Exam 2 Plasma membrane JHD

Plasma membrane

_______ is the boundary that separates the living cell from its surroundings

_______ exhibits selective permeability, allowing some substances to cross it more easily than others

Phospholipids

______ are the most abundant lipid in the plasma membrane

______ are amphipathic molecules, containing hydrophobic and hydrophilic regions

______ in the plasma membrane can move within the bilayer

Fluid mosaic model

_____ states that a membrane is a fluid structure with a "mosaic" of various proteins embedded in it

Hugh Davson and James Danielli

_____ proposed a sandwich model in which the phospholipid bilayer lies between two layers of globular proteins

Later studies found problems with this model, particularly the placement of membrane proteins, which have hydrophilic and hydrophobic regions

J. Singer and G. Nicolson

_____ proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water

Freeze-fracture

_____ studies of the plasma membrane supported the fluid mosaic model

_____ is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer

Unsaturated Fatty Acids; Saturated fatty acids

Membranes rich in _____ are more fluid that those rich in ______

Cholesterol

_____ has different effects on membrane fluidity at different temperatures

At warm temperatures (such as 37°C), _______ restrains movement of phospholipids

At cool temperatures, _______ maintains fluidity by preventing tight packing

Membrane

A ________ is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

Proteins determine most of the ______ specific functions

Peripheral proteins

______ are bound to the surface of the membrane

Integral proteins

_____ penetrate the hydrophobic core

The hydrophobic regions of an ______ consist of one or more stretches of nonpolar amino acids, often coiled into alpha helices

Transmembrane protein

Integral proteins that span the membrane are called _____

1. Transport

2. Enzymatic activity

3. Signal transduction

4. Cell-cell recognition

5. Intercellular joining

6. Attachment to the cytoskeleton and extracellular matrix (ECM)

Six major functions of membrane proteins

Cells

_____ recognize each other by binding to surface molecules, often carbohydrates, on the plasma membrane

glycolipids; glycoproteins

Membrane carbohydrates may be covalently bonded to lipids (forming ______ ) or more commonly to proteins (forming ______)

Hydrophobic (nonpolar) ; polar molecuels

_______ molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly

_______ such as sugars, do not cross the membrane easily

Transport Proteins

_____ allow passage of hydrophilic substances across the membrane

______ called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel

_____ is specific for the substance it moves

Channel proteins (AQUAPORIN)

_____ facilitate the passage of water

Transport proteins (CARRIER PROTEINS)

_____ bind to molecules and change shape to shuttle them across the membrane

Diffusion

_____ is the tendency for molecules to spread out evenly into the available space

Although each molecule moves randomly, ______ of a population of molecules may exhibit a net movement in one direction

The ______ of a substance across a biological membrane is passive transport because it requires no energy from the cell to make it happen

Dynamic equilibrium

At _____ , as many molecules cross one way as cross in the other direction

concentration gradient

Substances diffuse down their ______ , the difference in concentration of a substance from one area to another

No work must be done to move substances down the ______

Osmosis

_____ is the diffusion of water across a selectively permeable membrane

lower solute concentration; higher solute concentration

Water diffuses across a membrane from the region of _____ to the region of ______

Tonicity

_____ is the ability of a solution 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

Hypertonic

_____ Solute concentration is greater than that inside the cell; cell loses water

Hypotonic

______ Solute concentration is less than that inside the cell; cell gains water

cell walls

______ help maintain water balance

hypotonic solution; turgid

A plant cell in a _______ swells until the wall opposes uptake; the cell is now ______

Isotonic; flaccid (limp)

If a plant cell and its surroundings are _____, there is no net movement of water into the cell; the cell becomes ______ , and the plant may wilt

hypertonic ; plasmolysis

In a ______ environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called _____

Facilitated diffusion

In ______ , transport proteins speed the passive movement of molecules across the plasma membrane

channel proteins

______ provide corridors that allow a specific molecule or ion to cross the membrane

1. Aquaporins, for facilitated diffusion of water

2. Ion channels that open or close in response to a stimulus (gated channels)

3.Carrier proteins undergo a subtle change in shape that translocates the solute-binding site across the membrane

Channel proteins include:

Active transport

_____ uses energy to move solutes against their gradients

_____ moves substances against their concentration gradient

_____ requires energy, usually in the form of ATP

_____ is performed by specific proteins embedded in the membranes

_____ allows cells to maintain concentration gradients that differ from their surroundings

sodium-potassium pump is one type of _____ system

Voltage

Membrane potential is the _____ difference across a membrane

_____ is created by differences in the distribution of positive and negative ions

Ion pumps

____ maintain membrane potential

Electrochemical gradient: chemical force; electrical force

Two combined forces, collectively called the ________ , drive the diffusion of ions across a membrane: _______ and _____

chemical force; electrical force

A ______ is the the ion's concentration gradient ii. An ______ is the effect of the membrane potential on the ion's movement

electrogenic pump

1. An _____ is a transport protein that generates voltage across a membrane

2. The sodium-potassium pump is the major _____ of animal cells

3. The main _____ of plants, fungi, and bacteria is a proton pump

Cotransport

_____ occurs when active transport of a solute indirectly drives transport of another solute

Bulk transport

_____ across the plasma membrane occurs by exocytosis and endocytosis

____ requires energy

lipid bilayer; transport proteins

Small molecules and water enter or leave the cell through the _____ or by ______

Vesicles

Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via ______

Exocytosis

____ transport vesicles migrate to the membrane, fuse with it, and release their contents

Many secretory cells use ______ to export their products

Endocytosis

In _______ the cell takes in macromolecules by forming vesicles from the plasma membrane

_____ is a reversal of exocytosis, involving different proteins

1. phagocytosis; 2. pinocytosis 3. Receptor-mediated endocytosis

Three types of endocytosis:

1. _____1_____ cell eating

- In _____1_____ a cell engulfs a particle in a vacuole

- The vacuole fuses with a lysosome to digest the particle

2. _____2_____ cell drinking

- In _____2_____ molecules are taken up when extracellular fluid is "gulped" into tiny vesicles

3. _____3_____

- In _____3_____ , binding of ligands to receptors triggers vesicle formation