BIO Chapter 5
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This 5 page Class Notes was uploaded by Natalie Berry on Saturday September 17, 2016. The Class Notes belongs to BIO 101 at Missouri State University taught by Kyoungtae Kim in Fall 2016. Since its upload, it has received 24 views. For similar materials see Biology in Your World in Science at Missouri State University.
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Date Created: 09/17/16
Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important Chapter 5: The Plasma Membrane The nature of the plasma membrane Plasma membranes are different from other membranes because they constantly interact with the outside world while internal membranes do not The plasma membrane is extremely thin The membrane is very flexible because it’s made up pf fluid and fatty make up It is stable enough to stay together even though it’s constantly being reformed because of the materials that constantly move in and out of it To get a visual of this, imagine your skin remaking itself every 30 minutes Components of the plasma membrane include: The phospholipid bilayer Cholesterol Proteins Glycocalyx The phospholipid bilayer Remember: Phospholipid: molecules that have two long fatty acid chains linked to a phosphate bearing group Because fatty acid chains are lipids they are hydrophobic meaning they will not bond with water Phosphates are hydrophilic meaning they seek out water When phosphate and lipid compounds are just together they result in a phospholipid with a dual nature It’s phosphate “head” will seek water while it’s lipid “tail” will avoid it If you drop phospholipids in water, they form into two layers sandwiched together, tails on the inside heads on the outside The tails are on the inside because they’re hydrophobic and the head is on the outside because they are hydrophilic Phospholipid bilayer: component of the plasma membrane composed of two layer of phosphates arranged with their fatty acids pointing towards each other Helps give the membrane its fluid nature Because there are two layers of tails, the only substances that can get through easily are hydrophobic or very small This stems from a rule in chemistry: like dissolves like Ex. Fat dissolves in fats Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important So steroid hormones (also lipids) and fatty acids can get through because they dissolve in the lipid part This also means things like amino acids (hydrophobic) and ions will not dissolve so they can’t make it past without help Cholesterol Acts a patching substance on the bilayer keeping some substances from getting through They help keep the membranes fluidity without it, it would harden which is dysfunctional for a cell they do this by sitting between the bilayer’s “tails” keeping them from packing too close together when temperature rises it keeps the membrane from being too fluid Proteins Membrane protein lie on top of the bilayer There are 2 type: integral and peripheral Integral proteins: plasma membrane proteins that are bound to the membrane’s hydrophobic interior They can span the entire membrane or only part of it Peripheral proteins: plasma membrane proteins that lie on either side of the membrane but are not bound to its hydrophobic interior Are usually attached to integral proteins Peripheral proteins are often attached to elements of the cytoskeleton that help stabilize parts of the cell Proteins help immune system cells differentiate friend from foes Communication Cells communicate in a lot of ways: signals sent between neighboring cells or through hormones These signals are likely channeled through receptor proteins Receptor proteins: a plasma membrane protein that binds with a signaling molecule Receptors have binding sites with a very specific shape so they generally only bind with a single type of signaling molecule Glycocalyx Glycocalyx: an outer layer of the plasma membrane composed of short carbohydrate chains that attach to membrane protein and phospholipid molecules Plasma membrane: a membrane forming the outer boundary of many cells composed of a phospholipid bilayer that is interspersed with proteins and cholesterol and carbohydrate chains coating its exterior face Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important To sum it all up, it’s a loose, lipid structure peppered with protein and coated with sugars Diffusion, Gradients, and Osmosis All molecules are in constant motion and it’s random Liquid molecule bonds are weak so with this constant motion they can slide past each other to go from one place to another Liquid molecules will move from any initial ordered state to their most disordered state evenly distributed throughout a given volume This is diffusion Diffusion: the movement of molecules or ions from a region of their lower concentration Concentration gradient: the difference between the highest and lowest concentration of solute in a medium The tendency for any solute is to move from higher concentration gradient to lower concentration gradient Solutes can move up a grade, but it will cost energy Diffusion through membranes Osmosis: net movement of water across a semipermeable membrane from an area of low solute concentration to high Osmosis and cell environments Any given cell can lose water from its surroundings, gain it, or balance the flow This all depends on solute concentration outside the cell 3 terms describe these 3 conditions: Hypertonic: a fluid that has a higher concentration of solutes than another If the cell’s surroundings are hypertonic to the cytoplasm, water will flow out of the cell Isotonic: two solutions that have equal concentration of solutes If one of these solutions is the cell’s cytoplasm and the other is around the cell, water flow will be balanced Hypotonic: a fluid that has a lower concentration of solutes than another If a cell’s surroundings are hypotonic to the cell’s cytoplasm, water will flow into the cell Moving smaller solutions in and out Some molecules can move around with just diffusion Different molecules need different transportation Active transportation: any movement of molecules or ions across a cell membrane that requires the cost of energy Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important Passive transportation: any movement of molecules or ions across a cell membrane that does not require the cost of energy Passive transport Simple diffusion: a diffusion through a cell membrane that does not require a special protein channel Ex. Gas molecules (oxygen, carbon dioxide) are so small they just need to move down their concentration gradient to pass in and out of a cell Water can get through the bilayer with simple diffusion even though it’s hydrophilic because it’s so small Polar and larger molecules need to use protein channels Facilitated diffusion: which is passage of molecules through the plasma membrane that is aided by a transport protein Each transport protein acts as a conduit for only one substance or a small family of related substances Active transport For cells, some solutes are needed in greater concentration outside the cell They use pumps for this They extend energy and pump the needed materials out of themselves; this is active transport The energy for the transport is called ATP (adenosine triphosphate) Sodium Potassium Pump Allows the cell to maintain high concentration of potassium ions (K+) inside the cell and sodium ions (Na+) outside the cell Even though this takes a lot of energy, cells do it to have the capability to take in a large number of ions Moving larger substances in and out Pumps, channels, diffusion, and osmosis only move small substances Methods that move the larger substances are endocytosis and exocytosis Exocytosis: the movement of materials out of the cells through a fusion of transport vesicles with the plasma membrane When the vesicle meets the membrane its contents are released into the extracellular fluid Endocytosis: the movement of large materials into the cell by an enfolding of the plasma membrane It takes two major forms: pinocytosis and phagocytosis Pinocytosis There are several types but we are focusing on CME Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important The receptors in CME bind with molecules of the material that are brought into the cell Then they move to a protein coated pit across the membrane Then the pit deepens and pinches off creating a vesicle moving into the cell It’s important in getting nutrients and other substances into the cell It’s how cholesterol gets in the cell It can also allow certain invaders inside the cell Polio, the flu Pinocytosis: movement of large materials into a cell by creating transport vesicles that are produced through the folding of the membrane Phagocytosis Means “cell eating” This is how unicellular beings take in food It’s also how the human immune system cells ingest whole bacteria Brings in material 10x larger than pinocytosis Begins when the sends out an extension of its plasma membrane called pseudopodia (“false feet”) The “feet” surround the food and fuse their ends together The food is now in a vesicle moving inside the cell Then lysosomes break it down Phagocytosis: the movement of large materials into a cell by wrapping extensions of the membrane around the materials and fusing them together
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