Cell Membrane *Clip*

FLUID MOSAIC MODEL Properties of the cell membrane: Properties of the cell membrane: –Fluid-like because of the phospholipid bilayer –Pliable : vesicles can bud off or fuse with cell membrane –Selectively permeable

Properties  Asymmetrical – the two ½’s (top & bottom) are not identical

Mosaic  the proteins form different pattern according to the particular membrane and also within the same membrane at different areas.

Structural Component Lipids: a)Phospholipids is the main component that separates the outside and inside Hydrophilic Phosphate Head Hydrophobic 2 Fatty Acid Tails Phospholipid bilayer

Structural Components Hydrophobic tails (insoluble fatty acids) face each other.

 Polar molecules (salts, amino acids and sugars) cannot pass easily through the hydrophobic tails.  Individual phospholipid molecules are not bonded to one another.

b) glycolipids  Phospholipids with attached carbohydrate (sugar) chains.  Function: provide the cell with a signature; identification marker (identify cells to immune system)

c) cholesterol  Function: to make bilayer stronger, more flexible but less fluid.  Since cholesterol is a hydrophobic lipid, it makes the membrane less permeable to water soluble ions and molecules

d) Proteins  Integral proteins = proteins embedded within the bilayer  Transmembrane protein goes thru the entire bilayer  Peripheral proteins = proteins attached to the surface of the membrane. Transmembrane protein Peripheral Protein Integral Protein

d) Proteins con’t  Some proteins are held in place by cytoskeleton protein filaments, whereas other are free to drift laterally (creating the ever changing fluid mosaic). Cytoskeleton

i) Receptor Proteins  Are molecular trigger that set off cellular responses when specific molecules in the extracellular fluid such as hormones or nutrients bind to them.

ii) Recognition protein/glycoprotein  proteins with an attached carbohydrate chain projecting externally.  Function = identification tags or cell surface attachment sites Integral Protein Peripheral Protein Glycolipid Glycoprotein

iii) Transport Proteins  Regulate the movement of water-soluble molecules through the membrane. Carrier proteins have binding sites and often requires expenditure of NRG (ATP) to move molecules across the membrane

What might you need to move in and out of a cell? Water Sugar O2O2 CO 2 Starch

Can all materials move in and out of a cell easily? NO

FITS

Doesn’t FIT

How can the cell control what molecules enter and exit the cell?

Selective Permeable Membrane  Only some materials move easily in and out of the cell

What Moves and Why  Nutrients –Meet energy demands –Growth & repair  Water Balance –Chemical reactions!  Waste –Maintain normal functioning

Fluid Mosaic Model  Some molecules can enter the cell, some can’t  Can discriminate between different molecules of the same size

3 general ways in which substances can enter/exit the cell 1.Diffusion 2.Transport by proteins 3.Endocytosis/exocytosis

Diffusion  HIGH concentration to low concentration  SHARING IS CARING!

 Constant back and forth movement until happiness

What’s Moving - Particles  DIFFUSION = particles moving from HIGH concentration to LOW concentration until equilibrium is reached.  Is passive (requires no NRG input)

Factors affecting the rate of diffusion 1.Concentration gradient: a greater difference in concentration increases the rate of diffusion 2.Size & shape of molecules: smaller molecules diffuse more quickly 3.Temperature: heating speeds up diffusion

How does this process occur within the cell? The cell membrane has hydrophobic tail regions, which allow lipid soluble molecules (steroids, alcohol) to diffuse through the membrane. Water diffuses across the membrane through protein lined pores that extend through the membrane.

What’s Moving - Water  OSMOSIS = Special type of diffusion  Movement of water from area of High CONCENTRATION to low concentration until equilibrium is reached

Osmosis - concentration  Solute – particles that are dissolved in water  Solvent – liquid that dissolve the solute  Solution – combination of solute and solvent  Osmotic Pressure – the pressure due to osmotic movement of water. The greater the difference in concentration gradient across a membrane, the greater the osmotic pressure  Lots of solute in small volume = high concentration Mr. Solute

How does this process work within the cell? In cellular system, water can move easily across cell membranes, but other molecules can’t. CLIP

Osmosis  Where is the solute concentration higher? Higher concentration of solute Lower concentration of solute

Osmosis  Where is the water concentration higher? Higher concentration of solute Lower concentration of solute Lower concentration of WATER Higher concentration of WATER

Osmosis Higher concentration of solute Lower concentration of WATER Lower concentration of solute Higher concentration of WATER Water movement  Where will the water go?

What happens when a cell is placed in different types of solutions  Isotonic – same [ ] of solute as the cell - no net movement of water - no net movement of water - cell remains the same size - cell remains the same size  Hypertonic – greater [] of solute in the solution Hyper = more, lots, high - cell shrinks in size “crenation” - cell shrinks in size “crenation”  Hypotonic – lower concentration of solute in the solution Hypo = little, few, low - cell can swell and burst “lysis”  There terms are used to COMPARE 2 SITUATIONS

Quick Check  Which side is yellow hypertonic to?  Which side is yellow hypotonic to ? RIGHT LEFT

Where Will the Water Go? 80% H 2 O 20% Sugar 90% H 2 O 10% Sugar Water movement

Where Will the Water Go? 85% H 2 O 15% Sugar 85% H 2 O 15% Sugar Once H 2 O finished moving, both sides are isotonic to each other

Example  Where will the water go? Water movement 80% H 2 O 20% Sugar 90% H 2 O 10% Sugar Water movement

Example  What will the cell look like ? BEFORE AFTER Cell & beaker are isotonic

Example  Where will the water go? Water movement 80% H 2 O 20% Sugar 70% H 2 O 30% Sugar Water movement

Example  What will the cell look like ? BEFORE AFTER Cell & beaker are isotonic

Maximum to Cell Size?  Can a cell get too small or too big?  Absolutely!