Ch 5: The Working Cell (Dr. Kas)

pinocytosis

*is the same thing (as pagocytosis) except that fluids are taken into small vacuoles* "cell-drinking" engulf fluid and molecules such as sugar and proteins use to engulf luquid portion of blood and realease it to tissues while blood cells remain in the blood

animal membrane proteins

junction proteins, gap junctions, desmosomes, tight junctions

gap junctions

*let ions, glucose & other small molecules move through cytoplasm between adjacent cells* provide cytoplasmic channels from one cell to an adjacent cell, allowing ions, sugars, amino acids and other small molecules to pass, allowing communication between cells in tissues such as heart muscle and animal embryos.

concentration gradient

*A difference in the concentration of a substance across a space* Concentration = # of molecules in a given volume Movement is due to natural internal (heat) energy of the particles (Known as *Brownian motion*(Particles of matter have their own internal energy (remember all those electrons whizzing around the nucleus of an atom?) - so they constantly move, a property known as Brownian motion) Collide and scatter until evenly spread out Collision rate decreases But internal energy remains!) . If they are tightly packed together, or concentrated, many will collide and scatter, spreading out through a space. As they spread out, there are fewer of them close together, so the number of collisions decrease, and eventually the particles are evenly spread throughout the space or solution. (means that the whatevers move to where there are less whatevers so that they are equal on both sides)

isotonic

*A solution has SAME solute concentration as the cell* Water flows into and out of the cell at the same rate Cell size remains constant Plant cells aren't as firm in this solution, and become limp, or flaccid. The leaves wilt because the central vacuole isn't full.

fluid mosaic model

*Book*: Used to describe a membranes structure *the currently accepted model of cell membrane structure, depicting the membrane as a mosaic of diverse protein molecules embedded in a fluid bilayer of phospholipids molecules* *Video*: Mosaic= made up of a number of different things Fluid= all things are moving *PPT Notes*: Scientists use the term fluid mosaic to describe how the proteins drift about freely in the plane of the membrane, much like icebergs floating in a sea of phospholipids. The phospholipids themselves can drift laterally or even flip-flop. The reason cell membranes are so fluid is that the only "force" holding the phospholipids together is their hydrophobicity - there are no covalent, ionic, hydrogen, or any other type of molecular bond!! So they can break apart easily, but reform just as easily.

selective permeability

*Book*: plasma membrane exhibits this, it allows some substances to cross more easily *a property of biological membranes that allows some substances to cross more easily than others, and blocks the passage of other substances* *PPT Notes*: These hydrophobic tails play a key role in the membrane's function as a selective barrier. Non-polar substances such as lipids, CO2 and O2 pass through the lipid bilayer easily. Polar molecules such as sugars and ions do not. Polar molecules get across by using special proteins that act like channels or tunnels. These *transport proteins* are specific for the type of molecule that can be brought across. Even water, as small as it is, must use a special "aquaporin" channel protein to go through the membrane barrier. *controls what enters and exits the cell*

facilitated diffusion

*Diffusion of molecules across a membrane through channel (transport) proteins* for polar (hydrophilic) and charged particles that cannot move easily through the lipid bilayer: water, sugars, amino acids, ions (Na+, K+) *Does not require energy: molecules move with their concentration gradient* does not alter direction of flow is particle specific: water molecules use aquaporins *uses a transport protein* Facilitated means "to make easier". Transport proteins make it easier for molecules to enter or exit a cell. A transport protein is a type of protein that has a channel or groove in it that substances can travel down. The molecules still follow their concentration gradient so the cell doesn't use up any energy in this transport. The reason these molecules need help is that they are polar, or have ionic charges on them, and are rejected by the nonpolar membrane. BUT they are such important molecules that the cell makes special proteins to ferry them across. Even water, as small as it is and as essential as it is to the proper functioning of a cell, has a hard time getting through (recall, water is POLAR molecule), so the membrane has a special channel protein just for them. These are called "aquaporins". Dr. Peter Agre received the 2003 Nobel Prize in Chemistry for his discovery of aquaporins. Many of the transport proteins are specific to the type of particle that it will allow to pass through, but it is still a passive transport. Facilitated diffusion, although speeding up the transport of molecules, can't alter or change the direction of molecule flow - they simply go from high to low concentration.

