Microscopes and cell structure Flashcards
Magnification
The number of times larger an image appears , compared with the real size of the object.
magnification = image size / size of real object
Using a scale bar:
-measure the length of the scale bar(mm)
- measure the diameter of the structure (mm)
-length of structure/length of scale bar
-multiply by value shown on the scale bar
Resolution
The clarity of an image , the ability to distinguish two separate points .It allows more detail to be seen.
electron micrograph & photomicrograph
Photograph of an image seen using an electron microscope.
Photograph of an image seen using an optical microscope
Light (optical) microscope
- lenses focuses the rays of light and magnify the view of the thin slice of specimen
- different structures absorb different amounts of wavelength of light.
- Reflected light is reflected back to the observer via the objective and eyepiece lenses.
- can use living cells
Magnification ~ x1500-x2000
Resolution ~ 200nm(limited by the wavelength of light)
- Produces a photomicrograph
Transmission electron microscope (TEM)
- A high energy beam of electrons are passed through a thin slice of specimen
- the denser the structure the darker it appears as it absorbs more electrons
- focuses image onto a fluorescent screen or photographic plate to produce and black and white 2D image.
- requires a thin slice of specimen
Magnification ~ x 50 million
Resolution ~ 0.05 - 2nm
Scanning electron microscope (SEM)
- Focus a beam of electrons onto the specimen using electromagnetic lenses.
- secondary electrons bounce off and are detected and focused onto a screen.
- image is in black and white but false colour can be added.
- specimen must be placed in a vacuum and coated in precious metals.
- magnification~ x200,000
- resolution ~ 5-50nm
- 3D image
Laser Scanning confocal microscopes
- most modern technique
- uses laser light to illuminate the specimen and LIVE samples can be viewed.
- can visualise specific proteins and structures and watch them move.
- allow us to tag these with special dyes and antibodies.
- resolution ~200nm
- coloured
- 2D image (many planes of focus can be combined in a computer to construct a 3D image.
- cross section of the specimen can be seen by adjusting the plane of focus at different horizontal levels.
Electron microscopes
-electrons have a short wavelength meaning they have a higher resolution
-electron microscopes contain a vacuum so electrons can passthrough without bouncing off molecules in the air.
- resolution is 2000x better than light microscopes
- cannot view living specimen
- a beam of electrons pass down the microscope.
- focus the electron beam by using electromagnets called electromagnetic lenses.
3.specimen placed in the path of the electron beam
Stains
- allows us to contrast different structures
- makes the internal structures more visible
- creates a clearer image
- differential staining ~ use two different coloured stains simultaneously on the same specimen.
- do not use stains on LIVE specimen ~ instead we use light interference which shows an illuminated specimen against a dark background.
Examples:
iodine ~ cellulose in cell walls (yellow)
sudan red ~ lipids
crystal violet ~ groups of bacteria
acetic orcein ~ binds to DNA and stains chromosomes dark red.
eye piece graticule
- A measuring device.
- placed in the eyepiece of a microscope
- acts as a ruler when you view an object under the microscope
stage micrometer
- A precise measuring device
- placed on the stage
- used to calibrate the value of eyepiece divisions at different magnifications.
- 1mm in length (1000 micrometres)
- 100 divisions ( each 10 micrometres in length)
calculation method using graticules:
- find a length on the stage micrometer than aligns with a length on the eyepiece graticule.
- stage micrometer / eyepiece graticule
This tells us the length of one unit at that magnification - measure the object in graticule units
- value from step 3 x length of one unit (step 2) = actual object length
objective & value of one eyepiece division
x4 ~ 25
x10 ~ 10
x40 ~ 2.5
x100 ~ 1.0
Proteins that remain in cytoplasm
VS
proteins secreted by cells
Translation takes place on a free ribosome in the cytoplasm . example ~ cellular enzyme.
Translation takes place on a ribosome attached to the RER and makes its way through the RER and the golgi apparatus.
Nucleus
Houses nearly all the cells genetic material.
STRUCTURE:
- Double membrane ( nuclear envelope) ~ contain nuclear pores which allow molecules to enter and leave the nucleus.
ENTER ~ steroid hormones
LEAVE ~ rRNA
- Chromatin ~ consists of DNA coiled around proteins called histones .
The DNA and histone proteins form chromosomes which are only visible unless cell has undergone mitosis or meiosis. - Nucleolus ~ No membrane, produces ribosomal RNA (rRNA).Form part of the structure of ribosomes.
