AP Bio cell membrane and cell communication

Describe the process by which a G protein-coupled receptor initiates a signaling pathway

- very common - results in a single pathway response 1. G protein attached to cytoplasmic side of membrane. When GDP is attached to G protein = INACTIVE 2. ligand binds to receptor. Receptor changes shape and binds to G protein. Causes GTP to replace GDP on G protein 3. Activated G protein leaves receptor and binds to an enzyme. This activates the enzyme. The activated enzyme starts the pathway than ends in the cellular response 4. When the ligand leaves the receptor, the signaling stops. To stop the signal the G protein works as a GTPase - it hydrolyzes its bound GTP back to GDP. The inactive G protein leave the enzyme which returns enzyme to original shape. G protein now available for release

Describe the functioning of ligand-gated ion channel receptors

- when ligand binds, channel can close or open ex: neurotransmitters bind as ligands for sodium ion channels

Describe the communication between mating yeast cells that results in the fusion of two yeast cells

- yeast cells identify their mates by cell signaling 1. exchange of mating factors: each cell type secretes a mating factor that binds to receptors on the other cell type 2. mating: binding of the factors to the receptors induces changes in the cells that lead to their fusion 3. new a/a cell: the nucleus of the fused cell includes all the genes from the a and a cells

osmosis

diffusion of water from from high concentration of WATER to low concentration of water typically goes from hypotonic to hypertonic

describe in detail passive transport mechanisms (diffusion, osmosis, facilitated diffusion); think of examples of cells that would use these transport mechanisms

diffusion: - 2nd law of therodynamics: universe tends toward disorder - movement from high to low concentration (anything) osmosis: - diffusion of water from from high concentration of WATER to low concentration of water - typically goes from hypotonic to hypertonic facilitated diffusion: - Move from HIGH to LOW concentration through a protein channel - passive transport - no energy needed - facilitated = with help - ex: aquaporin

hypotonic

less solute, more water

Compare and contrast local & long distance signaling

local signaling - adjacent cells are signaled - chemical messengers released (ex: neurotransmitters via neurons) Long distance signaling - use of hormones: both plants and animals use hormones (ex: insulin) - can affect many cells in other parts of the body - protein or steroid types

Describe the effects of cholesterol and membrane fatty acid tails on membrane fluidity

membrane fat composition varies: - Fat composition affects flexibility - membrane must be fluid & flexible - about as fluid as thick salad oil - % unsaturated fatty acids in phospholipids keep membrane less viscous - cold-adapted organisms, like winter wheat increase % in autumn Cholesterol: - Serves as a membrane "temperature buffer" - higher temp - makes membrane LESS fluid by restricting phospholipid movement - lower temp - prevents membrane from becoming too solid by hindering close packing of phospholipids membrane fatty acid tails: - unsaturated fatty acid tails make the membrane more fluid than saturated ones (good for cold environments)

hypertonic

more solute, less water

define active transport

movement against concentration gradient, lot to high, requires ATP

Define and give examples of active transport; think of examples of cells that would use active transport

Plants have nitrate & phosphate pumps in their roots. Why? Nitrate for amino acids Phosphate for DNA & membranes Not coincidentally these are the main constituents of fertilizer. Na+/K+ pump in nerve cell membranes

Discuss the role of glycoproteins and glycolipids in cell-to-cell recognition

Play a key role in cell-cell recognition - ability of a cell to distinguish neighboring cells from another - important in organ & tissue development - basis for rejection of foreign cells by immune system - glycoprotein & glycolipid

cell communication methods

cell-to-cell contact local signaling long distance signaling

Define passive transport

no energy needed, substances move down a concentration gradient (high to low)

be able to use a set of data and graphing techniques to determine the sucrose molarity inside of a plant cell

where there is no change in mass, that is the molarity

Contrast integral proteins with peripheral proteins in regards to structure and function

