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cell structure (microscopes (staining (common= methylene blue and eosin,…
cell structure
microscopes
magnification
magnification= the amount an image has been enlarged by
resolution= the ability to distinguish between 2 points , the clarity of the image
magnification= image size / actual size
types of microscope
light
max resolution= 0.2 ym
max magnification= x 1500
pros: cheap, easy to use, portable, can be used to study whole specimens
use visible light which has a wavelength of 400-700nm
structures smaller than 100nm will not be seen by light microscope
adjust coarse knob to change focus
laser scanning confocal
use laser beams to scan a specimen which is tagged with fluorescent dye
the laser causes dye to give off light. the light is focused through a pinhole on detector and a computer generates 3D image
pin hole helps block out of focus light to produce clearer image
have depth selectivity = can focus on structures at different depths within specimen
high resolution and high contrast
electron
transmission
uses electromagnets to focus beam of electrons through specimen
denser parts absorb more electrons which make them look darker on final image
need thin specimens
max resolution= 0.0002ym
max magnification= more than x1 000 000 (up to x2 000 000)
specimen has to be chemically fixed by being dehydrated and stained
stained with metal salts
image formed is 2D and black and white
cons= large, expensive, require training to use
scanning
scan a beam of electrons across a specimen, knocking off electrons from specimen which are gathered by cathode ray tube to form image
max resolution= 0.002ym
max magnification= from x15 to x200 000
creates 3D, black and white image but computers can add false colour
specimen is placed in vacuum
cons= large, expensive, require training to use
staining
common= methylene blue and eosin
some of stain is absorbed by some parts of object more than others- creates contrast
different stains are used for different things (methylene blue binds to dna)
electron microscopes use heavy metals like lead as stains - metal ions scatter electrons creating contrast
acetic orcin= binds to dna staining chromosomes dark red
eosin= stains cytoplasm/ sudan red stains lipids
iodine= stains cellulose in cell walls yellowed starch granules blue black
how to prepare slide
dry mount
cut a thin slice of specimen
place on middle of clean slide using tweezers
put a coverslip on top
wet mount
pipette a small drop of water on clean slide and use tweezers to place specimen on water drop on slide
place coverslip on top avoiding air bubbles
place a drop of stain next to an edge of coverslip then put paper towel next to opposite edge
how to use a light microscope
1) clip slide containing specimen onto stage
2) select lowest powered objective lens
3) use the coarse adjustment knob to bring stage up to just below objective lens
4) look into eyepiece and use the coarse adjustment knob to move the stage downwards until image is focused
5) adjust focus with fine adjustment knob until image is clearer
calibartion
1) measure amount of ocular divisions in 1mm
2) stage micrometer measures in mm
3) this only works for each objective lens
4) change the magnification
eyepiece graticule= a measuring device which acts as a ruler when you view an object under a microscope
stage graticule= a precise measuring device, a small scale which is placed on microscope stage and used to calibrate the value of eyepiece divisions at different magnifications
eukaryotic cells and organelles
eukaryotic cells= complex and make up multicellular organisms
prokaryotic cells= smaller and simpler, single celled organisms
animal cells: plasma surface membrane, RER, nucleolus, nucleus, SER, lysosome, ribosome, nuclear envelope, Golgi apparatus, cytoplasm, mitochondrion
plant cells: same as animal cells + cell wall, vacuole and chloroplasts
functions of organelles
plasma membrane
description= made of mainly lipids and protein and found on surface of animal cells and just inside cell wall of plant
function= regulates movement of substances in and out of cell. has receptor molecules which allow it to respond to chemicals
cell wall
description= a rigid structure that surrounds cells made of cellulose or chitin
function= supports plant cells, maintains shape, are permeable (allow solutes to pass through)
nucleus
description= a large organelle surrounded by a nuclear envelope (double membrane) which contains pores. contains chromatin and nucleolus
function= controls activities of the cell (transcription of dna). pores allow substances to move between nucleus and cytoplasm. nucleolus makes ribosomes, nuclear envelope separates contents of nucleus from rest of cell, stores and transmits genetic info
lysosome
description= a round organelle surrounded by a single membrane, contain digestive enzymes, abundant in phagocycotic cells (wbcs)
function= contains digestive enzymes and are used to digest invading cells or worn out components of cell, separates enzymes from rest of cell
