Lecture 2: Cell Structure and Function Flashcards
Cell Structure and Function
four types of light microscopy:
bright-field
phase contrast
dark-field
fluorescence
________ scope
Specimens are visualized because of differences in contrast between specimen
and surroundings
Two sets of lenses form the image
* Objective lens (usually 10x -100x mag.) & ocular lens (usually 10x – 20x mag.)
Bright-field
how to calculate total magnification?
Total magnification = objective
magnification ✕ ocular magnification
- Maximum magnification is ~2,000X
_______: the ability to make an object larger
Magnification
_______: the ability to distinguish two adjacent objects as separate and distinct
Resolution
what is the limit of resolution for a light microscope?
0.2 μm (wavelength of light source can’t fit through anything smaller)
every light source produces a ____
wavelength
low wavelength = high energy
high wavelength = low energy
as wavelength ____, resolution improves
decreases
improving contrast results in a better final image, how do we improve contrast?
staining! we use organic dyes (contain Carbon) that bind to specific cellular materials, common stains are methylene blue, safranin, and crystal
violet
________ – One dye used to color specimen
Simple staining, sticks to everything possible! (non-specific)
________: coloured portion of a dye
Chromophore
what are the two types of simple stains?
Basic dye – positively charged chromophore
* Binds to negatively charged molecules on cell
surface
Crystal violet – basic
Acidic dye – negatively charged chromophore
* Repelled by cell surface
* Used to stain background
* Negative stain
what charge does the cell surface have?
negative charge
what are the three types of differential stains?
gram stain, acid fast stain, endospore stain
______: Separates bacteria into 2 groups based on cell wall
structure
The gram stain
_______ – cells that
retain a primary stain, crystal violet
* Purple
Gram positive
_______ – cells that
lose the primary stain
* Take color of counterstain, safranin
* Red or pink
Gram negative
gram negative cells have how many membranes?
2
gram positive cells have how many membranes?
1
what are the four steps of a gram stain?
Step 1: Flood a heat-fixed smear with crystal violet for 1 minute (all cells are stained purple)
Step 2: Add iodine solution for 1 min (helps crystal violet stick)
Step 3: decolourize with alcohol briefly, washes of crystal violet that is on outer membrane of gram negative cells to make them colourless, gram positive cells remain purple
Step 4: Counterstain with safranin for 1-2 minutes, all cells will be dyed pink but Purple overshadows Pink…
this results in gram positive cells being purple, and gram negative cells being pink-red
_________:
* Detects mycolic acid in the cell wall of the genus Mycobacterium
* Mycobacterium– retains primary stain (Fuchsia (pink))
* Anything else on slide – colour of counterstain
* Blue
Acid fast stain
what does an acid fast stain detect in cell wall of Mycobacterium?
mycolic acid, dyes it pink!
_________:
* Endospores retain primary stain (Green)
* Cells counterstained (Pink)
Endospore stain
_______:
* Phase ring amplifies differences in the refractive index of cell and
surroundings
- Improves the contrast of a sample without the use of a stain
- Allows for the visualization of live samples
- Resulting image is dark cells on a light background
Phase-contrast microscopy
________:
- Specimen is illuminated with a hollow cone of
light - Only refracted light enters the objective
- Specimen appears as a bright object on a dark
background - Used to observe bacteria that don’t stain well
Dark field microscopy
_______:
* Used to visualize specimens that fluoresce
* Emit light of one color when illuminated with
another color of light
Fluorescence microscopy,
higher wavelength absorbed, lower wavelength emitted
true/false: cells may fluoresce naturally, or after staining with fluorescent dye
true!
__________ microscopy:
* Uses a polarizer to create two distinct beams of polarized light
- Gives structures such as endospores, vacuoles, and granules a three-
dimensional appearance - Structures not visible by bright-field microscopy are sometimes visible by _____
Differential interference contrast (DIC)
what are the two ways to image a cell in 3D?
Differential interference contrast (DIC) and Confocal scanning laser microscopy
(CSLM)
________:
* Uses a computerized microscope coupled
with a laser source to generate a three-
dimensional image
- Computer can focus the laser on single
layers of the specimen - Different layers can then be compiled for a
three-dimensional image - Resolution is 0.1 μm
Confocal scanning laser microscopy
(CSLM)
Electron microscopes use electrons instead of ______ to image cells and structures
photons
Two types of electron microscopes?
