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46 terms

MCAT - Chap 3 - Microbio

Viruses
STUDY
PLAY
Simplest form of a virus
capsid (protein coat) + DNA or RNA (NEVER both)
How do virsuses differ from living things?
1. require host machinery to reproduce
2. do not metabolize organic nutrients (steal host ATP)
3. Living things have both RNA and DNA
Two types of virus infection
1. lysogenic infection
2. lytic infection
Lytic infection
virus takes over cell's repro machinery and begins reproducing new viruses
--> cell fills with virus until it lyses or bursts
--> latent period: time between infection and lysis
--> Virulent virus
Lysogenic infection
-lysoGENIC
-viral DNA integrated into chromosome
-if virus only have RNA, it also has reverse transcriptase, which makes the DNA
--> temperate virus
---> can be activated, at which point the virus becomes virulent
Retrovirus
-a plus-strand RNA virus
-uses reverse transcriptase to create DNA from RNA
-plus-strange RNA is basically like fake mRNA
Minus-strand RNA virus
-is the complement to an mRNA (or, to a plus-strand RNA virus)
-must be made into a plus-strand RNA virus and then transcribed
Viroids
small rings of naked RNA without capsids
Prions
-naked proteins can cause infections
-do not need RNA or DNA to reproduce
Prokaryotes
-no membrane-bound nucleus
-split into bacteria and archaea
-where archaea: extreme environments, similarities to eukaryotes
-bacteria: most prokaryotes
What do all organisms need to grow?
1. carbon
2. energy
3. electrons (usually from hydrogen)
What does it mean to fix CO₂? (CO₂ is an inorganic material, no hydrogens)
-reducing it and using the carbon to create --> energy-expensive
--> Calvin cycle
Autotrophs vs. Heterotrophs
Autotrophs: organisms that can use CO₂ as their only carbon source
Heterotrophs: use preformed, organic molecules as carbon source
How do all organisms get energy?
1. light
2. oxidation of organic or inorganic matter
Phototrophs vs. chemotrophs
Phototrophs: light as energy source
Chemotrophs: oxidation of organic or inorganic matter as energy source
Lithotrophs vs. organotrophs
Lithotrophs: electrons (hydrogren) from inorganic matter
Organotrophs: electrons (hydrogren) from organic matter
What is nitrogen fixation?
N₂ is converted into ammonia
Prokaryotes vs. eukaryotes
Prokaryotes:
-no nucleus
-single, circular, double-stranded DNA [Arachaea have histones, bacteria have other proteins, in this sense arachaea are more like eukaryotes]
-no membrane-bound organelles


Eukaryotes:
-yes nucleus
-
Nucleoid
Kind of like a nucleus but for prokaryotes
-aka chromatin body, nuclear region, nuclear body
--> nucleoid is NOT enclosed by a membrane
Bacteria shapes
-cocci = round
-bacilli = rod shaped

spirilla - helical, rigid
spirochetes - helical, not rigid
Mesosome (in prokaryotes)
--> invaginations of the plasma membrane (just little pockets, basically)
-exact function unknown
Inclusion bodies (prokaryotes)
-granules of organic or inorganic matter that are visible under a microscope
-can have a single layer membrane or not!
What's that plasma membrane all about?
-phospholipid bilayer
-phosphate group (ballon) + two fatty acids (two strings) + glycerol (the thing that connects them)
Amphipathic
-e.g. phospolipid bilayer
-both polar and non-polar
Micelle vs. liposome vs. bilayer sheet
Micelle - ballon outside, two strings inside
Liposome - a round lipid BI-layer
bilayer sheet - a liposome that's been ironed flat
Fluid mosaic model
-lipid bilayers are held together by intermolecular forces --> membrane is fluid and can move laterally, but can't seperate

Membrane fluidity can be tamped down by stuff in teh bipaler:
eukaryotic: cholestrol moderates membrane fluidity
prokaryotic: hopanoids moderate membrane fluiditiy
Brownian motion
particles always randomly moving through space
--> compounds have a tendency to mix completely over time
Concentration gradient direction (chemical, electrical)
chemical: high concentration --> low concentration

Electrical: positive charge --> negative charge
Two aspects of a compound that affect semi-permermeability
1. size: the larger, the less permeable
2. polarity: the greater the polarity, the less permeable

--> very large lipid soluable (nonpolar) molecules like steroid hormones can pass right through membranes
Hypertonic
hyper= above

To put a cell in a hypertonic solution means that the SOLUTION will have a higher concentration than the cell
Hypotonic
hyper= below

To put a cell in a hypotonic solution means that the SOLUTION will have a lower concentration than the cell
Hyrdostatic pressure
pressure of water within the cell
Osmotic pressure
pressure that needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane
Isotonic solution and water movement
water flows in
water flows out

SAME proportions
A cell in hypertonic solution
water flows out of cell
A cell in hypotonic solution
water flows into cell
What color do gram-positive bacteria stain?
positive = purple
--> thick peptidoglycan walls
What color do gram-negative bacteria stain?
negative = pink
--> thin peptidoglycan walls
Bacterial Reproduction
-bacteria don't reproduce sexually
-use 'genetic recombination'
Genetic recombination (3 types)
Genetic recombination:
1. conjugation (through plasmids)
2. transformation (picking up external DNA)
3. transduction ()
What's the word for bacterial asexual reproduction?
binary fission:
-circular DNA replicated similar to replication in eukaryotes
-a single cell splits in two
1. replication (increase in size, makes duplicate of chromosome)
2. cell divides
3. two separate and identical cells
Plasmid
small circles of DNA that exist and replicate independently of the bacterial chromosome
Two important plasmids?
F Plasmid: fertility factor
R Plasmid: resistance factor (confers lots of immunity from antibiotics)
Saprophytic (Fungi)
living off dead organic matter
Septa fungi
possess cell walls
chiting fungi
polysacharrode cell walls