Cell Membranes

Do Polar molecules surround themselves with nonpolar molecules?

No, even though polar molecules have positive and negative charged ends, they surround themsleves with other polar molecules

Nonpolar surround themselves with other non polar

Why don’t water and lipids mix?

Water is polar, and lipids are nonpolar

Phospholipids are amphipathic, what does this mean?

They have a charged polar region on one end and two long fatty acid nonpolar chains

What happens when phospholipids spontaneously aggregate?

They form a membrane

Are nonpolar fatty acid chains hydrophobic or hydrophilic? Where are they located?

Hydrophobic, in the middle of phospholipid

Are the polar regions hydrophobic or hydrophilic? Where are they located?

Hydrophilic, oriented toward surface (Close to polar water molecules)

What is the general structure of the membrane called

Fluid mosaic model

since there are no chemical bonds between the fatty acid chains, there can be a lot of lateral movement within the membrane, This IS KNOWN AS?

membrane fluidity

What are the Cell Membrane Functions

1. Selective barrier (Building) regulating the passage of substances in and out cell

2. Communicate between cells (receptionist); detect chemical signals from other cells

3. Connect adjacent cells (Bridge connecting parts of building) by membrane junctions

4. Anchor cells (Foundation of building) to the extracellular matrix

5. functions carried out by cell membrane proteins (Id scanning system)

SBCCACMP

What are the two main types of cell membrane proteins?

Integral (amphipathic)

Peripheral (Polar)

Integral Membrane proteins?

Feature:Amphipathic

Location: embedded within the lipid bilayer

Interaction: Strong hydrophobic interaction with the membrane lipids

Function: Transport molecules, cell communication (receptors)

If integral membrane proteins span the entire membrane, what are they then referred as?

Transmembrane proteins (ion channels and transporters)

Peripheral Membrane proteins

feature: polar proteins; don’t interact with phospholipid tails

Located: attached to inner or outer membrane surface

Interaction: Weak, polar interactions with membrane surfaces or integral proteins; easily detached

Function: cell signaling (cytoplasmic enzymes), anchoring

Since the membrane of____are made up of phospholipids, substances that dissolve in lipids diffuse rapidly across the cell membrane

Nonpolar substances: not charged

oxygen, carbon dioxide, fatty acids, steroid hormones, anesthetics

Since these are charged, they can’t diffuse across the lipid membrane. require small, selective, special channels. Some can and some can’t get through

IONS

Sodium channels, potassium channels, calcium channels

If we start with a solution in which the solute is more conentrated ine one region than other, the solute will redistribute until?

the concentration is the same throughout

What is responsible for Simple Diffusion?

Brownian Motion (Random thermal motion)

Molecules collide and bounce off eachother in different directions

What occurs when a high concentrated compartment is mixed with something simple

There is a flux from high conc→something simple

What happens when molecules are in diffusion equilibrium?

They collide with eachother moving equally around both compartments

Fluxes happen between both compartments but what is the difference between thes etwo fluxes?

The NET FLUX

What is the net flux in a diffusion equilibrium system?

0

The net Flux region is always from a region of____concentration to a region of ______ concentration

Higher; Lower

Do substances move uphill or downhill by diffusion?

Downhill

What is diffusion driven by?

Concentration gradient

The larger the concentration gradient the larger the____

Net flux

Does the body need to supply energy for diffusion?

NO

What factors influence the NET FLUX

1. Temperature

2. Molecular MAss

3. Surface Area

4. Viscosity of the Medium

Temperature

higher temp= greter molecular movement speed= greater net flux

Molecular mass

Larger molecular mass=lower speed of molecules= lower net flux

Surface area

Larger surface area= larger net flux

Viscosity of the Medium

Thinner medium=larger net flux

Ex. molecules diffuse more rapidly in air than water

Why do humans and any large organism have a circulatory system

Diffusion of oxygen over small distances happens faster than over large distances

Can ions diffuse across the lipid membrane since they are charged?

No

what do cells have for ions that can either be opened or closed

Membrane channels

What is the mechanism that can modify the conformation of transmembrane proteins to result in the opening or closing of a channel

GATING

what are the 3 ways in which ion channels can be gated?

Ligand

Voltage

Mechanically

Ligand gated channel

opens or closes when molecules bind to them

Voltage gated channels

Open or close when the membrane potential changes

Mechanically gated channels

Open or close when the membrane is stretched

Opposite charges____each other and like charges_____ each other

attract, repel

What is ion movement through membranes governed by

Electrochemical gradient

What kind of flux is the movement of molecules of diffsuion across membranes?

