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
Structure of cell membrane
Phospholipid bilayer
- Hydrophilic head on outside
- Hydrophobic tail on inside
Cholestrol
- Strengthen the membrane
- Prevent leakage of water and ions
Embedded proteins
- Channel proteins which are holes that are specific and can be controlled by chemicals/electrical signal
- Carrier proteins which change shape when a molecule binds to it
Glycoprotein
- Allows cells to recognise each other
- Receptors for neurotransmitters and hormones
Glycolipid
- Recognition site
- Help cells to attach to one another and form tissues
Fluid mosaic model
Fluid - phospholipids can move relative to one another
Mosaic - embedded proteins vary in shape and size
Membrane permeability required practical
Fresh rinsed beetroot in water in boiling tubes in water baths, use colourimeter to measure light absorption of pigmented water
Independent - temperature
Dependant - light transmission
Control - size of beetroot, volume of water
Diffusion
Net movement of molecules from a region of higher concentration to a region of lower concentration.
To increase rate of diffusion: High temperature Large surface area Short diffusion pathway Steep concentration gradient
Facilitated diffusion
Diffusion involving the presence of proteins to allow the passive movement of substances across plasma membranes.
Osmosis
Net movement of water from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
Water potential is the potential energy of water relative to pure water and is denoted by psi, ψ.
Osmosis in plant and animal cells
Plant cells
If the cell gains too much water it will become turgid, its protoplast pushed against the cell wall.
If the cell loses too much water, the cell will become plasmolysed, the protoplast pulled away from the cell wall.
Animal cells
If the cell gains too much water it will swell and burst, its membrane broken into fragments and its content released.
If the cell loses too much water, it will shrivel and shrink - in a red blood cell the haemoglobin becomes more concentrated, giving a darker appearance.
Osmosis required practical
Dried potato weighed and put in glucose solutions for 24 hours, taken out and dried and weighed again
Independent - concentration of glucose solutions
Dependent - percentage change in mass
Control - volume of solution, temperature, time left for
Active transport
Movement of molecules from a region of low concentration to a region of high concentration using ATP and carrier proteins
Co-transport
Transport of one substance coupled with that of another across a plasma membrane in the same direction through the same carrier protein
Co-transport of glucose
Sodium ions actively transported out of cells into blood through the sodium-potassium pump
Maintains much higher concentration of sodium in lumen of intestine than in cells
Carrying a glucose or amino acid molecule, the sodium ions diffuse from the lumen into the cells through co-transport proteins
Glucose/amino acids enter blood plasma by facilitated diffusion
