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MCB3020 Archaeal cell structure (ch. 4), eukaryotic cell structure (ch. 5) and viruses (ch. 6)

Terms in this set (83)

Features in common with Eukarya
genes encoding protein: replication, transcription, translation
Features in common with Bacteria
genes for metabolism
Elements that are unique to Archaea
unique rRNA gene structure, capable of methanogenesis
Archaea diversity
Highly diverse with respect to morphology, physiology, reproduction, and ecology
Archaea is best known for
growth in anaerobic, hypersaline, pH extremes, and high-temperature habitats. Also found in marine arctic temps and tropic waters.
Archaea shapes
like bacteria, cocci and rods are common shapes as well as branches and flat shapes but there are no spirochetes or mycelial forms yet
Archaea sizes
vary just like bacteria, typically 1-2 x 1-5 μm for rods, 1-5 μm in diameter for cocci
Smallest observed is 0.2 μm in diameter while the largest (so far) is a multicellular form that can reach 30 mm in length
Archaea cell walls vs Bacterial
Lack peptidoglycan, most common cell wall is S layer, may have protein sheath external to S layer and S layer may be outside membrane and separated by pseudomurein (similar to gram positive microorgs.)
6
How many major types of archaeal cell envelopes are known?
Archaeal Membranes
Composed of unique lipids, isoprene units (five carbon, branched) and ether linkages rather than ester linkages to glycerol

Some have a monolayer structure instead of a bilayer structure
Archaeal vs. bacterial cytoplasm
very similar, lack of membrane-enclosed organelles
may contain inclusion bodies like gas vesicles
all the usual components
- ribosomes
- nucleoid region
- inclusion bodies
Bacterial and archaeal ribosomal RNA
16S small subunit
23S and 5S in large subunit
at least one archaeon have additional 5.8S rRNA (also seen in eukaryotic large subunit)
How do proteins in ribosomes vary?
archaea more similar to eukarya than to bacteria, but there are some that are unique to archaea
The Nucleoid
Irregularly shaped region in bacteria and archaea
Usually not membrane bound (few exceptions)
Location of single circular chromosome and associated proteins
Some evidence for polyploidy in some archaeons
archaeal pili
not well understood as of yet, some composed of pilin protein and homologous to bacterial type IV pili proteins. Have a central lumen similar to bacterial flagella, but not bacterial pili
may be involved in archaeal adhesion mechanisms
Archaeal Cannulae
hollow, tubelike structures on the surface of thermophilic archaea in genus Pyrodictium. Function unknown butmay be involved in formation of networks of multiple daughter cells
Archaeal Hami
not well understood
'grappling hook' appearance
involvement in cell adhesion mechanisms
Two groups of eukaryotes which commonly possess microbial members
protists and fungi
Common Features of Eukaryotic Cells
Membrane-delimited nuclei , membrane-bound organelles that perform specific functions, Intracytoplasmic membrane complex
Purpose of Intracytoplasmic membrane complex
serves as transport system
Eukaryotic complexity
More structurally complex and generally larger than bacterial or archaeal cells
Eukaryotic cell wall
Unlike the peptidoglycan in the cell wall of Bacteria and Archaea, many eukaryotes lack or have a chemically distinct cell wall
Cell walls of photosynthetic algae have
cellulose, pectin, and silica
Cell walls of fungi consist of
of cellulose, chitin, or glucan
Eukaryotic cytoplasm
Consists of liquid, the cytosol, and many organelles
Eukaryotic cytoskeleton
vast network of interconnected filaments within the cytoplasmic matrix
filaments that form the cytoskeleton: microfilaments (actin), microtubules, intermediate filaments, and motor proteins
plays role in both cell shape and cell movement
Actin filaments
Small protein filaments, 4 to 7 nm in diameter
Scattered within cytoplasmic matrix or organized into networks and parallel arrays. Composed of actin protein
Involved in cell motion/shape changes
intermediate filaments
Heterogeneous elements of the cyto-skeleton, ~10 nm in diameter
Keratin and vimentin classes
Role in cell is unclear but they may play structural role
Microtubules
Shaped like thin cylinders ~25 nm in diameter of α- and β-tubulin, help maintain cell shape and are involved with microfilaments in cell movement as well as intracellular transport processes
Secretory Endocytic Pathway
Intricate complex of membranous organelles and vesicles that move materials into the cell from outside, from inside to outside, and within the cell
Endoplasmic reticulum (ER)
Golgi apparatus
Lysosomes
Endoplasmic Reticulum (ER)
Irregular network of branching and fusing membranous tubules and flattened sacs (cisternae - s., cisterna)
Rough ER
ribosomes attached
synthesis of secreted proteins by ER-associated ribosomes
Smooth ER
devoid of ribosomes
synthesis of lipids by ER-associated enzymes
Functions of the ER
Transports proteins, lipids, and other materials within cell
Major site of cell membrane synthesis
The Golgi Apparatus
Membranous organelle made of cisternae stacked on each other (rare exceptions will have nonstacked cisternae)
Cis and trans faces
Involved in modification, packaging, and secretion of materials
Dictyosomes
stacks of cisternae in the golgi apparatus
Lysosomes
Membrane-bound vesicles found in most eukaryotes
Involved in intracellular digestion
Contain hydrolases, enzymes which hydrolyze molecules and function best under slightly acidic conditions
Maintain an acidic environment by pumping protons into their interior
The Nucleus
Membrane-bound spherical structure that houses genetic material of eukaryotic cell
Chromatin
complex of DNA, histones, and other proteins
five types of histones form nucleosomes
H1, H2A, H2B, H3, and H4
chromatin condenses into chromosomes during division
Nuclear envelope
double membrane structure that delimits nucleus
continuous with ER
penetrated by nuclear pores
Purpose of pores
pores allow materials to be transported into or out of nucleus
Nucleolus
at least 1 nucleolus/nucleus in eukaryotes
Organelle but not membrane enclosed
Important in ribosome synthesis
Nucleolus and ribosome synthesis
directs synthesis and processing of rRNA
directs assembly of rRNA to form partial ribosomal subunits
ribosomes mature in cytoplasm
Eukaryotic Ribosomes
More mass than the 70s bacterial and archaea ribosomes 80S (40S and 60S)
May be attached to ER or free in cytoplasmic matrix , 60S bound subunit to ER
Free ribosomes
nonsecretory/nonmembrane proteins
some proteins are inserted into organelles
Endosymbiotic Hypothesis
Mitochondria, hydrogenosomes, and chloroplasts are all thought to have evolved from bacterial cells that invaded or were ingested by early ancestors of eukaryotic cells
Mitochondria
"The power houses of the cell" are found in most eukaryotic cells