- Transmission electron microscopes (TEM)
- Scanning electron microscopes (SEM)
_______:
Electron beam focused on
specimen by a condenser
* Magnets used as lenses
Electrons that pass through
the specimen are focused by
two sets of lenses
* Compound microscope
Electrons strike a fluorescent
viewing screen
Transmission Electron Microcope (TEM)
________: provided high magnification and resolution (0.2 nm) but the specimen but be very thin (20-60 nm) and must be stained with metals (lead or uranium)
TEM
how does staining specimen with metals help with visualization using TEM?
Bind to cell structures to make them more electron dense
Enables visualization of structures at molecular level
_______:
Specimen is coated with a thin film of heavy metal (e.g., gold)
* An electron beam scans the object
* Scattered electrons are collected by a detector, and an image is
produced
* Allows an accurate 3D image of specimen’s surface.
Scanning Electron Microscopy (SEM)
what is a big difference between bacteria and archaea?
archaea are ALWAYS non-pathogens, bacteria can be pathogens OR non-pathogens
what are the three types of cell morphology? shapes?
coccus (roughly spherical)
bacillus (rod shaped)
spirillum (spiral shaped)
what are the other three forms of cell morphology?
cells with unusual shapes (spirochete)
budding and appendaged bacteria
filamentous bacteria
true/false: Morphology typically does not predict physiology, ecology,
phylogeny, etc. of a prokaryotic cell
true!
what are the selective forces that can set cell morphology?
optimization for nutrient uptake (small cells and those with high surface-to-
volume ratio)
Swimming motility in viscous environments or near surfaces (helical or
spiral-shaped cells)
Gliding motility (filamentous bacteria)
________ size:
Average:
* E. coli ~ 1.0 x 3.0 µm
* Staphylococcus aureus ~ 1.0 µm diameter
Very small:
* Mycoplasma genitalium~ 0.3 µm
Very large:
* Epulopiscium fishelsonii~ 80 x 600 µm.
prokaryote
what is the advantage to cells being very small?
Small cells have more surface area relative
to cell volume than large cells (i.e., higher S/V)
* Support greater nutrient exchange per unit cell volume
* Tend to grow faster than larger cells
________:
* Thin structure that surrounds the cell
* Vital barrier that separates cytoplasm from environment
* Highly selective permeable barrier; enables concentration of specific
metabolites and excretion of waste products
Cytoplasmic membrane (cell or plasma membrane)
Composition of ________:
* General structure is phospholipid bilayer
- Contain both hydrophobic (fatty acid) and hydrophilic (glycerol-phosphate)
components - Can exist in many different chemical forms as a result of variation in the
groups attached to the glycerol backbone - Fatty acids point inward to form hydrophobic environment; hydrophilic
portions remain exposed to external environment or the cytoplasm
membranes
ester phospholipids contain:
glycerol
2 fatty acids
phosphate
side chain (optional)
phospholipids are…
Amphipathic – has both polar
and non-polar characteristics
Polar: molecule carries full or partial charge
* Hydrophillic
Non-polar: molecule is
uncharged
* Hydrophobic
_________:
* 8–10 nm wide
* Embedded proteins
* Stabilized by hydrogen bonds and hydrophobic interactions
* Mg2+ and Ca2+ help stabilize membrane by forming ionic bonds with
negative charges on the phospholipids
* Somewhat fluid
Cytoplasmic membrane
In gram-negative bacteria, _______ interacts with a variety of proteins (periplasmic proteins) that bind substrates or process large molecules for transport
cytoplasmic membrane
because gram (-) have a double membrane, lots of space between membranes to interact!
