Lecture 1 Parts of a Cell.docx

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Kenneth Yip

Lecture 1 Parts of a Cell February 28, 2013 6:05 PM Reading pgs. 617-624; 629-640  The typical Animal cell consists of many organelles and proteins within the cell membrane (i.e.; Golgi apparatus, ER, nucleus, microtubules, actin filaments, intermediate filaments, mitochondria, etc)  The plant cell consists of only the nucleus , ER, Golgi apparatus, mitochondria, and the plasma membrane Slide 11- Cellular functions at Membranes  The cytoplasm is the contents inside the cell and outside the nucleus, the cytosol is the fluid within the cytoplasm, and a lumen (cavity) refers to the inside of an organelle Slide 12- Cell Membranes  There are many interactions that occur to membranes  The cell plasma membrane divides the cell into compartments which restricts movement of molecules, also differentiating cytosol from the extracellular matrix. Aldo contain proteins that acts as signals for the cell advising it to respond to environmental cues and transferring information across the cell  Compartmentalization, scaffolding for biochemical activates, selectively permeable barrier, transporting solutes, responding to external signals, and interactions between cells Slide 13- Lipid Bilayer  Lipid arranged in a continuous double layer which serves as an almost impermeable barrier to the passage of most water soluble molecules.  All cells are amphillic with a non-polar hydrophobic end and polar hydrophilic end. The phospholipids contain a polar head and 2 non-polar hydrocarbon tails. One end of the tails is saturated while the other is unsaturated (contains one or more cis double-bonds, which creates a kink) the polar ends will attract to the water forcing the nonpolar tails to associate on the interior of the bilayer  Artificial lipid bilayers were created to further study of lipid proteins- planar phospholipid bilayers with edges were found to be unfavourable as the edges subjected the b hydrophobic parts of the biliary to water  The lipid bilayer: is comprised of basic units but provides a fluid structure that is capable of maintaining its structure even when irritated  Membrane proteins: are mobile in the lipid bilayer ex: through receptor channels,; these aspects maintain the fluid mosaic membrane model  Amphilic - polar or hydrophilic head and non-polar hydrophobic tail  Phospholipids in an aquatic environment spontaneously self-associate to form into a bi-layer  A leaflet= face; 2 faces = 1 membrane = lipid bilayer  Artificial lipid bilayer = liposomes - which can be used for study of lipid proteins, member protein projections, or delivery into cells (exodrugs) Slide 17 - Lipid Components - Phospholipids  A kink indicates the unsaturated tail- contains a double cis-bond  Are most abundant  The Hydrocarbon tails contain 14-24 carbons; one is saturated the other is unsaturated Slide 18 - Lipid Components - Steroids (cholesterol)  Animal plasma membranes contain lots of cholesterol which has a hydroxyl polar head attached to a rigid ring structure and a single nonpolar hydrocarbon tail. The cholesterol inserts its hydroxyl head next to the polar heads of the phospholipids the rigid ring structure interacts with the first few CH bonds of the tails restricting their movement, this also lowers the possibility of this area becoming deformed  plants cells not as much cholesterol and other plant steroids are present  Decreases the mobility of hydrocarbon tails due to plasma membrane being more permeable to water solubles  1:1 ratio of phospholipids to cholesterol Slide 19 - Lipid Components - Glycolipids  In animal cells is made from sphingosine that self-associate through Van der Waal attractions and bonds between their sugars, make up 5% of outer surface of the lipid bilayer, where they help protect from harsh conditions, can alter the electrical gradient of ions going through the membrane, or even provide channels for bacterial toxins  Sugar groups attached to lipid molecules  Lipids that are glycosylated in the Golgi apparatus and also transmitted to the outer layer  Found mainly in the outer leaflet of the plasma membrane Slide 21 - Cell Membranes - Fluid  Phospholipids are only made on the cytosolic side of the membrane, to add new cells to the outer leaflet translocator proteins must assist in flip-flopping phospholipids to the adjacent side  Phospholipids rapidly diffuse laterally within each leaflet and cannot move from one leaflet to the other (flip-flop) without the help of a phospholipid translocator Slide 22 - Membrane Fluidity  A membrane must be able to cope with environmental stresses and always maintain its fluidity. Fluidity of the bilayer is determined by compositions and temperature. If the phospholipids in the bilayer a have short tails (less interactions) or many double bonds (difficult to pack together) it becomes more difficult to freeze if temperatures drop  Cholesterol can also assist in stopping the membrane from crystallizing  Lower temperature = more rigid structure. The cis double bonds allow the bilayer to maintain fluid at low temperatures  Shorter hydrocarbon tails also increase fluidity at lower temperatures allowing tails to interact less  Phospholipid translocators are enzymes in the cell membrane that flip lipids from one leaflet to the other  Phospholipids are synthesized in the cytosolic leaflet of the ER Slide 24 - Cytosolic and Exoplasmic face  Plasma membranes are reversed for organelles within the plasma membrane (with the cytosolic face as the outer layer and exoplasmic face as the inner layer)  Mitochondria has inner and outer membrane (2 bilayers) due to its interior anaerobic structure (*prev. discussed) o intermembrane space = space between both membranes o Matrix =
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