A closer look at cell membranes
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A closer look at cell membranes. Chapter 5 Transport and other things. Reminders…. Your grades are done as follow: Class participation – in order to do that you need to check bostononline and do the readings suggested. Notebook – class notes and your own personal study notes

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A closer look at cell membranes

A closer look at cell membranes

Chapter 5

Transport and

other things


Reminders

Reminders…

Your grades are done as follow:

Class participation – in order to do that you need to check bostononline and do the readings suggested.

Notebook – class notes and your own personal study notes

Weekly quizzes

Workshops and special writings.

Final term test

Life skills


Some things you need to know

Some things you need to know…

All the classes are taken from your book… 

The themes are the ones we set out to covered in the class development indicators .

From the beginning you were told to read the themes related to the lectures covered in class.

To read from the book the themes covered is part of your responsibility.

In Bostononline you find references to your book and reading to be done.

The video and presentations are done to facilitate your learning process.

Next Class Quiz and Checking your notebook


Membrane structure and function

Membrane structure and function

  • LECTURE OBJECTIVES

  • Describe the structure and dynamic nature of the cell membrane

  • Demonstrate how extracellular signals generate intracellular events.

  • Summarize the physical laws and biological processes which govern solute and solvent transport across the cell membrane.

  • Establish how electrochemical gradients are responsible for establishing a membrane potential.


Cell membrane

Cell Membrane

  • Cell membrane--the barrier between what goes on in the cytoplasm and the cell's immediate environment.

  • Overall Structure of Cell Membrane

    • 1. Most of the cell membrane is composed of phospholipids.

    • The polar ends are lipophobic (=dissolves in lipid with difficulty); the fatty acid tails are lipophilic (=dissolves in lipids easily).

      • a. Proteins imbedded in the lipid bilayer have many different functions.

        • 1) Receptors

        • 2) Ion channels and carrier molecules

        • 3) Docking proteins

        • 4) Cell-adhesion molecules (CAMs)

        • 5) Glycoproteins, glycolipids, etc.

      • b. Cholesterol


Phospholipids

Phospholipids


Ion channels

Ion channels


Membrane transport cell membrane is selectively permeable

MEMBRANE TRANSPORT Cell membrane is selectively permeable

  • A. SOLVENT FLOW.

  • 1. Osmosis is movement of water down its own concentration gradient.

    • a. Colligative properties

    • b. Tonicity (Animation)

  • 2. Filtration - occurs when there is greater hydrostatic pressure on one side of a membrane than on the other

    • a. Solvent drag

    • B. SOLUTE FLOW--Physical principles governing movement of solutes.

  • 1. Diffusion (Example: movement of oxygen from lung to blood)

    • a. Factors influencing diffusion rate across the cell membrane.

      • 1) Concentration gradient

      • 2) Membrane permeability (solute)

      • 3) Surface area 4) Molecular weight of solute

      • 5) Membrane thickness


Membrane transport cell membrane is selectively permeable1

MEMBRANE TRANSPORT Cell membrane is selectively permeable

  • b. Fick's Law of Diffusion

  • 1) Importance of diffusion coefficient (e.g. K+ > Na+) 2. Facilitated diffusion (e.g., glucose transport from blood into the cells)

    • a. Involves a carrier molecule, but solute moves down its conc. gradient

    • b. Characteristics of carrier-mediated transport

  • 3. Active Transport

    • a. Movement of solute against a concentration gradient

    • b. Carrier-mediated transport

    • c. Energy (ATP) is expended

  • 1) Primary Active Transport

  • a) Structural and biochemical characteristics of the ATPase pump

  • b) Example: Na+/K+ ATPase pump (Animation)

  • 2) Secondary Active Transport

    • a) Co-transport of Na+ and glucose (Animation: Co-transport)


  • Osmosis

    Osmosis


    Fitration

    Fitration


    Fick s law of diffusion

    Fick´s Law of Diffusion


    Diffusion

    Diffusion


    Transport

    Transport

    • Passive Transport Processes

      • a) Diffusion: definition - is the movement of ions or molecules from regions of higher concentration to regions of lower concentration. (Down a concentration gradient)


    Transport1

    Transport


    Facilitated diffusion

    Facilitated Diffusion

    • This is similar to simple diffusion in the sense that it is diffusion (across a membrane) from a high concentration to a lower concentration. However, this time the rte of diffusion is greatly accelerated by the action membrane proteins that act as carrier molecules and aid in diffusion.

    • These "carrier proteins" are known as "Permeases"


    Active transport

    Active Transport

    • These are cell membrane processes that require energy. These processes are also (as far as we can tell) mediated by membrane carrier molecule. (Proteins)

    • "Active Transport" "pumps" materials across the membrane against the concentration gradient. I.e. from low concentration to high concentration therefore requires energy.


    Active transport1

    Active Transport


    Vesicular transport

    VESICULAR TRANSPORT

    • Phagocytosisof bacteria, deadcells, etc.