Inner surface of cytoplasmic membrane interacts with proteins involved in
_______ and other important cellular functions
energy-yielding reactions
ex: ETC
______ membrane proteins
* Firmly embedded in the membrane
________ membrane proteins
* One portion anchored in the membrane
Integral
Peripheral
archaeal membranes have ____ linkages between phospholipids
bacteria/eukarya have ____ linkages in phospholipids
ether
ester
true/false: based on climate, archaea adjust their membrane structure
true!
what do archaeal lipids have instead of fatty acids?
isoprenes
what are the two types of major lipids
glycerol diethers
glycerol tetraethers
T/F: archaeal membranes can exist as lipid monolayers, bilayers, or mixtures
true! variation in thermal stability
what is the difference between a lipid bilyaer and monolayer?
there’s space between phsopholipids in a bilayer, no space in a monolayer
In contrast to lipid bilayers, lipid monolayer membranes are extremely _________
heat resistant
T/F: in extreme temperatures, DNA has less G-C content to increase thermal stability by increasing # of H-bonds
FALSE! G-C content would INCREASE if we were to increase # of H-bonds
_________ function:
Permeability barrier
* Polar and charged molecules must be transported
Transport proteins accumulate solutes against the concentration gradient
Protein anchor
* Holds transport proteins in place (cytoskeleton)
Energy conservation
* Generation of proton motive force
membrane
three major classes of transport systems in prokaryotes
simple transport
group translocation
ABC system
All require energy in
some form, usually
proton motive force
or ATP
________:
Driven by the energy
in the proton motive
force
Simple transport
__________:
Chemical modification
of the transported
substance driven by
phosphoenolpyruvate
Group translocation
________:
Periplasmic binding
proteins are involved
and energy comes
from ATP.
ABC transporter
_______ transport in one direction across the membrane
Uniporters
_______ function as co-transporters
Symporters
______ transport a molecule across the membrane while simultaneously
transporting another molecule in the opposite direction
Antiporters
Simple transport:
Lac permease of Escherichia coli
- Lactose is transported into E. coli by the simple transporter lac
permease, a _______ – two molecules move across membrane in
same direction - Activity of lac permease is energy-driven
- Transports lactose and a H+ into the cell simultaneously
symporter
Group Translocation - e.g. __________ in E. coli
- Sugar is phosphorylated during transport across the membrane
- Moves glucose, fructose, and mannose
- Phosphoenolpyruvate (PEP) donates a P to a phosphorelay system
- P is transferred through a series of carrier proteins and deposited onto the
sugar as it is brought into the cell
phosphotransferase system
_________ transport systems
- Involved in uptake of organic compounds (e.g., sugars, amino acids),
inorganic nutrients (e.g., sulfate, phosphate), and trace metals - Typically display high substrate specificity
- Gram-negatives employ periplasmic-binding proteins and ATP-driven
transport proteins - Gram-positives employ substrate-binding lipoproteins (anchored to external surface of cell membrane) and ATP-driven transport proteins
ABC (ATP-binding cassette)
Outside the cell membrane
Rigid
Helps determine cell shape
Not a major permeability barrier
Porous to most small molecules
Protects the cell from osmotic
changes
cell walls of Bacteria and Archaea
______: prevents cell expansion – protects against osmotic lysis
- Protects against toxic substances – large hydrophobic molecules
Ex) detergents, antibiotics
Pathogenicity
* Helps evade host immune system
* Helps bacterium stick to surfaces
Partly responsible for cell shape
cell wall
gram (-) cell wall has…
two layers: outer membrane and peptidoglycan
gram (+) cell wall has…
one layer: peptidoglycan
_______:
Rigid layer that provides
strength to cell wall
Polysaccharide composed of:
* N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
* Amino acids
* Lysine or diaminopimelic acid
(DAP)
* Cross-linked differently in gram-
negative bacteria and gram-
positive bacteria
* Form glycan tetrapeptide
peptidoglycan
____ & ____ form disaccharide, creating lattice with amino acids to stabilize it
NAG and NAM
which one cross-links out of NAG and NAM?
only NAM
T/F: gram (+) have more layers of Nag/Nam
true! thicker peptidoglycan layer!
T/F: gram (-) have more layers of Nag/Nam AND an outer membrane
false! they have LESS because their layer of peptidoglycan is smaller due to the outer membrane being present
T/F: More than 100 different PG structures identified, Vary in peptide cross-links
and/or interbridge
True!
