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Catalyst (12/13). Where in the body are more microvilli found? Why? Kidney, intestines, nose, tastebuds —so the cell can absorb more of whatever substance (organs all involved in absorption) Where in the body are more cillia found? Why?

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Catalyst (12/13)

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Catalyst 12 13

Catalyst (12/13)

Where in the body are more microvilli found? Why?

Kidney, intestines, nose, tastebuds—so the cell can absorb more of whatever substance (organs all involved in absorption)

Where in the body are more cillia found? Why?

Nose, ears, throat, fallopian tubes—clear things, move the egg past, ears—help feel sound waves (sound into a chemical signal)


Ap biology chapter 7

AP Biology-Chapter 7

The Plasma Membrane


Plasma membrane functions

Plasma Membrane Functions

  • Be protective

  • Regulate transport in and out of cell or subcellular domain

  • Allow selective receptivity and signal transduction by providing transmembrane receptor that binds signaling molecules

  • Allow cell recognition

  • Provide anchoring sites for cytoskeletal filaments or components of the extracellular matrix

    • This allows the cell to maintain its shape and perhaps move to distant sites

  • Help compartmentalize subcellular domains

  • Regulate the fusion of the membrane with other membranes in the cell via specialized junctions

  • Provide passageway across the membrane for certain molecules


Ii membrane model

II. Membrane Model

  • Current Model: Fluid Mosaic Model

    • Brain child of Singer and Nicholson (1972)

      • Derived from a model proposed in the 1930s by Daffson and Danielli

        • Two layers of lipids that were coated with proteins

        • Fit the electron properties of membranes, but not all the details fit

        • Unable to account for all the things going into and out of the cell

          • Biggest problem was how their model would get polar molecules through—in their theory they would get stuck—but this is not what happens—especially with water (a polar molecule)


Ii membrane model1

II. Membrane Model

  • Four components to the Fluid Mosaic Model

    • Phospholipidbilayer

      • Direct from Daffson and Danielli

      • 3 types of lipids

        • Phospholipids

        • Glycolipids

        • Cholesterol

Phosphate

“attracted to water”

Fatty acid

“repelled by water”


Ii membrane model2

II. Membrane Model

  • Chunks of proteins that float IN the bilayer

    • New proposal


Catalyst 12 13

sugar

H2O

salt

polar

hydrophilic

heads

nonpolar

hydrophobic

tails

impermeable to polar molecules

polar

hydrophilic

heads

lipids

waste


Ii membrane model3

II. Membrane Model

  • Molecules can move around

    • Both lipids and proteins

    • Lipid bilayer acts like a liquid crystal

      • Array of molecules arranged in some relation to each other, but they are not fixed in position

      • Hydrocarbon chains in constant motion, so molecules are free to rotate and can move laterally

  • Not a lot of movement from one layer to another and if they do there are enzymes called flipases and flopases that put them back to where they started.

  • Fluidity has 2 meanings

    • Movement of molecules within the liquid crystal arrangement

    • Motion of the fatty acid side chains of phospholipid.


Ii membrane model4

II. Membrane Model

  • Lipid distribution on the two sides of the bilayer is asymmetric

    • Outside layer and inside layer are composed of different types of lipids


Iii membrane structure

III. Membrane Structure

  • Phospholipidbilayer in which a variety of proteins are embedded.

    • Fluidity of fatty acids

      • Function of type of fatty acid—saturated vs. unsaturated.

        • If saturated, there are one or more double bonds. This makes the fatty acid rigid and bent (kinked)

          • Kinks require a lot of space between the phospholipids and this would make the bilayer unstable

    • Nature’s solution—usually have one of each, unsaturated and saturated on each phospholipid

      • This is sufficient to maintain the lipid bilayer without it being too packed to move around or too much room that it falls apart


Iii membrane structure1

III. Membrane Structure

  • Role of cholesterol in animal membranes

    • Provides support helping to maintain membrane

    • Reduces the permeability of membrane to many molecules

      • (e.g. some hormones—estrogens and testosterone will not cross membranes loaded with cholesterol)

    • Sits in the “crook” of the unsaturated fatty acid side chains

    • No or little cholesterol in the inner membrane


Iii membrane structure2

III. Membrane Structure

  • Two types of membrane proteins

    • Integral (or transmembrane)

      • Stick all or partway through the membrane

      • To stick in the interior of the membrane the protein must have a hydrophobic surface

        • This goes against what we learned about protein folding—hydrophillic exterior and hydrophobic interior!

      • Tightly associated with the lipid bilayer. Cell biologists can release them only by disrupting the cell membrane with detergents

      • Different forms

        • Extend all the way through—transmembrane proteins

        • Partially embedded—either sticking out the interior or exterior


Catalyst 12 13

Polar areas

of protein

Nonpolar areas of protein


Iii membrane structure3

III. Membrane Structure

  • Peripheral

    • Sit on the cytoplamsic face of a membrane, with no part sticking into the membrane

    • Easy to dislodge


Catalyst 12 17

Catalyst (12/17)

Sketch a drawing of the plasma membrane. Be sure to include and label all components.

