Membrane Structure and Function

Home , Fluid mosaic model

Sylvia S. Mader

BIOLOGY Edition 10th

Inside heads Outside hydrophilic

bilayer

chain phospholipid carbohydrate tails hydrophobic

filaments filaments of cytoskeleton

glycolipid

extracellular

matrix matrix (ECM)

102 integral integral protein - cholesterol

glycoprotein

Hill Companies, Permission requiredInc. reproductionfor display.or - plasma plasma membrane

peripheral peripheral protein pp. 85 pp.

Membrane Membrane Structure

Chapter 5: Chapter PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor Biology Barjis, Isaac Dr. by prepared are Slides Lecture PowerPoint® Copyright © The McGraw Hill Companies Inc. Permission required for required Copyright Permission reproductionHill Companies or display Inc. McGraw© The

Outline

 Membrane Models  Fluid-Mosaic  Plasma Membrane Structure and Function  Phospholipids  Proteins  Plasma Membrane Permeability  Diffusion  Osmosis  Transport Via Carrier Proteins  Cell Surface Modifications

2 Structure and Function: The Phospholipid Bilayer

 The plasma membrane is common to all cells  Separates:  Internal living cytoplasmic from  External environment of cell  Phospholipid bilayer:  External surface lined with hydrophilic polar heads  Cytoplasmic surface lined with hydrophilic polar heads  Nonpolar, hydrophobic, fatty-acid tails sandwiched in between

3 Membrane Models

 Fluid-Mosaic Model  Three components:  Basic membrane referred to as phospholipid bilayer  Protein molecules  Float around like icebergs on a sea  Membrane proteins may be peripheral or integral  Peripheral proteins are found on the inner membrane surface  Integral proteins are partially or wholly embedded (transmembrane) in the membrane  Some have carbohydrate chains attached  Cholesterol

4 Animation

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plasma membrane

carbohydrate chain extracellular Outside matrix (ECM)

hydrophobic hydrophilic tails glycoprotein heads phospholipid glycolipid bilayer

Inside filaments of cytoskeleton

peripheral protein integral protein

cholesterol

7 Transmembrane Proteins

integral protein hydrophobic region

cholesterol hydrophilic regions

peripheral proteins

8 Lateral Migration of Membrane Proteins

integral protein hydrophobic region

cholesterol hydrophilic regions

peripheral proteins

9 Functions of Membrane Proteins

 Channel Proteins:  Tubular  Allow passage of molecules through membrane  Carrier Proteins:  Combine with substance to be transported  Assist passage of molecules through membrane  Cell Recognition Proteins:  Provides unique chemical ID for cells  Help body recognize foreign substances  Receptor Proteins:  Binds with messenger molecule  Causes cell to respond to message  Enzymatic Proteins:  Carry out metabolic reactions directly

10 Membrane Protein Diversity

Channel Protein: Carrier Protein: Cell Recognition Allows a particular Selectively interacts Protein: molecule or ion to with a specific The MHC (major cross the plasma molecule or ion so histocompatibility membrane freely. that it can cross the complex) glycoproteins Cystic fibrosis, an plasma membrane. are different for each inherited disorder, The inability of some person, so organ is caused by a persons to use transplants are difficult faulty chloride (Cl–) energy for sodium- to achieve. Cells with channel; a thick potassium (Na+–K+) foreign MHC mucus collects in transport has been glycoproteins are airways and in suggested as the attacked by white blood pancreatic and cause of their obesity. cells responsible for liver ducts. immunity. a. b. c.

Receptor Protein: Enzymatic Protein: Junction Proteins: Is shaped in such a Catalyzes a specific Tight junctions join way that a specific reaction. The membrane cells so that a tissue molecule can bind to protein, adenylate can fulfill a function, as it. Pygmies are short, cyclase, is involved in when a tissue pinches not because they do ATP metabolism. Cholera off the neural tube not produce enough bacteria release a toxin during development. growth hormone, but that interferes with the Without this because their plasma proper functioning of cooperation between membrane growth adenylate cyclase; cells, an animal hormone receptors sodium (Na+) and water embryo would have no are faulty and cannot leave intestinal cells, and nervous system. interact with growth the individual may die hormone. from severe diarrhea. d. e. f.

