Download Plasma Membrane

Plasma Membrane
Pre-Assessment
1. Which of the following statements concerning membrane
proteins is incorrect?
A. They can act as a channel, allowing the transport of ions
across the membrane.
B. They often require ATP to actively transport materials
across the membrane against a concentration gradient.
C. They may be receptor proteins that bind specific
molecules from the surrounding solution, which triggers
endocytosis (i.e., receptor-mediated endocytosis).
D. They are usually not particular about what types of
chemicals they will allow to cross the membrane.
2. Which molecule works to keep the membrane at
optimal fluidity?
3. Which molecule is both hydrophobic and hydrophilic
and aggregates as a bilayer to form the "fabric" of the
membrane?
4. Which molecule may function in facilitated diffusion?
5. Which molecule might serve as a binding site for a
hormone, thereby eliciting a response in the cell?
Phospholipid Bilayer
• Composed of fatty acid
tails connected to
glycerol heads
• non-polar (hydrophobic)
fatty acid interior
impedes passage of
water-soluble
substances (it is liquid
like a soap bubble)
• Polar heads (hydrophilic)
are water soluble
Components of a Plasma Membrane
• Phospholipids
• Proteins
– Integral proteins – completely penetrate the lipid bilayer;
they control the entry and removal of specific molecules
– Peripheral proteins – bound to the exterior surface of
the membrane; they have various functions
Components of a Plasma Membrane
• Cholesterol
– Inside near the fatty acid tails; helps to regulate
membrane fluidity and is important for membrane
stability
Fluid Mosaic Model
The 6 Membrane Protein Functions
1. Hormone binding sites – these proteins have
specific shapes exposed to the exterior that fit the
shape of specific hormones
2. Enzymes – catalyze chemical reactions; may be on
interior or exterior of the cell membrane; often
grouped together for a chain reaction (called
metabolic pathway)
3. Cell adhesion – proteins hook together to provide
temporary or permanent connections; these
connections referred to as junctions
4. Cell-to-cell communication – many include
carbohydrates attached to protein molecules on
outside of cell; they provide an ID tag letting other
cells know what type of cell they are
5. Channels for passive transport – integral proteins
that have a channel in them to allow substances to
move through; passive means substances move
through from high to low concentration
6. Pumps for active transport – integral proteins that
shuttle a substance from one side to the other by
changing their shape; this process requires energy
in the form of ATP