PASSIVE

No energy required

How can small nonpolar molecules diffuse?

Down their concentration gradient

By diffusion across lipid membrane

How do small ions diffuse

Down their electrochemical gradient

By diffusion through open channels

Can ions move freely through open channels if they have to go “uphill against their electrochemical gradient?

NO

large, fat insoluble molecules like proteins, amino acids and glucose can’t get in or out of the cell by these means

What two mechanisms do cells use to. accomplish the fact that ions can’t move freely through open channels?

1. Mediated transport

2. Vesicular transport

What is the role of membrane transport systems?

They transport molecules or ions inti or out of the cell

A type of transporter used by both mediated and vesicular transport

Carrier

All membrane transporter are_____proteins

transmembrane

How do mediated transporters work?

1. expose binding site to one side of membrane so solute can bind to it

2. Change shape and release solute on other side of membrane

What is the difference between mediated transport and simple diffusion?

Mediated transport requires binding to a transporter and simple diffusion occurs across membrane lipids or through open channels

What are the rules that Transporters and Protein-Ligand binding follow

1. Specificity

2. conformational changes in shape to transport ligand

3. Limited in number on membrane; displays saturation when all binding sites occupied

What are modifiers of mediated transport?

1. The concentration of ligand on either side of membrane

2. rate of transport (Protein kinetics)

3. Number of transporters

what are the two types of mediated transport?

Facilitated diffusion

Active Transport

Active Transport is___ and Requires____

Uphill (moves substances against electrochemical gradient), cellular energy

Facilitated diffusion is___and doesn’t require____

Downhill(along concentration gradient); cellular energy

What makes facilitated diffusion different from diffusion through membranes or channels?

It uses a transporter to move a solute(carrier)

has chemical specifcity

displays saturation

What is the main reason why we need a carrier for substances to go down their electrochemical gradient?

Size

glucose is a large, polar molecules, too large to diffuse through channels

What are the characteristics of facilitated diffusion?

Doesn’t require cellular energy

Uses transmembrane protein as carrier

HAs chemical specificity

Displays saturation when all available carriers used

Glucose transporters numbers in muscle and adipose tissue are regulated by what?

The hormone insulin

What happens when insulin is present ad what is the result?

The number of glucose transporters in the membrane is increased. The flux of glucose into cell increases and glucose levels in blood decrease

What are similarities between diffusion and facilitated diffusion?

THey don’t require cellular energy

MOlcules moved down electrochemical gradient

What are the 2 reasons as to why NA+ tends to leak into the cell

1. Concentration gradient

2. Electrical gradient

Active transports creates electrochemical Gradient? what happens as a result

Na+ must be pumped out all the time and moved against electrochemical gradient

Requires energy that comes from ATP which cmes from metabolism

The hydrolysis of ATP by the carrier protein provides____for transport

energy

The transporter for ATP Hydrolysis is an_____

ATPase enzyme

In addition to keepig its inside Na+ concentration low, Every cell in the body keeps its____conenctrations high at all times

K+

needs to be pumped in at all times

The same transporter pumps___out and pumps____in

Na+; K+

The hydrolysis of ATP by one carrier creates an ion gradient that drives a ____ carrier

Secondary

Since there is high extracellular Na+ and low Intracellular Na+, Na+ will tend to flow in, up or down its chemical gradient? What is stored in that gradient?

DOWN

POTENTIAL ENERGY: used to drive something else

What is the ion that provides energy in Active transport?

Na+; moves downhill its electrochemical graidentinto cell

Other solute is moved uphill against concentration gradient

What is it called when both molecules are moved in the same direction across the membrane?

Co-transport

Ex. Na+/Glucose Transporter moves glucose into the cell against its concentration graident by using energy from NA+ ions moving down concentration gradient

What is it called when molecules are moved in opposite directions across the membrane?

Counter-transport(Antiport)

Na+/Ca2+ Exchanger moves 3 Na+ ions into the cell to push one Ca2+ ion out of the cell against concentration gradient

Differences between Primary and Secondary transport?

Primary: energy provided by transporter, ATPAse enzyme

Secondary: uses stored energy of an electrochemical gradient to move ion and solute across membrane

Similarities between Primary and Secondary Active Transport?

Molecules moved against electrochemical gradient

Chemical specificity

display saturation

Use TRansmembrane proteins as carrier

require energy

What is it called when the plasma membrane folds into the cell and makes a small pocket that encloses material and pinches off forming a vesicle

Endocytosis

What is it called when vesicles in the cytoplasm fuse with plasma membrane and release contents outside of cell

Exocytosis