Section 5.1 Membrane Models

Section 5.1 Membrane Models

Unit Membrane Model

Reasons to doubt its validity

• Not all membranes have the same appearance
• They all don't necessarily have the same function

Section 5.1 Membrane Models

Fluid-Mosaic Model

The membrane is a fluid (1)___ bilayer in which (2) ___ molecules are either partially or wholly embedded.  The pattern of these (3) ___ molecules throughout the membrane is a (4) ___ pattern.

1. Phospholipid

2. Proteins

3. Protein

4. Irregular

Section 5.1 Membrane Models

Fig.2

Identify key components in Figure 5.2

Section 5.2 Plasma Membrane Structure and Function

Section 5.2 Plasma Membrane Structure and Function

Plasma Membrane

What does the Plasma Membrane do?

• Has a phospholipid molecule that has hydro - phylic/phobic heads/tails. Proteins in membrane may be peripheral or intergral proteins
• Integral Proteins move literally in membrane, some protrude from both ends (transmembrane proteins)
• Carbohydrate Chains - (of proteins), give cell "sugar coat (a.k.a. glycocalyx)

Section 5.2 Plasma Membrane Structure and Function

Phospholipid Bilayer

Describe with bullets, not with paragraphs

Concentration Gradient - move from an area where concentration is high to area where concentration is low

1. Diffusion and Osmosis

2. Transport by Carrier Proteins

3. Vesicle Formation

• Factors that influence diffusion: temperature, pressure, electrical currents, molecular size
• Osmosis - diffusion of water across a membrane due to concentration differences
• Osmotic Pressure - pressure that develops in a system due to osmosis: greater osmotic pressure = more likely water will diffuse in that direction

Section 5.2 Plasma Membrane Structure and Function

Phospholipid

Section 5.2 Plasma Membrane Structure and Function

Cholesterol

Describe with bullets, not with paragraphs

1. Another lipid that is found in animal cells

2. Strengthens and stiffens the membrane, regulating its fluidity

Section 5.2 Plasma Membrane Structure and Function

Glycolpipids, Glycoproteins

• Glycolipids - phospholipids with attached carbohydrate (sugar chains)
• Glycoproteins - proteins with attached carb (sugar) chains

Section 5.2 Plasma Membrane Structure and Function

Carbohydrate Chains

What are they, what do they do?

• Describe with bullets, not with paragraphs
• 1. Give the cell a "sugar coat:" the glycocalyx. Protects cell, adheres to cells and receives signals
• 2. Each cell has its own "fingerprint," based on its chain number, sequence, and whether if it's branched
• 3. I.E. immune system recognizes tissue of cells of foreign cells, rejects it because it doesn't have the correct carb chain sequence.

Section 5.2 Plasma Membrane Structure and Function

Fluidity of the Plasma Membrane

What is it, why is it important?

Describe with bullets, not with paragraphs

1. Dependent on lipid components

2.Greater concentration of unsaturated fatty acid = more fluid membrane

3.Proteins are free to drift laterally.

Section 5.2 Plasma Membrane Structure and Function

Protein Function

Channel Proteins

1. Involved in passage of molecules through membrane

2. A channel in which molecules can simply move through across the membrane

Section 5.2 Plasma Membrane Structure and Function

Protein Function

Carrier Proteins

1. Involved in passage f molecules through membrane

2.Combine with substance and help it move across membrane

3.Transports sodium and potassium ions across a nerve cell membrane.

Section 5.2 Plasma Membrane Structure and Function

Protein Function

Cell recognition proteins

1) They are glycoproteins

2) Helps the body recognize when it's being invaded by pathogens

Section 5.2 Plasma Membrane Structure and Function

Protein Function

Receptor Proteins

1) Have a specific shape for a specific molecule to bind with it

2) Causes protein to change its shape, bringing cellular response

3) Coordination of body movement based on signal molecules

Section 5.2 Plasma Membrane Structure and Function

Protein Functions

Enzymatic Proteins

1) Carry out metabolic reaction directly

2) Without the enzymes being attached to various membranes of cell, it couldn't perform these metabolic reaction

Section 5.2 Plasma Membrane Structure and Function

Sumary

The plasma membrane consists of a (1)___ that has the consistency of olive oil and accounts for the (2)___ of the membrane.  The integral (3)___, which are either partially or wholly embedded in the membrane, have specific functions.  Some are involved in (4)___, others are (5)___, and still others (6)___.