- peripheral: loosely bound to surface - integral: penetrate into lipid bilayer, often completely spanning the membrane function: integral: transporters, channels (see Potassium Channel), linkers, receptors, proteins involved in accumulation energy, and proteins responsible for cell adhesion. peripheral: temporary

Describe bulk transport across the membrane (exocytosis, endocytosis, phagocytosis, pinocytosis, receptor-mediated endocytosis); think of examples of cells that would use bulk transport

- Moving large molecules into & out of cell requires ATP! - through vesicles - endocytosis: bringing in - phagocytosis = "cellular eating" fuse with lysosome for digestion - pinocytosis = "cellular drinking" non-specific process - receptor-mediated endocytosis -- triggered by ligand signal - exocytosis: taking out (increases cell membrane

Describe the effect of Vibrio cholerae (the bacterium that causes cholera) on G proteins

- toxin binds and modifies G protein - modified G protein unable to hydrolyze Gtp to GDP - G protein remains "on" an continually activates Adenylyl cyclase which makes cAMP - cAMP activates cellular response - cells release salt and water follows by osmosis - results in profuse diarrhea and dehydration can quickly follow

Describe water potential; be able to calculate water potential (the equation will be provided); be able to predict the movement of water based on water potential

- Water moves from a place of greater water potential to a place of lesser water potential (net). - water potential is potential energy of water per unit volume relative to pure water - the tendency of water to leave one place in favor of another - As the concentration of a solute increases in a solution, the water potential will decrease accordingly. - effected by pressure and the amount of solute calculating water potential:

cytolysis

- animal cell explodes Example of avoiding it: Paramecium - a paramecium is hypertonic to the pond water that it lives in, and therefore water is continually entering the cell - to prevent cytolysis, a specialized organelle (contractile vacuole) pumps water out of the cell using ATP ---- turgid, turgor pressure in plant cells aided by a vacuole and the cell wall

Give examples of cellular responses resulting from signal transduction pathways

- can regulate genes by activating transcription factors that turn genes on or off

cell-to-cell communications

- cell junctions directly connect the cytoplasm of adjacent cells Ex: cardiac cells for rythmicity, plamodesmata between plant cells - surface receptors can give/send information

Describe/define second messengers; give two examples of second messengers

- first messenger is the ligand and the second messenger is any small, non-protein components of a signal transduction pathway - small, non-protein molecule - amplification, cascade multiplier, fast response

Describe the significance of transcription factors as a cellular response in signal transduction pathways

- molecule complexes that control which genes are turned on and transcribed to mRNA

describe different active transport systems

- moves molecules against concentration gradient - need to pump against concentration - protein pump - requires energy - ATP

Describe the process by which a receptor tyrosine kinase initiates a signaling pathway

- multiple pathway response 1. before signal molecule binds, tyrosine Kinase receptors are 2 separate subunits 2. binding of signal molecule causes 2 subunits to associate = DIMER 3. as a dimer, the tyrosine kinase is activated. Each subunit adds a phosphate from an ATP to the tail of the opposite subunit 4. the phosphorylated tails activate "relay proteins." Activated relay proteins lead to the cellular responses. Multiple pathways can be activated by this mechanism

Describe paracrine signaling & synaptic signaling

- paracrine signaling: secreting cell acts on nearby target cells by discharging molecules of a local regulator - synaptic signaling: a nerve cell releases neurotransmitter molecules into a synapse

Describe the functions of membrane proteins

- peripheral: loosely bound to surface - integral: penetrate into lipid bilayer, often completely spanning the membrane function - helps things across - determines most of membrane's specific functions - cell membrane & organelle membranes each have unique collections of proteins numerous functions of membrane proteins: - transporter - enzyme activity - cell surface receptor - cell surface identity marker - cell adhesion - attack to cytoskeleton types of membrane proteins: - channel: wide open passage - ion channel: gated - Aquaporins: water only, kidney and plant root cells - Carrier proteins - change shape - Transport proteins - require ATP - Recognition proteins - glycoproteins - Adhesion proteins - anchors - Receptor proteins - hormones

