membrane

Prokaryotic Gene Regulation

Lactose permease is a membrane-bound protein which allows lactose to pass

through the bacterial membrane. This is shown below:

E. coli

Immediately outside the plasma membrane is a cell wall about 10

Lipids

The lipids we'll be studying are phospholipids, the primary components of cellular membranes. Phospholipids are amphipathic; that is, they are both hydrophilic and hydrophobic. The "head" of a lipid moleule is negatively charged phosphate group and the two

A phospholipid bilayer is approximately 5 nm thick. This membrane is semipermeable,

membrane.

Control of the Cell Cycle

nuclear membrane, so that the nuclear contents are no longer separated

membrane in the daughter cells. A detailed discussion of the multiple

chromosomal condensation, breakdown of the nuclear membrane, alignment

reformation of two nuclear membranes around the two sets of recently

Membrane Proteins Introduction

Membrane Proteins Introduction

Membrane Proteins Introduction

Membranes are of crucial importance to life, because a cell must separate

metabolism. How does the E. coli know? It depends on its membrane

The cell shields itself behind its membrane, which is relatively

Therefore, cells have two major types of membrane proteins :

it. They are called intrinsic membrane proteins; yet others are adsorbed to

the surface of the lipid bilayer and are termed extrinsic membrane proteins

Membrane Transport Mechanisms

Membrane Transport Mechanisms

Membrane Transport Mechanisms

transmembrane domains is structured so that these domains are arrayed

in the plane of the membrane in a circle, thereby forming a cylinder, or,

staves of the barrel being one of the transmembrane domains. The center of

the barrel could constitute a hole in the plasma membrane that is isolated

from the lipid bilayer by an array of transmembrane domains around it.

hydrophilic side chains from the membrane-spanning chains surrounding

In practice, given the structure of known membrane proteins , these

through the plasma membrane, almost always simple ions like hydrogen,

called an ion channel. Alternatively, the transmembrane protein may

of the plasma membrane to the other, in which case it will be an ion pump.

Given the importance of membrane transport,

membrane. Diffusion is always down a concentration gradient. This limits

Facilitated diffusion utilizes membrane protein channels to allow charged

molecules (which otherwise could not diffuse across the cell membrane) to

from one side of the membrane to the other, but active transport is the only

ATP hydrolysis) at the membrane protein itself to cause a conformational

across the cell membrane, and then utilizing that gradient to transport a

across the cell membrane by using energy to pump protons out of the cell.

transmembrane protein. The lactose permease uses the energy of the proton

This coupled transport in the same direction across the cell membrane is

first step, generating a strong Na+ gradient across the cell membrane. Then

Receptors

Receptors

transmembrane proteins termed receptors that function to acquire

the cell through the plasma membrane . In effect, cell surface receptors act

transmembrane receptors, but we will focus only on a subset of them,

Transmembrane signal transduction

plasma membrane into the cell? Such transmission of information by a

terminal ectodomain, followed by a single membrane-spanning

transmembrane domain. At their C-termini in the cytoplasm, they have a

(physically transported) into the cell in order for this transmembrane

signalling to occur. All active transmembrane signal transduction occurs

the plasma membrane via their hydrophobic transmembrane domains, are

to diffuse laterally through the plane of the plasma membrane.

nearby in the plasma membrane. Often the GF ligand itself has two

Chemical Energetics

potentials in the membrane of nerve cells and fibers.)

becomes clearer when we consider active transport across a membrane,

Membrane transport proteins

Culturing cells in vitro

across the plasma membrane into the cell interior, informing the cell

Examples of Viral Replication Pathways

In lysis, the host cell's membrane is damaged and the cytoplasm is able

1.1 Membrane Structure and Composition

1.1 Membrane Structure and Composition

1.1 Membrane Structure and Composition

Biological membranes are bilipid layers . In a real cell the membrane

within the membrane. This leaves the charged phosphate groups facing out

into the hydrophilic environment. The membrane is approximately 5 nm thick.

to pass freely (diffuse) through the membrane. The lipid bilayer is virtually

through the membrane due so at differing rates depending upon their ability

to enter the hydrophobic interior of the membrane bilayer.

rapidly throughout the two dimensional surface of the membrane. This is known

as the fluid mosaic model of biological membranes (mosaic because it includes

The phospholipids can move to the opposite side of a bacterial cell membrane

times the size of the phospholipid. Membrane proteins diffuse throughout the

membrane in the same fashion, though at a slower pace because of their

"flip-flop" through the membrane to the opposite side, but this is uncommon.

the membrane, and for the hydrophobic tails to be exposed to the aqueous

There is a good diagram of the fluid mosaic model of a biological membrane in

The

Notice that there are molecules of cholesterol embedded in the membrane.

biological membranes. Cholesterol breaks up the Van der Waals interactions

membrane more fluid. Therefore, one way for a cell to control the fluidity

of its membrane is by regulating its level of cholesterol in the cell

membrane.

