Cell MembraneChapter 3 and 4 – 9th 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 BilayerThis 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
• http://www.youtube.com/watch?feature=fvwp&v=0c8acUE9Itw&NR=1
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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.
3 Sodium Ions out, 2 Potassium Ions in