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

OsmosisEx 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

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.

Active TransportThe 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

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.

http://highered.mcgraw-hill.com/olc/dl/120068/bio02.swfAnimation, baby!

Endocytosis & ExocytosisExocytosis Endocytosis

Definition Exporting 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 to Secrete 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 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 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 nucleus2. Cytokinesis – division of cytoplasm

Sister Chromatids• Identical copies of chromosomes attached

by a centromere.

Mitosis

4 phases:• Prophase • Metaphase• Anaphase• Telophase

http://www.cellsalive.com/mitosis.htm

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 furrowCell 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• http://wps.prenhall.com/esm_freeman_biosc

i_1/7/1948/498717.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

• http://www.gihealth.com/flashvideo/flash.html

Review of the cell

cycle

• http://www.cellsalive.com/mitosis.htm