Gram-______ cell walls
* Contain up to 90% peptidoglycan
* Common to have teichoic acids (acidic substances) embedded in
their cell wall
* Lipoteichoic acids: teichoic
acids covalently bound to
membrane lipids
positive
________: teichoic
acids covalently bound to
membrane lipids
Lipoteichoic acids
how are Nam and Nag connected in the backbone?
by glycosidic bonds
peptidoglycan strand is _____
helical, allows for 3-dimensional cross-linking
how many layers of peptidoglycan does E. Coli have?
One! because of presence of outer membrane (gram -)
why don’t humans have cell walls/peptidoglycan if they provide so much protection?
we’re multicellular, it would take SO much energy to build cell walls around everything
Prokaryotes that lack cell walls:
_______:
* Group of pathogenic bacteria
* Have sterols in cytoplasmic membrane – adds strength and rigidity to
membrane
_________:
* Species of Archaea
* Contain lipoglycans in membrane that have strengthening effect
Mycoplasmas
Thermoplasma
LPS stands for…
lipopolysaccharide (LPS) layer
OR the outer membrane
in gram negative bacteria, ~____% of cell wall contains peptidoglycan
10%
LPS consists of _______ and ______
* LPS replaces most of phospholipids in outer half of outer membrane
* Endotoxin (lipid A): the toxic component of LPS
core polysaccharide and O-polysaccharide
_______ (lipid A): the toxic component of LPS
Endotoxin
endotoxin (lipid A) is a…
potent immune activator, causes a massive immune response which causes inflammation/vasodilation which leads to sepsis and organ failure
_______: space located between cytoplasmic and outer membranes
* ~15 nm wide
* Contents have gel-like consistency
* Houses many proteins
Periplasm
______: channels for movement of hydrophilic low-molecular-weight
substances
Porins
how does alcohol wash prevent crystal violet stain from exiting peptidoglycan in gram (+) bacteria?
alcohol dehydrates cell walls so pores in wall close, trapping CV complex inside
________ cell walls:
No peptidoglycan
Typically no outer membrane
Pseudomurein
* Polysaccharide similar to peptidoglycan
* Composed of N-acetylglucosamine and N-acetyltalosaminuronic acid
* Found in cell walls of certain methanogenic Archaea
archaeal
T/F: Cell walls of some Archaea lack pseudomurein
true!
why do archaea use pseudomurein instead of peptidoglycan?
their environment may not support peptidoglycan structure (extreme living conditions) so they use pseudomurein instead!
_______:
* Most common cell wall type among
Archaea
* Consist of protein or glycoprotein
* Paracrystalline structure
* Some Archaea have only ______ (no other cell wall components)
* Most have additional cell wall elements
S-Layers
T/F: Because they lack peptidoglycan, Archaea are resistant to
lysozyme and penicillin
true!
______ – material bounded by plasma membrane (PM)
Cytoplasm
_______ – PM and everything within
* Macromolecules – amino acids, nucleotides, etc
* Soluble proteins
* DNA and RNA (nucleoid)
Protoplast
Proteins are made of polypeptides…
Polypeptide?
a long polymer of amino acids joined by peptide bonds
_______:
Region that contains the genome
The typical bacterial genome:
* Single circular double stranded (ds) DNA
chromosome
* May have one or more plasmids
* Smaller circular dsDNA
* Self-replicating
* Carry non-essential genes
* Selective advantage
* Ex) Genes for antibiotic resistance
the Nucleoid
______:
* Carries genetic info of all living cells
* Polymer of deoxyribonucleotides
DNA
T/F: everything alive is single-stranded
FALSE! everything living is double-stranded…
viruses are single-stranded and are NOT living
more evolved organisms have this type of ribosome
Plasma-membrane associated ribosomes
they’re membrane proteins that make proteins to be exported from the cell
__________:
- Polysaccharide / protein layers
- May be thick or thin, rigid or flexible
- Assist in attachment to surfaces
- Protect against phagocytosis
- Resist desiccation
Capsules and slime layers
capsules and slime layers ae outside of…
EVERYTHING! plasma membrane AND cell wall
T/F: capsule bacteria can’t be consumed by phagocytes
true! phagocytes have a standard for initial attachment that must be met- doesn’t include capsules
______:
* Filamentous protein structures
* Enable organisms to stick to surfaces or form pellicles
Fimbriae
_____:
* Filamentous protein structures
* Typically longer than fimbriae
* Assist in surface attachment
* Facilitate genetic exchange between cells (conjugation)
* Type IV ___ involved in twitching motility (by polymerizing/depolymerizing)
Pili
____ are SUPER generous with genetic information which is not so good for humans, since they give away harmful information to pathogens that want to harm us!
