Plasma Membrane

Plasma Membrane• The plasma membrane separates the internal

and external environments of the cell

• This description is known as the fluid-mosaic model

Fluid Mosaic Model

Fluid Mosaic Model

• The lipid bilayer phosopholipid heads are polar, hydrophilic

• Their phospholipid tails are hydrophobic

Plasma Membrane

• Proteins in a membrane consist of peripheral & integral proteins•Peripheral proteins:

• Integral proteins:

Proteins

Plasma Membrane• Both Phosopholipids and proteins can have

attached carbohydrate chains facing the outside of the cell

• This combined with peripheral proteins means that the 2 halves of the plasma membrane lipid bilayer are asymmetrically

Plasma Membrane Functions• The plasma membrane function differs from

cell to cell and the type of integral proteins largely determine the specific function: • Channel Proteins:

• Carrier Proteins: involved in the passage of molecules through membrane

Plasma Membrane Function• Cell Recognition Proteins: glycoproteins that help the body recognize invaders (pathogens) • Receptor Proteins: have a shape that allows a specific molecule to bind to it

• Enzymatic Proteins: carry out metabolic reactions, and without it these necessary reactions would be not occur

Plasma Membrane Permeability

• The plasma membrane is differentially permeable, which is why substances can move across the membrane while others cannot

• Most molecules move across the membrane due to a concentration gradient that is high on one side of the cell and low on the other

Plasma Membrane Permeability• Larger molecules and some ions or charged

molecules can’t move freely using concentration gradients

Diffusion and Osmosis • Diffusion is the movement of molecules from

a higher area to lower area of concentration

• It is a physical process that occurs with any type of molecule and doesn’t require any use of energy

Diffusion and Osmosis

• The properties of the plasma membrane allow only a few types of molecules to enter and exit the cell this way

• Several factors influence the rate of diffusion:

Diffusion and Osmosis

• Osmosis is the diffusion of water across a differentially permeable membrane from an area of high concentration to low

• Osmotic Pressure is the pressure that develops in a system due to osmosis

Diffusion and Osmosis

• Isotonic Solution:• The solute concentration and water concentration both inside and outside the cell are equal

Diffusion and Osmosis• Hypotonic Solution:• Can cause the cell to burst • Hypo=less than and refers to a solution with a lower concentration of solute • If a cell is placed in a hypotonic solution , water would enter the cell

• Cytolysis is used to refer to a burst cell

Diffusion and Osmosis• Hypertonic solution :• Hyper=more than and refers to a solution with a higher percentage of solute • If a cell is in a hypertonic solution water leaves the cell

• Plasmolysis is the shrinking of cytoplasm in a plant cell

Transport By Carrier Proteins• Facilitated transport: the passage of

molecules like glucose and amino acids, across the membrane by carrier proteins

• Active transport : when molecules or ions move through the plasma membrane, when an accumulation occurs

Active Transport• Usually chemical energy like ATP is required

for the carrier protein to combine with the molecule being transported

• A sodium-potassium pump is the most common example of these protein pumps

Na-K Pump

Examples of Osmosis

Your fingers in water• When your fingers are submerged in water

they become water logged • the massive amount of water out side of

your skin moves in causing you skin to expand, leading to wrinkles

Examples of Carrier Protein Importance• Improper functioning of Carrier proteins

can result in many different types of disorders, most considered genetic• Cysteinuria: causes the Cysteine Protein Carrier to malfunction allowing a build up of cysteine in urine and causes it to solidify • Other Vitamin carriers have been linked to people who develop breast cancer

Importance of Pumps

• A malfunctioning Na-K pump can cause a variety of disorders• Build ups of Na or Ca ions in cells lead to Chronic Obstructive Lung Disease (COLD)

Vesicle Formation• Exocytosis is when a vesicle fuses with the

plasma membrane as secretion occurs to the outside of the cell

Vesicle Formation• Endocytosis is when cells take in substances

by vesicle formation

• There are Three Types of Endocytosis

Vesicle Formation

• Pinocytosis occurs when vesicles form around a liquid or very small particles

• Phagocytosis is when the material taken into the cell by endocytosis is large (like food particles)

Vesicle Formation• Receptor Mediated Endocytosis is a form

of pinocytosis that uses receptor proteins shaped to a specific molecule

Vesicle Formation Disorders

• Hermansky-Pudlak syndrome•Pigment dilution, decreased visual acuity, a bleeding, and lysosomal accumulation that can lead to pulmonary fibrosis•Lysomes are made in the cell, serve their function and when are no longer needed are not destroyed, causing a build up of toxins in the cell

Cell Size

• Cells are small . This is an incredible advantage for multi-cellular organism

• A larger cell would require more nutrients and produce more wastes than a smaller cell

Cell Size

Cell Size• For example a cube shaped cell two units high, wide

and depth has a surface area of 24 units and volume of 8 units . A cube cell double the size, 4 units, would have a surface area of 96 units surface area and 64 units volume.

• The smaller has more surface area per unit of volume allowing for more efficient exchanges of nutrients at the cell surface

• Most actively metabolizing cells are small. A cell needs a surface area that can adequately exchange materials with its environment and surface area to volume ratios require that cell stay small

Cell Size