Chapter 5 Membrane Structure, Synthesis, and Transport Lecture Outline

Flashcards about membrane structure, synthesis, and transport

Biological Membranes

Plasma membrane (encloses the cytoplasm) and internal membranes that surround organelles

Cystic Fibrosis

A genetic disease caused by a mutation in a gene called CFTR which functions in the transport of chloride ions across the plasma membrane.

Phospholipid Bilayer

The framework of the membrane. Phospholipids are amphipathic molecules with a hydrophobic region faces in and hydrophilic region faces out

Fluid-mosaic model

Membrane is considered a mosaic of lipid, protein, and carbohydrate molecules; lipids and proteins can move relative to each other within the membrane

Transmembrane proteins (integral membrane proteins)

Proteins that have one or more regions physically embedded in the phospholipid bilayer; most transmembrane segments are alpha-helices

Lipid-anchored proteins (integral membrane proteins)

Proteins where a lipid-molecule is covalently attached to an amino acid side chain within the protein; lipid tails inserted into the membrane

Peripheral membrane proteins

Proteins that are Noncovalently bound either to integral membrane proteins that project out from the membrane, or to polar head groups of phospholipids

Fluidity of Membranes

Individual molecules remain in close association but can readily move within a membrane; Membranes are semifluid.

Lipid rafts

Lipids associate strongly with each other to form a unit within the larger sea of lipids in the membrane; high concentration of cholesterol and a unique set of membrane proteins

Flippase

Requires ATP to transport lipids between leaflets

Glycosylation

Process of covalently attaching a carbohydrate to a protein or lipid

Glycolipid

Carbohydrate attached to lipid

Glycoprotein

Carbohydrate attached to protein

Membrane Transport

Movement of ions and molecules across biological membranes

Passive transport

Requires no input of energy – down or with gradient

Simple diffusion

Substance moves across a membrane by passing directly through the phospholipid bilayer

Facilitated diffusion

Diffusion of a solute through a membrane with the aid of a transport protein

Active transport

Moves a substance from an area of low concentration to one of high concentration with the aid of a membrane protein; requires input of energy

Transmembrane gradient

Concentration of a solute is higher on one side of a membrane than the other

Electrochemical gradient

Both an electrical gradient and chemical gradient

Isotonic

Equal solute concentrations on either side of the membrane

Hypertonic

Solute concentration is higher on one side of the membrane

Hypotonic

Solute concentration is lower on one side of the membrane

Osmosis

Water diffuses through a membrane from an area with more water to an area with less water

Crenation

Shrinkage of a cell in a hypertonic solution

Osmotic Lysis

Swelling and bursting of a cell in a hypotonic solution

Plasmolysis

Plasma membrane pulls away from the cell wall (when water exits the cell)

Transport proteins

Transmembrane proteins that provide a passageway for the movement of ions and hydrophilic molecules across membranes

Channels

Form an open passageway for the facilitated diffusion of ions or molecules across the membrane

Gated channels

Open to allow the diffusion of solutes and close to prohibit diffusion; controlled by the noncovalent binding of small molecules called ligands

Aquaporin

A channel that allows water to pass through the membrane

Transporters

Conformational change transports solute across membrane; Principal pathway for uptake of organic molecules, such as sugars, amino acids, and nucleotides

Uniporter

Single molecule or ion transporter

Symporter or cotransporter

Two or more ions or molecules transported in same direction

Antiporter

Two or more ions or molecules transported in opposite directions

Primary active transport

Uses a pump and Directly uses energy to transport solute

Secondary active transport

Uses a different gradient/ a pre-existing gradient to drive transport

Exocytosis

Material inside the cell packaged into vesicles and excreted into the extracellular medium

Endocytosis

Plasma membrane invaginates (folds inward) to form a vesicle that brings substances into the cell

Receptor-mediated endocytosis

Receptor in the plasma membrane is specific for a given cargo; a vesicle forms to transport cargo into the cell

Pinocytosis

Membrane vesicles form from the plasma membrane to allow cells to internalize the extracellular fluid

Phagocytosis

An enormous membrane vesicle forms to engulf a large particle such as a bacterium

Functions of Biological Membranes

Selective uptake and export of ions and molecules, Cell compartmentalization, Protein sorting, Anchoring of the cytoskeleton, Production of energy intermediates such as ATP and NADPH, Cell signaling, Cell and nuclear division, Adhesion of cells to each other and to the extracellular matrix