Cell Membrane Chapter 3 and 4 – 9 th Grade Biology

Cell Membrane (Plasma Membrane) Outermost boundary of a cell Encloses the cell’s cytoplasm and organelles from its surroundings Regulates what enters and leaves the cell such as gases, nutrients, and waste.

Cell Membrane Structure Fluid structure (Not rigid like an egg shell) The membrane can choose what enters and leaves the cell Formed by a lipid (fat) layer

The Phospholipid Layer The lipid layer is made up of phospholipids Phospholipid: a phosphate group with two fatty acids attached Contains a polar “head” and two nonpolar “tails” POLAR HEAD NON-POLAR TAILS

Phospholipids Structure Polar “Head” is Hydrophilic or water loving Non-polar “Tails” are Hydrophobic or water fearing

Phospholipids

Phospholipid Bilayer Phospholipids form a bilayer to create the cell membrane

The Phospholipid Bilayer This bilayer is selectively permeable – it determines what can enter and leave the cell using proteins

Membrane Proteins Membrane proteins are imbedded in the bilayer Different types of proteins exist within the membrane: Transport Proteins – Transports materials in and out of the cell using channels Glycoproteins – Cell to cell communication Receptor Proteins – Helps cells communicate with environment to form a reaction Enzymes – Helps with reactions within the cell Structural Proteins – Gives cell support and shape Marker Proteins – Advertises cell type

Proteins within the Membrane

Crossing the Cell Membrane Some substances like water can pass freely through the phospholipid layer Other substances, like ions, need to use proteins to pass through due to size and polarity Different methods may require or not require energy Types of transport: PASSIVE and ACTIVE

Passive Transport This is the process of moving substances DOWN the concentration gradient to reach equilibrium Uses NO energy Types: Diffusion, Facilitated Diffusion, and Osmosis

Passive Transport : Diffusion The process that requires no energy and involves substances moving from an area of high concentration to an area of low concentration. Diffuse means “to spread out” Results from the random movement of molecules due to kinetic energy

Passive Transport : Facilitated Diffusion Facilitated diffusion is a type of passive transport Carrier Proteins, a type of transport protein, uses this method.

Facilitated Diffusion continued… Transport proteins are needed to allow specific substances to pass into and out of the cell Use channels, which are polar passageways, for ions and polar substances

Ion Channels Sodium (Na + ), Potassium (K + ), Calcium (Ca +2 ), and Chloride (Cl - ) are used for very important cell functions Functions such as nerve impulses, heart and muscle contraction These ions cannot freely pass through the bilayer, so they need ion channels.

Ion Channels An ion channel may be always open, or only open when stimulated This transport is passive, where no energy from the cell is required to move materials.

Passive Transport : Osmosis Osmosis is the diffusion of water down its concentration gradient through a semi-permeable membrane Moving from low solute concentration to high solute concentration (High water concentration to low water concentration) Solute molecules (sugar, ions) cannot pass through membrane so water must move across

Osmosis Hypertonic: Area with high concentration of solute Hypotonic: Area with low concentration of solute Isotonic: Areas of equal concentration R=1 Hypotonic Hypertonic Isotonic

Active Transport This method involves moving substances AGAINST the concentration gradient. Energy from the cell is required to move substances

Sodium – Potassium Pump Most important membrane pump in animal cells. Active transport pumps sodium ions out of the cell and potassium ions into the cell.