, making the cell expand and burst like an overfilled water balloon.

  • lysis releases hundreds of new phages, which can find and infect other host cells nearby.

Lysogenic infection

• Allows a phage to reproduce without killing its host.

• In the lysogenic cycle, the first two steps (attachment and DNA injection) occur just as they do for the lytic cycle.

• However, once the phage DNA is inside the cell, it is not immediately copied or expressed to make proteins.

  • Instead, it recombines with a particular region of the bacterial chromosome. This causes the phage DNA to be integrated into the chromosome.

• The integrated phage DNA, called a prophage, is not active: its genes aren't expressed, and it doesn't drive production of new phages. However, each time a host cell divides, the prophage is copied along with the host DNA

Virus that infects bacteria

bacteriophage

Viral DNA plus host cell DNA

prophage

Protein shell of a virus

capsid

Infection where virus combines its DNA with host cell’s DNA

lysogenic

Infection where host cell bursts, releasing viral offspring

lyctic

What is the body’s first defense against infection?

white blood cells

What is one way in which viruses commonly enter the body?

through mucous membranes in the nose or mouth

How do some viruses trick cells into letting them in?

by using their surface proteins as “keys” to the cell’s receptors

Why is it not easy to find a cure for the common cold?

because cold viruses often mutate as they move from one person to another

Why must a new flu vaccine be made every year?

New mutations of the flu appear every year that are different from the previous year’s flu.

Why might a person who has AIDS have a hard time fighting off normally harmless microorganisms?

The HIV virus attacks white blood cells from the body’s immune system

A vaccine is a weakened / strengthened version of the same pathogen that causes the disease that the vaccine is intended to prevent.

weakened

Vaccines work by provoking the body’s immune system into a mild / strong response, so that it will recognize the pathogen again in the future if it should encounter it.

mild

Vaccines cause the body’s immune system to react when it meets the surface proteins / cell membrane of a bacteria or virus.

surface proteins

Vaccines are usually one way / the only way that scientists can fight against the spread of a viral infection.

the only way

Contains RNA and uses a special enzyme to make a DNA copy

retrovirus

Rapid outbreak of an infection that affects many people

epidemic

Stimulates the body’s own immune response against invading microbes

vaccine

Bacteria and archaea together make up the most widespread group of organisms on Earth, the __________

prokaryotes

Some prokaryotes are poisoned if they come into contact with oxygen. Where might you find one?

a. in a desert

b. in the digestive tract of a cow

c. on a polar ice cap

d.in a body of water

b. in the digestive tract of a cow

Bacteria vs Archaea

bacteria:

• Common, widespread

• Cell walls contain a polymer called peptidoglycan.

archaea:

• Found in extreme environments.

• Cell walls membranes contain lipids that are
  not found in any other organism on Earth.

both:

• Small, single-celled organisms

• Have cell walls and plasma membranes

• Most have the ability to reproduce on their own.

true / false Binary fission, which means “division in half,” is a method scientists use when they are studying prokaryotes.

false

Can survive whether oxygen is present or not

facultative aerobe

Long whiplike structure in bacteria used
for movement

flagellum

Needs oxygen to survive

obligate aerobe

Cannot live in the presence
of oxygen

obligate anaerobe