CELL MEMBRANE DR.IMRANA EHSAN. Structure and function of cell components (i) Carbohydrates (ii)...
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Transcript of CELL MEMBRANE DR.IMRANA EHSAN. Structure and function of cell components (i) Carbohydrates (ii)...
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CELL MEMBRANECELL MEMBRANE DR.IMRANA EHSAN
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Structure and function Structure and function of cell componentsof cell components
(i) Carbohydrates(ii) Lipids(iii) Proteins(iv) Nucleic Acids(v) Membranes(vi) Cytoskeleton
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• The plasma membrane is the boundary that separates the living cell from its nonliving surroundings
The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others
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Cell membranesCell membranes
Many organelles contain or are enclosed by membranes, including ◦Plasma membrane◦Mitochondria◦Chloroplasts◦Nuclear envelope◦Endoplasmic reticulum◦Golgi apparatus◦Lysosomes◦Microbodies (aka perioxisomes)
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Cellular membranes are fluid Cellular membranes are fluid mosaics of lipids and proteinsmosaics of lipids and proteins
Phospholipids are the most abundant lipid in the plasma membrane
Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions
The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it.
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Structure of cell membraneStructure of cell membrane
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The Fluidity of MembranesThe Fluidity of Membranes
Phospholipids in the plasma membrane can move within the bilayer
Most of the lipids, and some proteins, drift laterally
Rarely does a molecule flip-flop transversely across the membrane
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As temperatures cool, membranes switch from a fluid state to a solid state
The temperature at which a membrane solidifies depends on the types of lipids
Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids
Membranes must be fluid to work properly; they are usually about as fluid as salad oil
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As temperatures cool, membranes switch from a fluid state to a solid state
The temperature at which a membrane solidifies depends on the types of lipids
Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids
Membranes must be fluid to work properly; they are usually about as fluid as salad oil
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Role of Cell MembranesRole of Cell Membranes
Based on the functions of the above organelles / membranes write down some of the roles of the membranes in the cells
(Leave some space as we will be adding to this list)
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Structure of Cell membranesStructure of Cell membranesFluid Mosaic Model
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Electron micrograph of cell Electron micrograph of cell membranemembrane
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Structure of Cell membranesStructure of Cell membranes
Lipids◦Remember lipids have hydrophilic head and
hydrophobic tails◦To avoid the hydrophobic tails coming in
contact with water a continuous bilayer sphere is formed.
◦Therefore hydrophobic interactions hold membranes together
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Structure of Cell MembranesStructure of Cell Membranes
Proteins◦Integral proteins (intrinsic)
Proteins that are embedded in the membrane They are held in place by hydrophobic interactions
(integral proteins have hydrophobic groups on their outer surface)
◦Peripheral proteins (extrinsic) Proteins attached to the surface of the membrane
(often forming non-covalent bonds with integral proteins)
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Proteins cont…Proteins cont…
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Function of membranes Function of membranes macromoleculesmacromolecules
◦Phospholipid bilayer Forms boundary to isolate cell contents from
environment Restricts passage of hydrophilic substances across
the membrane◦Cholesterol
Increases bilayer strength, flexibility Reduces membrane fluidity Reduces permeability to water-soluble substances
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Some proteins in the plasma membrane can drift within the bilayer
Proteins are much larger than lipids and move more slowly
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Function of Membrane ProteinsFunction of Membrane Proteins
Attachment◦Cytoskeleton◦Extracellular matrix
Intercellular Junctions◦Plasmodesmata◦Tight Junctions◦Gap Junctions◦Desmosomes
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Function of Membrane ProteinsFunction of Membrane Proteins
Transport◦Carrier Proteins◦Channel Proteins
ReceptorsEnzymesCell to Cell recognition
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Function of membrane protiensFunction of membrane protiens
Integral (Membrane-spanning or intrinsic) •Can span membrane several times • •Either move around or are kept in place
by cytoskeleton proteins Allows for cell polarity Associated (peripheral or extrinsic) •Loosely bound to membrane •Enzymes and structural proteins
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Learning ActivitiesLearning Activities
Use all resources to find out more about the functions of membrane proteins.
Based on the functions of proteins, add to your list on the role of membranes in cells