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Unit 3
The Cell
The Plasma Membrane
• The plasma membrane
acts as a fragile barrier
between the cell and its
surroundings.
• When studied it’s
referred to as a “fluid
mosaic”
• It is thought of as a
“sandwich” that wraps
around a cell.
Plasma Membrane
• The cell membrane
– The “bread” of the sandwich are made up of
phosphate bases.
– The “peanut butter” is the fatty acid tails of the
phospholipid.
– Think of proteins as jelly that penetrates
through the bread and is in the center of the
sandwich as well.
STRUCTURE: Described as fluid
mosaic because: it is composed of
many different parts that move around in a crowded
fashion
Main component:
•Properties of phosphate bases:
•Properties of fatty acid tails:
•Non-polar because:
Cholesterol:
Membrane Proteins:
•Two types:
•Function and structure of glycocalyx
The Plasma Membrane
• The phosphate bases:
– Found on the very outside and very inside of the
membrane
– Are polar- so they attract water, electrolytes, amino
acids and sugars (anything polar or ionic)
– They are hydrophilic
STRUCTURE: Described as fluid mosaic because: it is composed of
many different parts that move around in a crowded fashion
Main component:
•Properties of phosphate bases: polar
so they attract to water
(hydrophilic) and other charged particles; found on the
outside and inside of the membrane
•Properties of fatty acid tails:
•Non-polar because:
Cholesterol:
Membrane Proteins:
•Two types:
•Function and structure of glycocalyx
The Plasma Membrane
• The fatty acids:
– Non-polar: don’t allow charged particles
through but allow neutral particles like fats,
oxygen, carbon dioxide, alcohol and urea
through without help.
– Hydrophobic- water fearing
– The thickest part of the membrane
STRUCTURE: Described as fluid mosaic because: it is composed of
many different parts that move around in a crowded fashion
Main component:
•Properties of phosphate bases: polar so they attract to water
(hydrophilic) and other charged particles; found on the outside
and inside of the membrane
•Properties of fatty acid tails: non
polar, so they repel water
(hydrophobic); found on the inside of the membrane;
fats, oxygen, carbon dioxide, alcohol and urea can
move through this layer (non polar molecules)
•Non-polar because:
Cholesterol:
Membrane Proteins:
•Two types:
•Function and structure of glycocalyx
The Plasma Membrane
• Fatty acids make up the majority of the
membrane, so overall, the membrane is
non-polar.
– Polar molecules hover outside the membrane
and get help moving through
– Non polar molecules can move through on
their own.
*Show transport movie
STRUCTURE: Described as fluid mosaic because: it is composed of
many different parts that move around in a crowded fashion
Main component:
•Properties of phosphate bases: polar so they attract to water
(hydrophilic) and other charged particles; found on the outside
and inside of the membrane
•Properties of fatty acid tails: non polar, so they repel water
(hydrophobic); found on the inside of the membrane; fats, oxygen,
carbon dioxide, alcohol and urea can move through this layer (non
polar molecules)
•Non-polar because: the
tails make-up the majority of the
molecule
Cholesterol:
Membrane Proteins:
•Two types:
•Function and structure of glycocalyx
The Plasma Membrane
• Cholesterol
– Cholesterol is found along the membrane to
hold it together and give it form.
•Properties of fatty acid tails: non polar, so they repel water
(hydrophobic); found on the inside of the membrane; fats, oxygen,
carbon dioxide, alcohol and urea can move through this layer (non
polar molecules)
•Non-polar because: the tails make-up the majority of the molecule
Cholesterol: found
on the inside of the membrane; gives the
membrane some support/structure
Membrane Proteins:
•Two types:
•Function and structure of glycocalyx
The Plasma Membrane
• Membrane Proteins
– Embedded in the membrane and move around in the
“fluid”
– Some are integral proteins, which extend all the way
through.
– Some are peripheral proteins, which are found at the
surface, sometimes stuck to integral proteins.
•Properties of fatty acid tails: non polar, so they repel water
(hydrophobic); found on the inside of the membrane; fats, oxygen,
carbon dioxide, alcohol and urea can move through this layer (non
polar molecules)
•Non-polar because: the tails make-up the majority of the molecule
Cholesterol: found on the inside of the membrane; gives the membrane
some support/structure
Membrane Proteins:
•Two types: integral
proteins span the width of the
membrane; peripheral proteins lie on the outside or
inside (surface) of the membrane
•Function and structure of glycocalyx
The Plasma Membrane
• Proteins
– Many have branching sugar chains
(polysaccharides) extending out from their
surface.
– These polysaccharides mark the cell, like
identification.
– The sugar covering is called glycocalyx
Membrane Proteins:
•Two types: integral proteins span the width of the membrane;
peripheral proteins lie on the outside or inside (surface) of the
membrane
mark the cell, like a name
tag, so the body can recognize it as its own
•Function and structure of glycocalyx:
The Plasma Membrane
• Proteins have 6 functions in the membrane:
1. Adhesion proteins: serve as markers so other
cells know to bond together and form a tissue.
2. Recognizers: mark the cell so the immune
system recognizes it so the cell isn’t attacked
and lysed by its own body.
The Plasma Membrane
3. Receptor sites: Some proteins receive
electrical and other chemical messengers.
– Tell the cell to begin or end production of
something it is making
– Feedback mechanism
The Plasma Membrane
4. Enzymes: catalyse the thousands of
chemical reactions that take place along
the membrane and just inside the cell.
5. Attachment: Attach the membrane to
fibers which are the cell’s cytoskeleton
The Plasma Membrane
6. Transporters: Transfer nutrients and
molecules across the membrane into the
cell.
The Plasma Membrane
Some cells have special
adaptations to their membrane
that helps them perform their
job in the body:
• Microvilli: The outer layer of the
membrane creates finger
projections (similar to cilia) to
increase the surface area
– Found in cells that absorb high
amounts of molecules (kidneys
and intestines)