Proteins and Cell Membranes Flashcards
Describe the phosolipid bilayer
Phosphate head is hydrophilic as its polar so loves water
Fatty acid tail is hydrophobic so hates water
Arrange themselves so head is outwards and the tail is inwards so the membrane doesn’t allow ions through it
Describe the fluid mosaic model
Made of protein, glycoproteins, glycolipids, cholesterol
Permeable so small molecules can move through gaps between phospholipids
What evidence is there for the fluid mosaic model
It was a 3 lipid sandwich due to EM images but this didn’t allow for phosphate to be in water
Phosphate heads more dense so show up darker
2 types of protein - peripheral and integral
Freeze -fracture = fractured at weak points between lipid layesr and inner fractured surface coated in metal and smooth surface (lipid) and integral proteins
Mous - fuse with human cells - membrane protein labelled (green/red) remained separate but at 37C fused
Describe osmosis
Net movement of water molecules from an area of high concentration to an area of low concentration
Passive
Can diffuse both ways but net movement is to low concentration
More solute=less water molecules
Continues til isotonic
Describe diffusion
Net movement of particles from an area of high concentration to an area of low concentration
Passive
Describe facilitated diffusion
Some particles are too large to diffuse alone so carrier and channel proteins are needed and is passive
Carrier proteins: Changes the proteins shape releasing the molecule on the opposite side of the membrane
Channel proteins: Form pores in the membrane for charged particles to diffuse through
Describe active transport
Goes against conc gradient
1 phosphate groups removed from aTP and energy released which changes carrier protein shape
Describe exocytosis
Vesicles pinches off golgi and fuses with the cell membrane to release the contents from the vesicle
ATP needed
Describe endocytosis
Membrane surrounds the substance and pinches off to form a vesicle inside the cell containing the substance
ATP is needed
Define the primary strucutre
Specific sequence of amino acids held together by peptide bonds
Describe secondary strucutre
Folds to form beta pleated sheets and twists to form alpha helixes – hydrogen bonds
Describe tertiary structure
Further folding and twisting to form a 3D shape. More bonds ie disulphide (bonds between sulfur in cysteine), ionic and hydrogen as well as hydrophobic and hydrophilic attractions
R groups polar or non polar
Describe quaternary strucutre
The way a protein is held together
Describe fibrous proteins
Long insoluble chains coiled like rope
Held by lots of bonds
Example: Collagen – strong fibrous protein that forms connective tissue
Describe globular proteins
Sphere like compact protein that’s soluble as hydrophilic ends face outwards
Haemoglobin is made of four polypeptide chains and carries oxygen around the body in the blood
