Transcript The Cell Membrane

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AP Biology
MYP Biology: The Cell Membrane
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What are the functions of the cell membrane?
The cell membrane controls what goes in and out
of the cell and helps the cell to maintain
homeostasis. The membrane also helps the cell
maintain its shape and protects the cell.
What are phospholipids?
• Phospholipids are molecules with a polar
phosphate ‘head’ and two nonpolar fatty
acid tails.
Why do phospholipid bilayers form?
The polar heads of the phospholipids face outwards to
be near polar water molecules (they are hydrophilic).
The nonpolar tails of the phospholipids, which do not
like to be near water molecules, face within the bilayer
(they are hydrophobic).
Phospholipid bilayer
polar
hydrophilic
heads
nonpolar
hydrophobic
tails
polar
hydrophilic
heads
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Label the cell membrane structure
Protein Receptor
Phospholipids
Protein Channel
Cholesterol
What are the functions of the parts of the cell membrane?
Membrane Part
Function
Phospholipids
Makes up the basic bilayer structure of the membrane
Cholesterol
Within the bilayer; gives structure to fluid membrane
Protein Channel
Helps molecules pass through the membrane
Protein Receptor
Sends and receives signals to and from other cells
Why is the cell membrane called a “fluid mosaic?”
The cell membrane is often described
as a fluid mosaic since it is made up of
many different molecules and it is
flexible, not rigid.
What does it mean that the membrane is selectively-permeable?
The cell membrane being selectively-permeable
means that it allows some types of molecules to pass
in and out of the cell space, but not others.
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What factors determine how a molecule will cross the membrane?
• Size
• Charge / Polarity
• Concentration
Small, nonpolar molecules can pass through the
membrane without assistance if they are moving from
high to low areas of concentration.
All other types of particles need some sort of
assistance, such as a protein channel in order to pass
across the cell membrane.
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Any Questions??
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