Cells (3-3.8) Cell Structure Flashcards
What are microscopes?
They are instruments that produce a magnified image of an object.
What is magnification?
How many times bigger the image is when compared to the object.
What is the magnification formula?
Magnification= size of image divided by size of real object
What is resolution?
The minimum distance apart that two objects can be in order to to them to appear as separate items
What is cell fractionation?
The process where cells are broken up and the different organelles they contain are separated out
What happens before cell fractionation?
The tissue is placed into a cold buffered solution of the same water potential as the tissue
What are the two stages of cell fractionation?
Homogenation and Ultracentrifugation
What is homogenation?
When cells are broken up by a homogeniser (blender) to release organelles from the cell. The homogenate is the filtered to remove debris and any complete cells
What is ultracentrifugation?
The process by which the fragments in the filtered homogenate are separate in a machine (centrifuge)
For animal cells, describe the ultracentrifugation in the steps
1) tube of filtrate is placed in the centrifuge, spun at low speed
2) heavy organelles (nuceli) forced to bottom of tube, where they form a thin sediment
3) fluid at top (supernatant) is removed, leaving just the sediment (nuclei)
4) supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before.
5) next heaviest (mitochondria) are forced to bottom of tube
6) at each increased speed, the next heaviest organelle is sediment Ed and separated out
Why do light microscopes have poor resolution?
They have a relatively long wavelength of light
What are the two main advantages of an electron microscope?
1) Electron beam has a very short wavelength - can resolve objects well (high resolving power)
2) electrons are negatively charged - the beam can be focused using electromagnets
What needs to be created in order for an electron microscope to work effectively?
A near-vaccum has to be created within the chamber of an electron microscope
What are the two types of microscopes?
1) Transmission Electron Microscope (TEM)
2) Scanning Electron Microscope (SEM)
What does a TEM consist of?
An electron gun that produces a beam of electrons that’s is focuses onto the specimen by a condenser electromagnet.
What is the resolving power of a TEM?
0.1 nm
What are the main limitations of a TEM?
1) Whole system must be in a vaccum, therefore living specimens cannot be observed.
2) a complex ‘staining’ process is required and even then the image is not in colour
3) specimen must be extremely thin
4) image may contain artefacts
How does the SEM work?
SEM directs a beam of electrons on to the surface of the specimen from above. Beams then passed back and forth across a portion of the specimen in a regular pattern. Electrons are scattered by the specimen and the pattern of this scattering depends if contours if the specimen surface.
Does the SEM have a lower resolving power than TEM?
Yes, around 20nm
What is an eyepiece graticule?
It is a glass disc that is placed in the eyepiece of a microscope
What is etched on the glass disc?
A scale
How long is the scale and in how many sub divisions?
10mm long and in 100-sub divisions
What must be done first with the graticule before being used?
It has to be calibrated for a particular objective lens
What microscope do you need to calibrate an eyepiece graticule?
A stage micrometer
What is the scale on a stage micrometer?
2mm long and has 0.1nm (10micrometers)
How do you workout the graticule?
Mm divided by graticule x100
How do you calculate linear magnifications of drawings and photographs?
1) Measure length X-Y
2) convert measurement in drawing to microns (x1000)
3) new measurement divided by line representing in the cell = magnification
What is magnification formula?
Actual size divided by the size of the image
What is cell ultrastructure?
The internal structure of a cell that suits for it’s own function
What are the main things in eukaryotic cells?
They have:
A distinct nucleus
Membrane bound organelles
What are the eukaryotic organisms?
They are:
Animals
Plants
Algae
Fungi
What is the nucleus function?
Control centre producing mRNA and tRNA which allows for protein synthesis inside the cell (assembles ribosomes)
What does the nucleus contain (5 structures)?
Nucleoplasm
Chromatin
Nuclear pores
Nucleolus
Nuclear envelope
What is the function of the nucleoplasm?
It’s a jelly like substance making up the bulk of the nucleus
What is the function of Chromatin?
Protein bound linear piece of DNA
What is the function of the nuclear envelope?
It’s controls the entry and exit of substances in and out the nucleus
What is the function of the nuclear pores?
Allows for the passage of large molecules out of the nucleus
What is the function of the Nucleolus?
It is a spherical region that synthesise rRNA and assembles ribosomes
What is the function of the mitochondria?
It is the site of aerobic respiration
What are the 4 structures found in a mitochondria?
Matrix (ribosomes and DNA)
Cristae
Outer membrane
Inner membrane
What is the role of an outer membrane for a mitochondria?
It controls entry and exit of molecules
What is the role of the inner membrane for a mitochondria?
It contains Cristae (infolding of membrane) that have enzymes attached to carry out respiration.
What is the role of the matrix in a mitochondria?
It allows for the production of their own proteins and contains enzymes involved in respiration
What is the function of the endoplasmic reticulum?
It’s a series of sheet like membranes that produces proteins to allow the rest of the cell to function
What are the two types of endoplasmic reticulum?
Rough and smooth
What does RER have on the outer surfaces of the membrane?
Ribosomes
What is the function of RER?
Large surface area for synthesis of proteins and gylcoproteins.
Provides a pathway for the transport of substances like proteins through the cell
What is the function of SER?
Synthesise, store and transport both lipids and carbohydrates.
What is the function of the golgi apparatus?
modify, sort, and package macromolecules that are synthesized by the cell
What is the golgi apparatus made out of?
Cisternae and vesicles