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.”

• ______- 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

• Membrane molecules are held in place by relatively weak ______________ interactions.

• Lipids and some proteins drift ___________

• .. but rarely _________ from one layer to the other.

1. Membranes are _______

• Phospholipids drift ________, proteins drift _________

•Some proteins do not drift due to being ____________

Fig. 7.5a

Fig. 7.6

1. ____________- fluidity decreases as temperature decreases due to tighter packing of phospholipids

2. Its ______________-

• __________ fatty acids make membranes more fluid because the ____ prevent tight packing.

•What affects membrane fluidity?

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

Fig. 8.4c

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

Fig. 7.5b

Fig. 7.5c

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

• 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

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

Fig. 7.9

• 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.

3. Membrane ________________ are important for cell-cell recognition

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

• 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) don’t pass through easily- these must cross membrane via ______

________________

4. Membranes are ____________________

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

5. __________________ is diffusion across a membrane

•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

Fig. 7.11a

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

6. _______ is the passive transport of water

• ________ is the diffusion of water across a _________________________ membrane

Fig. 7.12 Selectively permeable membrane

• If place an animal cell in

7. Cell survival depends on balancing water _________ and loss

- an isotonic environment -___ net movement of water

- a hypertonic environment –cell________

- a hypotonic environment –cell ______ and ______.

Fig. 7.13

Animal Cell

Plant Cell

• 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 _____________________

8. Specific proteins facilitate _______ __________ of water and selected solutes:

• 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

_________ transport

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

• is performed by specific ____________ embedded in the membranes.

• ____ supplies the energy for most ________ transport.

• requires metabolic ____________

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

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.

Summary of transport mechanisms

Know these

term

s!

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

10. In _____________, a membrane protein couples the transport of _____ solutes

• 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

• 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.

12. __________ and __________ transport large molecules

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

• _____________- 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

• _______________, “cellular drinking”, a cell creates a vesicle around a droplet of extracellular fluid.

• This is a __________________ process.

Fig. 7.20

• ____________________________- (another form of endocytosis)

•_______________ in what substances are being transported.

•triggered by _________ ______________interaction (which triggers the formation of a vesicle)• enables a cell to “____________” compounds

Fig. 7.20