Rough endoplasmic reticulum (RER)
The intracellular transport system ~ the cisternae form channels for transporting substances from one area of the cell to another.
STRUCTURE:
- sheets of membranes forming flattened sacs called cisternae which contain enzymes.
- membranes of the cisternae are covered with ribosomes.
- Ribosomes is where translation takes place for proteins which are secreted from the cell.
- these proteins actively pass through the membrane into the cisternae and are transported to the golgi apparatus for modification and packaging.
Smooth endoplasmic reticulum (SER)
STRUCTURE:
- a system of membranes forming cisternae
- no ribosomes on its surface.
- make and store lipids and carbohydrates that can then be passed through the golgi apparatus to be modified.
Golgi apparatus
- consist of sheets of flattened sacs called cisternae.
- have secretory vesicles which bring material to and from the golgi apparatus.
Modify proteins :
- add sugar molecules ~ glycoproteins
- add lipid molecules ~ lipoproteins
- fold into 3D shape
Package proteins:
- stored in the cell
OR
- moved to the plasma membrane to be either incorporated or exported.
Mitochondria
- Produce the energy carrying molecule , ATP, for aerobic respiration
- Double membrane (inner & outer) with a fluid filled space between them.
- The inner membrane is highly folded into CRISTAE which increases the SA for enzymes.
- inner part is a fluid filled MATRIX
- Loop of DNA ~ contain the genes required for some of the enzymes involved in aerobic respiration.
- Ribosomes ~ synthesise the proteins encoded by the mitochondrial DNA.
Lysosomes
- from the golgi apparatus , a number of proteins are packaged into vesicles which go on to form lysosomes.
- single membrane
- Powerful hydrolytic (digestive) enzymes ~ digest large molecules into smaller soluble molecules.
- internal fluid ~ acidic as this the optimum PH for lysosmal enzymes.
- Key role in phagocytosis . example ~ in white blood cells.
- destroy organelles that are damaged or no longer functional.
Chloroplasts
Function ~ where photosynthesis takes place.
Large organelles ~ 4-10 nanometres long.
Structure:
DOUBLE MEMBRANE ~ control which molecules enter and leave the chloroplast.
THYLAKOIDS~
- membrane - bound discs
-where light DEPENDENT reactions take place.
- contain the chlorophyll and enzymes needed for the light dependent reactions.
GRANUM~ formed by thylakoids stacked on top of each other , so light can be absorbed more efficiently.
LAMELLAE:
- flattened discs
- connect thylakoids on different grana.
-play a role in the light dependent reactions
- allow chemicals to pass between the grana.
STROMA ~
- fluid filled matrix
- where light INDEPENDENT reactions take place
- contain enzymes needed for the light independent reactions.
GLUCOSE~ converted into polysaccharide starch which is stored int he chloroplast as starch granules.
LOOP OF DNA ~ contains the genes which encode some of the proteins needed for photosynthesis.
RIBOSOMES ~ synthesise the proteins encoded by the chloroplast DNA.
Cytoskeleton
- A complex network of protein fibres that run throughout the cytoplasm.
- non membrane bound
Micro(actin) filaments:
- narrowest diameter
- narrow fibres containing the protein actin which contract.
- involved in cell movement.
- play a role during cell division (cytokinesis)
Intermediate fibres :
- formed from a number of different proteins.
- protect against mechanical stress.
- anchor the nucleus within the cell
- enable cell to cell signalling
- adhere to basement membrane.
Microtubules:
-greatest diameter
- formed from subunits of the protein TUBULIN
- Tubulin subunits ~ assemble to form tubulin polymers which then form hollow microtubules:
- these are involved in the movement of organelles
- form spindle fibres involved in the movement of chromosomes during mitosis and meiosis.
- determine shape of cells
Centrioles
- found in simple plants ad algae but not flowering plants or most fungi.
- Animal cells contain a pair of centrioles which are made of microtubules.
- The two centrioles lie at right angles to each and are found near the nucleus.
- Pair of centrioles ~ centrosome.
- play a role in the assembly of the spindle fibres during cell division but not essential
- form the cilia and flagella (undulipodia)
Cilia and flagella (undulipodia)
Cilia :
- hair like organelles that extend from the surface of certain cells.
- found in trachea and fallopian tube.
- some do not move.
Flagella :
- whip like organelles that are found on the surface of certain cells e.g sperm.
- moves the cell
- bigger than cilia
- usually only one.
BOTH:
Running through the centre we find nine pairs of microtubules arranged in a circle with another pair of microtubules in the centre.(9+2 structure)
Contain microtubules to allow movement.
