cell membrane

آية آية البقرة 3232البقرة

احمد .د محمد رمضان[email protected]

CellCell• Basic unit of structure and function Basic unit of structure and function

of the body.of the body.– Highly organized molecular factory.Highly organized molecular factory.

• 3 principal parts:3 principal parts:– Membrane.Membrane.– Cytoplasm and organelles.Cytoplasm and organelles.– Nucleus.Nucleus.

Human CellHuman Cell

Cell MembraneCell Membrane

PhospholipidsPhospholipids• The phospholipids The phospholipids are arranged in a are arranged in a bilayerbilayer, with , with

their their polarpolar, , hydrophilic phosphate heads facing hydrophilic phosphate heads facing outwardsoutwards, ,

• and their and their non-polar, hydrophobic fatty acid tails non-polar, hydrophobic fatty acid tails facing each other facing each other in the middle of the bilayer.in the middle of the bilayer.

ProteinProtein

• PERIPHERAL PROTEINSPERIPHERAL PROTEINS, located on both the , located on both the Internal and External Surface. Internal and External Surface.

• INTEGRAL PROTEINS:INTEGRAL PROTEINS: Proteins that are Proteins that are Embedded in the Lipid Bilayer Embedded in the Lipid Bilayer

Functions of proteins Functions of proteins

• Channels or PoresChannels or Pores• carrierscarriers• Enzymes.Enzymes.• Pumps.Pumps.

CarbohydratesCarbohydrates• The carbohydrates The carbohydrates are attached to are attached to

the membrane proteins or sometimes the membrane proteins or sometimes to the phospholipids. to the phospholipids.

Functions:Functions:Protection. Protection. Cell recognition. Cell recognition. Antigens such as the ABO antigens on Antigens such as the ABO antigens on

blood cells.blood cells.

Function of cell Function of cell membranesmembranes

• Forms boundary between the contents of Forms boundary between the contents of the cell and its external environment.the cell and its external environment.

• Regulates the passage of substances into Regulates the passage of substances into and out of the cell (certain substances).and out of the cell (certain substances).

• Enables the cell to communicate with the Enables the cell to communicate with the external environment (receptor proteins external environment (receptor proteins that receive chemical messenger molecules that receive chemical messenger molecules e.g hormones from other cells).e.g hormones from other cells).

MembraneMembrane

TransportTransport

Movement of molecules / Movement of molecules / substances in and out of cellsubstances in and out of cell

Cell membranes are a barrier to most Cell membranes are a barrier to most substances, and this property allows substances, and this property allows materials to be concentrated inside materials to be concentrated inside cells, excluded from cells, or simply cells, excluded from cells, or simply separated from the outside separated from the outside environment.environment.

Methods by which substances can Methods by which substances can move across a cell membrane:move across a cell membrane:

– Passive Transport (simple diffusion, Passive Transport (simple diffusion, facilitated diffusion and osmosis).facilitated diffusion and osmosis).

– Active Transport.Active Transport.

– Bulk transport Bulk transport (Exocytosis and (Exocytosis and Endocytosis)Endocytosis)

Movement of substances in Movement of substances in and out of celland out of cell

Movement of substances in Movement of substances in and out of celland out of cell

Passive transportPassive transport

• Passive transport is the transport of Passive transport is the transport of substances by substances by a trans-membrane a trans-membrane protein molecule or through lipid bilayer.protein molecule or through lipid bilayer.

• No energy required No energy required

• Move due to gradientMove due to gradient

Simple DiffusionSimple Diffusion  

•A few substances can diffuse directly A few substances can diffuse directly through through the lipid bilayerthe lipid bilayer part of the part of the membrane. (such as H2O, O2 and membrane. (such as H2O, O2 and CO2).CO2).

•Small water-soluble molecules can Small water-soluble molecules can pass through pass through channels.channels.

Factors affecting Factors affecting DiffusionDiffusion    

The rate of diffusion The rate of diffusion directly directly proportional with:proportional with:

1.1. Concentration gradient.Concentration gradient.2.2. Solubility in the membrane.Solubility in the membrane.3.3. Temperature.Temperature.4.4. Surface area of the membrane.Surface area of the membrane.

The rate of diffusion The rate of diffusion inversely inversely proportional with:proportional with:

1.1. Molecular weight of diffusible substance.Molecular weight of diffusible substance.2.2. Thickness of the membrane.Thickness of the membrane.

Facilitated diffusionFacilitated diffusion– Their transport must therefore be Their transport must therefore be

"facilitated" by proteins ("facilitated" by proteins (CarriersCarriers).).– It is similar to simple diffusion in the sense It is similar to simple diffusion in the sense

that it does that it does not require energy and not require energy and transport is again down an transport is again down an electrochemical gradient.electrochemical gradient.