1. plasma membrane

2. fluidity

3. proteins

4.passage of molecules

5.receptors for signal molecules

6. play an enzymatic role

Section 5.3 Permeability of the Plasma Membrane

Section 5.3 Permeability of the Plasma Membrane

differentially permeable

definition

Section 5.3 Permeability of the Plasma Membrane

concentration gradient

definition

Section 5.3 Permeability of the Plasma Membrane

Summary

The plasma membrane is (1)___ permeable.  Certain substances can freely pass through the membrane, and others cannot.  Those that cannot freely cross the membrane may be (2)___ across by either (3)___ or by (4)___.

1. differentially

2. transported 

3. carrier protein

4. vesicle formation

Section 5.3 Permeability of the Plasma Membrane

Diffusion and Osmosis

diffusion

Section 5.3 Permeability of the Plasma Membrane

Diffusion and Osmosis

solution

Section 5.3 Permeability of the Plasma Membrane

Diffusion and Osmosis

Summary

Molecules (1)___ down their (2)___.  A few types of small molecules can simply (3)___ through the (4)___.

1. diffuse

2. concentration gradient

3. diffuse

4. plasma membrane

Section 5.3 Permeability of the Plasma Membrane

Osmosis

definition

Section 5.3 Permeability of the Plasma Membrane

Osmosis

osmotic pressure

Section 5.3 Permeability of the Plasma Membrane

Osmosis

Isotonic Solution

• Solute concentration and water concentration inside/outside cell are equal
• There is no net gain/loss of water
• Tonicity - strength of the solution

Section 5.3 Permeability of the Plasma Membrane

Osmosis

Hypotonic Solution

• Solution that causes a cell to swell or burst
• A solution that has more solution inside it than outside it (less water in cell, more water out of it)
• Causes water to rush in, attempting to equalize the concentrations
• Turgor Pressure - swelling of a plant which causes expansion of cytoplasm b/c central vacuole gains water
• Helps maintain plant's erect position

Section 5.3 Permeability of the Plasma Membrane

Osmosis

turgor pressure

Section 5.3 Permeability of the Plasma Membrane

Osmosis

Hypertonic Solution

• Solutions that cause a cell to shrink
• Higher solute concentration outside cell, causes water from inside the cell to rush out

Section 5.3 Permeability of the Plasma Membrane

Summary

In an (1)___, a cell neither gains nor loses (2)___.  In a (3)___, a cell gains (4)___.  In a (5)___, a cell loses (6)___ and the (7)___ shrinks.

1. isotonic solution

2. water

3. Hypotonic Solution

4.water

5.Hypertonic solution

6.water

7.cell

Section 5.3 Permeability of the Plasma Membrane

Transport by Carrier Proteins

Summary

Some of the (1)___ in the plasma membrane are (2)___.  They transport biologically useful (3)___ into and out of the (4)___.

1.proteins

2.carriers

3.molecules

4.cell

Section 5.3 Permeability of the Plasma Membrane

Transport by Carrier Proteins

Facilitated Transport

• Explains passage of glucose and amino acid molecules across plasma membrane
• Does not require expenditure of energy b/c molecules are moving down concentration gradient  

Section 5.3 Permeability of the Plasma Membrane

Transport by Carrier Proteins

Active Transport

• Utilize carrier proteins and expenditure of energy to move molecules against their concentration gradient
• Chemical energy ATP is used
• Organelles that involve active transport have many mitochondria
• Proteins involved in active transport called pumps
• Sodium-Potassium Pump - carrier protein in membrane that moves sodium ions out of cell, and potassium ions into the cells

Section 5.3 Permeability of the Plasma Membrane 

Transport by Carrier Proteins

Summary

During (1)___ transport, small molecules follow their (2)___.  During (3)___, small molecules and (4)___ move against their (5)___.