ANNOUNCEMENTS:

--cell analogy poster due TOMORROW

--cell quiz (chpt 6) THURSDAY


Iii membrane structure4

III. Membrane Structure

  • Structure and function of membrane proteins

    • Channel proteins: allows a particular molecule or ion to cross the plasma membrane freely.


Iii membrane structure5

III. Membrane Structure

  • Carrier proteins: selectively interacts with a specific molecule or ion so that it can cross the membrane.


Iii membrane structure6

III. Membrane Structure

  • Cell recognition proteins: glycoproteins—a protein with a carbohydrate chain attached sticking above the membrane surface.

    • The carbohydrate chains of the glycoproteins combined with the carbohydrate chains of the glycolipids forms the glycocalyx.

    • The glycocalyx serves as the cell’s “fingerprint”

      • Mark the cell as belonging to a particular individual and tissue

      • Causes difficulties in organ transplants—patient’s cells do not recognize the glycocalyx fingerprint of the donor organ and therefore reject it.


Iii membrane structure7

III. Membrane Structure

  • Receptor protein: is shaped in such a way that a specific molecule can bind to it (signal transduction).


Iii membrane structure8

III. Membrane Structure

  • Enzymatic protein: catalyzes a specific reaction.


Many functions of membrane proteins

Many Functions of Membrane Proteins

“Channel”

Outside

Plasma

membrane

Inside

Transporter

Enzymeactivity

Cell surfacereceptor

“Antigen”

Cell adhesion

Cell surface identity marker

Attachment to thecytoskeleton


Membrane is a collage of proteins other molecules embedded in the fluid matrix of the lipid bilayer

Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer

Glycoprotein

Glycolipid

Transmembrane

proteins

Peripheral

protein

Filaments ofcytoskeleton

Extracellular fluid

Phospholipids

Cholesterol

Cytoplasm

1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model


Ap biology chapter 71

AP Biology-Chapter 7

Selective Permeability


I the plasma membrane is semipermeable

I. The plasma membrane is semipermeable

  • The structure of the plasma membrane affects which types of molecules can freely pass through it.

    • Because the structure of the membrane is predominantly lipid, how lipid soluble a molecule is predominantly defines its ability to cross the membrane.

      • Small hydrophobic (nonpolar or non charged) molecules freely cross the membrane

      • Ions don’t freely cross the membrane. Charged=polar


I the plasma membrane is semipermeable1

I. The plasma membrane is semipermeable

  • The size of the molecule also influences its diffusibility, but the influence of size is secondary

    • Large uncharged or charged molecules do not freely cross the membrane

    • H20, which is polar but very small, does cross the membrane freely. Able to pass quickly through when fatty acid chains move momentarily out of the way.

1st –charge

2nd– size

  • Why H2O?

  • Is a dipole

  • Not high charge (like ions)—only slightly charged

  • Osmotic pressure


I the plasma membrane is semipermeable2

I. The plasma membrane is semipermeable

The permeability of membranes to ions and large molecules is due mainly to the activity of specialized membrane proteins.


Ii molecules cross the plasma membrane in both passive and active ways

II. Molecules cross the plasma membrane in both passive and active ways

  • Passive transport

    • Two types

      • Diffusion: molecules move from higher to lower concentration (that is down their gradient) until they are distributed equally

        • Osmosis: the diffusion of H2O across a semipermeable membrane.

(no energy needed)

2nd Law of Thermodynamics—universe tends toward disorder (entropy)

Molecules move from HIGH to LOW concentration

osmosis


Ii molecules cross the plasma membrane in both passive and active ways1

II. Molecules cross the plasma membrane in both passive and active ways

  • Facilitated diffusion: a carrier (or channel) protein speed the rate at which a solute crosses the membrane in the direction of decreased concentration. The carrier protein undergoes a change in shape as I moves a solute across the membrane.

Facillitated diffusion


Ii molecules cross the plasma membrane in both passive and active ways2

II. Molecules cross the plasma membrane in both passive and active ways

  • Active transport

    • Three types

      • Carrier-mediated active transport: small molecules and ions move against their concentration gradient. Carrier protein AND energy needed.

        • Sodium-potassium pump: sodium out, potassium in (example of carrier mediated active transport)

          • 3 Na+ ions carried out for each 2 K+ ions carried in, therefore, the inside of the cell is negatively charged compared to the outside.

(requires the use of energy—usually ATP)


Catalyst 12 13

Na+/K+ pump


Ii molecules cross the plasma membrane in both passive and active ways3

II. Molecules cross the plasma membrane in both passive and active ways

“out”

“cell”

  • Exocytosis: vesicles, often formed by the ______________________ & carrying a specific molecule, fuse w/ the plasma membrane as secretion occurs.

    • Example: insulin is secreted into the blood stream by insulin-secreting cells through the process of exocytosis.

golgi apparatus

Where in the body does a lot of exocytosis happen?


Catalyst 12 171

Catalyst (12/17)

Sketch a drawing of the plasma membrane. Be sure to include and label all components.

