Biological membranes Nucleotides are the building blocks of nucleic acids Nucleotide comprised of a pentose sugar a base and a phosphate group Adenine A always pairs with Thymine T Guanine G always pairs with DNA Deoxyribonucleic acid double stranded RNA Ribonucleic acid single stranded Like DNA RNA has adenine guanine and cytosine but RNA has uracil A gene is a particular sequence of nucleotides in DNA that contains the instructions for specific individual protein Fluid Mosaic model describes structure of membrane partially fluid partially solid Components of membrane phospholipid bilayer cholesterol protein 1 Phospholipid Bilayer fatty acid component double bonds and kinks in molecule lead to fluid nature of membrane phospholipid structure has hydrophobic hydrophilic properties Fluid Mosaic Model Membrane is a bilayer because there are two layers of phospholipid hydrophobic fatty acid tails face each other Lateral movements of phospholipids also lead to fluidity 2 Cholesterol slots between fatty acids regulates fluidity cholesterol helps to regulate membrane fluidity 3 Protein Membrane is up to 50 protein think of a sea of lipid icebergs of protein Protein is situated in two ways intergral proteins go through membrane presents a hydrophilic channel through a hydrophobic interior peripheral proteins keep to one side of the bilayer inside the cell Roles for membrane protein cell recognition cell communication hormones transport energy capture and release Forms a hydrophilic channel through the hydrophobic interior Membrane is selectively permeable diffusion high concentration to low concentration concentration gradient difference in concentration between two adjoining areas Pure water has high energy lower energy if solute is present Flows from high concentration to low concentration Osmosis movement of water from low to high solute concentration isotonic solute concentration is the same on both sides of membrane no net flow of water hypertonic solute concentration is higher outside the cell water leaves cell hypotonic solute concentration is higher inside the cell water enters cell Passive transport NO ENERGY is required to move molecules across the membrane Facilitated diffusion transport Protein forms a hydrophilic channel through a hydrophobic environment This requires a concentration gradient but no expenditure of energy Both cases involve movement WITH concentration gradient Active transport energy is required to move molecules across the membrane against a concentration gradient The sodium potassium pump works to maintain a low concentration of sodium Na ions outside the cell and a high concentration of potassium K ions inside the cell Movement of bigger materials Phagocytosis cell ingestion of relatively large particles food intake immune response Phago eating cytosis cell How cells take up cholesterol Receptor mediated endocytosis LDL low density lipoprotein Endocytosis movement of smaller material Exocytosis export of molecules from cell
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