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CELLS AND ORGANELLES AND SHIT
YIKES

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Cells are the smallest unit of life classified as a living thing
All cells come from pre-existing cells
All cells contain the hereditary info necessary for regulating cells functions and for transmitting info to the
next generation of cells (DNA)
Abiogenesis: the process by which life arises from simple organic compounds
Organelle: A special subunit within a cell that has a specific function, usually enclosed within it's own
membrane
Ultrastructure: internal structure of a cell which suits for its job

ORGANELLES, MY MAN

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Fucking nucleus
o Nuclear pores: around 300 of the, ,allow passage of large molecules eg mRNA
o Nuclear envelope: double plasma membrane, continuous with RER at points so has ribosomes on
surface, yay
o Nucleolus: small spherical region manufactures rRNA and builds ribosomes, can be more than one
o Chromatin: nuclear material, my man
Purpose?
o Control centre of cell via mRNA, tRNA, protein synthesis
o Retains genetic material
o Manufactures ribosomes and RNA needed for proteins
Mitochondria
o Double plasma membrane: for controlling entry and exiting of subtances
o Cristae: folded extensions of inner membrane, provide a heck tonne of SA for attachment of
proteins and other enzymes involved in respiration
o Matrix: fluid that contains proteins, lipids, ribosomes, mitochondrial DNA (single stranded, one
large loop, similar to bacterial), ATP synthase particles, means mitochondria can control
production of some of its own proteins
Purpose?
o Site of aerobic resp
o Responsible for most of the production of ATP from respiratory substrates
o Numbers and sizes in cells varies with metabolic activity going down, obvs
Chloroplasts
o Typically disc shaped

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o Chloroplast envelope: double plasma membrane lol
o Granum: stacks of up to 100 thylakoids, where light absorption part of PS takes place, multiple
membranes = large SA for attachment of chlorophyll, electron carriers, enzymes
o Thylakoids: disc like structures contain chlorophyll
o Stroma: fluid filled matrix, where synthesis of sugars takes place, contains all enzymes needed and
also starch
o DNA and ribosomes: 4 quick and easy manufacture of all enzymes and proteins needed for PS
Endoplasmic reticulum
o Two types, rough and smooth
o Rough
 Double membrane
 3D system of sheet like membranes that enclose a network of tubules and flattened sacs
called cisternae
 Provides a pathway for materials throughout the cell
 Large SA and ribosomes for synthesis of proteins and glycoproteins
o Smooth
 No ribosomes on surface, often more tubular
 Synthesises, transports, stores lipids and carbohydrates
o Prevalent in cells that manufacture or store, eg liver and secretory cells
Golgi apparatus
o Found in almost all Eukaryotic cells
o Similar to SER in appearance but more compact, ends are flared
o Cisternae: stacks of membranes making up flattened sacs
o Vesicles: Small, hollow rounded structures, used to carry stuff
o Process goes as follows:
 Proteins and lipids produced by ER pass through GA in strict sequence
 Labelled for accurate sorting and sending to the right place
 Proteins often modified by adding non- protein components, then transported in vesicles
 Vesicles can then fuse with CSM and release contents outside of cell
Lysosomes
o Vesicles with enzymes in them
o Can be lysozymes, which hydrolyse the walls of certain bacteria
o Can release enzymes…
 Outside of cell (exocytosis)
 Into phagocytic vesicle inside cell (phagocytosis)
o Lots in secretory and phagocytic cells, obvs
o Function?
 Hydrolyse pathogenic material ingested by phagocytes
 Exocytosis
 Digest worn out organelles into useful chemicals
 Completely break down cells after death (autolysis)

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Ribosomes
o Smol cytoplasmic granules, not membrane bound, consists of large and small subunit, both
containing rRNA and protein
o Two types, 80S which are bigger and found in eukaryotic cells
o And 70S, which are smaller and found in PK cells, mitochondria and chloroplasts
Cell wall
o Plants = cellulose
o Algae = cellulose and/or glycoproteins
o Fungi = chitin, glycan and glycoproteins
o Bacteria = murein
o Consists of:
 A number of polysaccharides
 Thin layer called middle lamella
 Marks boundary between adjacent cell walls, also cements adjacent cells together
o Function?
 Mechanical support so cell doesn’t burst under osmotic pressure
 Strengthens plant as a whole, rigidity allows tropisms and more complex structures
 Allows water to pass along it and so contribute to transpiration
Vacuoles
o Fluid filled sac bounded by single membrane called a tonoplast
o Contains solutions of mineral salts, sugars, amino acids, wastes, sometimes pigments
o Supports herbaceous plants by making cells turgid
o Sugars and amino acids can act as a temporary food store
o Pigments colour petals, attract pollinating insects

