PLASMA MEMBRANE

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PLASMA MEMBRANE

• Main component is the PHOSPHOLIPID

Phosphate group
Hydrophilic head -polar
Fatty acids
Hydrophobic tail -nonpolar
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Simplified Cell Membrane
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More complete plasma membrane
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The Plasma Membrane is
selectively permeable
This means it allows some things to pass but
keeps some things out
What can pass and what cannot? Where do things
pass through?
Some through lipids Some need the proteins
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Categories of how things enter/leave the cell
passive transport no energy
ACTIVE TRANSPORT
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Passive Transport

• Diffusion
• Depends on concentration gradients
• Goes from high concentration to low
  concentration
• Diffusion stops when there is no more
  concentration gradient

The system is then said to be in equilibrium
Individual molecules still are moving however
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Lipid portion of the plasma membrane
Small nonpolar molecules can pass through O2, CO2
Lipids can pass -ex steroids
Na
Charged ions cannot pass through
How can they get in or out??????
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Facilitated Diffusion
STILL DIFFUSION
Direction of movement of molecules????
Needs help (facilitation) of a protein.
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OSMOSIS

• DIFFUSION OF WATER ACROSS A SELECTIVELY PERMEABLE
  MEMBRANE
• STILL DIFFUSION
• PASSIVE
• NO ENERGY REQUIRED

Uses channel proteins called aquaporins
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The direction that WATER goes during osmosis
depends on the amount of dissolved solutes on
either side of the membrane
If there are more solutes, there is less
available water
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Isotonic Hypertonic Hypotonic terms used to
compare solutions.
they refer to the concentration of solutes in
that solution
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ACTIVE TRANSPORT
Moves molecules AGAINST their concentration
gradient -uphill -requires a membrane protein
-source of energy -usually ATP
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Large molecules may cross the membrane by
exocytosis and endocytosis

• Exocytosis
• -substances move out of the cell by packaging
  them in vesicles which fuse with the plasma
  membrane

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Movement of large materials across the membrane
Endocytosis ? bringing into the cell by way of
vesicle (vacuole) formation
Phagocytosis (cell eating) -large particles
Pinocytosis (cell drinking) -dissolved solutes
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Pincytosis is indiscriminate. Cells use
receptor-mediated endocytosis to take up specific
substance
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What Do All Cells Have in Common?

• An outer membrane (the plasma membrane)
• Genetic material (DNA)
• Something to build proteins (ribosomes)

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Enzymatic Activity
Examples disaccharides in small intestine
many enzymes involved in photosynthesis and
cellular respiration
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Signal Transduction
Protein may have binding site for a hormone
which relays a message to the inside of the
cell.
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Intercellular joining
Examples in animal cells -tight
junctions -gap junctions -anchoring junctions
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Tight Junctions
Proteins hold cells together and dont allow
passage of material between cell. Important in
epithelial cells lining intestine. Nutrients
inside intestine must pass THROUGH cells. Not
between.
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Gap Junctions
Allow for passage of molecules from cytoplasm of
one cell to the next. Allows for direct
communication. Found in cardiac muscle and some
neurons. Speeds nerve impulse transmission
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Cardiac muscle cells
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Plant cell junctions
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Cell-cell recognition
Glycoproteins may serve as ID tags that are
recognized by other cells
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Attachment to the cytoskeleton and the
extracellular matrix
Protein and carbo mix located outside the cells
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Cell Types

• Cells can be categorized into one of the
  following two groups
• PROKARYOTIC
• EUKARYOTIC

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Prokaryotes

• Literally means NO nucleus
• Earliest fossils are prokaryotes
• Have DNA (but not organized into a nucleus)
• Have ribosomes (to build proteins)
• Are simple cells
• Have no membrane bound organelles
• Include the bacteria and archaea

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Prokaryote
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A
B
D
C
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EUKARYOTIC CELLS

• Contain a nucleus and membrane bound organelles
• Includes us, plants, fungi, protists