pili
pili can only give information using ______ transmission, not passed down to offspring
horizontal
HOW do pili pass information?
using their hollow channel (pilus), connnects cytoplasmic environment of one cell to another
_______:
Visible aggregates in cytoplasm
Carbon storage polymers
* Poly-β-hydroxybutyric acid (PHB): lipid
* Glycogen granules: glucose polymer
Polyphosphates: accumulations of inorganic phosphate
Sulfur globules: composed of elemental sulfur
Magnetosomes: magnetic storage inclusions
cell inclusion bodies
_______: accumulations of inorganic phosphate
Polyphosphates
_______: composed of elemental sulfur
Sulfur globules
______: magnetic storage inclusions
Magnetosomes
elemental sulfur is at what stage?
intermediate reduction stage
we use carbon storage polymers for…
fight/flight! quick source of energy for blood glucose glycolysis from glycogen granules
we use polyphosphates for….
storage of phosphate and energy
we use sulfur globules for…
energy generation, oxidzied sulfur can be food for other molecules and sulfate can be an electron acceptor (ETC)
we use magnetosomes…
to give the cell magnetic properties and allow it to orient itself in a magnetic field
_______: magnetic movement
magnetotaxis
________:
Confer buoyancy in planktonic cells
Spindle-shaped, gas-filled
structures made of protein
Function by decreasing cell density
Impermeable to water
Gas vesicles
_______:
Highly differentiated cells resistant to heat, harsh chemicals, and radiation
Dormant stage of bacterial life cycle
Ideal for dispersal via wind, water, or animal gut
endospores
only gram _____ can make endospores
positive
T/F: endospores can survive extreme environments, only go into active form when conditions are ideal to them
true!
a ______ cell is capable of normal growth, is metabolically active
vegetative
an _____ is a dormant cell, formed inside of a mother cell
endospore
endospores are triggered by….
lack of nutrients, takes about 8-10 hours
Protective features of the endospore
______:
* Spore coat and cortex – protect against chemicals, enzymes, physical
damage, and heat
* Two membranes – permeability barriers against chemicals
_______:
* Dehydrated – protects against heat
* Ca-dipicolinic acid and SASPs
* Protect against DNA damage
Layers
Core
T/F: endospores can resist
Boiling for hours
UV, g radiation
Chemical disinfectants
Dessication
Age
true!
what are the seven stages of the lifecycle of a spore forming bacterium?
Stage 1: Asymmetric cell division
* DNA replicates
* Identical chromosomes pulled to opposite ends of the cell
Stage 2: Septation
* Divides cell into 2 unequal compartments:
* Forespore (prespore)
* Mother cell
Stage 3: Mother cell
engulfs the forespore
* Forespore surrounded by
two membranes
Stage 4: Formation of the cortex
* Thick layers of peptidoglycan form between the two membranes
* Highly cross-linked layer – core wall
* Loosely cross-linked layer – cortex (~½ of spore volume)
Stage 5: Coat synthesis
* Protein layers surround the core wall
* Spore coat
* Exosporium
* Protect the spore from chemicals and enzymes
Calcium, dipicolinic acid and small acid soluble proteins (SASPs) accumulate in
the core
* Help stabilize DNA
Stage 6: Endospore matures
* Core is dehydrated
* ~ 10 – 30% of a vegetative cell’s water
content
Stage 7: Mother cell is lysed
* Mother cell disintegrates
* Mature spore is released
______:
hollow protein filaments
must be stained to view
flagella
T/F: flagella can be used to support evidence for identification of bacteria
true! can be used for identification
_______ – single flagellum
* Polar or subpolar
Monotrichous
_________ – Flagella at opposite ends
Amphitrichous
________ – Multiple flagella in a single tuft
Lophotrichous
________ – Flagella distributed around cell
Peritrichous
flagellar structure:
- ________
* Rigid helical protein ~ 20 µm long
* Composed of identical protein subunits –
flagellin - _______
* Flexible coupling between filament and
basal body - ________ (motor)
* Consists of central rod that passes through
series of rings:
* L ring – LPS layer
* P ring – Peptidoglycan
* MS ring – Membrane
* C – ring – Cytoplasm (associated
with membrane).
