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Cell Structure & Membranes
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everything you need for cell structure and membrane functions
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Cell-Surface Membranes also known as plasma membraneGlycolipid lipid +
protein Glycoprotein
Channel Protein Carrier Protein
t
+ carb carb
IEEE
no
8D Cholesterol
g
Phospholipid Cholesterol
• polar head group
Protein • steroid ring structure
• non-polar hydrocarbon tail
• binds to hydrophobic tails
Structure + Function • makes membrane rigid - less fluid, as it makes the
phospholipids pack tightly
• Semi-Permeable Phospholipid Bilayer- • strength + support (animals cells don’t have cell
hydrophilic head + hydrophobic tail inwards wall)
• Regulates materials entering and exiting cell • regulates fluidity and flexibility of membrane
• Fluid- molecules are constantly moving, • less ions lost from cell
fluid combination of lipids, proteins and carbs Transport Proteins
• Mosaic- protein molecules are unevenly Specific solute
• protein molecules acts as carriers or channels
distributed • Carrier Proteins- complementary shape to polar
• Small, lipid soluble, non-polar molecules
diffuse through e.g. CO2, O2 molecules e.g. glucose, ions, amino acids + aids
• Water is polar, so can’t diffuse through, transport by facilitated diffusion or active transport
Undergoes conformational change (100x
instead moves through aquaporins -> protein pumps slower 10^4 molecules s-1)
• Phospholipid bilayer restricts passage of polar • Channel Proteins- size and charge allows ions and
and water soluble ions molecules to diffuse by facilitated diffusion, form
water-filled pores i.e. 10^6-10^7 s-1
Phospholipids Proteins
Polar phosphate head • other proteins acts as receptors e.g. for insulin
• hydrophilic which attaches to cell membrane, have specific
• made up of choline, phosphate & glycerol tertiary structure to allow complementary peptide
Long, non-polar lipid tails based hormones to bind
• repelled by water • Integral Proteins- permanently embedded
• fatty acids • Peripheral Proteins- penetrate just one
In water, phospholipids self-organise with head on surface
outside and tails inside, forming micelles or liposome • could also be used for intracellular joining- for
bilayers tight junctions and plasmodesmata
• molecules flow past each other laterally but can’t • used for enzymatic activity in metabolic activities
e.g. electron transport chain
move vertically
Glycoproteins/Glycolipids
• act as receptors, glycoproteins can be involved
in cell-cell recognition as they can act as
antigens to be recognised by immune system
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