    • Receptor-mediatedendocytosis and exocytosis


    Movement across membranes

    Movement Across Membranes

    • Simple diffusion: Movement of a solute from an area of high concentration to an area of low concentration.

    • Facilitative diffusion: Solute combines with a transporter protein in the membrane.


    Movement across membranes1

    Movement Across Membranes


    Movement across membranes2

    Movement Across Membranes

    • Osmosis

      • Movement of water across a selectively permeable membrane from an area of high water concentration to an area of lower water.

    • Osmotic pressure

      • The pressure needed to stop the movement of water across the membrane.


    Active transport2

    Active Transport

    • Requires energy & membrane proteins

    • Substance moved AGAINST its concentration gradient


    Vesicle mediated transport

    Vesicle Mediated Transport

    • Vesicles or vacuoles can fuse with the cell membrane


    Exocytosis

    Exocytosis

    • Exocytosis: Vesicles form inside the cell, move outward, fuse with the cell membrane, and expel their contents.


    Endocytosis three types

    Endocytosis: Three Types

    • Phagocytosis (cell eating): a solid substance brought into the cell

      • What organelle will fuse with the vesicle once inside the cell?

    • Pinocytosis (cell drinking): substance is a fluid

    • Receptor-Mediated: molecule attaches to a specific receptor on the cell surface before a vesicle forms around the molecule


    Receptor mediated endocytosis

    Receptor-Mediated Endocytosis

    • Note the receptors and path of the LDL

    • Correlate this slide with the information in your book.


    Plasma membrane review

    Plasma Membrane - review

    • Phospholipidbilayer

    • Peripheral proteins

    • Integral proteins

    • Transmembrane proteins

    • Sterols

    • Glycocalyx carbohydrates


    Plasma membrane review1

    Plasma Membrane - review

    • Selective permeability allows passage of some molecules

    • Simple diffusion

    • Facilitative diffusion

    • Osmosis

    • Active transport

    • Endocytosis

      • Phagocytosis: Pseudopods extend and engulf particles

      • Pinocytosis: Membrane folds inward bringing in fluid and dissolved substances


    Testing your knowledge

    Testing your knowledge

    Questions to answer in the process


    Questions

    Questions…

    • Describe the fluid mosaic model of membrane structure. What are the functions of the major components? Which components do not move easily? Why don't they?

    • Give at least four different functions for the proteins that are embedded in the cell membrane.

    • What is Fick's law of diffusion? What factors influence the rate of diffusion across a membrane? Give examples of how membranes might be altered in a biological system to change the rate of diffusion. Can you give a few examples of where diffusion is important for proper physiological function

    • What are desmosomes, tight junctions, and gap junctions? Under which circumstances is each important?

    • Compare and contrast the major avenues of water transport across the cell membrane. Give an example of where each is important in human physiology. How are solutes transported across the cell membrane? Compare and contrast the functional characteristics of each transport mechanism. Give an example of how each is important in human physiology.


    Questions1

    Questions…

    • Give at least four different functions for the proteins that are embedded in the cell membrane.


    Reasoning and problem solving

    REASONING AND PROBLEM SOLVING

    • Because of its charge, glucose normally diffuses through the cell membrane very slowly. However, facilitated diffusion of glucose occurs more rapidly as long as the carrier molecules are not saturated. Given Fick's Law of Diffusion, which parameter(s) must change to permit this more rapid diffusion in the presence of a carrier. Explain.

    • What are the possibilities for how drugs might act at the level of the receptor? In class, I said that a drug could act by competitive inhibition. But some drugs act on the receptor by allosteric (=noncompetitive) inhibition. How might a drug inhibit a receptor in an allosteric manner?

    • In carrier-mediated transport of Solute Q, there is always the possibility that a similarly-shaped molecule might compete for the transport protein (that is, act as a competitive antagonist to transport of the Solute Q). Graph the rate of Solute Q transport (Y axis) against increasing Solute Q concentration (X axis) in the 1) presence and 2) absence of a set amount of competitive antagonist. Explain. Would you expect to find a similar effect in other systems which employ this "lock and key" interaction (e.g., between a substrate and its enzyme or a neurotransmitter and its receptor)? Explain.


    Review and cell membrane proteins

    Review and Cell Membrane Proteins

    Looking at what we saw and adding some new stuff


    A closer look at cell membranes

    Cell Membrane Views


    A closer look at cell membranes

    Phospholipid Molecule


    A closer look at cell membranes

    • Function of Cholesterol

    • Provide structural support, prevent small molecule to pass

    • Prevent tight packing and transition


    A closer look at cell membranes

    Microdomains on plasma membrane

    Lipid rafts (~ 50nm)

    Choresterol

    Sphingolipids (long saturated chains)