ribosome
description= a small organelle attached to RER or floats in cytoplasm. made up of proteins and r rna, 20nm
function= site of protein synthesis
RER (rough endoplasmic reticulum)
description= a system of membranes enclosing a fluid filled space (cisternae) and covered in ribosomes
functions=folds and processes proteins made at ribosomes, cisternae form channels for transporting substances from one area of cell to another
SER (smooth endoplasmic reticulum)
description= a system of fluid filled membranes (cisternae) but NOT covered in ribosomes, contains enzymes involved in lipid metabolism
functions=synthesizes and processes lipids, cholesterol and steroid hormones
vesicle
description= a small fluid filled sac in cytoplasm surrounded by membrane
function= transports substances in and out of cell and between organelles - formed by cell membrane, Golgi apparatus and RER
Golgi apparatus
description=a group of fluid filled flattened sacs- vesicles found on edges
function= processes and packages new lipids and proteins. makes lysosomes
mitochondrion
description= oval shaped. have a double membrane- inner is highly folded to make cristae. inside contains matrix which has enzymes, 2-5 ym
function= site of aerobic respiration and where ATP is stored, self replicating
chloroplast
description= a small flattened structure surrounded by double membrane and contains thylakoid membranes which are stacked to make grana that are linked together by lamellae, contain loops of dna and starch grains, 4-10ym
function= site of photosynthesis , light dependant in grana, light independent in stroma
centriole
description= small hollow cylinders made of microtubules made from tublin
function= involved in the separation of chromosomes during cell division and forming cilia and undulipodia
cilia
description= found on cell surface and have a ring of 9 microtubules inside with two microtubules in the middle
function= microtubules allow cilia to move - moves substances across cell surface, contain receptors involved in cell signalling
flagellum
description= have 9 pairs of microtubules in a ring and 2 microtubules in the centre
function= contract and make flagella move, propelling cell forward
vacuole
description= contains fluid surrounded by tonoplast membrane
function= maintains cell stability and keeps it turgid supporting it
prokaryotic cells
eukaryotic vs prokaryotic
size: e cells= 10-100ym, p cells= less than 2 ym (smaller)
dna: e cells= linear, p cells=circular (plasmids)
nucleus: e cells have nucleus,
p cells dont
organelles: e cells= lots of membrane bound organelles, p cells= no membrane organelles e.g. mitochondria, ER, chloroplasts, Golgi
ribosomes: e cells= larger ribosomes, p cells= smaller
cell walls are made of different polysaccharids (peptidoglycan instead of cellulose
different flagellas
cytoskeleton is less developed with no centrioles
binary fission vs mitosis
bacterial
need an electron microscope to be seen
similarities- they have= plasma membrane cytoplasm, ribosomes, dna/rna,
features of prokaryotic= a protective waxy capsule, plasmids, flagella, pili (hair like projections that enable bacteria to adhere to host cells and allow passage of plasmid from one to another)
organelles working together
protein production e.g. hormones
1) instructions for protein/ hormone are in dna
2) the specific instruction to make the protein/ hormone is the gene for the protein
3) nucleus transcribes the instructions on DNA onto mRNA
4) mRNA leaves nucleus through nuclear pore and attaches to a ribosome which is attached to RER
5) the ribosome reads the instructions on the mRNA and uses the code to assemble the protein/ hormone (translation) which is passed into its cisternae.
6) the assembled protein inside the RER is pinched off onto a transport vesicle and transported to the Golgi apparatus via microtubule and motor proteins
7) the vesicles fuse with the cis face of the Golgi apparatus and proteins/ hormones enter
8) the proteins the proteins are structurally modified before leaving the Golgi apparatus in vesicles from its trans face
9) secretary vesicles carry proteins that are to be released from the cell
10) the vesicles move towards and fuse with the cell surface membrane releasing contents by EXOCYTOSIS
cytoskeleton
cytoskeleton is made up of microfilaments made from actin each 7nm, intermediate filaments about 10nm, microtubules made of tublin 18-30nm, cytoskeletal motor proteins (enzymes) involved in hydrolysis of ATP
functions
support organelles and keep them in position
microfilaments help strengthen cell and maintain shape
movement of materials within cells e.g. chromosomes during cell division - motor proteins walk down tublin threads and drag organelles from one part of cell to other
cytoskeleton can propel/ move cell (if has cilia/ flagellum)
intermediate filaments anchor nucleus in cytoplasm, enable cell signalling, allow cells to adhere to basement membrane -stabilising tissue