Ch 5 Membrane Structure & Function• Structure• Traffic across – Passive transport • Diffusion • Osmosis • Facilitated diffusion – Active transport – Endo & exocytosis
Functions of Membrane Proteins• Transport• Enzyme activity• Signal transduction• Intercellular joining• Cell to cell recognition• Attachment to cytoskeleton
Structure of Membrane• Phospholipids & proteins• Fluid mosaic model• Factors that affect fluidity: – Fatty acid type – Temp• Types of proteins – Integral – Peripheral
Traffic Across Mem• Selective permeability (ease & rate) depend on 2 things: 1. discriminating barrier of lipid bilayer – Impermeable to larger polar & ions – Perm to nonpolar – How about water?2. Transport proteins
Osmosis• Why important?• Relative terms used to compare concentration of inside vs outside of cells – Hypertonic – Hypotonic – Isotonic• Water always moves toward hypertonic• Solutes move from high to low concentration.
Animal cells in hypotonic & hypertonic solutions
Cells in a hypotonic solution gain water & swell; possiblyburst if no cell wall.Cells in a hypertonic solution lose water & shrink.Cells in an isotonic solution have no net gain or loss ofwater.
Osmoregulation – control of water balance• Ex of how orgs stabilize water loss & uptake: – Freshwater paramecium
OsmosisEx of how orgsstabilize waterloss & uptake:Marine org - shark
Passive transport• Diffusion across a membrane• Requires no energy b/c molecules moving down concentration gradient (H to L)• 3 types – Diffusion – Osmosis – Facilitated diffusion
• Diffusion of solutes across membrane w/ Facilitated Diffusion help of proteins – Large polar or ions – proteins • Specific • Can be sat • Can be inhibited – Protein transports solute Cystic Fibrosis by • Changing shape • Selective channels
Cystic FibrosisCause:Humans have a gene encoded in their DNA which manufactures a special protein known as CFTR, Cystic Fibrosis Transmembrane Conductance Regulator. This protein controls the flow of chloride ions across the cell membrane.
The pumping of solutes against Active Transport their gradient (L to H)• Nonspontaneous• Requires energy (usually ATP)• Maintains steep ionic gradients (potential energy)• Ex: Na/K pump
ActivetransportIon pumps – pump ions across membrane – generate voltage across mem – Electrochemical gradient – combo of concentration gradient & electrical gradient – Na/K pump is ex
Endocytosis & Exocytosis• Methods for very large molecules & particles to get into & out of the cell• Requires energy b/c requires movement of the plasma membrane. http://highered.mcgraw-hill.com/olc/dl/120068/bio02.swf Animation, baby!
Endocytosis & Exocytosis Exocytosis EndocytosisDefinition Exporting Importing of macromolecules by macromolecules by fusion of vesicles to pm forming vesicles with pmVesicles come Budded from ER or Pm & sinks inward &from Golgi pinches off into cytoplasmUsed to Secrete products - Incorporate insulin extracellular large substances
Since cells can’t continue to grow larger,they must split, or divide at some point.
Cell Cycle2 parts:• Interphase – period of growth & DNA synthesis (copying)• Mitotic phase – period of cell division (1 cell divides into 2 cells) I love cells, baby!
Interphase – time of cell growth & copying of DNA3 phases of interphase:• G1 – growing & ribosomes making proteins• S – synthesis (or copying) of DNA (sister chromatids formed)• G2 – growing & getting ready to divide
Cells spend most of their time in interphase. DNA is in chromatin (stringy) form.
Mitotic Phase – time of cell divisionConsists of 2 main phases:1. Mitosis – division of nucleus2. Cytokinesis – division of cytoplasm
Sister Chromatids• Identical copies of chromosomes attached by a centromere.
Prophase• DNA condenses into chromosomes• Nuclear membrane disappears• Centrioles move toward poles• Spindle fibers form & attach to chromosomes
Metaphase• Sister chromatids lined up on metaphase plate with spindle fibers attached to them.
Anaphase• Sister chromatids get pulled apart to poles as spindle fibers shorten.
Telophase• New nuclear membrane forms around chromosomes at each pole• Chromosomes “unpack” into chromatin• Cell membrane begins to pinch in (animals cells) or cell plate develops (plant cells)
Cytokinesis – division of the cytoplasm Cell plate Cleavage furrow
Control of the Cell Cycle• Enzymes control cell cycle so cells divide at the right times• Cancer – uncontrolled cell division caused by a change in the DNA that codes for the making of the control enzymes