Types of carrier Types of carrier proteinsproteins

– A uniport carrier:A uniport carrier: transport one substance. transport one substance. – A symport carrier:A symport carrier: transport two substances in transport two substances in

the same direction. the same direction. – An antiport carrier:An antiport carrier: transport two substances in transport two substances in

the opposite directions.the opposite directions.

Factors affecting transport Factors affecting transport rate in Facilitated diffusionrate in Facilitated diffusion

– Number of carriers.Number of carriers. – Carrier activity.Carrier activity.

– Presence of carrier inhibitors.Presence of carrier inhibitors. – Presence of competing substances.Presence of competing substances.

OsmosiOsmosiss• Osmosis is the diffusion of water across a membrane. Osmosis is the diffusion of water across a membrane.

• Water molecules can diffuse freely across a membrane, Water molecules can diffuse freely across a membrane, down their concentration gradient, so water therefore down their concentration gradient, so water therefore diffuses from a dilute to a concentrated solution (more diffuses from a dilute to a concentrated solution (more solute molecules).solute molecules).

Osmosis:diffusion of H2O through a semipermeable membrane from a diluted to a concentrated solution.

Osmotic pressure:is the pressure required to stop osmosis completely

There are three possible There are three possible concentrations of concentrations of

solution to consider:solution to consider:

• HypotonicHypotonic– Solutes in cell more than outsideSolutes in cell more than outside– Outside solvent will flow into cellOutside solvent will flow into cell

• IsotonicIsotonic– Solutes equal inside & out of cellSolutes equal inside & out of cell

• HypertonicHypertonic– Solutes greater outside cellSolutes greater outside cell– Fluid will flow out of cellFluid will flow out of cell

Osmosis in animal cellsOsmosis in animal cells

Active transportActive transport• Active transport is used to move ions or Active transport is used to move ions or

molecules molecules against a concentration gradientagainst a concentration gradient (low concentration to high concentration).(low concentration to high concentration).

• Requires energy. Requires energy.

• The energy is supplied by The energy is supplied by ATPATP which is released which is released by breaking ATP by breaking ATP   ADP + Pi + energy  ADP + Pi + energy

• Cells that use a lot of active transport have many Cells that use a lot of active transport have many mitochondria to produce the ATP needed.mitochondria to produce the ATP needed.

Active transport- Against conc. gradient- Use carrier

-Needs energy

Types of Active transportTypes of Active transport• Primary Active transport:Primary Active transport: energy is energy is

supplied directly from ATP breakdown. supplied directly from ATP breakdown. The best example: Na-K Pump.The best example: Na-K Pump.

Ca pumpCa pump

• Secondary Active transport:Secondary Active transport: The The energy is supplied indirectly from energy is supplied indirectly from ATPATP..The best example: glucose & amino-acid The best example: glucose & amino-acid

transport in the intestine & kidney.transport in the intestine & kidney.

The Sodium-Potassium PumpThe Sodium-Potassium Pump

• The sodium-potassium pump uses active The sodium-potassium pump uses active transport to move 3 sodium ions to the transport to move 3 sodium ions to the outside of the cell for each 2 potassium ions outside of the cell for each 2 potassium ions that it moves in.that it moves in.

• It is found in all human cells, especially It is found in all human cells, especially nervenerve and muscle cells.and muscle cells.

• One third of the body’s energy expenditure is One third of the body’s energy expenditure is used to operate the sodium-potassium pump.used to operate the sodium-potassium pump.

Inside Outside

Na+

Na+

Na+

K+K+K+

K+

Na+

Na+

Na+

Inside Outside

Na+ Na

+Na+

K+K+

K+

K+

22ryry (Indirect) Active (Indirect) Active TransportTransport

• Indirect ATP use: Indirect ATP use: uses Euses Epot.pot. stored in concentration stored in concentration gradientgradient (of Na (of Na++ and K and K++))

• Coupling of ECoupling of Ekinkin of one of one molecule with movement molecule with movement of another moleculeof another molecule

• Example: NaExample: Na++ / Glucose / Glucose symportersymporter

– other examplesother examples

• 2 mechanisms for Glucose 2 mechanisms for Glucose transporttransport

Bulk transportBulk transport– Large molecules (such as proteins, Large molecules (such as proteins,

polysaccharides and nucleotides) and even polysaccharides and nucleotides) and even whole cells are moved in and out of cells by whole cells are moved in and out of cells by using using membrane vesiclesmembrane vesicles. .

Endocytosis

• EndocytosisEndocytosis is the transport of materials into a is the transport of materials into a cell. cell.

• Materials are enclosed by a fold of the cell Materials are enclosed by a fold of the cell membrane, which then pinches shut to form a membrane, which then pinches shut to form a closed vesicle. closed vesicle.