    Other proteins


    A closer look at cell membranes

    Phospholipids in cell signaling

    PKC

    Calcium

    GEF, AKT, migrating front


    Summary

    Summary

    Lipid molecules: phospholipids, cholesterol, glycolipid, all amphipathic

    Lipid bilayer, hydrophobic inside and hydrophilic outside

    Subdomains on membrane, asymmetry important for functions

    Phospholipids as signals


    A closer look at cell membranes

    Membrane Proteins

    Integral membrane protein

    Peripheral membrane protein

    Glycosylphosphatidylinositol (GPI) anchor protein


    A closer look at cell membranes

    Fatty acid chain (acyl, N-terminal) or prenyl group modifications (C-terminal)


    A closer look at cell membranes

    Membrane proteins are glycosylated

    Sugar are added in the lumen of the ER and Golgi apparatus, therefore, sugar are outside of cell surface

    Cytosol has reduced environment, preventing disulfide bonds


    A closer look at cell membranes

    Membrane proteins are diffusible


    A closer look at cell membranes

    Proteins restrictions

    Tight Junction is one kind of them

    Proteins and lipids on the outer layers can’t move to other compartments


    Types of transport proteins

    Types of Transport Proteins

    • Uniport carries a single molecule across a membrane

      • Ex: Glucose enters a cell

    • Symport moves two different molecules at the same time in the same direction. Both must bind to protein

      • Ex: Na+ and Glucose enter a cell

    • Antiport two molecules move in opposite directions

      • Ex: Na+ and K+ move through a membrane

    • These proteins can be inhibited by molecules that mimic the normally transported molecules.


    Test your knowledge

    Test your knowledge

    • 1)      What is a cell membrane?

    • 2)      What are some functions of the cell membrane?

    • 3)      Does water cross the cell membrane? How?

    • 4)      What determines the flow of water through the membrane? What does diffusion mean? How does it work?

    • 5)      Will the final concentration of water in and out of the cell the same or different?

    • 6)      Does everything cross the cell membrane?

    • 7)      What would happen to a cell if the concentration of water in the cell was less then the concentration of water outside the cell?

    • 8)      What would happen to a cell if the concentration of water in the cell was greater then the concentration of water outside the cell?


    Answers

    Answers

    • 1)   It is the outer layer of the cell much like the cell’s skin. It holds the cell together and regulates what can flow into and out of the cell.

    • 2)  Holds cell together. Let’s some things through and keeps others out.

    • 3)  Yes.  It flows through pores in the cell membrane.

    • 4)  Water can flow through the cell membrane’s pores. Water will flow until the concentration of the water in and out the cell is in equilibrium.

    • 5)  It will be the same because water will flow through the membrane until equilibrium is reached.

    • 6)  No, some molecules will not fit through the pores in the cell membrane.

    • 7)  Water would flow into the cell. The cell would grow and / or burst.

    • 8)  Water would flow out of the cell. The cell will shrink.


    Laboratory

    Laboratory

    Looking at how the cell work live!!!!

    CellMembranes and DiffusionLab


    Cell membranes and diffusion lab

    CellMembranes and DiffusionLab

    • “The cell is an open system exchanging energy and matter with the environment”

      • “describing how materials diffuse across the cell membrane in terms of concentration gradients”

      • “describing how the semi-permeable nature of the cell membrane allows the process of osmosis”


    Objectives outcomes

    Objectives / Outcomes

    • Experience the effect of concentration gradients on diffusion through a class activity.

    • See the process of diffusion.

    • An opportunity to think scientifically and to understand and use the scientific process. In other words, writing a hypothesis, designing an experiment, observing, recording, and interpreting observations, and forming conclusions from data.

    • Self-evaluation / critique of their lab design.

    • Applies concepts learned during the lab to other situations.


    Materials

    Materials

    • 1 -150 mL beaker

    • 5 g of cornstarch

    • 5 g of sugar

    • Iodine solution

    • Glucose test strips

    • Hot water

    • 2 Petri dishes

    • Pipettes

    • Eggs

    • Pin

    • Stirring rod


    Procedure

    Procedure

    • Make groups of 4.

    • Crack an egg in half, saving the large end containing the air sac.

    • Using a straight pin, CAREFULLY pierce the large end of the eggshell.

      • You may use a file the end of the egg to make it easier to pierce. DO NOT break the top end of the air sac membrane.

    • Using a pipette, place 1 mL of water into the eggshell. Float the shell "boat" in the dextrose/cornstarch solution provided.

      • DO NOT LET THE EGG SHELL SINK OR PLUNGE IN THE WATER. The solution in the beaker must remain separate from the water in the egg for this part of the experiment or you will have faulty results.

    • After 15 minutes, use a pipette to place 1 mL of the water from the eggshell into the Petri dish labeled “Inside Cell”.

    • Pipette 1 mL of the water from the beaker into the Petri dish labeled “Outside Cell”.

    • Test each solution with a glucose test strip. (A dark brown color indicates the presence of sugar).

    • In the Observations/Data section, write your observations.

    • Test each solution with A DROP of iodine (A blue/purple color indicates the presence of starch.)

    • In the Observations/Data, write your observations.


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