MD Flashcards
the unit structure of all living things
cell
the basic and smallest unit of living matter
cell
First described by Robert Hooke from a thin slice of cork
cell
fundamental unit of life
cell
Cell theory
- All living things are composed of one or more cells
- Cells are the fundamental building block of life
- All cells come from pre-existing cells (life begets life)
Lipid and protein layer surrounding the cytoplasm1
cell membrane
rigid outer-layer of the cell, of varying chemical composition
cell wall
the hereditary material, DNA
nuclear material
contains organelles, enzymes, chemicals. it’s the site of most cellular metabolic activity
cytoplasm
Properties of all cells
- Compartmentalization and metabolism
- Growth
- Evolution
Properties of some cells
- Motility
- Differentiation
- Communication
Basic Types of Cells
-Prokaryotic
-Eukaryotic
- (Greek for “before the nucleus”)
– always have a cell wall, a plasma membrane and a cytoplasm that contains a nucleoid and many ribosomes
Prokaryotic
- (Greek for “true nucleus”)
- always have a plasma membrane, a membrane-bound nucleus, and a cytoplasm that contains a cytoskeleton and membranous organelles, in addition to ribosomes
Eukaryotic
- (Bacteria and Archaea) have no nucleus.
- DNA appears as a granular structure associated with the membrane = the nucleoid
- Only approximately 3% of the nucleoid is DNA.
- Genetic material consists of one single circular DNA molecule
Prokaryotes
Prokaryotes also frequently carry one or more smaller independent circular DNAs called
plasmids or episomes
do not integrate into the main chromosome
Plasmids
can reside in the cell as independent molecules or can integrate into the main chromosome.
Episomes
Both are generally not essential for bacterial growth.
plasmids or episomes
Carry genes that confer desirable traits to the bacteria
Antibiotic resistance
Allow transfer of genetic information from one cell to another by means of
conjugation
Prokaryotes (e.g. E. coli)
- Genome is approx. 4.7 Mbp long
- Sequence det. in 1997
- Dimensions of cell = 1.5 x 2 to 6 μm.
- Therefore, DNA has to be strongly compacted to fit into the cell otherwise it would have a diameter of 430 μm, or a length of a bout 1 mm.
are characterized by a nuclear membrane that surrounds their genetic patrimonium.
Eukaryotes
- is an organelle with a diameter of several μm and is mostly visible in the light microscope.
Nucleus
- The membrane has some 3,000 to 4,000 pores of 9 nm diameter,
allow the passage of macromolecules up to 60,000 Dalton (Da) and contains numerous proteins involved in active transport of small and macromolecules in (proteins, cDNA) and out (mature mRNA) of the nucleus.
Nucleus
DNA replication and transcription take place in the
Nucleus
protein synthesis occurs in the
Cytoplasm
Categories in classifying life (i.e microorganisms)
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Prokaryotes
Live on earth’s extreme aquatic environment
Methanogens, extreme halophiles & thermophiles
Domain Archaea (Archaebacteria)
The most diverse and widespread prokaryotes
Cyanobacteria, spirochetes, chlamydia
Domain Bacteria (Eubacteria)
Composed of eukaryotes
Protists (slime molds, protozoa, and algae)
Fungi (unicellular yeasts, multicellular molds, and mushrooms)
Plants (algae, mosses, ferns, conifers, and flowering plants)
Animals (sponges, worms, insects, and vertebrates)
Domain Eukarya
Discovery of Archaea in the 70’s by
Carl Woese, 1977
Phylogenetic classification
Essential macromolecules are conserved
Must have been present in ancestors
16S RNA (18S in Eukarya) undergoes a slow evolution
It is therefore an excellent phylogenetic marker
Analysis of 16S RNA (16S rDNA) facilitated by PCR & sequence analysis
contains an enormous variety of prokaryotes.
All known disease-causing (pathogenic) prokaryotes are Bacteria , as are thousands of nonpathogenic species.
A large variety of morphologies and physiologies are also observed in this domain.
Bacteria
Two phyla exist in the domain Archaea, the Euryarchaeota and the Crenarchaeota.
Each of these forms a major branch on the archaeal tree.
Archaea
Most cultured Archaea are __________, with species capable of growth at the highest temperatures, salinities, and extremes of pH known for any microorganism.
extremophiles
The organism ________, for example, is a hyperthermophile capable of growth at up to 1138 C,
Pyrolobus
and the methanogen ________ can grow up to 1228 C.
