Membrane Structure, Synthesis, and Transport

Plasma Membrane

The biological membrane that separates the internal contents of a cell from its external environment

Biological Membrane

Any membrane made by living cells, Can be the plasma membrane or an internal membrane that surrounds an organelle

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

Important biological functions of biological membranes (8)

Fluid-Mosaic Model

The accepted model of the biological membrane, Its basic framework is the semifluid phospholipid bilayer with a mosaic of proteins, Carbohydrates may be attached to lipids or proteins

Semifluid

A property of biological membranes in which movement of membrane components occurs only in two dimensions

Leaflet

Half of a phospholipid bilayer

Integral and Non-Integral

Types of membrane proteins (2)

Transmembrane Protein

A type of integral protein that has one or more regions physically embedded in the hydrophobic interior of a membrane’s phospholipid bilayer

Lipid-Anchored Protein

A type of integral protein that is attached to a membrane via a lipid molecule

Peripheral Membrane Protein

A type of non-integral protein that is noncovalently bound to a region of an integral membrane protein that projects out from the protein or noncovalently bound to the polar head group of a phospholipid

Liquid Rafts

A set of lipids that tend to travel together and are embedded with associated proteins and cholesterol

Length of phospholipid tail, Extent of fatty acid saturation, Presence of cholesterol

Factors affecting membrane fluidity (3)

More fluid

A shorter phospholipid tail means less interaction which means the membrane is…

Less fluid

A longer phospholipid tail means more interaction which means…

More fluid

Unsaturated fatty acids mean a more kinked structure which means…

Less fluid

Saturated fatty acids mean a more linear structure which means…

Increase; Decrease

When the phospholipid bilayer does not have cholesterol, high temps _______ fluidity and low temps _____ fluidity

More; Less

When the phospholipid bilayer has cholesterol, lower temperatures mean the bilayer is _____ fluid, and higher temperatures mean the bilayer is _____ fluid.

Endoplasmic Reticulum (ER)

An organelle that consists of labyrinthine membrane structure, Synthesis occurs here

Lateral Diffusion

How lipids are transferred at the nuclear envelope

Vesicle Transport

How lipids are transferred in the golgi, lysosomes, vacuole, and plasma membrane

Lipid Exchange Protein

How lipids are transferred in any membrane in the cell

Glycosylation

The attachment of a carbohydrate to a lipid or protein

Glycolipid

The attachment of a carbohydrate to a lipid

Glycoprotein

The attachment of a carbohydrate to a protein

Passive Transport

Type of membrane transport that does not require ATP and moves down the concentration gradient

Active Transport

Type of membrane transport that requires ATP and moves up the concentration gradient

Primary, Secondary, Bulk

Types of active transport (3)

Diffusion, Osmosis

Types of passive transport (2)

Simple, Facilitated

Types of diffusion (2)

Diffusion

Type of transport that does not not require energy and transports a molecule down the concentration gradient from areas of high concentration to low concentration

Osmosis

The diffusion of water due to concentration differences

Size, Polarity, Charge, Concentration

Characteristics that affect a molecule’s efficiency in passing the phospholipid bilayer (4)

Small; Large

_____ solutes cross barriers faster than _____ ones. (size)

Nonpolar; Polar

_____ solutes cross barriers faster than _____ ones. (polarity)

Noncharged; Charged

_____ solutes cross barriers faster than _____ ones. (charge)

Higher

The rate of movement of a solute will be higher when its concentration is…

Isotonic

Cell neither gains or loses water

Hypertonic

Cell gains water (In the context of diffusion)

Hypotonic

Cell loses water (In the context of diffusion)

Crenation

When an animal cell is placed in a hypertonic solution, water will exit the cell, causing the cell to shrink

Osmotic Lysis

When an animal cell is placed in a hypotonic solution, water will enter the cell, causing the cell to rupture

Plasmolysis

When a plant cell is placed in a hypertonic solution, water will exit the cell, causing the plasma membrane to pull away from the cell wall and shrink

Turgor Pressure

When a plant cell is placed in a hypotonic solution, water will enter the cell, causing the plasma membrane to exert pressure against the cell wall; The cell expands, but does not rupture

Channels

Transport proteins that can be gated to allow controlled entry into the cell

Ligand

A small molecule recognized and bound by a specific protein, Usually controls the gates of channel proteins

Aquaporin

Specialized membrane channel that allows the facilitated diffusion of water through the plasma membrane

Transporters/Carrier Proteins

Membrane proteins that allow entry of solutes upon a conformational shift of the protein

Uniporters, Symporters, Antiporter

Types of carrier proteins (3)

Uniporters

Carrier proteins that transport one molecule across the cell membrane at a time

Symporters

Carrier proteins that transport two or more molecules across the cell membrane in the same direction

Antiporter

Carrier proteins that transport two or more molecules across the cell membrane in opposite directions

Primary Active Transport

Transport that uses a pump to transport proteins using energy

Secondary Active Transport

Transport that uses a symporter to transport one molecule down its concentration gradient and one molecule against its concentration gradient

Bulk Transport

The form of active transport utilized by cells to carry out exocytosis and endocytosis

Endocytosis

The process in which the plasma membrane brings substances into the cell

Exocytosis

The process in which the plasma membranes expels substances into the cell

Vesicles, Vacuoles

Organelles used by cells to perform endo/exocytosis (2)

Receptor method, Pinocytosis, Phagocytosis

Types of endocytosis (3)