Site of tricarboxylic acid cycle activity

Site where ATP is generated by electron transport and oxidative phosphorylation

About the same size as bacterial cells
Mitochondria Reproduction
via binary fission just like bacterial cells
Mitochondrial Structure
outer membrane, inner membrane, matrix enclosed by inner membrane
outer membrane of mitochondria
contains porin proteins similar to Gram-negative bacteria
inner membrane of mitochondria
highly folded to form cristae (s., crista)
location of enzymes and electron carriers for electron transport and oxidative phosphorylation
Matrix enclosed by inner membrane of mitochondria
contains ribosomes, mitochondrial DNA, enzymes of tricarboxylic acid cycle and catabolism of fatty acids
Hydrogenosomes
Small energy conservation organelles in some anaerobic protists, descended from common mitochondrial ancestor
Hydrogenosome characteristics
double membrane, no cristae, usually lack DNA
ATP is generated by fermentation process rather than respiration
CO2, H2, and acetate are products
Chloroplasts
Type of plastid
pigment-containing organelles observed in plants and algae

Site of photosynthetic reactions

Surrounded by double membrane
Chloroplast Structure
The stroma (a matrix) within inner membrane which contains DNA, ribosomes, lipid droplets and thylakoids
thylakoids
flattened, membrane-delimited sacs
grana (s., granum) - stacks of thylakoids, site of light reactions (trapping of light energy to generate ATP, NADPH, and oxygen)
Stroma
site of dark reactions of photosynthesis (formation of carbohydrates from water/CO2)
Algal chloroplasts many contain
a pyrenoid which
participates in polysaccharide
synthesis
eukaryotic flagella
100-200 μm long
move in undulating
fashion
eukaryotic cilia
5-20 μm long
beat with two phases,
working like oars
Main differences with Eukaryotes
True membrane bound nucleus, DNA w histones, more than one chromosome, plasmids are rare, introns in genes, nucleolus, mitochondria/chloroplasts, cytoskeleton, 80S
Viruses
protein and nucleic acid
Viroids
only RNA
Satellites
only nucleic acids
Prions
proteins only
Viruses, significance
Major cause of disease, important members of aquatic world, important in evolution and important model systems in molecular bio
Properties of viruses
Virion - complete virus particle
consists of at least 1 molecule of DNA/RNA in protein coat, may have additional layers
cannot reproduce independent of living cells nor carry out cell division but can exist extracellularly
What do virions infect?
Bacterial viruses called bacteriophages (phages)
Few archaeal viruses
Most are eukaryotic viruses
plants, animals, protists, and fungi
how are virions classified
into families based on
genome structure, life cycle, morphology, genetic relatedness
The structure of viruses
Virion size range is ~10-400 nm in diameter and most viruses must be viewed with an electron microscope, nucleocapsid, envelopes
All virions contain
a nucleocapsid which is composed of nucleic acid (DNA or RNA) and a protein coat (capsid)
some viruses consist only of a nucleocapsid, others have additional components
Viroids
Infectious agents composed of closed, circular ssRNAs Do not encode gene products Replication requires host cell DNA-dependent RNA polymerase , cause plant diseases
Satellites
Infectious nucleic acids (DNA or RNA), Encode one or more gene products, Require a helper virus for replication
human hepatitis D virus is satellite, requires human hepatitis B virus
satellite viruses encode their own capsid proteins when
helped by a helper virus
satellite RNAs/DNAs
do NOT encode their own capsid proteins
Prions, what do they do
Proteinaceous Infectious Particle, Cause a variety of degenerative diseases in humans and animals
Prion caused diseases
scrapie in sheep
bovine spongiform encephalopathy (BSE) or mad cow disease
Creutzfeldt-Jakob disease (CJD) and variant CJD (vCJD) in humans
kuru in humans
PrP^c
(prion protein) is present in "normal" form (abnormal form of prion protein is PrPSc)
PrP^sc
causes PrPC protein to change its conformation to abnormal form
Newly produced PrP^Sc molecules
convert more normal molecules to the abnormal form through unknown mechanism
Neural loss
Evidence suggests that PrPC must be present for neural degeneration to occur

Interaction of PrPSc with PrPC may cause PrPC to crosslink and trigger apoptosis

PrPC conversion causes neuron loss, PrPSc is the infectious agent
All prion caused diseases
have no effective treatment, result in progressive degeneration of the brain and eventual death
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