Download The Cell Membrane 2015

THE CELL MEMBRANE
The Key to Cellular Transport
Some Membrane Terms
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Many substances can diffuse across biological
membranes, but some are too large or too strongly
charged to cross the lipid bilayer.
If a substance is able to diffuse across a membrane,
the membrane is said to be permeable to it.
A membrane is impermeable to substances that
cannot pass across it.
Most biological membranes are selectively
permeable, meaning that some substances can pass
across them and others cannot.
Characteristics of the Cell Membrane
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Made of phospholipids
– arranged in two layers called a bilayer
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Selectively permeable
-it controls “selects” what can enter or leave the cell
-some materials are allowed through others aren’t
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Fluid Mosaic Model
- made of different molecules – phospholipids, proteins,
cholesterol
- the molecules aren’t static but can move “fluid”
Lipid bi-layer – the heart of the
membrane
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Phospholipids are arranged into 2 layers
- called a bilayer
Phospholipids: Phosphate Heads
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Polar/hydrophillic – attracted to water and
charged particles
Phospholipids: Lipid Tails
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Nonpolar/hydrophobic – repel water and charged
particles
Cholesterol
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Found in bilayer – helps to hold the membrane together
while adding to fluidity of the membrane
Glycoproteins
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Proteins with carbohydrates attached – identifies the cell type
-allows it to bind with other cells of the same type
Receptor Proteins
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recognize and bind with substances outside of the cell,
causing changes inside the cell
Enzymes
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Allow reactions to occur- light reactions and ETS occur with
enzymes in membrane
Transport Proteins
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Proteins that extend across the membrane – provide a way for
large or charged molecules to cross the membrane
Types of Transport Proteins
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Ion Channels- allow certain charged particles to cross the
membrane – passive transport
Carrier Proteins – bind to a specific molecule and carry it
across the membrane
- facilitated diffusion – proteins carry molecules with the
concentration gradient /no cellular energy is required
- active transport – proteins carry molecules against the
concentration gradient/ cellular energy is required