cell membrane chapter 3 and 4 – 9 th grade biology
TRANSCRIPT
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Cell MembraneChapter 3 and 4 – 9th Grade Biology
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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.
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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
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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
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Phospholipids
Structure
• Polar “Head” is Hydrophilic or water loving
• Non-polar “Tails” are Hydrophobic or water fearing
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Phospholipids
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Phospholipid Bilayer
• Phospholipids form a bilayer to create the cell membrane
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The Phospholipid Bilayer
This bilayer is selectively permeable – it determines what can enter and leave the cell using proteins
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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
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Proteins within the Membrane
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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
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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
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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
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Passive Transport : Facilitated Diffusion
• Facilitated diffusion is a type of passive transport
• Carrier Proteins, a type of transport protein, uses this method.
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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
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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.
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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.
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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
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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
Hypoto
nic
Hypert
on
ic
Isoto
nic
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Active Transport
• This method involves moving substances AGAINST the concentration gradient.
• Energy from the cell is required to move substances
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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.
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3 Sodium Ions out, 2 Potassium Ions in