ANNOUNCEMENTS:

--cell analogy poster due TOMORROW

--cell quiz (chpt 6) THURSDAY


Ii molecules cross the plasma membrane in both passive and active ways4

II. Molecules cross the plasma membrane in both passive and active ways

“in”

“cell”

  • Endocytosis: cells take in substances by vesicle formation. A portion of the plasma membrane invaginates to surround the substance and then pinches off to form an intracellular vesicle

    • Two types

      • Phagocytosis: when the material to be taken in is large, such as a food particle or another cell (eg. Macrophages engulf bacteria or other pathogens and worn out cells)

      • Pinocytosis: occurs when vesicles form around a liquid or very small particle. (Occurs in blood cells, cells that line the kidney tubules, or intestinal wall and plant root cells)

      • Phagocytosis can be seen with the light microscope, but an electron microscope is needed to see the vesicles formed in pinocytosis.

“cell eating”

“cell drinking”


Catalyst 12 13

Hydrolytic enzymes

Endocytosis and digestion of pathogen (bacteria)


Catalyst 12 13

Endocytosis and digestion of food particle


Ii molecules cross the plasma membrane in both passive and active ways5

II. Molecules cross the plasma membrane in both passive and active ways

  • Receptor-mediate endocytosis: is a form of pinocytosis that allows cells to take up specific kinds of molecules and then sort them within the cell.

    • Ligand: a macromolecule that bind to a plasma membrane receptor

    • Coated pit: when ligands bind the their receptors this causes the receptors to gather in the “coated pit” that has a layer of a fibrous protein called clathrin.

    • Clathrin is a fibrous protein that coasts many vesicles that leave the golgi apparatus. It appears to aid in the formation of vesicles

    • The fate of the vesicle and ligand depends on the ligand.

      e.g. after hormones enter and act on the cell, the hormone (ligand), the receptors, and the vesicle fuse with a lysosome and are digested.

      e.g. when cholesterol enters the vesicle and receptors are recycled back to the plasma membrane

Controlled by receptor proteins

Hormone/vitamin


Iii diffusion across cell membrane

III. Diffusion across cell membrane

  • Cell membrane is the boundary between inside & outside…

    • separates cell from its environment

Can it be an impenetrable boundary?

NO!

OUT

waste

ammonia

salts

CO2

H2O

products

IN

food

carbohydrates

sugars, proteins

amino acids

lipids

salts, O2,H2O

OUT

IN

cell needs materials in & products or waste out


Catalyst 1 9

Catalyst (1/9)

What do you already know about osmosis?

Diffusion of water across a semipermeable membrane


I osmosis the diffusion of water across a semipermeable membrane

I. Osmosis: the diffusion of water across a semipermeable membrane

  • Passive transport

  • Depends on the concentration of solutes on each side of the membrane

  • Tonicity:

    • Hypertonic: higher concentration of solute molecules

    • Hypotonic: lower concentration of solute molecules

    • Isotonic: same concentration of solute molecules

    • NOTE: water moves from hypotonic to hypertonic solution (FIX THIS IN YOUR NOTES!!!!!!!)

No energy needed (down gradient)

“Above normal or over”

“Below normal”

“Same” or “equal”


Catalyst 12 13

  • Water Potential: a concept that helps to describe the tendency of water to move from one area to another, particularly into or out of cells. (ψ)

    • Water potential determines the rate and direction of osmosis

    • Is measured in units of pressure—kPa, MPa, bar


Two factors affect water potential

TWO FACTORS affect Water Potential

  • Solute Concentration

    • Pure water has a water potential of zero (ψ=0)

    • A solution will have a lower concentration of water molecules, so it will have a NEGATIVE water potential

    • Addition of solutes lowers the water potential

  • Pressure

    • In a plant cell, pressure exerted by the rigid cell wall that limits further water uptake (osmosis into the cell).

    • When a plant cell is fully inflated with water it is called turgid.


Catalyst 12 13

ψp

  • Pressure potential is important in plant cells because they are surrounded by a cell wall which, is strong and rigid.

  • When water enters a plant cell, its volume increases and the living part of the cell presses on the cell wall.

  • The cell wall gives very little and so pressure starts to build up inside the cell.

  • This has the tendency to stop more water entering the cell and also stops the cell from bursting.

  • When a plant cell is fully inflated with water, it is called turgid.

  • Pressure potential is called turgor pressure in plants)

ψp

ψp

ψp


Catalyst 12 13

Water moves from a place of high water potential to a place of low water potential.

  • Equation given on AP Test

    • Water potential (Ψ)=ψp+ψs

hypotonic

hypertonic

This is an open container, so the ψp= 0

This makes the ψ = ψs

High water potential

Low water potential

The ψs=-0.23, so ψ is -0.23MPa, and water moves into the solution.


Catalyst 12 13

hypertonic

hypertonic


Catalyst 12 13

Pressure (ΨP)

(ΨS)

Turgid!


Catalyst 12 13

No net movement

1

Isotonic

A=B

same

2

A hyper

B hypo

A is lower

BA

A hypo

B hyper

3

B is lower

AB


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