Cell Membrane Structure & Function Biology 11 Ms. Lowrie

Homeostasis Definition: Definition: –Constant state or balance within our internal environment even when the external environment changes Required by each cell to continue life Required by each cell to continue life Maintained by cell membrane Maintained by cell membrane

Cell Membrane Selectively permeable Selectively permeable –Allows some molecules to pass through while stopping others –a.k.a. semi-permeable Permeability Permeability –Degree to which substances can pass

Parts of the Cell Membrane

extracellular fluid (outside cell) cytoplasm (inside cell) microfilaments peripheral protein integral protein cholesterol glycolipid glycoprotein carbohydrate chain head tails phospholipid bilayer

Fluid Mosaic Model Fluid Fluid –Phospholipids not attached & are able to move Mosaic Mosaic Mixture, variety Mixture, variety –Made of many parts –Proteins floating throughout it

Fluid Mosaic Model

Phospholipid Bilayer Two layer membrane Two layer membrane Phospholipids are NOT attached together Phospholipids are NOT attached together –Flexible –Small holes will seal quickly

Phospholipids Heads point outward Heads point outward –Hydrophilic Water attracting/loving Water attracting/loving Tails point inward Tails point inward –Hydrophobic Water repelling/ Water repelling/fearing

Why are cells round? Because they are surrounded by fluid...

Carbohydrate Chain Chain of sugar molecules Chain of sugar molecules Gives identity (unique marking) Gives identity (unique marking) for each type of cell for each type of cell –Similar to a “fingerprint” May be attached to a protein or a lipid May be attached to a protein or a lipid

Cell Identity Donation Donation –Blood –Organs Immune system Immune system

extracellular fluid (outside cell) cytoplasm (inside cell) glycolipidglycoprotein carbohydrate chain

Glycoprotein Protein on outside of membrane Protein on outside of membrane –With carbohydrate chain attached Gives identity Gives identity glycoprotein

Glycolipid Phospholipid on outside of membrane Phospholipid on outside of membrane –With carbohydrate chain attached Gives identity Gives identity

Integral Protein Protein extending through bilayer Protein extending through bilayer Contains channels Contains channels Moves molecules in/out Moves molecules in/out a.k.a: a.k.a: –Carrier … –Channel … –Gatekeeper … –Transport … –Membrane …

Peripheral Protein Protein on inside layer of membrane Protein on inside layer of membrane Attaches to microfilaments for support Attaches to microfilaments for support

Cholesterol Embedded in membrane Embedded in membrane Allows membrane to function Allows membrane to function in all temperatures

Not all cholesterol is bad! In high temperatures In high temperatures –Keeps membrane rigid In low temperatures In low temperatures –Keeps membrane flexible –Prevents cells from freezing

Microfilaments –a.k.a. “filaments of cytoskeleton” Provides support for membrane Provides support for membrane

Other Parts Extracellular fluid Extracellular fluid –Fluid outside cell Cytoplasm Cytoplasm –Fluid inside cell

What do you see?

Questions Answer: Answer: –#1, 2 & 5 (pg 49) Hints: Hints:#1 “molecular structure” means what it is made of “molecular structure” means what it is made of#5 Look for 3 functions in the text Look for 3 functions in the text

#1 – Molecular Structure Phospholipid bilayer – –Hydrophilic heads facing out – –Hydrophobic tails facing in Embedded with: – –Proteins (peripheral & integral) – –Glycoproteins – –Glycolipids – –Cholesterol

#2 – Fluid Mosaic Model Fluid: – –Phospholipids that are not attached to each other Can easily move around and reposition – –Flexible Mosaic: – –Embedded with proteins mixed throughout

#5 – Protein Functions Allow materials to move into and out of cell (integral) Cell recognition/identity (glycoprotein) Support (peripheral) Receptor sites for hormones

Extra Questions A. Why is it important for the cell membrane to be fluid? B. Define: selectively permeable, impermeable, permeable. Which term applies to the cell membrane? Why? C. Why do cells need an ‘identity’? D. Why is cholesterol important? E. List 3 materials that move into or out of cells. F. Contrast a cell membrane & cell wall.

A – Fluid Membrane Allows for some movement without damage Phospholipids rejoin quickly if a small hole is made

B – Permeability Selectively/Semi – some things are allowed in or out Impermeable – nothing … Permeable – everything … Cell membrane = selectively permeable – –Protects the cells

C – Cell Identity Blood donation Blood donation Organ transplant Organ transplant Immune system Immune system –Detects invaders Allows cells to function in all temperatures Allows cells to function in all temperatures High temperatures: High temperatures: –Keeps membrane rigid Low temperatures: Low temperatures: –Keeps membrane flexible –Prevents cells from freezing D – Cholesterol

E – What Moves? In: Water Water Oxygen Oxygen Carbon dioxide Carbon dioxide Glucose (sugar) Glucose (sugar) Minerals Minerals Nutrients NutrientsOut: Water Water Oxygen Oxygen Carbon Dioxide Carbon Dioxide Wastes Wastes

F – Membrane vs. Wall Cell Membrane Living Made of proteins & phospholipids Materials pass between phospholipids Found in plant and animal cells Cell Wall Nonliving Made of cellulose Materials pass through small pores Found in plant cells only

Any Questions