1.Facilitative

2.concentration gradient

3.active transport

4.ions

5. concentration gradient

Section 5.3 Permeability of the Plasma Membrane

Vesicle Formation

Exocytosis

• A vesicle fuses with plasma membrane as secretion happens
• Golgi Apparatus produces vesicles that carry products to membrane
• Membrane becomes part of the plasma membrane
• Cause growth

Section 5.3 Permeability of the Plasma Membrane

Vesicle Formation

Endocytosis

• Takes in substances for vesicle formation

Section 5.3 Permeability of the Plasma Membrane

Vesicle Formation

Endocytosis - phagocytosis

• Brings in large material like food or viruses
• Endocytic vesicle might fuse with a lysosome, starting to digest already

Section 5.3 Permeability of the Plasma Membrane

Vesicle Formation

Endocytosis - pinocytosis

• how a cell "drinks"
• occurs when vesicles form around a liquid or small particles
• Pinocytosis is a very small operation (seen with an electron microscope)

Section 5.3 Permeability of the Plasma Membrane

Vesicle Formation

Endocytosis - Receptor-Mediated Endocytosis

• Type of pinocytosis
• A specific receptor protein only allows one type of protein to bind with it
• Found in a place called the coated pit, layer of protein on cytoplasmic side
• Very selective, more efficient than ordinary pinocytosis
• Involved in uptake and transfer and exchange of substances between cells

Section 5.3 Permeability of the Plasma Membrane

Vesicle Formation

Summary

Substances are secreted from a cell by (1)___.  Substances enter a cell by (2)___.  (3)___ allows cells to take up specific kinds of molecules and then they are released within the cell.

1.exocytosis

2.endocytosis

3.Recepter-mediated endocytosis

Section 5.4 Modification of Cell Surfaces

Section 5.4 Modification of Cell Surfaces

Junctions Between Cells

Anchoring Junctions

Section 5.4 Modification of Cell Surfaces

Cell Surfaces in Animals

Junctions Between Cells - Adhesion Junctions

They are internal cytoplasmic plaques, joined by internal filaments (joining the cytoskeleton cell)

Found in heart and bladder and stomach, where it stretches

Desmosome - single point of attachment between adjacent cells

Section 5.4 Modification of Cell Surfaces

Cell Surfaces in Animals

Junctions Between Cells - desmosome

• A single point of attachment between the adjacent cells

Section 5.4 Modification of Cell Surfaces

Cell Surfaces in Animals

Junctions Between Cells - Tight Junctions

Where proteins actually attach to each other, creating a zipper-like fastening

Found in intestine, kidney's

Section 5.4 Modification of Cell Surfaces

Cell Surfaces in Animals

Junctions Between Cells - Gap Junction

Allows cells to communicate

Channel is lined by six plasma membrane proteins

Adds strength to cells, allows ions to pass between them

Important to heart and smooth muscle

Section 5.4 Modification of Cell Surfaces

Extracellular Matrix

3 Point Summary

• A nonliving meshwork of polysaccharides and proteins in close association with the cell that produced them.
• Collagen and elastin fibers are structural proteins in extracellular matrix
• Collagen gives matrix strength
• Elastin gives resilience
• Can become quite flexible, as in cartilage, or rock solid like bone

Section 5.4 Modification of Cell Surfaces

Plant Cell Walls

Cell Wall

Section 5.4 Modification of Cell Surfaces

Plant Cell Walls

plasmodesmata

Living cells are connected by a plasmodesmata, which are numerous narrow, membrane-lined channels that pass through the cell wall.

Cytoplasmic strands allow direct exchange of specific molecules

All of the 5 following proteins are integral proteins

peripheral proteins take part in stabilization and shape of plasma membrane