Cells Flashcards
What are methods of studying cells?
Microscopy
Cell fractionation
Define magnification and resolution.
Magnification - how many times bigger the image is when compared to the object
Resolution - the minimum distance apart that two objects have to be for them to be distinguished as separate objects.
What is the equation for magnification?
Magnification = image size/actual size
Describe the process of cell fractionation
The tissue is placed in a cold buffered solution of the same water potential
Cells are broken up by a homogeniser (blender) - this releases organelles from the cell
The homogenate (the resultant fluid) is filtered to remove debris
The filtrate is placed in the centrifuge and spun initially at slow speeds
The heaviest organelles, like nuclei, are forced to the bottom of the tube where they form a thin sediment or pellet
The fluid at the top of the tube, the supernatant, is transferred to another tube and spun faster
This is repeated until the organelles are all split up
Why does the tissue have to be in a cold buffered solution of the same water potential at the start?
Cold - to reduce enzyme activity that might break the organelles.
Buffered - so that the pH does not fluctuate and alter organelle structure or affect enzyme functionality
Is of the same water potential as the tissue - to prevent organelles from bursting or shrinking as a result of osmotic gain or loss of water
What are the different types of microscopes?
Light microscope
Electron microscope
• Transmitting electron microscope
• Scanning electron microscope
Light microscope vs electron microscope
Light microscope: Cheap Portable Staining to provide contrast Less magnification and resolution Uses light passing up from the specimen Focussed by objective and eyepiece lens Light has a longer wavelength
Electron microscope: Expensive Very large No colour More magnification and resolution Uses a beam of electrons Focussed using electromagnets Electrons have a shorter wavelength Living specimens cannot be observed - specimens coated in metal and viewed in vacuum
Transmission electron microscope vs scanning electron microscope
TEM:
Beam of electrons pass through thin specimen
2D image of inner structure
Specimen must be very thin
SEM:
Beam of electrons scattered from surface of specimen
3D image of specimen surface
Less magnification and resolution than TEM
What is the difference between eukaryotic and prokaryotic cells?
A eukaryotic cell is a cell which contains membrane-bound organelles
A prokaryotic cell is a cell that does not contain membrane-bound organelles
Another difference is that most eukaryotic cells have a nucleus, whereas prokaryotic cells do not
What are the common organelles in eukaryotic cells and what is their function?
Nucleus - contain the genetic material
Mitochondria - release energy in the form of ATP; respiration
Ribosome - protein synthesis
Cell membrane - control what goes in and out of the cell
Smooth endoplasmic reticulum - production and transportation of lipids
Rough endoplasmic reticulum - production and transportation of proteins
Golgi apparatus and vesicles - modify and transport proteins
Lysosome - contains enzymes to break up organelle debris
Cell wall - provide strength, structure and support
Chloroplast - photosynthesis
Vacuole - stores water and provides support
What are the common organelles in prokaryotic cells and what is their function?
Genetic material - free floating circular DNA
Plasmids - small rings of DNA
Capsule - layer of slime
Cell wall - made of polypeptides and polysaccharides
Cell membrane - control what goes in and out of the cell
Mesosome - helps with respiration
Ribosomes - smaller than eukaryotic
Flagellum - locomotion
Cell cycle
G1 - first growth phase, cell grows, increases in size
S - synthesis phase, DNA replicated
G2 - second growth phase, organelles replicate, further growth of cell
M - mitosis, cytokinesis
G1, S and G2 are all part of interphase
Stages of mitosis
Prophase - chromosomes condense, nuclear membrane disintegrates, spindle fibres start to form
Metaphase - chromosomes line up across the equator of the cell and attach to the spindle fibres via their centromeres
Anaphase - spindle fibres contract, chromatids are pulled apart at their centromeres
Telophase - chromosomes start to unravel, nuclear membranes start to form
Mitotic index
Ratio of cells undergoing mitosis to total cells
Measure of rate at which cells are dividing
The number of cells at each stage of mitosis is proportional to the time spent in each phase
Mitotic index = number of cells in mitosis / number of cells
A high mitotic index can be used to diagnose cancer
Virus structure
Viruses are non-living particles
They have genetic material, a capsid and attachment proteins