Methanopyrus
Although all Archaea are chemotrophic, _________-can use light to make ATP but in a way quite distinct from that of phototrophic organisms.
Halobacterium
- Eukaryotic microorganisms are related by cell structure and phylogenetic history.
- The phylogeny of Eukarya based on ribosomal RNA sequencing shows plants and animals to be farthest out on the branches of the tree; such late- branching groups are said to be the “most derived.”
- By contrast, some of the earlier-branching Eukarya are structurally simple eukaryotes, lacking mitochondria and some other organelles.
Microbial Eukarya
– system for naming organisms
Established in 1735 by Carolus Linnaeus
Nomenclature
Nomenclature established in 1735 by
Carolus Linnaeus
Binomial system = Scientific name, Latin
- Genus + specific epithet
“Escherichia coli” - Underlined (when handwritten) or italicized (computerized)
“ Escherichia coli or Escherichia coli” - After it’s mentioned once, it can be abbreviated with the initial of the genus followed by the specific epithet.
E. coli
can, among other things, describe an organism, honor a researcher, or identify the habitat of a species.
Scientific names
The genus of the bacterium Escherichia coli is named for a scientist
Theodor Escherich
whereas its specific epithet, coli, reminds us that E. coli live in the
colon, or large intestine
Acellular Entities
Viruses
Subviral entities
Subviral entities
Defective viruses
Viroids
Prions
Viruses are genetic elements that cannot replicate independently of a living cell, called the
host cell
do possess their own genetic information and are thus independent of the host cell’s genome.
- rely on the host cell for energy, metabolic intermediates, and protein synthesis.
- are therefore obligate intracellular parasites that rely on entering a suitable living cell to carry out their replication cycle.
- However, unlike genetic elements such as plasmids, viruses have an extracellular form, the virus particle, that enables them to exist outside the host and that facilitates transmission from one host cell to another.
viruses
To multiply, viruses must enter a cell in which they can replicate, a process called
infection
Some viruses cannot infect a host cell alone and rely on other viruses, known as _________, to provide certain functions.
helper viruses
Far more interesting are those defective viruses, referred to as ________, for which no intact version of the same virus exists; these defective viruses rely on unrelated viruses as helpers.
satellite viruses
are infectious RNA molecules that differ from viruses in lacking a capsid.
Despite this lack, they have a reasonably stable extracellular form that travels from one host cell to another.
Viroids
are small, circular, single-stranded RNA molecules that are the smallest known pathogens.
They range in size from 246 to 399 nucleotides and show a considerable degree of sequence homology to each other, suggesting that they have common evolutionary roots.
Viroids
- cause a number of important plant diseases and can have a severe agricultural impact.
- A few well-studied viroids include coconut cadang-cadang viroid (246 nucleotides), citrus exocortis viroid (375 nucleotides), and potato spindle tuber viroid (359 nucleotides).
- No viroids are known that infect animals or prokaryotes.
Viroids
- are infectious agent composed of protein in a misfolded form.
- not considered living organisms but are misfolded protein molecules which may propagate by transmitting a misfolded protein state.
Prions
a gene in your DNA which encodes for prion protein
PRNP
is a protein on the surface of your cells
prion protein or PrP
are genetic elements that cannot replicate
independently of a living cell, called the host cell.
• However, viruses do possess their own genetic information and
are thus independent of the host cell’s genome.
Viruses
rely on the host cell for energy, metabolic intermediates,
and protein synthesis.
Viruses
unlike genetic elements such as plasmids, viruses have
an extracellular form, the ,_________________, that enables them to exist
outside the host and that facilitates transmission from one host cell
to another.
virus particle
• Some viruses cannot infect a host cell alone and rely on other
viruses, known as helper viruses, to provide certain functions.
• Far more interesting are those defective viruses, referred to as
satellite viruses, for which no intact version of the same virus
exists; these defective viruses rely on unrelated viruses as
helpers.
Defective Viruses
• When a pathogenic prion enters a host cell that is
expressing native prion protein, it promotes the conversion
of PrPC protein into _______.
.
• Thus the pathogenic prion does not subvert host enzymes
or genes as a virus does; rather, it “replicates” by
converting native prion proteins that already exist in the
host cell into the pathogenic form.
PrPSc
• As the pathogenic prions accumulate, they form insoluble
aggregates in the neural cells.
• This leads to disease symptoms that are invariably
neurological and, in most cases, are due to destruction of
brain or related nervous tissue.
Mechanism of prion misfolding