Filament
Hook
Basal Body
T/F: flagella have different basal body structures for gram (+) vs. gram (-)
true!
Energy to turn the flagella comes from the _________
* Gradient of protons (H+) across the
cytoplasmic membrane
* High [H+] outside
* Low [H+] inside
proton motive force (PMF)
_____ proteins form a channel that allows H+ to move into the cytoplasm
* Provides the energy to turn the flagellum
Mot
flagellum turn like a ______ to drive the cell forward
propeller
steps of flagella synthesis:
several genes are required…
MS ring is made first
then other proteins and hook are made next
filament grows from tip and pushes cap upwards
________
flagellated cells move
slowly in a straight line
Peritrichously, filaments are all over circumference of cell
______ flagellated cells
move more rapidly and
typically spin around
Polarly
_______ : Flagella-independent motility
gliding motility
________ is…
Slower and smoother than swimming
* Requires surface contact
* Mechanisms
* Excretion of polysaccharide slime
* Type IV pili (twitching)
* Gliding-specific proteins
gliding motility
why does gliding motility require surface contact?
for H bonds, Van der Waals interactions and electrostatic interactions
______: response to chemicals
Chemotaxis, relative to a chemical (could be an attractant or a repellent)
______: response to light
Phototaxis
_____: response to oxygen
Aerotaxis
______: response to ionic strength
obligate anaerobes must avoid oxygen because its toxic to them!
Osmotaxis
hypertonic env. = risk of dehydration
hypotonic env. = risk of bursting
isotonic = ideal
______: response to water
Hydrotaxis
in chemotaxis, bacteria respond to temporal NOT ______ difference in chemical
spatial
if there’s no attractant chemical present, bacteria move in random movement but if there’s an attractant present…
directed movement, chemotaxis
bacteria use a ______ walk to move away/towards attractant/repellent
biased random walk, they move in the right direction but randomly (still runs and tumbles)
how do we measure chemotaxis?
by inserting a capillary tube containing an attractant or a
repellent in a medium of motile bacteria
then see how many go into/away from the tube!
_______ have:
Lower surface area to volume
ratio
Need more sophisticated
transport mechanisms
Grow slower
Eukaryotes
________:
Genetic material is housed in
a nucleus
Generally larger than
prokaryotes
Complex internal structure
Membrane bound
organelles
Intra-cytoplasmic membranes used for transport
Cytoskeleton
Divide by mitosis and meiosis
Eukaryotes
________
* Site of photosynthesis
* Chlorophyll
* Surrounded by 2 membranes
* DNA (single circular) and ribosomes (70S)
Chloroplasts
chloroplasts used to be a gram ____ bacteria!
negative
_______
* Site of respiration and oxidative
phosphorylation
* Surrounded by 2 membranes
* DNA (single circular) and ribosomes (70S)
Mitochondria
mitochondria used to be a gram _____ bacteria!
negative!
______ evolved from bacteria
* Evidence
* Semi-autonomous
* Circular chromosomes
* Lack histones
* 70S ribosomes
* Two membranes
* Outer membrane has porins
Mitochondria and chloroplasts
outer membranes of Mitochondria and chloroplasts have porins, this feature in indicative of what bacterial origin?
gram negative !
_______:
* Most closely related to Rickettsia
* Proteobacteria
* Obligate intracellular pathogens
* Ex) Rocky-mountain spotted fever
Mitochondria
_______:
* Most closely related to
Cyanobacteria
* Blue-green algae
Chloroplasts
_______:
Acellular infectious particles
Obligate intracellular pathogens
Reproduce only inside of living
cells
Lack independent metabolism
Composed of at least 2 parts:
Nucleic acid genome (DNA or RNA) and protein coat (capsid)
* Together = Nucleocapsid
viruses
Some ____ have an envelope – layer of lipid surrounding the
nucleocapsid
viruses
the envelope surrounding some viruses is NOT a plasma membrane, what is it?
phospholipid bilayer
what makes an enveloped virus so hard to identify in our systems?
the envelope has some of our proteins in it, so he can’t be identified!