Another way for the cell to control the fluidity of its membrane is to

Membrane Proteins

Membrane Proteins

Membrane Proteins

Transmembrane Proteins

Membrane proteins are either extrinsic or intrinsic. Extrinsic membrane

proteins are entirely outside of the membrane, but are bound to it by weak

Intrinsic membrane proteins, the class we are mainly interested in, are

embedded in the membrane. Many of them extend from one side of the membrane

to the other and are referred to as transmembrane proteins.

membranes. In fact, more than half the energy that are bodies consume

else but transport ions across plasma membranes of nerve cells. How can

ions be transported across membranes that are effectively impermeable to

plasma membranes and extend from one side of the membrane through to

the other. Such transmembrane proteins can function to effect ion

hydrophobic inner layers of the plasma membrane?

If we examine the detailed structures of many transmembrane

plasma membrane, and a hydrophilic domain at the C-terminus protrudes

into the cytoplasm. The transmembrane domain, because it is made of

hydrophobic inner layers of the plasma membrane. Because these

transmembrane domains anchor many proteins in the lipid bilayer,these

by the need to solubilize proteins that are embedded in lipid membranes

For reasons that are not well understood, many transmembrane

membrane. A typical mammalian cell may have several hundred distinct

types of glycoprotein studding its plasma membrane. Each of these

Multi-membrane-spanning proteins

depicting membrane proteins having single transmembrane domains

involves certain membrane proteins that have multiple transmembrane

when embedded in the plasma membrane actually weaves back and forth

between opposite sides of the plasma membrane. Some think such proteins

membrane proteins. A commonly used type of structure seen in many

hundreds of serpentine transmembrane proteins involves 7 hydrophobic

domains inserted into the plasma membrane separated by hydrophilic

G Protein Receptors

G Protein Receptors

The body uses 7 membrane-spanning serpentine receptors for an astounding

these mating factors are once again 7 membrane-spanning serpentine

adrenergic receptor is a 7 membrane-spanning, serpentine receptor

embedded in the plasma membranes of these cells. As is the case with the

membrane. Instead, single receptor molecules will change their 3

Characteristics of Prokaryotes and Eukaryotes

They are both membrane bound.

and eukaryotes is that eukaryotes have a nucleus and membrane-bound

Structure and Function of Organelles

membrane structure allows the energy generation to proceed, but we

RNAs intricately bound together. Ribosomes have no membrane.

eukaryotes. Mitochondria have two membranes, an inner and an outer,

infoldings, of the inner membrane, This serves to increase the surface

area of membrane on which membrane-bound reactions can take place.

The existence of this double membrane has led many

other photosynthesizing organisms. They also have a double membrane.

membrane bound sacs called vesicles. These sacs can be targetted at

membrane-bound lysosome .

membrane, the cytoplasm, and the cytoskeleton. The cell membrane is so

Membrane Transport Problem Answers

Membrane Transport Problem Answers

Membrane Transport Problem Answers

which two molecules/ions move together across the membrane is called

the plasma membrane in about 15 minutes. Yet no matter how many times

a) Explain.Transmembrane proteins don't generally `flip-flop'

across the cell membrane. This is because of the thermodynamics

regulating the different regions of the protein-membrane interaction.

membrane.

the plasma membrane, would you expect to see any changes in the movement

of esgfun throughout the membrane?Yes, you would expect esgfun to move

throughout the membrane more slowly, because cholesterol increases the

fluidity of the membrane - without it the membrane is less fluid, and

Neurons and other excitable cells have membranes that are

polarized: there is a voltage difference across the plasma membrane such

channels in the plasma membrane. The Na+/K+ pump moves 3 Na+ out of the

are open all the time, and determine the permeability of the membrane to

each ion. As ions diffuse across the membrane, (Na+ in and K+ out) a

membrane is most permeable.) Normally, resting membranes are much more

potential, when Na+ channels are open, the membrane is much much more

permeable to Na+ than to K+. At that point, Na+ determines the membrane

Membrane potentials can be measured with a voltmeter and two

Based on your knowledge of transport across cell membranes, propose

Cell Biology Chapter

Introduction to Membranes

Membrane structure and composition

diagramFluid Mosaic Model

Membrane proteins structures

Domains

Glycoproteins

Multi-membrane-spanning proteins

Receptors

Growth Factor Receptors

Transmembrane signal transduction

G Protein Receptors

epinephrine

Cytoplasmic signal transduction

Signalling cascades

Membrane transport mechanisms

Diffusion

Facilitated diffusion

Active transport

The Glucose-Na+ Transport System

module not yet titled

membrane structure and composition

membrane-associated proteins and carbohydrates

other roles and activities of membranes

7.012 Cloning Project: Agricultural Biotechnology

* translated ORF1 has several possible membrane-spanning domains

module not yet titled

roles of membranes in eukaryotic cells

Lwoff's Pathways - Viral Replication

In lysis, the host cell's membrane is damaged and the cytoplasm is able

3.5 Solving Enzyme Kinetics Problems

in the membrane. The characteristics of the two transport proteins are as