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cell structure & organelles Cheat Sheet (DRAFT) by

cts module year exammmm

This is a draft cheat sheet. It is a work in progress and is not finished yet.

cell types

prokar­yotic cells
simple cells that have no nucleus - unicel­lular bacteria
eukaryotic cells
complex cells with a nucleus & organelles - all fungi, flants, animals

plasma­lemma (plasma membrane) function

- flexible yet sturdy semi-p­erm­eable regulator
- covers & protects the cell
- controls what goes in & out
- links to other cells
- flies 'flags' to tell other cells ' who' it is
- lipids act as barrier to certain polar substances
- transm­embrane (integral) proteins act as 'gatek­eepers' allowing passage of specific molecules & ions

plasma membrane proteins

ion channel (integral)
allows specific ion to move through water-­filled pore
carrier (integral)
carries specific substances across membrane by changing shape. carrier proteins = transp­orters.
receptor (integral)
recognises specific ligand & alters cell's function in some way
enzyme (integral & periph­eral)
catalyses reaction inside­/ou­tside cell depending on which direction the active site faces)
linker (integral & periph­eral)
anchors filaments inside & outside plasma membrane, providing structural stability & shape for the cell. may also partic­ipate in movement of the cell/link two cells together
cell-i­dentity marker (glyco­pro­tein)
distin­guishes your cells from anyone else's (except identical twin)
small, neutra­lly­-ch­arged, lipid-­soluble substances can freely pass. water is unique - it is highly polar yet is still freely permeable

diffusion (passive)

the passive, random spread of particles from [high] -> [low]
depends on: amount of substance, concen­tration gradient, temper­ature, SA & diffusion distance

ion channels (passive)

allow passive movement of specific ions down electr­och­emical gradient
distin­guished by their ion select­ivity
regulated/ 'gated' holes through membrane
flow through ion channels is near thermo­dynamic equili­brium
gating mechanisms dependent on: voltage, ligands, temper­ature, pH, mechanical stress

transp­orters (carriers)

allow passive movement of solutes across membrane down concen­tration gradient
example is GLUT1 - glucose transp­orter - binds to carrier at membrane side where concen­tration is highest, protein changes shape, releases solute on other side
concen­tra­tio­n-g­radient dependant
exhibit saturation kinetics

osmosis (passive)

- the passive net movement of water through a select­ively permeable membrane from an area of high water concen­tration to one of lower water concen­tration & is opposed by hydros­tatic pressure
- occurs when membrane is permeable to water but not solutes
- water can pass through plasma membrane through lipid bilayer by simple diffusion or through aquaporins (integral membrane proteins)
tonicity = a measure of a solution's ability to change the volume of cells by altering their water content. semi-p­erm­eable membranes separate fluid compar­tments therefore osmosis of water is free to occur between any fluid space & another.

primary active transport mechanisms (pumps)

required for solutes that need to move against concen­tration gradient
requires energy through hydrolysis of ATP
exhibit saturation kinetics
crucial for mainta­ining cell volume & ionic gradients respon­sible for setting resting membrane potential & generating action potentials

secondary active transport mechanisms

use energy stored in Na+ or H+ concen­tration gradients to drive transport of other solutes against their concen­tration gradients
gradients are already establ­ished by primary active transport
indirectly use energy from ATP hydrolysis
antipo­rters carry two substances across membrane in opposite directions
symporters carry two substances across membrane in same direction

vesicular transport

small, spherical sac formed by budding off from a membrane
endocy­tosis (3 x types)
materials move into a cell in a vesicle
vesicles fuse with the plasma membrane, releasing their contents into the extrac­ellular fluid, important for neurot­ran­smitter signalling
combin­ation of endocy­tosis & exocytosis

(1) receptor mediated endocy­tosis

receptor protein recognises & binds a specific particle: choles­terol containing low density proteins (LDL's), vitamins, antibo­dies, hormones
clatharin molecules form a basketlike structure on cytosolic side of membrane forming a vesicle
fuses with endosome
receptors recycled
vesicles bud off endosome to transport particle were required in cell

(2) phagoc­ytosis

cell engulfs large particles such as viruses, bacteria or dead cells
two main phagoc­ytes: macrop­hages & neutro­phils

(3) bulk-phase endocy­tosis (pinoc­ytosis)

no receptor proteins involved
transport of extrac­ellular fluid
plasma membrane folds inward


intrac­ellular fluid surrou­nding the organe­lles, site of many chemical reactions which usually release energy & provide building blocks for cell mainte­nance, structure, function & growth
specia­lised structures within cell


actin/­myosin, generate movement, mechanical support
interm­ediate filament
stabilise organelle position, attach cells together
made of tubulin, determine cell shape, movement of organe­lle­s/v­esicles
network of protein filaments throughout cytosol, provides structural support for cell, three types ^

motile projec­tions of cell surface

short, hair-like projec­tions from cell surface, move fluids along surface
longer than cilia, move entire cell, sperm's tail


site of protein synthesis, large amounts of rRNA, attached to outer surface of nuclear membrane & ER
endopl­asmic reticulum
network of membranes in shape of flattened sacs/t­ubules
connected to nuclear envelope, series of flattened sacs, surface studded with ribosomes, produces secretory, membrane & organellar proteins. attach carboh­ydrates to proteins (glyco­pro­teins)
network of membrane tubules, no ribosomes, synthe­sises fatty acids/­ste­roids, detoxifies certain drugs (alcohol, pesticides & carcin­ogens)
consists of 3-20 flattened, membrane sacs called cisternae. modify, sort & package proteins for transport to different destin­ations. proteins are transp­orted by various vesicles (secre­tory, membrane & transport)
vesicles that form from golgi & contain powerful digestive enzymes. low internal pH (5) due to H+-ATPase
smaller than lysosomes, detoxify several toxic substances such as alcohol using oxidase enzymes, abundant in liver
contin­uously destroy unneeded, damaged or faulty proteins, found in cytosol & nucleus, contain a multitude of protease enzymes
generate ATP by aerobic respir­ation, prevalent in active cells: muscle­/li­ver­/ki­dneys, self-r­epl­icate during times of increased cellular demand or before cell division, contain own DNA - inherited only from your mother, plays important role in apoptosis, cristae = series of folds of inner membrane, matrix = large central fluid-­filled cavity
nuclear envelope
double membrane separating nucleus from cytoplasm
nuclear pores
numerous openings in nuclear envelope, control movement of substances between nucleus & cytoplasm
spherical body that produces ribosomes