______ genomes:
DNA or RNA- never both
Single stranded or double stranded
Circular or linear
Can be in several pieces – segmented
Genome size
* Smallest ~ 3.6 kb for some ssRNA viruses (3 genes)
* Largest > 150 kbp for some dsDNA viruses (> 100 genes)
viral
DNA viruses infiltrate the _____
nucleus- SUPER dangerous
______– Protein coat that surrounds the genome
Allows transfer of viral genome between host cells
Made of identical polypeptides – protomers
Helical capsids
* Protomers form a spiral cylinder
* Nucleic acid genome coiled inside
* Ex. Tobacco mosaic virus capsid is
made of ~ 2100 identical protomers.
Capsid
_______ capsids
* Regular geometric shape with 20 triangular faces
* Exhibit symmetry
* Protomers aggregate to form
capsomeres
* Ex. Human papillomaviruses
have form their capsids from
pentamers (clusters of 5)
Icosahedral
_______
* Geometric head with an attached helical
tail
* Genome is carried in a polyhedral head, helical tail is used to inject DNA into a host
cell
Binal capids
_________ large DNA viruses
* Viruses with complex multi-layered structure
* 0.75 µm in diameter, 1200 kbp DNA
* Larger than some bacteria
Nucleocytoplasmic
_____ – a lipid bilayer surrounding the nucleocapsid that was acquired from the host membrane
Envelope
LOOKS like a plasma membrane because it CAME from one
enveloped viruses are easier to destroy than naked viruses, because….
if we destroy the envelope, we automatically destroy the viruses key
_______:
Consists of host lipids and viral proteins – spikes
Ex. Influenza virus
Flexible helical capsid, surrounded by an envelope
Two major spikes: hemaglutanin (H) and neuraminidase (N)
envelope
________ (phage) – viruses that
infect bacteria
Bacteriophage
T/F: viruses infect all domains of life
true!
____ – infect and multiply only
inside of animal cells
Animal viruses
T/F: viruses can jump species barrier through mutations
true!
T/F: Most viruses are specific to a single host
species
true
Virus must attach to _______ receptors on the host cell surface
specific
T/F: Some viruses infect more than one species
true!
steps of viral replication cycle:
- Adsorption – attachment to the host cell
* Involves specific receptors on the host cell surface
* Ex) LPS, outer membrane proteins or glycoproteins - Penetration and uncoating – entry into the host cell
* Bacteriophage – usually inject their nucleic acid into the cell
* Leave the capsid outside the cell as a “ghost” - Synthesis of viral nucleic acids and protein
* Viral genes are expressed and viral proteins are synthesized (by the host’s
own ribosomes)
* Viral genome is replicated (by the host’s replication machinery) - Assembly of new virions
* Viral proteins are assembled into capsids, and then genomes are packaged
into nucleocapsids
* Viruses do not reproduce by division - Release of new virions
* Two basic strategies:
i. Naked viruses usually accumulate, eventually lysing the host cell to
release progeny – lytic infection
ii. Enveloped viruses are usually released by budding
* Virions push through the cytoplasmic membrane without killing
the host cell – persistent infection
entry into the cell by animal viruses:
Fusion with the plasma
membrane (unique to enveloped viruses)
Endocytosis
* Binding to specific receptors
triggers normal endocytic
activity
In either case, once inside:
* The capsid is removed
* Viral genome is released into the cell
naked viruses MUST enter the cell using what entry method
endocytosis
enveloped viruses can enter the cell using which two techniques?
fusion with the plasma membrane OR endocytosis
________ – release of enveloped viruses
* Viral proteins inserted into the host membrane – Spikes
* Nucleocapsid associates with the spikes, and buds through the
membrane to form the envelope
Budding
how does influenza use budding to release enveloped viruses?
Neuraminidase (N)
Allows new virions
to exit the host cell
Hemagglutanin (H)
Allows viruses to
adsorb to the next
host