hypotonic

*Solution has LESS solute than the cell* Water flows INTO the cell from the solution Cell swells up Animal cells lyse Plant cell walls prevent lysis, central vacuole fills with water, supports plant to stand upright . This means water molecules are more concentrated outside the cell than inside. Water diffuses into the cell. If too much water enters, the cell membrane may expand until the cell bursts. An example of a hypotonic solution is fresh water. Animal cells will burst, or lyse (broken apart) unless they have a special adaptations for removing excess water. The rigid plant cell wall prevents the membrane from expanding too much. In fact, all that extra water fills the central vacuole and pushes the plasma membrane and cytoplasm against the cell wall, making the cell very firm. This helps the entire plant stand upright instead of drooping. It's why grocery stores constantly spray their produce, to keep the veggies like lettuce, carrots and celery firm and fresh looking under those hot lights!

hypertonic

*Solution has MORE solute than the cell* Water flows OUT of the cell into the solution Animal cell shrivels and dies, plant cells plasmolyze Salt, sugar used for food preservation Salt water and over-fertilization of plants A hypertonic solution (hyper means "above") has a higher concentration of dissolved particles than a cell. This means the water concentration is higher in the cell, so water flows out of the cell. In this case, an animal cell starts to shrivel, and a plant cell's plasma membrane pulls away from the wall, a phenomenon called plasmolysis (the plant cell is said to be plasmolyzed.) Important applications for this are (1) preserving foods in high sugar or salt solutions (kills bacteria and mold cells) and (2) salt water killing plants (over fertilizing lawns does the same thing).

exocytosis

*The opposite of endocytosis, exocytosis expels molecules from the cell that are too large to pass through the plasma membrane by diffusion or other transport methods* Vesicle forms around material to be exported from cell proteins sent from Golgi apparatus Vesicle containing the particles merge with the plasma membrane and releases particle outside of the cell A plasma cell producing antibodies A bacterial cell producing a toxin Neurons releasing neurotransmitters

endocytosis

*The process by which a cell takes in liquids or fairly large molecules outside of the cell by engulfing them in a membrane* brings large molecules into the cell and packages them in vesicles. STEPS: Part of the plasma membrane forms a pocket around large particles on the cell surface Pocket breaks off to form a vesicle that takes the particles into the cell Vesicle fuses with lysosome to break down contents TYPES: phagocytosis, pinocytosis, and receptor-mediated endocytosis

receptor proteins

*a membrane protein that binds an extracellular signal molecule, known as a ligand, and performs an action in response. * transmit chemical signals across the membrane to cause a cellular response A membrane receptor binds to ligands that cannot cross the membrane and must remain outside the cell. This binding causes the receptor to change shape and causes a cascade of responses as the signal is relayed from one internal molecule to another until the final response is made. The transmission of chemical signals from the external environment to internal parts of a cell through a pathway of several other molecules is called signal transduction. The membrane receptors bind to specific ligands (much like a lock and key) which ensures that the right cell gets the right signal at the right time. Typically, a large number of ligands are produced and bind to cells in a tissue, coordinating their response to a change in their external environment. Usually, the message is for new proteins to be produced (for example, the cell may produce specific hormones or antibodies,) or for cell division to produce new cells. steps: reception (when ligand fits the receptor) transduction (when they are all hitting each other to get the message across) cell response (cell gets the message and does whatever it was supposed to do)

plasma membrane

*a thin flexible cell membrane that separates the cell from it's external environment* (outer cell membrane that forms the boundary of a cell - creates barrier between the cell and its external environments) it is selectively permeable (semipermeable) it maintains homeostasis by allowing nutrients to enter the cell, and expelling waste products key to how it works is structure

glycoproteins

*act as ID tags* so cells can be recognized- and not attacked- by immune system cells proteins with a carbohydrate attached These are the markers used to type tissues (heart tissue, lung, kidney, etc.) used for organ transplants. me: like a dog tag identifying who it is to other cells

junction proteins

*bind adjacent cells together to form tissues, interactions* Intercellular junctions are how cells interact with and adhere to other cells to form tissues. There are three main types of intercellular junctions in animal cells: tight junctions, desmosomes, and gap junctions