STUDYING CELLS

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Magnification = how much bigger an image is = size of image / size of object
Resolution = how detailed an image is = minimum distance apart two objects have to be to be perceived
as separate
o Depends on wavelength of radiation and type of lens used
o Typical optical = 200nm or 0
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1nm
o But this is rarely achieved
o Difficulties preparing specimen can limit resolution
o Higher energy electron beam needed for highest resolution may damage or destroy specimen

SCANNING ELECTRON MI CROSCOPE

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SEM
Directs thin beam of electrons to surface of specimen from above, the beam is then passed back and
forth across portion of a specimen in a regular pattern that depends on the contouring of the specimen’s
surface
3D computer image from analysis of electrons and secondary electrons produced
Theoretical resolving power is 20nm, but same issues exist as mentioned for the TEM

LIMITATIONS TO ELECTRON MICROSCOPES

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Must be in vaccum
Complex staining required, just for B&W image
Artefacts happen
Theoretical resolving power oft not achieved
Specifically for the TEM
o Specimen must be super thin
o 3D image can only be built using lots of cross sections, a slow and complicated process

CELL FRACTIONATION

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Process in which cells are broken up and different organelles are separated out
Tissue cut up, placed in cold, buffered solution of the same water potential
o Cold to reduce enzyme activity that might break down the organelles
o Buffered to keep pH from fluctuating and altering structures, affecting enzymes
o Same water potential to prevent osmotic damage
Homogenation
o Cells broken up by homogeniser, releasing organelled
o Resultant fluid (homogenate) is then filtered to remove whole cells and large bits of debris
Ultracentrifugation

o Process in which fragments in filtered homogenate are separated out in a centrifuge
ULTRACENTRIFUGATION OF ANIMAL CELLS

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Tube of filtrate placed in centrifuge, spun at low speeds
Heaviest organelle (nuclei) forced to bottom of tube, forms thin sediment/ pellet
Supernatant removed, transferred to another tube, centrifuged again at higher speed
next heaviest organelle (mitochondria) is forced to the bottom of the tube
so the process continues, separating out different organelles each time ~

TEMPORARY MOUNTS
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has specimen immersed in water, or another liquid that soon evaporates
o cell will dry out in 1 or 2 hours and become distorted
o staining adds colour to otherwise transparent structures
o different colours are due to different densities of the chemicals that bind with the stain
o be sure there are 0 air bubbles when u lower the cover slip, my man

MICROSCOPE MEASUREMENTS AND CALCULATIONS

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graticule scale (or EPGU SCALE) is the smaller one
the larger scale is the stage micrometer scale, of which the smallest subdivisions are equal to 10Mm
o this DOES NOT CHANGE and can be used to find out the value of the smallest subdivisions of the
graticule scale and therefore the actual size of the image being observed

CELL SPECIALISATION, ORGANISATION

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Tissues: group of cells that perform a similar function
Organs: combinations of tissues that are coordinated to perform a variety of functions , although often
with one predominant function
Organ systems: organs working together as a single unit, grouped together to perform functions more
efficiently
Basically shit needs to be organised for maximum efficiency, because cells are specialised and cannot
do everything on their own ~

PROKARYOTIC CELL DIF FERENCE

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No nucleus or nuclear membrane
Smaller 70S ribosomes
Cell walls made of murein
No membrane bound organelles
Circular strand of DNA, and no introns in this DNA, nuceloid
Rings of DNA called plasmids

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Instead of chloroplasts, bacterial chlorophyll
May have outer mucilaginous layer (slime capsule)

STRUCTURE OF BACTERIA

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Slime capsule: provides protection and helps groups of bacterium to adhere together for further
protection
Cell wall: physical barrier for certain substances, protects against mechanical damage and osmotic lysis
Cell surface membrane: selectively permeable, controls entre and exit of material
Cytoplasm: contains enzymes, ribosomes, oil droplets, glycogen granules
Plasmids: only in certain species, can reproduce independently, how resistance is swapped around,
vectors in genetic engineering
Flagellum: only certain species, used to move lol

MORE STUFF ABOUT BACTERIA

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Every habitat of world, versatile, adaptable, very successful
Small, 0

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