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Chapter 7

Terms in this set (58)

The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others
The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others
Concept 7.1: How are Cellular membranes are fluid mosaics of lipids and proteins?
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What is the most abundant in the plasma membrane?
Phospholipids
Phospholipids are amphipathic molecules, meaning what?
containing hydrophobic and hydrophilic regions
What exists as a stable boundary between two aqueous compartments?
A phospholipid bilayer
What model states that a membrane is a fluid structure with a "mosaic" of various proteins embedded in it?
The fluid mosaic model
Variations in lipid composition of cell membranes of many species appear to be adaptations to what?
adaptations to specific environmental conditions
Ability to change the lipid compositions in response to temperature changes has evolved in organisms that live where?
that live where temperatures vary
A membrane is a collage of different proteins, often grouped together, embedded where?
embedded in the fluid matrix of the lipid bilayer
what determine most of the membrane's specific functions?
Proteins
what are bound to the surface of the membrane?
Integral proteins penetrate the hydrophobic core
Peripheral proteins
what penetrates the hydrophobic core>
Integral proteins
Six major functions of membrane proteins
1.Transport
2. Enzymatic activity
3. Signal transduction
4. Cell-cell recognition
5. Intercellular joining
6. Attachment to the cytoskeleton and extracellular matrix (ECM)
Which of the following amino acids would most likely be present in the outer side of a transmembrane domain of an integral membrane protein?
a) a charged amino acid like lysine
b) a polar amino acid like serene
c) a special amino acid like glycine or proline
*d)* a hydrophobic amino acid like valine
e) any of the above, with no preference
HIV INFO
HIV must bind to the immune cell surface protein CD4 and a "co-receptor" CCR5 in order to infect
a cell
HIV cannot enter the cells of resistant individuals that lack CCR5 (4-16% of European decent)
Cells recognize each other by binding to molecules. Describe what they contain and location?
containing carbohydrates, on the extracellular surface of the plasma membrane
Membrane carbohydrates may be covalently bonded to what?
to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)
What is on the external side of the plasma membrane and varies among species, individuals, and even cell types in an individual?
Carbohydrates
Membranes have distinct inside and outside faces
The asymmetrical distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is determined when?
when the membrane is built by the ER and Golgi apparatus
Concept 7.2: How do membrane structures result in selective permeability?
A cell must exchange materials with its surroundings, a process controlled by the plasma membrane

Plasma membranes are selectively permeable, regulating the cell's molecular traffic
What can dissolve in the lipid bilayer and pass through the membrane rapidly
Hydrophobic (nonpolar) molecules, such as hydrocarbons
Examples of Hydrophobic (nonpolar) molecules,
(Examples: steroids and capsaicin)
Do Hydrophilic molecules including ions and polar molecules cross the membrane easily?
NO!
What allows passage of hydrophilic substances across the membrane?
Transport proteins
Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel, what are they called?
Some transport proteins, called channel proteins
Channel proteins called aquaporins facilitate what?
the passage of water
what protein binds to molecules and change shape to shuttle them across the membrane?
carrier proteins,
A transport protein is specific for the what?
substance
Concept 7.3: Passive transport is diffusion of a substance across a membrane with no energy investment
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What is the tendency for molecules to spread out evenly into the available space?
Diffusion
Substances
diffuse down their concentration gradient, the region along which the density of a chemical substance increases or decreases
concentration gradient
No work must be done to move substances down the concentration gradient
The diffusion of a substance across a biological membrane is passive or not passive? why?
The diffusion of a substance across a biological membrane is passive transport because no energy is expended by the cell to make it happen
Osmosis
Osmosis is the diffusion of water across a selectively permeable membrane
How does water diffuses across a membrane
Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides
Tonicity is the ability of a surrounding solution to do what?
to cause a cell to gain or lose water
Isotonic solution
Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
Solute concentration is greater than that inside the cell; cell loses water
Hypertonic solution
Hypotonic solution
Solute concentration is less than that inside the cell; cell gains water
the control of solute concentrations
Osmoregulation
What is Turgid ( normal?)
Hypotonic ( Lysed)
What is Flaccid?
Isotonic (Normal)
What is Plasmolyzed?
Hypertonic ( Shriveled)
help maintain water balance
Cell walls
A plant cell in a hypotonic solution swells until what?
until the wall opposes uptake; the cell is now turgid (firm)
If a plant cell and its surroundings are isotonic, then what happens?
there is no net movement of water into the cell;
the cell becomes flaccid (limp)
In a hypertonic environment, plant cells do what?
lose water; The membrane pulls away from the cell wall causing the plant to wilt, a usually lethal effect called plasmolysis
Which of the following statements about osmosis is correct?

a) If a cell is placed in an isotonic solution, more water will enter the cell than leaves the cell.

b) Osmotic movement of water into a cell would likely occur
if the cell accumulates water from its environment.

c) The presence of aquaporins (proteins that form water
channels in the membrane) should speed up the process
of osmosis.

d) If a solution outside the cell is hypertonic compared to the cytoplasm, water will move into the cell by osmosis.

e) Osmosis is the diffusion of water from a region of lower water concentration to a region of higher water concentration.
The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis.
In facilitated diffusion, transport proteins do what?
speed the passive movement of molecules across the plasma membrane
Transport proteins include what types of proteins?
include channel proteins and carrier proteins
Channel proteins provide corridors that allow what?
a specific molecule or ion to cross the membrane
Aquaporins
facilitate the diffusion of water
Ion channels do what?
facilitate the diffusion of ions
Some ion channels, called ______ open or close in response to a stimulus
gated channels
draw a channel protein
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draw a carrier protein
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Concept 7.4: Active transport uses energy to move solutes against their gradients
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Facilitated diffusion is still passive and the transport requires no energy
Active transport moves substances against their concentration gradients and requires energy, usually in the form of ATP
Active transport is performed by specific proteins embedded in the membranes
Active transport allows cells to maintain concentration gradients that differ from their surroundings
Example sodium-potassium pump (Na+/K+ ATPase) is
Facilitated diffusion is still passive and the transport requires no energy
Active transport moves substances against their concentration gradients and requires energy, usually in the form of ATP
Active transport is performed by specific proteins embedded in the membranes
Active transport allows cells to maintain concentration gradients that differ from their surroundings
Example sodium-potassium pump (Na+/K+ ATPase) is
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