Campbell Biology Chapter 7 Membranes
Transport Proteins
(channel or carrier) are often needed to allow hydrophilic molecules to cross the plasma membrane; specific to substances moved
Hydrophobic
(nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly
Active transport
-moves substances against their concentration gradients -requires energy, usually in the form of ATP -performed by specific proteins embedded in the membranes -allows cells to maintain concentration gradients that differ from their surroundings
Passive transport
: diffusion of a substance across a biological membrane; no energy is expended by the cell to make it happen
membrane
A ___________ is a collage of different proteins, often grouped together, embedded in the fluid matrix of the lipid bilayer; not randomly placed
The solution is hypertonic
A cell is placed into a solution and the cell shrinks. What is true regarding the solution?
selective permeability
A cell must exchange materials with its surroundings, a process controlled by the plasma membrane allowing some substances to cross it more easily than others, regulating cells molecular traffic
Turgid
A plant cell, in a hypotonic solution, swells until the wall opposes uptake;Aka Firm
high, low
Diffusion of molecules from _________ concentration to _________ concentration gradient until they are about the same; "down the concentration gradient"
Cell Walls
Help maintain water balance
Proteins in the membrane contribute to the mosaic quality of the membrane while the lateral and rotational movements of phospholipids contribute to its fluidity.
How does the "fluid mosaic model" describe the structure of the plasma membrane?
Flaccid
If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; Aka limp
Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall
If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells?
Facilitated diffusion
In ___________ __________, transport proteins (including channel and carrier proteins) speed the passive movement of molecules across the plasma membrane
Plasmolysis
In a hypertonic environment, plant cells lose water and the membrane pulls away from the cell wall causing the plant to wilt, a usually lethal effect called
channel; carrier
In facilitated diffusion, __________ proteins provide openings in the plasma membrane for substances to flow through without changing structure, and __________ proteins allow passage of substances through the plasma membrane after undergoing a subtle change in shape.
water, low, high
In osmosis _________ diffuses across a membrane from the region of ________ solute concentration to the region of _______ solute concentration until the solute concentration is equal on both sides
Vesicles
Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via
Glycolipids
Membrane carbohydrates covalently bonded to lipids
Glycoproteins
Membrane carbohydrates may be covalently bonded to proteins, (more common)
3 Membrane proteins
Peripheral proteins, Integral proteins, and Transmembrane proteins
amphipathic
Phospholipids are_________ molecules, containing hydrophobic and hydrophilic regions
The cell will decrease in size as water flows out of it
Red blood cells contain approximately a 2% concentration of solutes. A red blood cell is placed into a solution that contains a 4% concentration of solutes to which the cell is not permeable. What will happen to the red blood cell? The cell will decrease in size as
Isotonic solution
Solute concentration is the same inside and outside the cell; no net water movement across the plasma membrane
Hypertonic solution
Solute concentration outside the cell, is GREATER than inside the cell; cell loses water
Hypotonic solution
Solute concentration outside the cell, is LESS than inside the cell; cell gains water
the plasma membrane allows some substances to flow through it more easily than others
The plasma membrane exhibits selective permeability. This means that __________.
Transports sodium ions out of the cell and transports potassium ions into the cell
The sodium-potassium pump __________.
6 functions of membrane proteins
Transport Enzymatic activity Signal transduction Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and extracellular matrix (ECM)
Plasma membrane
What cell structure exhibits selective permeability between a cell and its external environment?
Active transport requires energy from ATP, and facilitated diffusion does not.
Which of the following is a correct difference between active transport and facilitated diffusion?
These proteins exhibit both hydrophilic and hydrophobic properties.
Which of the following is correct regarding integral proteins?
These proteins are found only on the surface of the plasma membrane.
Which of the following is correct regarding peripheral proteins?
Phospholipids
Which of the following molecules are most abundant in the plasma membrane?
Carbon dioxide
Which of the following molecules is most likely to passively diffuse across the plasma membrane?
A cell placed in a hypotonic solution
Which of the following plant cells would exhibit the most turgor pressure?
It is a passive process.
Which of the following statements about diffusion is true?
Passive transport permits the solute to move in either direction, but the net movement of the population of solute molecules occurs down the concentration gradient of the molecule.
Which of the following statements about passive transport is correct?
Phospholipids form a selectively permeable structure
Which of the following statements about the role of phospholipids in the structure and function of biological membranes is correct?
Membrane carbohydrates function primarily in cell-cell recognition.
Which of the following statements concerning carbohydrates associated with the plasma membrane is correct?
a nonpolar molecule, such as a hydrocarbon
Which of the following substances would be most likely to pass through the plasma membrane without the help of a transport protein?
A large polar molecule
Which of the following would be least likely to diffuse through a plasma membrane without the help of a transport protein?
Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane.
Which of these statements describes some aspect of facilitated diffusion?
Because it moves solutes against their concentration gradients.
Why is energy required for active transport?
Bulk transport
_______ ________ across the plasma membrane occurs by exocytosis and endocytosis where small molecules and water enter or leave the cell through the lipid bilayer or via transport proteins (requires energy)
phospholipid bilayer
a ________ can exist as a stable boundary between two aqueous compartments
Transport proteins
allow passage of hydrophilic substances across the membrane specific for the substance it moves
Peripheral proteins
are bound to the surface of the membrane
Transmembrane proteins
are integral proteins that span the membrane
Phospholipids
are the most abundant lipid in the plasma membrane
Dynamic Equilibrium
as many molecules cross the membrane in one direction as in the other
Proteins
determine most of the membrane's specific functions
Osmosis
diffusion of water across a selectively permeable membrane
Plasma Membrane
is the boundary that separates the living cell from its surroundings;
Hydrophilic
molecules including ions and polar molecules do not cross the membrane easily
Integral proteins
penetrate the hydrophobic core
cell recognition
recognize each other by binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane
fluid mosaic model
states that a membrane is a fluid structure with a "mosaic" of various proteins embedded in
Tonicity
the ability of a surrounding solution to cause a cell to gain or lose water
Endocytosis
the cell takes in macromolecules by forming vesicles from the plasma membrane; is a reversal of exocytosis, involving different proteins
Diffusion
the tendency for molecules to spread out evenly into the available space
Exocytosis
transport vesicles migrate to the membrane, fuse with it, and release their contents OUTSIDE the cell; used by secretory cells to export their products