attachment proteins

*bind the ECM microfilaments of the cytoskeleton* called integrins form a bridge between the cell surface and cytoplasm me: attach the ECM to the cytoskeleton to help support the membrane cause it doesn't just float there by itself

enzymes

*catalyze (cause or accelerate (a reaction) by acting as a catalyst) chemical reactions* ex: convert polymers to monomers and back may be grouped so product of one becomes reactant of another Membrane enzymes may be grouped to carry out sequential reactions, so that the initial reactant (a substrate) is converted into a product that then becomes the reactant for the next enzyme, and so on, until the final product is made. me: they make reactions happen faster than they usually would so one enzyme will change a circle to a square, but that's still not the shape the cell needs to it sends it to its buddy (another enzyme next to it) which changes the square to a triangle which is what the cell needs.

homeostasis in plasma membrane

*cells maintain homeostasis by regulating the movement of materials into and out of the cytoplasm* (allows vital chemical reactions to occur in a balanced environment moves water and nutrients in, waste products out) PM is selectively permeable which is what enables this regulation Substances move across membranes because of their concentration gradients. (Cells need to move substances such as water, nutrients, dissolved gases, ions, and wastes in and out on a regular basis to maintain an internal balance suitable for life, or to maintain homeostasis. Recall that homeostasis is needed because vital chemical reactions (metabolism) can take place only within a limited range of conditions. Those materials must move across the plasma membrane, which acts like a "gatekeeper" due to it's selective permeability, which means it allows some, but not all, materials to cross.)

carrier proteins

*change shape (hold onto their passengers and change shape to shuttle them across the membrane)* require energy (ATP) to move particles against their concentration gradient (a.k.a. active transport) no energy needed if particles move with the concentration gradient (a.k.a. facilitated diffusion)

tonicity

*concentration of solutes* Compares the concentration of dissolved particles (solute) to the concentration of water (solvent) in a solution. The higher the concentration of solute, the lower the concentration of water Needs a frame of reference: 2 solutions must always be compared tonicity usually refers to the solution in which a cell is placed *is a term that describes the ability of a surrounding solution to cause a cell to gain or lose water* (It is important to consider the concentration of dissolved particles in a solution when studying osmosis. The higher the concentration of dissolved particles, the lower the concentration of water molecules in the same solution. ) isotonic, hypotonic, hypertonic

transport proteins

*enable polar, ionic and large substances to move through the membrane* Transport proteins provide channels for certain molecules to cross over the membrane. 2 types, particle specific (the transport protein is specific for the substance it translocates, allowing only a certain substance to cross the membrane): *channel and carrier*

desmosomes

*fasten cells together in strong sheets* function like rivets attach muscle cells to each other in a muscle

tight junctions

*form a continuous seal to prevent fluid leakage* bind cell membranes very tightly against each other, forming a continuous seal around cells and prevent leakage of extracellular fluid across epithelial surfaces. For example, tight junctions between skin cells make our skin watertight by preventing leakage between cells in our sweat glands.

channel proteins

*have a groove that acts as a tunnel to move polar molecules and ions through the membrane* do not change shape but are specific for one type of particle ex: aquaporins are specifically for water to pass through

types of proteins

*integral proteins* (transmembrane) penetrate the hydrophobic core extend all the way through the membrane some have channels for passage of hydrophilic molecules *peripheral proteins* not in the membrane but attached to integral proteins and the cytoskeleton provide a strong framework for animal

Plasma Membrane Structure

*made of proteins and phospholipids* *Proteins* determine the membrane's specific functions Different types of cells contain different sets of membrane proteins, and the various membranes within a specific cell type have a unique collection of proteins. Proteins determine most of the functions of the membrane. There are 2 major types *Phospholipids* are the main component, and they are made of a a phosphate head (phosphorous) and a lipid (2 fatty acid tails and the glycerol) (fatty tails can be saturated or unsaturated) the head is hydrophilic (polar) the lipid tails are hydrophobic (non-polar)

diffusion

*movement of ANY substance from an area of HIGH concentration to one of LOW concentration across a space of across a membrane* Examples are small lipids, which easily pass through the phospholipid bilayer of a cell membrane, and many small nonpolar molecules such as carbon dioxide and oxygen. Diffusion down concentration gradients is the sole means by which oxygen enters your cells and carbon dioxide passes out of cells. Since cells continuously use oxygen and produce carbon dioxide as a waste product of metabolism, the concentrations of each are higher on the opposite sides of a plasma membrane, so they are continuously exchanged.

