Mcat Bio: Microbiology

Front 1

Features of a lysogenic infection

Back 1

-Viral DNA is incorporated into host DNA (or if the virus has an RNA and the enzyme reverse transcriptase, the DNA is reverse transcribed and then incorporated).
- Virus in this form is known as a temperate virus.
- Virus is said to be dormant or latent while it remains incorporated and may have no effect (known as a provirus or prophage if host is a bacterium)
- Stress may cause dormant virus to become active.

Front 2

Plus vs Minus strand RNA viruses

Back 2

Plus-strand indicates that proteins can directly be translated from the RNA. Examples include common cold (unenveloped) and AIDS (enveloped retrovirus)
Minus-strand is the complement to mRNA and must be transcribed to plus-RNA before being translated. Examples include measles, rabies, flu.

Front 3

Define a retrovirus

Back 3

Carries the enzyme reverse transriptase in order to create DNA from its RNA.
Eg. HIV

Front 4

Define:
1. Viroids
2. Prions

Back 4

1. Viroids are rings of naked RNA without capsids and only infect plants.
2.Naked proteins which cause infections in animals and can reproduce without DNA or RNA.

Front 5

Define spike proteins

Back 5

Proteins encoded from viral nucleic acids which protrude from the envelope of the host. These proteins bind to receptors on other host cells causing the virus to be infectious.
Antibodies work by detecting these spike proteins.
Note: these proteins may change since RNA polymerase does not contain a proofreading mechanism.

Front 6

Key feature of prokaryotes and classification.

Back 6

Do not have membrane bound nucleus.
Divided into Archae and Bacteria. Archaea have as much in common with eukaryotes as they do with bacteria.

Front 7

Different sources of carbon.

Back 7

- Autotrophs are capable of using CO2 as their sole source of carbon (carbon is reduced through an energy expensive process via the calvin cyccle)
Heterotrophs use preformed organic molecules as their source of carbon.

Front 8

Different sources of energy for prokaryotes.

Back 8

Phototrops - use light
Chemotrophs - oxidation of orgranic and inorganic matter.

Front 9

Lithotrophs vs organotrophs

Back 9

Lithotrophs obtain electrons and hydrogens from inorganic matter, organotrophs do so from organic matter.

Front 10

Define carbon dioxide fixation

Back 10

Process by which CO2 is reduced to create organic molecues through a process known as the Calvin cycle.

Front 11

Define nitrogen fixation

Back 11

Process by which N2 is converted to ammonia. Is a very enery expensive process.

Front 12

Features of chemoautotrphy

Back 12

Very energy expensive. Requires large amounts of substrate. Large environmental impact.
All known chemoautotrophs are prokaryotes.

Front 13

Features of a virus

Back 13

Comparable in size to large proteins.
Contains a capsid - protein coat.
Contains either DNA or RNA but not both.
Some viruses may surround themselves with a lipid envelope either borrowed from the host or snythesized using the host cell machinery.

Front 14

Define virion

Back 14

A mature virus outside the host cell.

Front 15

Differences between viruses and living organisms

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1. Viruses always require host cell machinery to reproduce.
2. Do not metabolize nutrients - use host ATP.
3. Viruses in active form are not separated from the external environment.
4. Can possess DNA or RNA but never both.
5. Can be crystallized w/o losing ability to infect.

Front 16

Describe process of viral infection.

Back 16

1. Virus adsorbs to cell surface by attaching to a receptor on the host membrane (usually a glycoprotein).
2. Nucleic acid penetrates into the cell. In bacteriophage, this usually occurs via the tail. In eukaryotes, by an endocytotic process.
3. Virus infects either through the lytic or lysogenic pathways.

Front 17

Describe the lytic infection.

Back 17

Virus commandeers the host machinery and begins to reproduce. Cell may eventually burst (lysis) or release the viruses in a reverse endocytotic process.
Time between infection and production of first virus: eclipse period.
Time before lysis: latent period.
Virus following the lytic cycle is called a virulent virus.

Front 18

Define plus-strand RNA

Back 18

RNA from which proteins can be directly translated.

Front 19

Define minus-strand RNA

Back 19

RNA which is the complement to mRNA and must be transcribed before translation can occur. Examples include measles.

Front 20

Define retrovirus

Back 20

virus which possesses reverse transcriptase which creates DNA from RNA, which is then incorporated into the host.

Front 21

Other types of viruses

Back 21

Double stranded RNA viruses, single and double stranded DNA viruses.

Front 22

Viroids

Back 22

Small rings of naked RNA without capsids.

Front 23

Location of periplasmic space in gram positive and negative bacteria

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"Gram +: between plasma membrane and cell wall

Front 24

External features of bacteria

Back 24

Capsule(protection), slime layer (can be washed off), fimbraie/pili : not used in motility, used to attach to surfaces; flagella - made of flagellin (different from eukaryotic flagella

Front 25

Features of flagella

Back 25

Long, hollow, rigid helical cylinders made from the globular protein called flagelng. They rotate ccw to propel, cw to tumble and change direction. Propelled using proton gradient.

