2.1.1 Microscopy Flashcards
How does the resolution differ between a light, electron and laser microscope?
TEM - 0.5nm
SEM - 3-10nm
Laser scanning confocal - 15-20nm
Light microscope - 200nm
How does the magnification differ between a light and electron microscope?
Electron (TEM and SEM) - x500,000
Light - x1,500
What are the differences between a scanning electron microscope and a transmission electron microscope?
SEM: beams sent across surface of specimen - produces 3D images, lower resolution
TEM: higher resolution, electrons sent through specimen
Explain the structure of a compound light microscope.
Two lenses - eyepiece at top to look through, objective lens that produces a further magnified image
Light comes from below the stage to illuminate the specimen
How does a laser scanning confocal microscope work?
A laser beam is moved along a specimen and reflected by a dichroic mirror and through an objective lens back onto the specimen. The light emitted from the specimen is filtered through to the detector. Light that is reflected close to the focal plane produces a clear image.
Why do electron microscopes produce greater detail than light microscopes?
Electrons have a much smaller wavelength (less than 1nm) than light waves
What is chromatic abberation?
The effect of refraction of different wavelengths of light through slightly different angles, resulting in a lack of focus.
What are artefacts?
Something that isn’t typical of the cell’s structure, but is the result of a process such as staining
Explain dry mount preparation.
Sample placed on slide, cover slip over the sample
e.g. hair sample
Explain wet mount preparation.
Sample suspended in liquid, cover slip over the sample
e.g. aquatic organisms
Explain squash slide preparation.
Wet mount prepared, then cover slip is pressed down over sample
e.g. root tips to look at cell division
Explain smear slide preparation.
Sample smeared thinly along slide, then cover slip placed on top
e.g. blood sample
What is positive staining?
Positive stain attracted to negative ions within cytoplasm of cells that absorb the stain
e.g. crystal violet, methylene blue
What is negative staining?
Negative stain repels negative ions within cytoplasm, so they stand out when all else is stained
e.g. congo red, nigrosin, safranin
What does acid fast stain do?
Helps differentiate acid-fast bacteria (Mycobacterium) from other bacteria. A lipid solvent carries carbolfuchsin dye into the cells, then it’s washed with acid-alcohol solution. It retains the dye while other bacteria lose the stain and are exposed to methylene blue stain.
What is the magnification formula?
Actual size = Image size / Magnification
State the difference between resolution and magnification.
Magnification - Refers to the amount of times the image has been enlarged
Resolution - Refers to the ability to distinguish between two different points
What are four differences between a prokaryotic and a eukaryotic cell?
- Prokaryotic cells have smaller ribosomes (70s instead of 80s)
- Prokaryotic cells are unicellular
- Prokaryotic cells have no nucleus
- Prokaryotic cells have no membrane bound organelles
What are four similarities between a prokaryotic and eukaryotic cell?
1) Have ribosomes
2) DNA is basis for genes
3) Have cell membranes
4) Have cytoskeleton
How is the cytoskeleton important?
1) Aids cell transport:
Microtubules and microfilaments, that make up the cytoskeleton, help move organelles - microfilaments attach to vesicles to pull them in to the cell (endocytosis), also guide vesicles around the cell
2) Enabling cell movement:
Microfilaments continually in the process of assembly and disassembly - results in forces that move the cell
3) Mechanical strength:
Intermediate filaments provide this
How is the rough endoplasmic reticulum involved in protein synthesis?
Has ribosomes bound to its surface where protein synthesis can occur
How is the golgi apparatus involved in protein synthesis?
It modifies the proteins, if needed, and packages them into vesicles to the edge of the cell to leave via exocytosis
How are the ribosomes involved in protein synthesis?
Site of protein synthesis, comprised of 2 subunits in which the RNA goes to be transcripted
Explain the role of the organelles in protein synthesis.
mRNA travels out of the nucleus to either the ribosomes at the RER or floating in the cytoplasm. Transcription occurs at the ribosomes. The proteins are packaged in vesicles and transported to the golgi apparatus via the cytoskeleton. Any necessary changes occur at the golgi apparatus, then it’s further packaged into a vesicle and approaches the cell membrane.
State the definition of exocytosis.
A substance, wrapped in a vesicle, moving out of the cell
State the definition of endocytosis.
A substance, wrapped in a vesicle, moving into the cell
What is the function of the nucleus?
Contains almost all of the DNA, so is the control hub of the cell - has pores to allow substances in and out
What is the function of the nucleolus?
Makes ribosomal RNA to form the ribosomes
What is the function of the nuclear envelope?
To protect the DNA from being damaged in the cytoplasm, and to control what enters and leaves the nucleus
What is the function of the RER?
Has ribosomes on it that are the site of protein synthesis
What is the function of the SER?
Synthesis lipids and carbohydrates. Stores ions needed by cell later
What is the function of the golgi apparatus?
Processes proteins and transports them to where they need to go (either lysosomes or cell membrane). Golgi bodies metabolise large proteins into smaller proteins and combine protein and carbs to make molecules
What is the function of the ribosomes?
Site of protein synthesis
What is the function of mitochondria?
Respiration takes place here and ATP is produced, which is the energy source for the cell. Can produce their own enzymes and replicate themselves (mtDNA)
What is the function of the lysosomes?
Contain digestive enzymes to break down waste into simple compounds. Transfer waste to the cytoplasm to be used as new cell-building materials
What is the function and structure of chloroplasts?
Carry out photosynthesis to ‘food’ for the plant. Contain DNA and ribosomes - can make their own proteins.
Double membrane structure, flattened sacs called thylakoids (several join to form grana), the grana are joined by lamellae membranes
What is the function of the plasma membrane?
To control what substances enter and exit the cell
What is the function of the centrioles?
Move chromosomes around by forming spindle fibres during cell division
What is the function of the cell wall?
Provide the plant cell with its shape. The cell contents push against the wall, making it rigid and providing structural support. Also, it defends from invading pathogens
What is the function of the flagella?
Propels the cell forward to find ‘food’
What is the function and structure of the cilia?
Beat in a rhythmic manner to move substances that are near the cell
Structure consists of two central microtubules surrounded by 9 pairs of microtubules (9+2 arrangement). Pairs of parallel microtubules slide over each other to cause the cilia to move
