Bio 1100 Chapter 5 - Voytek PDF

Preview

Summary

Voytek...

Description

Chapter 5: Membrane Transport and Cell Signaling  Life at Edge ● Plasma membrane exhibits  ● Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions ● A phospholipid bilayer can exist as a stable boundary between two aqueous compartments 

Fluidity of Membranes ●

Effects of Cholesterol on Membrane Fluidity ● As temperatures cool,   ○ Temperature depends on the types of lipids ● Membrane remains fluid to a lower temperature if it is rich in phospholipids with unsaturated hydrocarbon tails ● Membranes  ● Cholesterol has different effects on membrane fluidity at different temperatures ○ At w  arm temperatures, cholesterol  ○ At c ool temperatures, it  by preventing tight packing 

Membrane Proteins and Their Functions ● A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer ● penetrate the hydrophobic interior of the lipid bilayer ○ Span the membrane are called transmembrane proteins ● loosely bound to the surface of the membrane 

Role of Membrane Carbohydrates in Cell-Cell Recognition ● Cells recognize each other by binding to surface molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane

● Membrane carbs may be covalently bonded to lipids (forming  ) or, more commonly, to proteins (forming  ) ● Carbohydrates on the external side of the plasma membrane vary among species, individuals, and even cell types in an individual



Selective Permeability ● A ●

of substances across cellular boundaries , regulating the cell’s molecular traffic

Permeability of the Lipid Bilayer ●

, such as hydrocarbons, can  of the membrane and cross it easily ○ Sugar does not cross the membrane easily



Transport Proteins  have a hydrophilic channel that certain molecules or ions can use as a

● ● tunnel ○ ●

facilitate the passage of water bind to molecules and change the shape to shuttle them across the

membrane ● A transport protein is specific for the substance it moves 

Passive Transport is Diffusion of a Substance Across a Membrane w/ No Energy 

●

 ○ Movement from high concentration to low concentration ○ ● Substances  their concentration gradient,  ● The diffusion of a substance across a biological membrane is  is expended by the cell to make it happen

because 



Effects of Osmosis on Water Balance ●





● ○ Or , water diffused from the region of high water concentration to the region with low water concentration 

Water Balance of Animal Cells is the ability of a surrounding solution to cause a cell to gain or lose water : solute concentration is the same as inside the cell; no net water movement across the plasma membrane ● : solute concentration is greater than that inside the cell; cell loses water ● : solute concentration is less than that inside the cell; cell gains water ● ●



Water Balance of Plant Cells ●  ● A until the cell wall opposes uptake; the cell is now turgid (very firm) ● If a  , there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt ● In a  , eventually the membrane pulls away from the wall, a usually lethal effect called plasmolysis 

Facilitated Diffusion: Passive Transport Aided by Proteins ● In  , transport proteins speed the passive movement of molecules across the plasma membrane ● 2 types of transport proteins that carry out facilitated diffusion ○ Channel proteins and carrier proteins ● Channel proteins include: ○ Aquaporins, for facilitated diffusion of water ○ Ion channels that open or close in response to a stimulus (gated channels) ● Carrier proteins undergo a subtle change in shape that translocates the solute binding site across the membrane



Active Transport ● Facilitated diffusion speeds transport of a solute by providing efficient passage through the membrane but does not alter the direction of transport ●  ● ○ (ATP) ● Allows cells to maintain concentration gradients that differ from their surroundings ● The  is one type of active transport system 

How Ion Pumps Maintain Membrane Potential ● ●



is created by   ● Two combined forces, collectively called the  , drive the diffusion of ions across a membrane ○ ○  ● An  is a  that generates voltage across a membrane

 

Cotransport: Coupled Transport by a Membrane Protein ●

occurs when active transport of a solute indirectly drives transport of other

solutes ● Plant cells use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell

Bulk Transport by Exocytosis and Endocytosis ● Large molecules, such as polysaccharides and proteins, cross the membrane in bulk by means of vesicles ● Bulk transport requires energy ● In 

, transports 

migrate to the 

with is, and 

 ● Many secretory cells use exocytosis to export products ● In 

, the 

sand particulate matter by 

● 3 types of endocytosis: ○ : cellular eating ○ cellular drinking ○ 

Local and Long-Distance Signaling ● may communicate by direct contact ● have  that directly  of adjacent cells ● These are called   ● The free  from  is a type of   ● In many other cases,  ● Regulators travel only short distances ● One class of these, growth factors, stimulates nearby cells to grow and divide ● This type of  is called   ● Another  type of local signaling  ● This  consists of an  moving along a nerve cell that triggers  molecules ● These diffuse across the space between the nerve cell and its target, triggering a response in the target cell ● In  , 

● In hormonal signaling in  molecules that 

, 



Three Stages of Cell Signaling:  A Preview ● Earl W. Sutherland discovered how the hormone epinephrine acts on cells ● Sutherland suggested that cells receiving signals undergo three processes ○ ○ ○

Reception ● A signaling molecule binds to a receptor protein causing it to change shape ● There are  ○ ○  

Transduction by Cascades of Molecular Interactions ● Signal transduction involved multiple steps ● Multistep pathways can amplify a signal; a few molecules can produce a large cellular response ● Provide more opportunities for coordination and regulation ● in which  to the next molecule in the pathway thereby activating it ● ●

Regulation of Transcription or Cytoplasmic Activities ● Many signaling pathways regulate the synthesis of enzymes or other proteins, usually by turning genes on or off in the nucleus...