2.1.1 - Cell structure Flashcards
What is cell theory
The theory that all living organisms are made up of one or more cells and that cells only arise via the division of pre-existing cells.
What does microscopy allow?
the ability to observer and investigate the many different cells types and the various different cell structures.
What is an artefact
Structures visible on an image that having been formed during the sample preparation, which aren’t actually present in the cell, ie are bubbles or mesosomes
light microscope energy source
Visible light
how does a light microscope work
lenses made of glass bend light that has passed through the specimen such that you see a magnified image
thickness of light microscope specimens
thin/flat
why must light microscopes have thin/flat specimens
so the light can pass through the specimen into you eyes
advantages of light microscope (6)
we can see true colours
living processes can be seen
inexpensive to buy and maintain
easy sample preparation
sample preparation less likely to cause artefacts
straightforward
why are stains used (2)
cell = colourless, so the stains make specific parts visible
contrast
how to calculate overall magnification of light microscope
magnification of eyepiece lens x magnification of objective lens
light microscope magnification
x1500
light microscope resolution
200nm
laser scanning confocal microscope energy source
ultraviolet light
why does an LSCM have a higher resolution that light microscope
ultraviolet light has a shorter wave length than visible light.
shorter wave length = higher resolution
how to prepare specimen for LSCM
cell treated with antibodies which bind to specific proteins
the antibodies have floutesecnt dyes attaches, which absorbs light from the laser and re-emits the light of a specific wavelength
or
cells can be genetically modified to produce fluorescent proteins which reveal their own location.
LSCM, how does it work
laser scans across the specimen in a fixed plain, illumination only a single point at a time
high resolution, but 2D ‘slice’
many slices can be put into a computer programme to create a 3D image.
LSCM advantages
it can show the precise location of one or more specific types of protein at different depths within a cell.
if the cell in prepared appropriately, living cells can be viewed, and changed over time can be tracked, such as the position and length of spindle fibres during cell division.
TEM and SEM energy source
beam of electrons, which is then picked by electromagnetic which are used as lenses
how does a TEM work/ preparation
thin section of cell is stained with a heavy metal such as gold. the electron beam passes through the specimen and onto a detector, but the are where the heavy metals atom are the electrons can’t pass through and are blocked, providing contrast to the image
TEM image description
Flat, but extremely detailed due to high resolution, artificially coloured, 2D
TEM magnification
x500000
TEM resolution
0.5 nm
how does a SEM work/ preparation
thin section of cell is stained with a heavy metal such as gold. the electron beam is directed across the surface specimen, and where the heavy metal is the electrons are reflected of the surface of the cell and create an image on the detector
SEM image description
Surface view of a cell where the image has a 3D appearance
SEM magnification
x100000
SEM resolution
5nm
advantages of electron microscopes
very high resolution and magnification
disadvantages of electron microscopes
black and white image produces, however artifical colours can be added using a computer, and the components must be digitally enhanced for non-experts to interpret the image
sample preparation is technically demanding
much training and practice is needed
very large and not portable
very expensive to buy and maintain
vacuum must be maintained so the electron beam isn’t scattered by gas particles, meaning the cell is dead
the sample preparation is generally more likely to form artefacts than light microscopes
disadvantages of light microscopes
low resolution and magnification
what do you call the outer most membrane?
plasma membrane or cell surface membrane
what are the three types of slide preparations for light microscopy, and which is the most effective
- Smear
- Squash
- Sectioning (most effective)
Describe smear preparation
spreading the sample evenly across a microscope slide, so it forms a thin layer, (so light can pass through)
add colour stain if needed
add coverslip on top of the specimen
advantages of smear preparation
Living cell can be viewed
Describe squash preparation
tissue is placed onto a slide
add stain if needed
place coverslip of specimen and gently press down gently to spread out / squash the sample into a thin layer
advantages of squash preparation
living cells can be viewed
describe sectioning preparation
tissue is first fixed and preserved using formaldehyde
embedded in solid wax or resin
very thinly sliced with a device called a microtome
place onto a slide and stain if needed
place coverslip over the specimen
disadvantages of sectioning preparation
living cells CANNOT be viewed
example of smear preparation
blood
example of squash preparation
root tip in which is undergoing mitosis
Why do we use stains
enables cells or cell components to become visible which were previously invisible .
provides contrast between structures so different component or cell types can be distinguished from one another
enable identification of cell types, organelles or specific biological molecules
give an example of a stain used in light microscopy
methylene blue - Binds to DNA, so nucleus looks blue
give an example of a heavy metal used in electron microscope
Gold
1mm is how many micrometers
1000um
1mm is how many nano meters
1000000nm
1um is how many nano meters
1000 nm
Magnification definition
The number of times larger the size of an image is compared to the real object
what is the magnification triangle
Resolution defintion
The ability to distinguish two close points as sepatate objects
why is it not worthwhile to magnify above x1500 with a light microscope
The resolution of the LM is not high enough to make it useful to magnify above x1500; no further detail would be seen in the image. The resolution of the LM is 200nm, limited by the long wavelength of light
ultrastrucutre definition
fine details of cell structure
organelle definition
a cell component with a specific structure and function
eukaryote cell
A cell with a nucleus and other membrane bound organelles.
eukaryote cell size
10-100um
prokaryote definition
cells without a membrane bound nucleus or organelles.
prokaryote size
1-2um
cell wall materials
prokaryotes - peptidoglycan
fungi - chitin
plant- cellulose
protocists - cellulose cell wall
how would you describe the shape of endoplasmic reticulum
and what is the funciton of each type
membrane bound flatted tubes called cisterna with an internal space called the lumin containing specific proteins.
rer - proteins synthesis
ser - lipid synthesis
how would you describe the shape of the golgi, and what is its function
membrane bound flatted discs called cisternae with a lumin containg specialsed ezumes.
role - modify proteins and packaging into secratory vesicles
creates lysosomes.
lysosomes shape and function
spherical membrane-bound organelle containing hydrolytic enzymes such as protease.
digest old/faulty organelles
digestion of engulfed pathogens
THE MEMBRANE IS IMPORTANT BECAUSE IT ENSURE THAT THE HYDROLYTIC ENZYMES DO NOT LEAK OUT AND CASUE DAMGE TO THE CELL.
mitochondria shape and function
chloroplast design and function
double membrane structure
fluid within is called the stroma, contains many enzymes needed in photosynthesis
thylakoid membranes contain chlorophlyll
msny thylakoid are in a blob shape called the granum
vacuole function
membrane enclosed compartment
storage role
maintains cell turgor - water moves into the vacuole via osmosis, increases vacuole volume, prssure exerted against cell wall which cant expand therfore cell becomes turgid
centrioles design and function
short cylinder-shaped strucutre at a right angle to each other
made of microtubles
only in animal cells
flagella
cell movement
9 +2 arrangement of microtubles
an extenision of the plasma membrnae
cytoskeleton deffinition
a network of protein strands found in the cytoplasm of te cytoskeleton
microtubles
made of tubulin
- transport vesicle and organelle movements
- movement of chlorplast
centrioles - organise spindle fibres during cell division
- cell movement via a flagella
microfillaments
very fine threads of actin
give the cell mechanical strength and determines the cell shape
nucleolus function
production of RNA
