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The Human Cell.docx

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Physiology 1021
Bob Larose

Module 3: Human Cell Page 1 of 7 Basic Cell Organelles  Centrioles – bundles of microtubules that direct movement of DNA strands during cell division  Endoplasmic Reticulum – site of synthesis, storage, and transport of proteins and lipids; 2 types: o Rough (Glanular) ER = covered in rows of ribosomes, site of protein synthesis (then packaged into vesicles and transported to golgi apparatus) o Smooth ER = no ribosomes, site of lipid and fatty acid synthesis  Golgi Apparatus – packages proteins from the rough ER into vesicles; 2 types of vesicles produced: o Secretory Vesicles = used to transport proteins out of the cell (extracellular environment) in a process called secretion o Storage Vesicles = storage for use within the cell (ie. lysosomes)  Ribosomes – manufacture proteins from amino acids under the control of the cell’s DNA; made of RNA and protein; 2 types: o Free Ribosomes = float in cytoplasm, often form in groups of 10-20 known as polyribosomes o Fixed Ribosomes = attached to the rough ER  Lysosome – storage vesicle produced by the golgi apparatus; acts as a digestive system for the cell (contain enzymes to destroy damaged organelles, kill bacteria, and break stuff down)  Mitochondrion – generates ATP (cellular mechanism for energy storage and transfer) o Powerhouse of cell o More energy needs = more mitochondrion in a cell o Even if cell is not undergoing division, mitochondrion can replicate itself (ie. when there is increased energy demands, like in regularly exercised muscles)  Cell Membrane – regulates the passage of substances in and out of the cell; also plays an important role in detecting chemical signals from other cells and in forming physical links with adjacent cells  Nucleolus – contains specific DNA that produces RNA in ribosomes; is found in the nucleus Module 3: Human Cell Page 2 of 7 The Cell Membrane  Separates intracellular and extracellular environments  Selectively permeable 1. Hydrophilic Head of Phospholipid – faces out into the water base solutions and outside of the cell (likes water), POLAR 2. Hydrophobic Tail of Phospholipid – oriented away from the extra and intracellular solutions into the cell membrane, NON POLAR 3. Cholesterol Molecule – found in the non-polar lipid layer (where tails are); helps make membrane impermeable to some water soluble molecules, and also helps keep the membrane flexible over a wider temperature range 4. Associated Protein: Enzyme – attached to either intra or extracellular surface of membrane; acts as a catalyst for reactions inside or outside of the membrane 5. Carbohydrate Molecule – forms a protective layer (“glycocalyx”) that plays a role in the immune response of the cell and in recognition of other cells in the body 6. Membrane Spanning Protein – embedded in the phospholipid bilayer; acts as a gate or channel to control the movement of certain substances in/out of cell 7. Structural Proteins – generally attached to inside surface of the cell membrane; supports and strengthens the membrane, anchors cell organs to the intracellular side of the membrane Phospholipids  Phosphate “head” + fatty acid (lipid) “tail”  Because of hydrophobic tail and hydrophilic head, they align into a lipid bilayer when thrown in water  the hydrophobic tails create a barrier to water and water-soluble substances (ions, glucose, urea)  fat soluble substances (oxygen, carbon dioxide, steroid hormones) can penetrate the membrane Module 3: Human Cell Page 3 of 7 Functions of Membrane Proteins 1. Receptors for the attachment of chemical hormones and neurotransmitters 2. Enzymes that help with chemical reactions or breakdown molecules 3. Ion channels or pores that allow water-soluble substances, like ions, into the cell 4. Membrane-transport carriers that transport molecules across the membrane (this may include gated channels) 5. Cell-identity markers, like antigens or glycoproteins. Antigens are foreign particles that can stimulate the immune system. Crossing the Membrane (Membrane-Transport Mechanisms) 1. Endocytosis/Exocytosis (pinocytosis for small molecules) – for large molecules that cannot pass through lipid bilayer o Molecules (made by ER) are packaged in a vesicle and sent to the golgi apparatus o Golgi apparatus modifies the molecules and again packages them into another vesicle that will Exocytosis move to the plasma membrane o Vesicle membrane merges with the plasma membrane and the molecules leave the cell without actually crossing the plasma membrane o Reverse is endocytosis 2. Diffusion – movement of molecules from ↑concentration to ↓concentration down what is called the chemical concentration gradient o when molecules are spread out evenly and the net movement is zero, it is at equilibrium o electrically charged molecules (ions like Na ) move to areas of opposite charge (down the electrical gradient) o charged ions can move both down their electrical and chemical concentration gradient  if these are in opposite directions, the movement of the ion will depend on the balance of the 2 gradients and will stop moving when the molecules reach electrochemical equilibrium (when the electrival force is equal and opposite to the chemical force) o Does not require energy (powered by concentration gradient of molecule) Module 3: Human Cell Page 4 of 7 o Diffusion through Lipid Bilayer – fat-soluble molecules only (oxygen, carbon dioxide, fatty acids, and some steroid hormones) o Diffusion through Protein Channels – water and water-soluble molecules (water, ions)  Rate of movement of molecules through protein channels is limited by several factors: 3. Facilitated Diffusion – water-soluble substances (sugars) that are too big for protein channels can still cross the membrane by attaching to specific protein carriers (channels) on the membrane o This attachment causes a change in the proteins channel`s shape, resulting in wither the opening of a protein channel, or the protein rotates the molecule to the inner surface of the membrane where it is
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