Describe the fluid mosaic model of the cell membrane/ purpose of the cell membrane

- phospholipids are not in a solid, static structure (fluid) - lots of different components (mosaic) function: - cells need an outside and inside - separate a cell from its environment - cell membrane is the boundary - not an impenetrable boundary (things have to come in and go out)

Discuss how signal transduction pathways may be amplified

- second messengers - multiple things all going at once

Describe the process by which intracellular receptors activate a cellular response; give an example of an ligand that binds with an intracellular receptor (ex. testosterone)

- target protein is INSIDE the cell - must be hydrophobis signal molecule 1. the steroid hormone testosterone (ligand) passes through the plasma membrane 2. testosterone binds to a receptor protein in the cytoplasm, activating it 3. the hormone receptor complex enters the nucleus and binds to specific genes 4. the bound protein stimulates the transcription of the genes into mRNA

Describe/define a phosphorylation cascade; discuss the role of protein kinases & protein phosphatases in phosphorylation cascades

1. relay molecule activates protein kinase 2. active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase. 3. Active protein kinase 2 then catalyzes the phosphorylation (and activation) of protein kinase 3 4. Finally, active protein kinase 3 phosphorylates a protein that brings about the cell's response to the signal 5. enzyme called protein phosphatases (pp) catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse Protein Kinase: - strop a phosphate from ATP and transfer it to another protein, activating that protein Phosphatases: - remove the phosphate from the activated protein, deactivating it

Describe water balance in animal vs. plant cells

Animal cells in hypotonic solution: will gain water, swell, and possibly burst in hypertonic solution: will lose water, shrivel, and probably die in isotonic: will remain stable (this is the ideal state) Plant cells in hypotonic solution: will gain water, swell, but won't explode as a result of the cell wall. Rather, it will be plump and ideal for the plant cell in hypertonic solution: will lose water and wilt (plasmolysis) in isotonic solution: will actually wilt somewhat, and will not be plump and stiff in the way that is ideal for a plant cell

isotonic

equal solute, equal water

Predict the movement of water based on on differing concentration of substances separated by a semipermeable membrane

high to low concentration, hypo to hyper

Describe the 3 main stages of cell signaling (reception, transduction, response)

how does it work? signal transduction pathways: - convert signals on a cell's surface into cellular responses - are similar in microbes and mammals, suggesting an early origin reception: - a signal molecules (ligand) binds to a receptor protein - ligand and receptor have a unique bonding transduction: - signal initiated by conformational change of receptor protein - signaling cascades relay signals to target - multistep pathways can amplify a signal - second messengers involved response: - cell signaling leads to regulation of cytoplasmic activities or transcription - signaling pathways regulate a variety of cellular activities

identify and describe the function of each of the components of the cell membrane (phospholipids, proteins (peripheral & integral), glycoproteins, glycolipids, cholesterol)

phospholipids: - membrane is phospholipid bilayer - hydrophilic phosphate heads - hydrophobic lipid tails - polar, nonpolar, polar what molecules can get through directly? - fats/other lipids - slip directly through without aid - small nonpolar molecules (oxygen, carbon dioxide) Proteins: - peripheral: loosely bound to surface - integral: penetrate into lipid bilayer, often completely spanning the membrane function - helps things across - determines most of membrane's specific functions - cell membrane & organelle membranes each have unique collections of proteins membrane carbohydrates: - Play a key role in cell-cell recognition -- ability of a cell to distinguish neighboring cells from another -- important in organ & tissue development -- basis for rejection of foreign cells by immune system -- glycoprotein & glycolipid Cholesterol: - Serves as a membrane "temperature buffer" - higher temp - makes membrane LESS fluid by restricting phospholipid movement - lower temp - prevents membrane from becoming too solid by hindering close packing of phospholipids