Download Module 2 2.1.1 Cell Structure

Module 2 2.1.1 Cell Structure
By Ms Cullen
Organisms
• All living organisms are made of cells they are
either:
Unicellular – for example bacteria, which only
consist of 1 cell
or
Multicellular – where the organism is made
up of more than 1 cell, could be as many as
millions of cells.
Cells under the • Identify the 2 types of
generalsied cell as seen
light microscope
under the light microscope.
• Annotate diagrams in your
handbook with the
function of each of the
organelles.
• Note differences between
the 2 types of generalised
cells.
Cells under the light microscope
How the light microscope works
1. Light passes from the bulb under the stage,
through a condenser lens, then through the
specimen.
2. The beam of light is focussed through the
objective lens and then through the eyepiece
lens.
3. There are usually 3 or 4 objective lenses with
different magnifications x4, x10, x40 and x100 in
an oil immersion lens.
4. The eyepiece lens is usually x10.
Magnification
• Magnification – to work out magnification
multiply the magnification of the two lenses
together.
• eg. x 10 eyepiece lens and x 20 objective lens:
10 x 20 = 200 x magnification.
• What would the magnification be using a
x100 objective lens with a x 10 eyepiece lens?
• Light microscopes can magnify up to x 1400.
Resolution
Resolution is how clear an image is.
• Two objects which are close together viewed
under the light microscope may appear as a
single image and magnifying can only make
this single image larger, not increase the
resolution.
• The maximum resolution of a light microscope
is 200nm. Objects closer together than this
are not seen as separate.
Preparation of specimens
• Staining – coloured stains are chemicals used to bind
to chemicals on or in the specimen, allowing the
specimen to be seen more easily.
Stain
Use
Colours produced
Methylene blue
Staining living cells
Dark blue nucleus, light
blue cytoplasm
Iodine solution
Staining living plant cells
Very dark blue starch
grains
Acidified
phloroglucinol
Staining lignin (substance in cell Bright Red
walls of xylem vessels)
Acetic orcein
Staining nuclei and
chromosomes
Red
Eosin
Only stains dead cells
Pink
Methylene green
Staining plant cell walls
Green
Preparation of specimens
• Sectioning – process in which specimens are
embedded in wax and thin sections are cut
without distorting the structure of the
specimen.
• This is particularly useful when making
sections of soft tissue eg. brain.
Activity 2.1
Prepare and view specimens under a light
microscope.
1. Use methylene green and iodine solution to look
at onion cells
2. Prepare an unstained temporary mount of
Elodea
3. Use methylene blue stain to look at your cheek
cells
4. Use potato and iodine solution to prepare a
slide showing graduation of staining
Units of measurement
To put things in perspective………..
…..a pin head is 1,000,000 nm across
…. a human hair is about 80,000 nm (or 80μm) in diameter!
Unit
Symbol
Equivalent in
metres
Fraction of a metre
Metre
m
1
one
Decimetre
dm
0.1
one tenth
Centimetre
cm
0.01
one hundredth
Millimetre
mm
0.001
one thousandth
Micrometre
μm
0.000 001
one millionth (10-6)
nanometre
nm
0.000 000 001
one thousand
millionth (10-9)
Eyepiece graticules
• These are used to measure the size of a specimen.
• These are microscopic rulers, 1mm long and divided into 100
divisions.
• Each division is 0.01mm or 10μm.
Eyepiece lens
magnification
Objective lens
magnification
Total
magnification
Value of 1
eyepiece division
(μm)
X 10
X4
X 40
25
X10
X 10
X 100
10
X 10
X 40
X 400
2.5
X 10
X 100 (oil
immersion lens)
X 1000
1.0
Activity 2
Use worked example on P.7 Heinemann OCR AS
Biology book to work out size of amoeba Figure 1
P.6.
Use the graticules and previous table (also P.7
in textbooks) to work out the size of the
nucleus in your cells under the microscope.
Magnification and micrographs
Look at example on P. 7 in
textbook
Actual size = image size
magnification
See example fig 4 P.7
I
A x M
• Now have a go at Exam Q5 on blood cells
Activity 2.2 Magnification and
Calibration
1. Calibrate eyepiece graticule measurements
with a stage micrometer’s μm
2. Calculate the size of a specimen
3. Estimate the size of microscopic structures
4. Answer Qs at end of activity and on follow up
sheet
1. Count the number of divisions on the stage micrometer, that
overlap with the eyepiece graticule scale.
