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
vesicle |
small, spherical sac formed by budding off from a membrane |
endocytosis (3 x types) |
materials move into a cell in a vesicle |
exocytosis |
vesicles fuse with the plasma membrane, releasing their contents into the extracellular fluid, important for neurotransmitter signalling |
transcytosis |
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 |
cytoplasm
cytosol |
intracellular fluid surrounding the organelles, site of many chemical reactions which usually release energy & provide building blocks for cell maintenance, structure, function & growth |
organelles |
specialised structures within cell |
cytoskeleton
|
microfilament actin/myosin, generate movement, mechanical support
|
|
intermediate filament stabilise organelle position, attach cells together
|
|
microtubule 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
cilia |
short, hair-like projections from cell surface, move fluids along surface |
flagella |
longer than cilia, move entire cell, sperm's tail |
organelles/structures
ribosomes |
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 |
RER |
connected to nuclear envelope, series of flattened sacs, surface studded with ribosomes, produces secretory, membrane & organellar proteins. attach carbohydrates to proteins (glycoproteins) |
SER |
network of membrane tubules, no ribosomes, synthesises fatty acids/steroids, detoxifies certain drugs (alcohol, pesticides & carcinogens) |
golgi |
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) |
lysosomes |
vesicles that form from golgi & contain powerful digestive enzymes. low internal pH (5) due to H+-ATPase |
peroxisomes |
smaller than lysosomes, detoxify several toxic substances such as alcohol using oxidase enzymes, abundant in liver |
proteasomes |
continuously destroy unneeded, damaged or faulty proteins, found in cytosol & nucleus, contain a multitude of protease enzymes |
mitochondria |
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 |
nucleolus |
spherical body that produces ribosomes |
|