membrane transport

*refers to the methods that a cell uses to move substances into and out of the cytoplasm* types: passive, active, bulk

active

*requires cell to expend energy* ions (idk) Other molecules are very important for the cell to get in (or out) but because of their chemical properties, can't cross the membrane freely. *Carrier protein uses energy to pump substances AGAINST their concentration gradients* energy provided by ATP carrier protein changes shape to pick up the substance returns original shape when substance is released (Na-K pump transports 3 Na ions out of the cell for every 2 K ions it pumps in (neurons) Proton pump transports hydrogen ions (protons) Sucrose pump transports sugars into a cell) Some cells acquire molecules even though there are already more inside the cell than outside - or the reverse, get rid of substances when there are already a lot on the outside. This means they need to move substances AGAINST their concentration gradient, from where they are less concentrated to where they are highly concentrated. To accomplish this task a cell has to spend energy and use a special type of transport molecule, called a carrier protein, to do so. (It's called a carrier protein to distinguish it from the channel proteins used in facilitated diffusion). The carrier protein recognizes its specific substance and using ATP for energy, pumps the substance against the gradient, changing shape while doing so. Once the substance is released, the carrier protein goes back to its original shape, ready to pick up more substance. One type of transport system that works this way is the Na-K pump found in animal cells, which exchanges Na+ for K+ across the plasma membrane (the cell tries to get rid of sodium and bring in potassium). Other pumps include the proton pump, which transports hydrogen ions (protons) and couples that with other particle transport, and the sucrose pump, which moves sugars into a cell from the sap. steps: na bind to the carrier protein then atp puts a phosphate that makes the protein change shape and let the na's out on the other side, then the K's bind to the carrier proteins and the proteins returns to its original shape

extracellular matrix

*surrounds animal cells* ECM composed of glycoproteins, collagen, proteoglycans, and fibronectin

osmoregulation

*the control of water balance, in hypotonic or hypertonic environments* Animal cells must carry this out contractile vacuole -- fills with fluid that enters from a system of canals radiating throughout the cytoplasm when full the vacuole and canals contract expelling fluid from the cell

osmosis

*the diffusion of water across a selectively permeable membrane* a special type of diffusion water flows from high to low concentrations of WATER molecules free water not bound to solutes - it is specific for water molecules only, no other substance, although other molecules by be diffusing right along with the water, they aren't considered. The crucial thing to remember is that only free water molecules - that is, those not bound to solute particles - are able to diffuse. You may have noticed that the skin of your fingers wrinkles after taking a long shower or bath, or after washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Through osmosis, water moves into the epidermal skin cells. Our skin cells, which contain a lot of solute, is hypertonic to these solutions, producing the swelling that appears as large wrinkles. The natural skin oils inhibit the movement of water into skin cells, thus soapy water results in wrinkling faster than plain water because the soap removes the natural layer of oil from our skin. If a membrane, permeable to water but not to a solute, separates two solutions with different concentrations of solute, water will cross the membrane, moving down its own concentration gradient, until the solute concentration on both sides is equal. Notice that only the free water molecules "osmose".

phagocytosis

*the engulfment of a particle by wrapping cell membrane around it, forming a vacuole* "cell-eating"? engulfs debris, bacteria etc in phagosites (special types of cell) and lysosomes break it down)

phospholipid bilayer

*two layered membrane forms when phospholipids are placed in water* the hydrophilic head points towards the water/aqueous cytoplasm while the hydrophobic tails point inwards away from the water (forms a hydrophobic core with no water) [The hydrophilic phosphates face the aqueous (watery) cytoplasm inside the cell, and the aqueous extracellular environment (outside the cell) because they are attracted to water. The hydrophobic F.A. tails are tucked inside the membrane, shielded from water.]