2. The 1mm stage micrometer has 100 divisions. Therefore
each division is worth 10 μm.
3. Calculate the size of the overlapping region of the stage
micrometer by multiplying the number of divisions by 10
μm. Add to table.
4. Record the number of eyepiece graticule units (EPGU).
5. Divide the stage micrometer measurement by no of EPGU
and this will give you the value of each of the EPGU.
Objective
lens used
Sizes of overlapping regions
Conversion
Calculation
of the two scales
number/µ
(µm ÷
Stage
Number of
m per
EPGUs)
micrometer/µm
EPGUs
EPGU
(no. of divisions x 10µm)
x4
10
40
Microscope and Biological Drawing
Skills
• Clear, continuous lines for your sketch, use a
SHARP pencil!
• NO SHADING!
• Diagram should cover at least 50% of space
given.
• All label lines should be straight – use a ruler.
• Label lines should touch the structure you are
identifying.
• Label lines should not have arrows on the end.
The Electron Microscope
Microscopy: Electron microscope
• The filament acts as an
electron gun emitting
electrons as it is heated.
• They are attracted to a
positively charged electrode
(anode).
• The condenser & objective
lenses are electromagnets
that straighten the beam
focusing it on the specimen
Microscopy: Electron microscope
• The projector lenses focus
an image onto the viewing
screen.
• A vacuum is needed inside
the chamber to avoid
scattering the electrons.
• Specimens must be dead.
• Resolution is typically
1nm, but up to 0.20nm.
The Electron Microscope
Microscopy: Electron microscope
• There are two types of electron
microscope:
• Transmission (TEM): The electron beam
passes through a very carefully prepared
extremely thin slice of specimen.
• Scanning (SEM): The electrons are
reflected from the surface of specimen.
3D images are produced.
Transmission electron micrographs
Scanning electron micrographs
Light & electron microscopes
Light
Radiation used
Magnification
Resolution
Focusing by
Biological material
(dead or alive?)
Size
Appearance
Preparation of
material
Cost of unit
Electron
The development of the light
microscope
• Light microscopes have continued to develop
with new technologies.
• Fluorescent microscopes use a higher light
intensity and specimens which have been treated
with fluorescent chemicals or ‘dyes’.
• Fluorescence is the absorption and re-radiation of
light.
• Light of a lower wavelength and lower energy is
emitted and used to produce a magnified image.
Laser Scanning Confocal
Microscopy
• This moves a single spot of light across a
specimen, causing it to fluoresce where
organelles have been treated with dye.
• The emitted light is filtered through a
pinhole aperture.
• Only light radiated from very close to the
focal plane is detected.
• The focal plane is the distance that gives the
sharpest focus.
• Very thin sections of specimens are
examined. Light from elsewhere is removed.
Giving very high resolution images.
• 2D images are produced but a 3D image can
be produced by creating images at different
focal planes.
Laser Scanning Confocal
Microscopy
• The beam splitter is a dichroic
mirror, which only reflects one
wavelength of light from the laser
and allows other wavelengths to
pass through.
• The position of the 2 apertures
means the light waves from the
laser follow the same path as the
light waves radiated when the
sample fluoresces.
• This means they both have the
same focal plane, hence the name,
confocal.
Laser Scanning Confocal
Microscopy - Advantages
•
•
•
•
Non-invasive.
Used in diagnosis of eye diseases.
Being developed for endoscopic procedures.
Can be used to see distribution of molecules
within cells and is therefore being used in
development of new drugs.
• In the future it may be used to perform virtual
biopsies. https://www.youtube.com/watch?v=g5U-n4Toq60
Generalised Animal and Plant
Cells under the Electron
Microscope
• List the organelles that
can be seen in the cells
under the electron
microscope that could
not be seen under the
light microscope.
Comparison of plant and
animal cell ultra structure
Eukaryotic cells
• Eukaryote means ‘true nucleus’.
• They contain a number of distinct organelles,
which have membranes that allow various
processes to take place inside of them.