11 Science Focus: Cell Signaling

a. egg embryo newborn

1. Receptor: Binds to a signaling 3. Response:Targeted protein(s) molecule, becomes activated and bring about the response(s) noted. initiates a transduction pathway plasma Targeted Cellular signaling membrane protein: response: molecule Altered shape or movement of cell receptor structural activation protein

Altered metabolism or a function enzyme 2. Transduction pathway: Series of cell of relay proteins that ends when a protein is activated. unactivated receptor nuclear protein Altered gene envelope expression and the amount of gene a cell protein regulatory Cytoplasm Nucleus protein

12 Types of Transport: Active vs. Passive

 Plasma membrane is differentially (selectively) permeable

 Allows some material to pass

 Inhibits passage of other materials  Passive Transport:

 No ATP requirement

 Molecules follow concentration gradient  Active Transport

 Requires carrier protein

 Requires energy in form of ATP

13 Animation

15 Types of Membrane Transport: Overview

charged molecules and ions

H2O

noncharged molecules

macromolecule

phospholipid molecule

protein

16 Types of Transport: Diffusion

 A solution consists of:  A solvent (liquid), and  A solute (dissolved solid)  Diffusion  Net movement of solute molecules down a concentration gradient  Molecules both ways along gradient  More move from high to low concentration than vice versa  Equilibrium:  When NET change stops  Solute concentration uniform – no gradient

17 Gas Exchange in Lungs: Diffusion Across Lung

O2 O2 O2

O O2 2

O2 oxygen

O2 O2 O2

O2 bronchiole

alveolus capillary

18 Types of Membrane Transport: Diffusion

time time

crystal dye

a. Crystal of dye is placed in water b. Diffusion of water and dye molecules c. Equal distribution of molecules results

19 Animation

20 Animation

 Osmosis:  Special case of diffusion  Focuses on solvent (water) movement rather than solute  Diffusion of water across a differentially (selectively) permeable membrane  Solute concentration on one side high, but water concentration low  Solute concentration on other side low, but water concentration high  Water diffuses both ways across membrane but solute can’t  Net movement of water is toward low water (high solute) concentration  Osmotic pressure is the pressure that develops due to osmosis

22 Types of Transport: Osmosis

less water (higher more water (lower percentage of solute) percentage of solute) <10% 10% water solute

more water (lower 5% thistle >5% less water (higher percentage of solute) tube percentage of solute) a. c.

differentially permeable membrane

beaker

23 Animation

24 Animation

 Isotonic Solution  Solute and water concentrations equal on both sides of membrane  Hypotonic Solution  Concentration of solute lower than on other side  Cells placed in a hypotonic solution will swell  May cause cells to break – Lysis  Hypertonic Solution  Concentration of solute higher than on other side  Cells placed in a hypertonic solution will shrink – Plasmolysis

26 Osmotic Effects on Cells

Animal plasma cells membrane

nucleus

In an isotonic solution, there is no In a hypotonic solution, water In a hypertonic solution, water net movement of water. mainly enters the cell, which may mainly leaves the cell, which burst (lysis). shrivels (crenation).

Plant cells

cell wall nucleus central vacuole plasma membrane

chloroplast

In an isotonic solution, there is no In a hypotonic solution, vacuoles In a hypertonic solution, vacuoles net movement of water. fill with water, turgor pressure lose water, the cytoplasm shrinks develops, and chloroplasts are (plasmolysis), and chloroplasts seen next to the cell wall. are seen in the center of the cell.

