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Prokaryotic cell structure + viruses


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Can you see viruses by light microscopy?
No. Viruses are very small (<100nm), and LM has a maximum resolution of 200nm.
What is the principle of light microscopy (LM)?
LM passes light through a specimen and then through glass lenses to magnify the images of the small specimen sample.
What is magnification in microscopy?
The ratio of an objects image size to its real size.
How much can a light microscope magnify?
1000 times
What is resolution in microscopy?
A measure of image clarity which looks at the distance between two points which can be separated and distinguished as separate points.
What is contrast in microscopy?
The difference in brightness between a dark and a light area of an image.
How do you enhance contrast in microscopy?
By staining or labeling cell components.
What is the principle of electron microscopy (EM)?
It focuses an electron beam through the specimen (TEM) or on its surface (SEM) using magnetic electron lenses.
What is transmission electron microscopy (TEM)?
TEM sends a beam of electrons through an ultra-thin specimen, while the beam interacts with the specimen as it passes through.
What is scanning electron microscopy (SEM)?
SEM sends a beam of electrons at a coated sample, while the beam interacts with surface constituents.
What can you see with TEM?
Intracellular structures seen through a sample ultra-thin section.
What can you see with SEM?
Topology of the cell surface.
What is fluorescence microscopy?
A type of LM in which fluorescence or phosphorescence is used insted of reflection and absorption of light to study cells
What does cell fractionation do?
Takes cells apart and separates major organelles and other subcellular structures from one another.
How can you separate cell constituents?
By cell fractionation
What are the typical components of a prokaryotic cell?
Fimbriae, cell wall, capsule, flagella, plasma membrane, bacterial chromosome, nucleoid, ribosomes
Why are prokaryotes small?
They are small because they need a large surface to volume ratio, since their metabolic rates increase faster then the surface's area ability to exchange nutrients.
Why do prokaryotic cells need a small cell volume?
To ensure minimum ressource consumption.
Why do prokaryotic cells need a large surface area?
To ensure maximum material exchange, and consecutively high substrate uptake.
The average prokaryote, how much smaller is it compared to an eukaryote?
Prokaryotes are 20 to 200 times smaller then eukaryotic cells.
Are there any multicellular prokaryotes?
No, however prokaryotes can grow together in clumps called colonies.
What are the most common prokaryotic shapes?
Cocci (sphere), bacilli (rods) and spirals.
What is the difference between a gram positive and a gram negative cell wall?
Gram positives have a thick peptydoglycan layer (50-90% of cells envelope) and one membrane, whereas gram negative have two membranes in between which there is a thin peptydoglycan layer (10% of cells envelope).
How does the Gram stain stain Gram positive cells?
Crystal violet attches to the rich peptydoglycan layer and stains it blue. Organic solvents like acetone cannot remove the stain from the thick peptydoglycan wall.
How does the Gram stain stain Gram negative cells?
Crystal violet attaches to the thin peptydoglycan layer staining it blue, but afterwards organic solvents like acetone which pass through the membrane removes the stain easily so the cells appear pink ot without color.
What is peptydoglycan?
It is a polymer of aminoacids (therefore peptido-) and sugars (glycan, N-acetylglucosamine and N-acetylmuramic acid) which is specific to the cell walls of bacteria.
What are prokaryotic cells using sex pili for?
Transfer of DNA from a donor to an acceptor cell.
What type of genetic material can bacteria transfer through the sex pili?
Plasmids and chromosomal fragments
What is conjugation?
DNA transfer between two prokaryotic cells which are temporarily joined.
What are certain prokaryotes doing with a conductive pili?
They use the conductive pili to transfer electrons from energy metabolism outside of the cell in a process called extracellular respiration.
What confers conductivity to a pili?
The alignment of peptides which stacks the aromatic aminoacids in the center of the pili structure, resulting in a tunneling effect due to delocalization of electrons in the aromatic rings.
What is a plasmid?
Small circular DNA molecule, physically separated from the chromosomal DNA, and which can replicate independently.
What can plasmids be used for?
Genetic engineering, by transforming cells using plasmids which carry genes with specific functions.
Do prokaryotes have internal membrane structures and organelles?
Not usually. However, some prokaryotes have internal membranes like for example tylakoid membranes.
Give 3 examples of internal membranes in prokaryotes?
Folded respiratory membranes; tylakoid membrane; and anammox membrane
What does the thylakoid membrane do in cyanobacteria?
It is the site of light-dependent reactions during photosynthesis.
What is the anammoxosome?
It is the largest compartment of the anammox cells which is dedicated strictly to energy metabolism, and it is free of DNA and ribosomes.
Are viruses alive?
According to how we define life, viruses are NOT alive because they cannot carry their own metbolism, or replication.
What is a virus?
It is a small infectious agent, which contains a nucleic acid (RNA or DNA) in a protein capsid. The nucleic acid will infect a host cell, and hijack its replication machinery.
What is a lytic cycle?
A viral replication cycle in which the virus injects its own nucleic acid into the host, takes over the replicating machine of the host, makes viral DNA and proteins, builds new viruses, lyses the host cell to release new viruses and infect other cells.
What is a lysogenic cycle?
A viral replication cycle in which the virus injects its own nucleic acid into the host, attaches itself into the host DNA, and acting as an inert DNA segment it replicates when the host cell divides. It causes no harm to the infected cell.