Chapter 3 Cell structure Flashcards
what is magnification and what is it controlled by
Magnification = By how much an image is enlarged under a microscope.
Controlled by: The power of the lenses used.
what is resolution and what is it controlled by
Resolution = The minimum distance between two objects at which a microscope can distinguish them as separate entities.
Controlled by: The wavelength of the illumination used.
what is the equation to calculate magninfication
Magnification = image size/ actual size
what is cell fractionation
Cell fractionation and centrifugation is the process by which cells are broken up and their organelles separated (by size) ready for study
what are the conditions of the solution that cells must be placed in before fractionation
Cold - to reduce enzyme activity that could damage the organelles
Buffered - to maintain constant pH and prevent proteinsfrom denaturing causing damage
Isotonic - to prevent cell organelles bursting or shrinking by osmosis
what is homogenisation
When cells are broken up by a homogeniser (blender) to release the organelles
what are the steps for ultracentrifugion
Cut the tissue and place it in a cold, buffered and isotonic
Grind the tissue using a mortar and pestle
The filtrate is placed in a centrifuge and spun at slow speed
The heaviest organelles (e.g. nuclei) are forced to the bottom and form a thin pellet
The fluid at the top (supernatant) is removed
The supernatant can then be re-spun at a faster speed to gain the next heaviest organelles (e.g. chloroplasts)
The process is repeated
why is the resolution higher in electron microscopes
The electron beam has a very short wavelength and the microscope can therefore resolve objects well - it has a high resolving power.
how is the electron beam focussed in an electron microscope
Using electromagnets
what are the advantages of electron micorscopes
Advantages:
Resolution is 0.1nmTEM/20nmSEM
Produce detailed images of organelles
3D images-shows contours (SEM)
what are the disadvantages of electron microscopes
Disadvantages:
Electron beams deflected by air molecules - vacuum needed
Expensive
Skill & training needed
Artefacts can be present
TEM – very thin specimen required
what are some characteristics of a TEM
high magnification
higher resolution compared to a SEM
live specimens cannot be used as a vacuum is required
A 2D image is produced
artefacts are possible
real colour cannot be seen
what are some characteristics of a SEM
high magnification
lower resolution compared to a TEM
live specimens cannot be used as a vacuum is required
A 3D image is produced
artefacts are possible
real colour cannot be seen however staining can be added
What is an artefact
When looking at a prepared sample (e.g. a cell or a group of cells) under a microscope, you can sometimes see things that aren’t actually part of the specimen. These are known as artefacts. Artefacts can be a variety of things, such as: dust. air bubbles.
What are the requirements for a biological drawing
Smooth neat lines with no hairy edges of overlaps
No shading
Labels horizontal or vertical and drawn with a pencil & ruler
Lines just touching the part they are labelling
Magnification
Scale bar
Annotation – eg. Nucleus dark in colour
How do you calibrate an eyepiece graticule
1)Line up the scale on the eyepiece with the
scale on the stage micrometer (slide)
2)The stage micrometer is a 1cm scale
divided into 10ths of a mm.
3) Read off the stage micrometer to work out
what your eyepiece units are worth.
4) Repeat for the other objective lenses you
will be using
5) Finally: Replace the stage micrometer with the slide you would like to view and use the eyepiece to measure.
What are the characteristics and functions of a nucleus
Contains genetic material and controls cell activity.
Made up of:
The nuclear envelope – double membrane that controls material entry and exit
Nuclear pores – allows large molecules like mRNA out of the nucleus
Chromatin – made of proteins and DNA. Controls the cell activity
Nucleolus – makes ribosomes
What are the characteristics and functions of a mitochandria
Double membrane – outer controls flow of materials in/out
Cristae – extensions of inner membrane. Increased SA for attachment of enzymes
Matrix – Semi rigid. Contains protein, lipid and trace DNA
What are the characteristics and functions of a ribosome
2 sub-units containing RNA and protein
2 types:
80S type – eukaryotic cells about 25nm diameter
70S type – prokaryotic cells (smaller)
Found free in cytoplasm or in the RER
What are the characteristics and functions of both types of endoplasmic reticulum
2 types of endoplasmic reticulum:
Rough ER – ribosomes on surface
Large SA for protein synthesis
Pathway to transport proteins out of cell
Smooth ER – no ribosomes
Synthesises, stores and transports lipids
Synthesises, stores and transports carbohydrates
What are the characteristics and functions of the golgi apparatus
Adds carbohydrate to protein to make glycoproteins
Produces secretory enzymes
Secretes carbohydrates
Transports and modifies lipids
Forms lysosomes
What are some differences between prokaryotes and eukaryotes (table)
Labelled picture of an animal cell
Labelled picture of a plant cell
Labelled picture of a nucleus
Labelled picture of a mitochondrion
Labelled picture of a ribosome
Labelled picture of the rough endoplasmic reticulum
Labelled picture of a Golgi apparatus
Labelled picture of a lysosome
Labelled picture of a chloroplast
Picture of the cell cycle
