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Tour of a Typical Cell
Anatomy and Physiology- Anusha Murali
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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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ECF and ECM
Cells of the human body are surrounded by Extracellular Fluid.(mostly water) andExtra cellular matrix.( may be solid or gel like) - ECM would depend on the type of tissue.
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Plasma Membrane
• Helps define the outer shell of a cell.• Inside the membrane is the cytoplasm which
contains everything except the nucleus.• Functions of a Plasma Membrane:• ------ keeps the inside of the cell in and outside
of the cell out.• ------Controls what passes through the cell.
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Plasma membrane
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Cellular membranes are fluid mosaics 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.
http://www.youtube.com/watch?v=Rl5EmUQdkuI
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Phospholipid bilayer
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The 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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Lateral movement(~107 times per second)
Flip-flop(~ once per month)
Movement of phospholipids
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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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ViscousFluid
Unsaturated hydrocarbontails with kinks
Membrane fluidity
Saturated hydro-carbon tails
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Proteins in Cell Membrane
• Structural Proteins• Glycoproteins• Channels
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Structural Proteins
• Examples are Cadherin, Integrin, Spectrin Functions: Connect the cell to 1.neighboring cells2.To the extracellular matrix3.To the cytoskeleton inside the cell. These structural proteins form a link between
the inside and outside the cell.
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Structural Proteins
• Structural proteins are responsible for creating cell junctions.
• Cell adhesion molecules (CAMs) are proteins located on the cell surface involved in binding with other cells or with the extracellular matrix (ECM) in the process called cell adhesion.
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Types of Proteins
• Cadherin- Calcium dependent adhesion molecule- important in fetal development.
• Integrin - act as adhesion receptors, transporting signals across the plasma membrane in multiple directions.
• Spectrin- is a cytoskeletal protein that lines the intracellular side of the plasma membrane.
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Channel Proteins
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Channel Proteins
• Have a hollow central pore or channel that allows water or small charged particles such as sodium, potassium, calcium and chloride to pass into or out of the cell.
• These substances cannot enter or leave the cell without the channel because of their polarity or charge makes them unable to penetrate a lipid bilayer.
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Selective Membrane
• Channels are very selective about which substances are allowed to cross the membrane and when.
• Example • Aquaporins : Will let water cross but will not
let H+ or OH- to cross.• This selective property is important in
controlling the cell’s ph.
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Glycoproteins
proteins with carbohydrate attached to it.•These proteins are usually found in the plasma membrane with the carbohydrate group projecting into the ECF.
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Glycocalyx
• The layer of carbohydrate groups surrounding a cell is called Glycocalyx.
• Helps distinguish own healthy cells from diseased cells, transplanted cells.
• Helps cells binds to extracellular substances which is important for cell recognition
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Structure of the typical lipid bilayer of the Plasma Membrane.
• Integral proteins are those that pass through the bilayer.
• Peripheral proteins are associated with the inner surface of the plasma membrane.
• Most integral proteins are modified by carbohydrate addition to their extracellular domains.
• Membranes also contain carbohydrate modified lipids (glycolipids) in addition to the more common phospholipids and cholesterol that constitute the bulk of the lipid content of the membrane.
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