Front 26

Key difference between prokaryotes and eukaryotes

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Prokaryotes do not have a nucleus, eukar. have at least one. Pkyts for the most part have no complex, membrane bound organelles

Front 27

Nuclear structire of prokaryotes.

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- Do not have a nucleus. Instead have a single circular double stranded molecule of DNA. - molecule twisted into supercoils with assoc. histones (archaea) and histone equivalents (bacteria)

Front 28

Structure formed by prkyt DNA, RNA and protein complex visible under a microscope

Back 28

nucleoid

Front 29

Bacterial shapes

Back 29

cocci, bacilli, spirilla (rigid helical), spirochetes (non-rigid helical)

Front 30

T/F prkyts have RNA and ribosomes

Back 30

True - prkyt ribosomes are smaller.

Front 31

Mesosome

Back 31

Present in some pkyts in various shapes. Appear as bubbles in microscope. Thought to be involved in cell wall formation during division

Front 32

Inclusion bodies

Back 32

Granules of organic or inorg. Matter which may or may not be bound by a mebrane

Front 33

Main component of plasma membrane

Back 33

Composed of a phospholipid bilayer. Note: phospholipid is ampiphatic

Front 34

Micelle formation

Back 34

Spherical structure formed by ampiphatic mols. in aq. soln. The molecules aggregate with the polar end facing outwards and non-polar end facing inwards.

Front 35

Liposome

Back 35

Vesicle surrounded and filled by aq soln. Formed when critical mass of phospholipids are agitated by UV

Front 36

Proteins that traverse from inside to outside of cell

Back 36

Intrinsic/Integral proteins.

Front 37

Proteins that exist only on one surface

Back 37

Extrinsic/peripheral proteins.

Front 38

T/F: membrane lipids and proteins move easily from one leaflet to the other

Back 38

FALSE since lipid or protein would have to traverse across the non-polar core

Front 39

Cholesterol present on euk. or pkyt cell membranes?

Back 39

Euk cells. Pkyt cells have hopanoids insteand which are equivalent to cholesterol

Front 40

Role of cholesterol on euk. membranes

Back 40

regulates fluidity

Front 41

Fluid mosaic model

Back 41

A model used to conceptualise cell membranes, in it, the membranes are described as a structually and functionally asymmetric lipid bilayer studded with embedded proteins that aid in cross-membrane transport.

Front 42

Diffusion is caused by:

Back 42

Brownian motion

Front 43

Rate of diffusion governed by:

Back 43

Electro-chemical gradient

Front 44

Direction of diff.

Back 44

Direction of greatest entropy

Front 45

Semipermeability

Back 45

Allowing passage of certain, especially small, molecules or ions but acting as a barrier to others. Degree of permeability governed by both size and polarity

Front 46

How is water mostly transported to the cell?

Back 46

Leakage channels. Water transport solely through the bilayer would be too slow. Note: these channels are a consequence of irregularly shaped integral proteins, and are not explicitly designed to transport water.

Front 47

Features of facilitated diff.

Back 47

- requires transport proteins - occurs down a conc. Gradient - makes the membrane selectively permeable to certain substances (usually ones that are too large or charged to passively diffuse)

Front 48

Active transport

Back 48

Transport of substances against the conc. Gradient with the expense of ATP.

Front 49

Primary vs secondary active transport

Back 49

-Primary: ATP breakdown directly causes substance transport Secondary: ATP breakdown establishes the conc. gradient of another substance. Energy in this gradient then harnessed for the active transport.

Front 50

Protoplast

Back 50

Plasma membrane of bacterium and everything inside. Usually surrounded by a lipid envelope

Front 51

What is bacterial cell wall made of?

Back 51

Peptidoglycan (aka murein) - a series of disaccharide polymer chains w/ amino acids. These chains are connected by amino acid interbridges. It is more elastic and porous than cellulose

Front 52

Features of gram-positive bacteria

Back 52

Thich peptidoglycan cell wall absorbs the gram stain and shows up as purple. Have a cell wall 4x thicker than plasma membrane

Front 53

Features of gram-negative bacteria

Back 53

Appear pink when stained. Thin peptidoglycan cell wall. Outside the cell wall, bacteria has a lipid bilayer which is more porous than the cell wall. This bilayer has lipopolysaccharides which can form a barrier against antibodies

Front 54

Location of periplasmic space in gram positive and negative bacteria

Back 54

Gram +: between plasma membrane and cell wall Gram -: between cell wall and outer bilayer

Front 55

External features of bacteria

Back 55

Capsule(protection), slime layer (can be washed off), fimbraie/pili : not used in motility, used to attach to surfaces; flagella - made of flagellin (different from eukaryotic flagella

Front 56

Features of flagella

Back 56

Long, hollow, rigid helical cylinders made from the globular protein called flagelng. They rotate ccw to propel, cw to tumble and change direction. Propelled using proton gradient.