receptor-mediated endocytosis

*uses receptors in a receptor-coated pit to interact with a specific protein, initiating the formation of a vesicle* specific triggered when membrane receptors bind to specific external molecules (protein-cholesterol, or protein bonded to ion) the external protein and cargo are brought into the cell in a vescicle

hypercholesterolemia

Membrane lacks or has defective LDL cholesterol receptor Harmful levels of cholesterol accumulate in the blood Human cells use receptor-mediated endocytosis to take in cholesterol for use in the synthesis of membranes and as a precursor for the synthesis of other steroids. Cholesterol travels in the blood in particles called low-density lipoproteins (LDLs), complexes of lipids and proteins. These particles act as ligands (a general term for any molecule that binds specifically to a receptor site of another molecule) by binding to LDL receptors on membranes and then entering the cells by endocytosis. In humans with familial hypercholesterolemia, an inherited disease characterized by a very high level of cholesterol in the blood, the LDL receptor proteins are defective or missing, and the LDL particles cannot enter cells. Instead, cholesterol accumulates in the blood, where it contributes to early atherosclerosis, the buildup of lipid deposits within the walls of blood vessels, causing them to bulge inward and impede blood flow.

dynamic equilibrium

Molecules that are evenly spread throughout a solution (or space) are said to be in dynamic equilibrium. *Dynamic* - even though the particles are evenly spread out they move back and forth continuously due to their internal energy *Equilibrium* - Net concentration is the same on both "sides" of a space or membrane This means that the molecules don't remain still (they keep moving due to their internal energy) but just as many move in one direction as move in the opposite direction . The concentration is the same throughout the solution (or space), so equilibrium (a balance) is reached, but the molecules continue to move (dynamic).

cell membranes

PPT: *control the transport of substances into and out of cells* regulate the transport in and out to maintain homeostasis by responding to the external environment *Compartmentalizes organelles* maintains a specific chemical environment within each compartment it encloses so that the body can carry out its functions properly in its own special environment Compartmentalization is considered an evolutionary advance in cellular structure. composed of proteins and lipids

cholesterol

animal membranes contain cholesterol (strengthens and stabilizes membrane by acting as a wedge) plant cells do not have cholesterol (depend on cell wall for strength unsaturated FA tails prevent tight packing in cold temperatures) Cholesterol is a steroid (lipid) that "bolsters" the membrane by acting as wedges. Unlike plants, animal cells don't have cell walls to protect them, so they are very fragile and could be damaged and break open easily if there were only phospholipids making it up. The cholesterol is necessary for this function, but it has a bad reputation because high levels in our blood are linked to increased risk for cardiovascular disease.

membrane proteins

enzymes, glycoproteins, transport proteins includes channel proteins and carrier proteins, and attachment proteins

bulk

for large/numerous particles, requires energy types: endocytosis, and exocytosis Some molecules are so large it takes a special mechanism to get them into or out of the cell A cell uses two mechanisms to move molecules too large to go across membranes by diffusion or active transport proteins: endocytosis and exocytosis *the material transported is packaged within a vesicle that fuses with the plasma membrane. Phospholipids fuse together Energy is required* (Bulk transport is needed to move large molecules, such as proteins and polysaccharides or even larger across the membrane. Transport of macromolecules into and out of cell involves the use of vesicles. A cell uses energy to move a large substance or large amounts of a substance using vesicles. Depending on which direction the transport takes, bulk transport occurs by exocytosis in which transport vesicles migrate to the plasma membrane and fuse with it, releasing their contents, or endocytosis, in which vesicles formed by the cell membrane surround a particle on the surface of the cell and bring it into the cell.)

passive

movement of molecules that requires no energy to be expended by the cell types: diffusion (=moving down concentration gradient = passive transport), osmosis (a special typed of diffusion), facilitated diffusion Some molecules can pass through membranes very efficiently without any energy expended by the cell Cells have to continually import and export substances, and if they had to expend energy to move every particle, they would require an enormous amount of energy to stay alive. Fortunately, many molecules enter and exit a cell without requiring the cell to work. Passive transport is the movement of molecules across a cell membrane without energy input from the cell.. Remember it's the CELL that doesn't need to expend any energy - the molecules move because of their own INTERNAL energy. We say that molecules move down their concentration gradients - that is, they move from a region of higher concentration to a region of lower concentration. There are 3 types of passive transport - diffusion, facilitated diffusion, and osmosis.