• DNA is enclosed by a nuclear membrane.
• Their ribosomes have a diameter of approx
22nm and are known as 80S ribosomes.
• Divided into plant cells and animal cells.
• Larger than prokaryotic cells. Diameter of cell
is usually around 20-40 μm.
Electron micrograph: Animal cell (liver
cell or hepatocyte)
Electron micrograph: Plant cell
(leaf palisade cell + stomata, right)
Cell ultra structure
• Using ‘OCR Biology’ P.12-13 and ‘Advanced
Biology for You’P.32-7 - make notes & diagrams
on the structure and function of the following
cell organelles:
NUCLEUS, NUCLEOLUS, ROUGH ENDOPLASMIC
RETICULUM, SMOOTH ENDOPLASMIC
RETICULUM, GOLGI APPARATUS, LYSOSOMES,
CHLOROPLASTS, MITOCHONDRIA, RIBOSOMES,
CENTRIOLES AND MICROTUBULES, CELLULOSE
CELL WALL, PLANT VACUOLES.
• Divide these into those found in both plant and
animal cells and those unique to each.
Cytoskeleton - Function
• Provide mechanical strength to cells
• Aid transport within cells
• Enables cell movement
Cytoskeleton
• The cytoskeleton is a network of protein fibres
that give the cell it’s shape and stability.
• Some of the fibres known as actin filaments,
like the fibres found in muscle cells, can move
past each other. This allows some cells, eg
white blood cells, and some organelles to
move.
• Other fibres known as microtubules can be
used to move microorganisms through liquid,
or waft liquid past a cell.
Cytoskeleton
• Other proteins are able to move organelles
along fibres.
• This is how chromosomes are moved during
mitosis and how vesicles move from ER to
golgi apparatus.
• The proteins are called microtubule motors
• They use ATP during these movements.
http://thomson.fosterscience.com/Biology/UnitCellsAndCellProcesses/InteractiveCell.htm
Flagella (undulipodia) and Cilia
• In eukaryotes flagella (undulipodia) and cilia
are the same, although undulipodia are
longer.
• They are hair like projections from the surface
of the cell
• Each one consists of a cylinder containing 9
microtubules in a circle and 2 microtubules in
a central bundle.
• Undulipodia and cilia move because the
microtubules use ATP.
Flagella (undulipodia) and Cilia
• In sperm the undulipodia form the tail,
allowing the whole cell to ‘swim’.
• In ciliated epithelial tissue, the beating
movement if the cilia moves substances across
the surface of the cells eg mucus
Flagella (undulipodia) and Cilia
• Undulipodia usually occur in ones or twos on a
cell, whereas cilia occur in large numbers on a
cell.
• Cilia are less than 10 μm long
Prokaryotic cells
• Make up prokaryotic organisms: Bacteria &
Blue-Green Bacteria.
• Simple cells without a nucleus or distinct
(true) cell organelles.
• Prokaryote means ‘before-nucleus’.
• They were probably the first organisms to
evolve on Earth
• Contain about 0.2% of the number of genes
found in eukaryotes.
Bacteria: Escherichia Coli
Structure of Prokaryotic Cells
• They are 1-5 μm, so much smaller than eukaryote
cells.
• Rigid MUREIN (sometimes called peptidoglycan)
strengthened cell wall (not cellulose), which
maintains shape & prevents osmotic damage.
• Potentially Flagella for movement. They are
simple compared with eukaryotic flagella being
composed of a single cylinder of protein subunits.
Structure of Prokaryotic Cells
• Potentially inner extensions of the cell surface
membrane called MESOSOMES. These are sites of
respiration by enzymes as there are no mitochondria.
• Ribosomes are smaller than those found in
eukaryotic cells (approx 18nm) and are known as 70S
ribosomes.
• A single bacterial chromosome of about 2000 genes
(no nucleus) in the nucleoid.
• DNA rings which can replicate separately from the
main chromosome called PLASMIDS. These have
been utilised in recombinant DNA technology, for
example producing human Insulin.
Bacterial structure
Comparison of prokaryotes &
eukaryotes
Prokaryotes
Organisms
Size
Nucleus?
Cell walls
Organelles
Flagella
Eukaryotes
Complete end of unit Qs on
worksheet.