The%20plasma%20membrane%20is%20selectively%20permeable

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CHAPTER 7MEMBRANE STUCTURE AND FUNCTION

• The plasma membrane is selectively permeable

• Contains
• ________ (mostly phospholipids)
• ___________
• ______________(minor amounts)

• _______________ molecules- have both hydrophobic
  regions and hydrophilic regions.
• The _________________ model describes cell
  membranes
• A membrane is a fluid structure with proteins
  embedded or attached to a double layer of
  phospholipids.

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• ______- S.J. Singer and G. Nicolson presented a
  revised model - the ____________ model
• __________ regions of proteins and phospholipids
  are in maximum contact with ______
• __________ regions are in a ____________
  environment.

Fig. 7.3
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1. Membranes are _______

• Membrane molecules are held in place by
  relatively weak ______________ interactions.
• Lipids and some proteins drift ___________
• .. but rarely _________ from one layer to the
  other.

Fig. 7.5a

• Phospholipids drift ________, proteins drift
  _________
• Some proteins do not drift due to being
  ____________

Fig. 7.6
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• What affects membrane fluidity?

• ____________- fluidity decreases as temperature
  decreases due to tighter packing of phospholipids
• Its ______________-
• __________ fatty acids make membranes more fluid
  because the ____ prevent tight packing.

Fig. 7.5b
3. _____________- __________ the movement of
phospholipids and _______ fluidity.

• To maintain enzymes activity and permeability,
  the membrane must be fluid, about as fluid as
  _____________.

Fig. 7.5c
Fig. 8.4c
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2. Membranes are mosaics of ________ and
_____________
Where does most of a membranes function reside?
Answer- In the ____________

• There are two populations of membrane proteins.
• ______________proteins- loosely bounded to the
  surface of the membrane, interacting with other
  proteins

• ___________proteins- penetrate the hydrophobic
  core of the lipid bilayer, often completely
  spanning the membrane (a transmembrane protein).

Fig. 7.8
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• Membranes are _____________ ( i.e. they have
  distinctive inside and outside faces)
• proteins are directional
• _____________ are only on the outer surface
• Recall- Manufactured in _____
• Functions-
• __________
• signal transduction
• cell-cell __________________
• enzymatic activity
• attachment to extracellular matrix

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• The proteins in the ___________________ may
  provide a variety of major cell functions.

Fig. 7.9
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3. Membrane ________________ are important for
cell-cell recognition

• The membrane plays the key role in cell-cell
  ___________________.
• To distinguish one type of neighboring cell from
  another.
• Organization as tissues and organs in
  development.
• ______________ of foreign cells by the immune
  system.

• ________________ covalently bond to lipids
  (forming _____________) and proteins (forming
  _________________).

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4. Membranes are ____________________

• Many small molecules (e.g. sugars, amino acids,
  and other nutrients) and ions (e.g. Na, K,
  Ca2, and Cl-) moves across the plasma membrane
  in both directions.
• However, substances do not move across the
  barrier indiscriminately membranes are ________
  ____________________.
• ____________ molecules (hydrocarbons, CO2, O2)
  pass through easily
• ______ (e.g. Na) and _______ (e.g. water) dont
  pass through easily- these must cross membrane
  via ______
• ________________

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5. __________________ is diffusion across a
membrane

• ____________ is the tendency of molecules of any
  substance to spread out in the available space

Fig. 7.11a

• In the absence of other forces, a substance will
  diffuse from where it is more concentrated to
  where it is less concentrated, down its
  concentration gradient.
• Termed _________________- no ________ is
  required

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6. _______ is the passive transport of water

• Ions move from more concentrated (hypertonic) to
  less concentrated (hypotonic)

• ________ is the diffusion of water across a
  _________________________ membrane

Fig. 7.12
Selectively permeable membrane
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7. Cell survival depends on balancing water
_________ and loss

• If place an animal cell in

- an isotonic environment -___ net movement of
water
- a hypertonic environment cell________
- a hypotonic environment cell ______ and ______.
Animal Cell
Plant Cell
Fig. 7.13
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8. Specific proteins facilitate _______
__________ of water and selected solutes

• Three types of molecular transport across a
  membrane
• _________- Passive movement of molecules down a
  concentration gradient
• _________________- The passive movement of
  molecules down its concentration gradient via a
  transport protein
• _______________- The active transport of
  molecules against a _____________________

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_____________________

• Requires ______________ proteins
• have specific _________________ for the solute.
• become _____________ when they are translocating
  passengers as fast as they can.
• can be ______________by molecules that resemble
  the normal substrate.

• Example- water channel proteins, _______________,
  facilitate massive amounts of diffusion.

Fig. 7.15
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9. ______ transport is the pumping of solutes
_________ their gradients

• _________ transport

• requires metabolic ____________
• is critical for a cell to maintain its internal
  concentrations of ____________________.

• is performed by specific ____________ embedded in
  the membranes.
• ____ supplies the energy for most ________
  transport.

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Summary of transport mechanisms
Know these terms!
Fig. 7.17 Both diffusion and facilitated
diffusion are forms of passive transport of
molecules down their concentration gradient,
while active transport requires an investment of
energy to move molecules against their
concentration gradient.
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10. In _____________, a membrane protein couples
the transport of _____ solutes

• A single ATP-powered pump that transports one
  solute can indirectly drive the active transport
  of several other solutes through __________ via a
  different protein.

• Example- Plants use the gradient of ________
  ions that is generated by proton pumps to drive
  the active transport of amino acids, sugars, and
  other ___________ into the cell.

Fig. 7.19
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12. __________ and __________ transport large
molecules

• Large molecules, such as polysaccharides and
  proteins, cross the membrane via _________.
• _______________- a transport vesicle budded from
  the Golgi apparatus is moved by the cytoskeleton
  to the plasma membrane.
• When the two membranes come in contact, the
  bilayers fuse and spill the contents to the
  outside.

• ________________- _______________ and particulate
  matter enter the cell by forming new ___________
  from the plasma membrane.

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• _____________- a type of ______________
• the cell engulfs a particle by extending
  ____________around it and packaging it in a large
  vacuole, then digesting it when the vacuole fuses
  with a _____________.

Fig. 7.20
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• _______________, cellular drinking, a cell
  creates a vesicle around a droplet of
  extracellular fluid.
• This is a __________________ process.

Fig. 7.20
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• ____________________________- (another form of
  endocytosis)

• _______________ in what substances are being
  transported.
• triggered by _________
  ______________interaction (which triggers the
  formation of a vesicle)

Fig. 7.20

• enables a cell to ____________ compounds