lec 2 - cell structure

what type of lipids make up the lipid bilayer 

mostly phospholipids (75%) 
glycolipids (5%) 
cholesterol (20%) 
plus small amounts of other lipids e.g. PIP2

what is the lipid bilayer permeable to: 

non polar 
uncharged 
lipid soluble 
impermeable to: 
ions 
large, charged molecules 
water soluble 
needs a channel or transporter proteins specific to solute 

plasma membrane proteins 

proteins needed for transport (channels, transporters), signalling (receptors), and connection (ECM/other cells) 
integral - anchored to membrane and peripheral - on inside or outside of membrane, may attach to integral proteins or phsopholipids

fluid mosaic model 

membrane is dynamic 
lipids can move within their monolayer 
proteins can move, be added, taken away 
membrane components reflect function of the cell 

passive transport 

requires concentration/electrochemical gradient 
lipid soluble/nonpolar/uncharged 

facilitated transport 

requires concentration gradient 
water soluble/polar/charged 
uses channel/pore or transport/carrier 

active transport 

moves against concentration gradient 
requires ATP either directly or indirectly 

bulk transport 

large molecules or large volumes of small molecules 
mediated by vesicles

cytoskeleton functions 

helps maintain cell shape and structure 
helps maintain internal organisation 
essential for: cell division, cell movement, vesicle movement within cells 
dynamic - changes to meet needs of cell 

microfilament structure

actin 
~7nm 
two protofilaments twisted into a helix 
assembled into large filaments, networks, 3D structures 

microfilament function 

movement - muscle contraction
cell junctions - adherens junctions
cell structure - cortical network 
microvilli - increase surface area

microtubules structure 

tubulin 
~25nm diameter 
interacts with motor proteins 
organelle movement and vesicle trafficking 
motility - cilia and flagella 

microtubule function 

organelle movement and vesicle trafficking 
motility - cilia and flagella

intermediate filaments structure 

~10nm 
50+ types made  of various proteins 
cytokeratins mist abundant in GI/renal epithelium 
cytokeratin - support network within cell, cell junctions 

intermediate filament function

support network within cell 
cell junctions - desmosomes and hemidesmosomes - resist shearing forces

what are organelles 

subcellular structures with specific functions 
often membrane bound 
form defined areas and environments within the cell 

nucleus 

usually one per cell
control centre of the cell 
contains most of the cell's DNA - euchromatin and heterochromatin 
contains nucleolus - makes rRNA and ribosomal subunits 
surrounded by nuclear envelope - double membrane, continuous with ER 

endomembrane system 

interconnected system that includes: 
endoplasmic reticulum 
golgi apparatus 
vesicles 

endomembrane system function 

modify, package and move proteins and lipids 

smooth ER

lacks ribosomes on surface
synthesises lipids 
metabolises carbohydrates 
detoxification processes 
stores calcium ions (used as a signal within the cell) 

rough ER

covered in ribosomes on outer surface
role in protein synthesis - proteins enter lumen of rER, proteins are modified, folded and packaged into vesicles, transported to Golgi 

Golgi apparatus/complex 

series of membrane sacs and vesicles
vesicles from ER arrive at cis face 
proteins modified, glycosylated, sorted into vesicles 
vesicles leave from trans face 

vesicles 

membrane bound 
move via motor proteins walking along microtubules 
transport vesicles - move contents within cell
secretory vesicles - move contents out of cell

mitochondria 

site of cellular respiration 
double membrane structure 
number per cell depends on energy demands
generate energy - consume glucose and oxygen, produce CO2, water and energy: ATP

microfilament

microtubules

intermediate filaments