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

Remember diffusion… Traffic Across Membrane

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; possibly burst if no cell wall. Cells in a hypertonic solution lose water & shrink. Cells in an isotonic solution have no net gain or loss of water.

Osmoregulation – control of water balance Ex of how orgs stabilize water loss & uptake: –Freshwater paramecium

Osmosis Ex of how orgs stabilize water loss & 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

Facilitated Diffusion Diffusion of solutes across membrane w/ help of proteins –Large polar or ions –proteins Specific Can be sat Can be inhibited –Protein transports solute by Changing shape Selective channels Cystic Fibrosis

Cause: 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 CFTR gene is located on chromosome 7. Cystic Fibrosis is

Active Transport The pumping of solutes against their gradient (L to H) Nonspontaneous Requires energy (usually ATP) Maintains steep ionic gradients (potential energy) Ex: Na/K pump

Active transport

Ion 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. Animation, baby!

Endocytosis & Exocytosis ExocytosisEndocytosis DefinitionExporting macromolecules by fusion of vesicles to pm Importing of macromolecules by forming vesicles with pm Vesicles come from Budded from ER or Golgi Pm & sinks inward & pinches off into cytoplasm Used toSecrete products - insulin Incorporate extracellular large substances

Endocytosis 3 types: Phagocytosis – cell “eating” solid particles (uses pseudopodia) Pinocytosis – cell “drinking” fluid droplets Receptor mediated endocytosis – importing specific macromolecules

Since cells can’t continue to grow larger, they must split, or divide at some point.

Cell Cycle 2 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 DNA 3 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 division Consists of 2 main phases: 1.Mitosis – division of nucleus 2.Cytokinesis – division of cytoplasm

Sister Chromatids Identical copies of chromosomes attached by a centromere.

Mitosis 4 phases: Prophase Metaphase Anaphase Telophase

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 Cleavage furrow Cell plate

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

Cell Cycle Control _1/7/1948/ cw/index.htmlhttp://wps.prenhall.com/esm_freeman_biosci _1/7/1948/ cw/index.html

Internal Vs external signals Internal – the checkpoints External – growth factors, density dependent inhibition, anchorage dependence

cancer Tumor Begign Malignant Metastasis Radiation & chemo

Cancer Forms tumors & can spread through body - metastasize

Causes of Cancer Environmental factors UV radiation from sun Tobacco Viral infections Genetic

How to prevent cancer: Low fat, high fiber diet Vitamins Exercise Don’t smoke Use sunscreen Regular doctor appointments

Removal of colon polyps

Review of the cell cycle ellsalive.co m/mitosis.ht mhttp:// ellsalive.co m/mitosis.ht m