27 Animation

28 Types of Transport: Carrier Proteins

 Facilitated Transport

 Small molecules

 Can’t get through membrane lipids

 Combine with carrier proteins

 Follow concentration gradient  Active Transport

 Small molecules

 Move against concentration gradient

 Combining with carrier proteins

 Requires energy

29 Animation

30 Types of Membrane Transport: Facilitated Transport

Inside

plasma membrane carrier protein

solute

Outside

31 Animation

Outside carrier + protein K K+ K+ K+

Inside

1. Carrier has a shape that allows it to take up 3 Na+

33 Facilitated Transport: The Sodium-Potassium Pump

Outside carrier K+ protein K+

K+ K+

K+ K+ K+

K+

Inside

1. Carrier has a shape that allows it to take up 3 Na+.

ATP

2. ATP is split, and phosphate group attaches to carrier

34 Facilitated Transport: The Sodium-Potassium Pump

carrier Outside protein K+ K+

K+ K+

K+ K+ K+

K+

Na+ Inside

1. Carrier has a shape that allows it to take up 3 Na+.

ATP

2. ATP is split, and phosphate group attaches to carrier

K+ K+

3. Change in shape results and causes carrier to release 3 Na+ outside the cell.

35 Facilitated Transport: The Sodium-Potassium Pump

Outside carrier + protein K K+

K+ K+

K+ K+ K+

K+

Inside

1. Carrier has a shape that allows it to take up 3 Na+.

ATP

2. ATP is split, and phosphate group attaches to carrier.

K+ K+

K+ K + P K+ K+

3. Change in shape results and causes carrier to release 3 Na+ outside the cell.

4. Carrier has a shape that allows it to take up 2K+.

36 Facilitated Transport: The Sodium-Potassium Pump

Outside carrier + protein K K+

K+ K+

K+ K+ K+

K+

Na+ Inside

1. Carrier has a shape that allows it to take up 3 Na+.

ATP

2. ATP is split, and phosphate group attaches to carrier.

+ K+ K+ K

K+ K+ K+

K+

K+ P K+ P K+ K+

5. Phosphate group is released 3. Change in shape results and from carrier. causes carrier to release 3 Na+ outside the cell.

4. Carrier has a shape that allows it to take up 2 K+.

37 Facilitated Transport: The Sodium-Potassium Pump

Outside carrier + protein K K+

K+ K+

K+ Na+ K+ K+ K+

K K+

Na+ Inside

1. Carrier has a shape that allows it to take up 3 Na+.

+ ATP K+ K

6. Change in shape results and 2. ATP is split, and phosphate causes carrier to release 2K+ group attaches to carrier. inside the cell.

+ K+ K+ K

K+ K+ K+

K+

K+ P K+ P K+ K+

5. Phosphate group is released 3. Change in shape results and from carrier. causes carrier to release 3 Na+ outside the cell.

4. Carrier has a shape that allows it to take up 2 K+.

38 Animation

39 Types of Transport: Membrane-Assisted Transport  Macromolecules transported into or out of the cell inside vesicles  Exocytosis – Vesicles fuse with plasma membrane and secrete contents  Endocytosis – Cells engulf substances into pouch which becomes a vesicle

 Phagocytosis – Large, solid material into vesicle

 Pinocytosis – Liquid or small, solid particles go into vesicle

 Receptor-Mediated – Specific form of pinocytosis using a coated pit

40 Membrane-Assisted Transport: Exocytosis

plasma membrane Outside

Inside secretory vesicle

41 Membrane-Assisted Transport: Three Types of Endocytosis

plasma membrane paramecium

pseudopod vacuole forming

vacuole

m a. Phagocytosis 399.9

vesicles forming

solute vesicle

b. Pinocytosis 0.5 m

receptor protein

coated coated pit vesicle

solute coated vesicle coated pit

c. Receptor-mediated endocytosis

42 Animation

43 Cell Surface Modifications: Junctions

 Cell Surfaces in Animals

 Junctions Between Cells

 Adhesion Junctions

 Intercellular filaments between cells

 Tight Junctions

 Form impermeable barriers

 Gap Junctions

 Plasma membrane channels are joined (allows communication)

44 Cell-Surface Modifications: Junctions

plasma cytoplasmic membranes plaque plasma plasma membranes membranes

tight junction membrane filaments of proteins channels cytoskeleton

intercellular filaments intercellular intercellular space intercellular space space a. Adhesion junction b. Tight junction c. Gap junction

45 Cell Surface Modifications

 Extracellular Matrix

 External meshwork of polysaccharides and proteins

 Found in close association with the cell that produced them  Plant Cell Walls

 Plants have freely permeable cell wall, with cellulose as the main component

 Plasmodesmata penetrate cell wall

 Each contains a strand of cytoplasm

 Allow passage of material between cells

46 Cell-Surface Modifications: Extracellular Matrix

Inside (cytoplasm) actin filament

integrin elastin

fibronectin proteoglycan collagen Outside (extracellular matrix)

47 Cell-Surface Modifications: Plasmodesmata

cell wall

cell wall middle lamella

plasma plasma membrane membrane cell wall cell wall

cytoplasm cytoplasm

plasmodesmata

Cell 1 Cell 2

0.3mm

48 Review

 Membrane Models

 Fluid-Mosaic

 Plasma Membrane Structure and Function

 Protein Functions

 Plasma Membrane Permeability

 Diffusion

 Osmosis

 Transport Via Carrier Proteins

 Cell Surface Modifications

Sylvia S. Mader

BIOLOGY Edition 10th

Inside heads Outside hydrophilic

bilayer

chain phospholipid carbohydrate tails hydrophobic

filaments filaments of cytoskeleton

glycolipid

extracellular

matrix matrix (ECM)

102 integral integral protein - cholesterol

glycoprotein

Hill Companies, Permission requiredInc. reproductionfor display.or - plasma plasma membrane

peripheral peripheral protein pp. 85 pp.

Membrane Membrane Structure