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Transcript
Unit 3 The Cell The Plasma Membrane • The plasma membrane acts as a fragile barrier between the cell and its surroundings. • When studied it’s referred to as a “fluid mosaic” • It is thought of as a “sandwich” that wraps around a cell. Plasma Membrane • The cell membrane – The “bread” of the sandwich are made up of phosphate bases. – The “peanut butter” is the fatty acid tails of the phospholipid. – Think of proteins as jelly that penetrates through the bread and is in the center of the sandwich as well. STRUCTURE: Described as fluid mosaic because: it is composed of many different parts that move around in a crowded fashion Main component: •Properties of phosphate bases: •Properties of fatty acid tails: •Non-polar because: Cholesterol: Membrane Proteins: •Two types: •Function and structure of glycocalyx The Plasma Membrane • The phosphate bases: – Found on the very outside and very inside of the membrane – Are polar- so they attract water, electrolytes, amino acids and sugars (anything polar or ionic) – They are hydrophilic STRUCTURE: Described as fluid mosaic because: it is composed of many different parts that move around in a crowded fashion Main component: •Properties of phosphate bases: polar so they attract to water (hydrophilic) and other charged particles; found on the outside and inside of the membrane •Properties of fatty acid tails: •Non-polar because: Cholesterol: Membrane Proteins: •Two types: •Function and structure of glycocalyx The Plasma Membrane • The fatty acids: – Non-polar: don’t allow charged particles through but allow neutral particles like fats, oxygen, carbon dioxide, alcohol and urea through without help. – Hydrophobic- water fearing – The thickest part of the membrane STRUCTURE: Described as fluid mosaic because: it is composed of many different parts that move around in a crowded fashion Main component: •Properties of phosphate bases: polar so they attract to water (hydrophilic) and other charged particles; found on the outside and inside of the membrane •Properties of fatty acid tails: non polar, so they repel water (hydrophobic); found on the inside of the membrane; fats, oxygen, carbon dioxide, alcohol and urea can move through this layer (non polar molecules) •Non-polar because: Cholesterol: Membrane Proteins: •Two types: •Function and structure of glycocalyx The Plasma Membrane • Fatty acids make up the majority of the membrane, so overall, the membrane is non-polar. – Polar molecules hover outside the membrane and get help moving through – Non polar molecules can move through on their own. *Show transport movie STRUCTURE: Described as fluid mosaic because: it is composed of many different parts that move around in a crowded fashion Main component: •Properties of phosphate bases: polar so they attract to water (hydrophilic) and other charged particles; found on the outside and inside of the membrane •Properties of fatty acid tails: non polar, so they repel water (hydrophobic); found on the inside of the membrane; fats, oxygen, carbon dioxide, alcohol and urea can move through this layer (non polar molecules) •Non-polar because: the tails make-up the majority of the molecule Cholesterol: Membrane Proteins: •Two types: •Function and structure of glycocalyx The Plasma Membrane • Cholesterol – Cholesterol is found along the membrane to hold it together and give it form. •Properties of fatty acid tails: non polar, so they repel water (hydrophobic); found on the inside of the membrane; fats, oxygen, carbon dioxide, alcohol and urea can move through this layer (non polar molecules) •Non-polar because: the tails make-up the majority of the molecule Cholesterol: found on the inside of the membrane; gives the membrane some support/structure Membrane Proteins: •Two types: •Function and structure of glycocalyx The Plasma Membrane • Membrane Proteins – Embedded in the membrane and move around in the “fluid” – Some are integral proteins, which extend all the way through. – Some are peripheral proteins, which are found at the surface, sometimes stuck to integral proteins. •Properties of fatty acid tails: non polar, so they repel water (hydrophobic); found on the inside of the membrane; fats, oxygen, carbon dioxide, alcohol and urea can move through this layer (non polar molecules) •Non-polar because: the tails make-up the majority of the molecule Cholesterol: found on the inside of the membrane; gives the membrane some support/structure Membrane Proteins: •Two types: integral proteins span the width of the membrane; peripheral proteins lie on the outside or inside (surface) of the membrane •Function and structure of glycocalyx The Plasma Membrane • Proteins – Many have branching sugar chains (polysaccharides) extending out from their surface. – These polysaccharides mark the cell, like identification. – The sugar covering is called glycocalyx Membrane Proteins: •Two types: integral proteins span the width of the membrane; peripheral proteins lie on the outside or inside (surface) of the membrane mark the cell, like a name tag, so the body can recognize it as its own •Function and structure of glycocalyx: The Plasma Membrane • Proteins have 6 functions in the membrane: 1. Adhesion proteins: serve as markers so other cells know to bond together and form a tissue. 2. Recognizers: mark the cell so the immune system recognizes it so the cell isn’t attacked and lysed by its own body. The Plasma Membrane 3. Receptor sites: Some proteins receive electrical and other chemical messengers. – Tell the cell to begin or end production of something it is making – Feedback mechanism The Plasma Membrane 4. Enzymes: catalyse the thousands of chemical reactions that take place along the membrane and just inside the cell. 5. Attachment: Attach the membrane to fibers which are the cell’s cytoskeleton The Plasma Membrane 6. Transporters: Transfer nutrients and molecules across the membrane into the cell. The Plasma Membrane Some cells have special adaptations to their membrane that helps them perform their job in the body: • Microvilli: The outer layer of the membrane creates finger projections (similar to cilia) to increase the surface area – Found in cells that absorb high amounts of molecules (kidneys and intestines)