• There are two types of endocytosis:There are two types of endocytosis:– pinocytosispinocytosis– phagocytosisphagocytosis

EndocytosisEndocytosis

PinocytosisPinocytosis

• When the materials and the vesicles When the materials and the vesicles are small (such as a protein are small (such as a protein molecule) the process is known as molecule) the process is known as pinocytosispinocytosis (cell drinking). (cell drinking).

PinocytosisPinocytosis

PhagocytosisPhagocytosis

• If the materials are large (such as a white If the materials are large (such as a white blood cell ingesting a bacterial cell) the process blood cell ingesting a bacterial cell) the process is known as is known as phagocytosisphagocytosis (cell eating). (cell eating).

• E.g: E.g: – Kuffer cell in liver engulf worn-out erythrocytes and Kuffer cell in liver engulf worn-out erythrocytes and

bacteria.bacteria.– White blood cells (neutrophils and macrophages)White blood cells (neutrophils and macrophages)– Amoeba engulf a food particle. Amoeba engulf a food particle.

PhagocytosisPhagocytosis

PhagocytosisPhagocytosis

ExocytosisExocytosis

• ExocytosisExocytosis is the transport of is the transport of materials out of a cell. It is the exact materials out of a cell. It is the exact reverse of endocytosis. reverse of endocytosis.

• Materials to be exported must first Materials to be exported must first be enclosed in a membrane vesicle, be enclosed in a membrane vesicle, usually from the RER and Golgi Body. usually from the RER and Golgi Body.

ExocytosisExocytosis

• Hormones and digestive enzymes are Hormones and digestive enzymes are secreted by exocytosis from the secretory secreted by exocytosis from the secretory cells of the intestine and endocrine glands.cells of the intestine and endocrine glands.

• Sometimes materials can pass straight Sometimes materials can pass straight

through cells without ever making contact through cells without ever making contact with the cytoplasm by being taken in by with the cytoplasm by being taken in by endocytosis at one end of a cell and passing endocytosis at one end of a cell and passing out by exocytosis at the other end. out by exocytosis at the other end.

ExocytosisExocytosis

Exocytosis

Choose the best answer:

QuestionsQuestions

Introduction and cell function

11 - -The rate of diffusion of a The rate of diffusion of a substance increases whensubstance increases when::a-a- The temperature decreases. The temperature decreases.

b- b- The molecular weight decreases. The molecular weight decreases.

c- Membrane permeability decreases.c- Membrane permeability decreases.

d- The concentration difference d- The concentration difference decreases.decreases.

22 - -Facilitated diffusionFacilitated diffusion::

a- Occurs against concentration a- Occurs against concentration gradient.gradient.

b- Needs energy derived from ATP.b- Needs energy derived from ATP.c- Needs carrier and does not need c- Needs carrier and does not need

energy.energy.d- Substances can move from low d- Substances can move from low

concentration to high concentration to high concentration.concentration.

33 - -Osmosis meansOsmosis means::

a- Passage of substances from high a- Passage of substances from high concentration to low concentration.concentration to low concentration.b- Passage of substances from low b- Passage of substances from low

concentration to high concentration.concentration to high concentration.c- Passage of water from diluted fluids c- Passage of water from diluted fluids

to concentrated fluids.to concentrated fluids.d- Passage of water from concentrated d- Passage of water from concentrated

fluids to diluted fluids.fluids to diluted fluids.

44 - -In active transportIn active transport::a- substances pass from a low concentra-a- substances pass from a low concentra-

tion to a high concentration and need tion to a high concentration and need energy.energy.b- substances pass from a high concentra-b- substances pass from a high concentra-

tion to a low concentration and need tion to a low concentration and need energy.energy.

c- water passes from diluted fluids to c- water passes from diluted fluids to concentrated fluids.concentrated fluids.

d- the substance transported must dissolve d- the substance transported must dissolve in the lipid bilayer of the cell membrane.in the lipid bilayer of the cell membrane.

True or false questions

11 - -The cell membraneThe cell membrane::

a- a- maintains the cell shape and maintains the cell shape and structurestructure . .

b- b- has selective permeability to has selective permeability to certain ionscertain ions. .

c- c- can detect chemical signals can detect chemical signals coming from other cells.coming from other cells.

d- d- is composed of lipids only.is composed of lipids only.

22 - -Cell membrane Cell membrane proteinsproteins::

a- penetrate the lipid bilayer and a- penetrate the lipid bilayer and act as ion channels.act as ion channels.

b- act as receptors for hormones b- act as receptors for hormones and neurotransmitters. and neurotransmitters.

c- act as carrier in facilitated c- act as carrier in facilitated diffusion.diffusion.

d- prevent transport of ions.d- prevent transport of ions.

55 - -PhagocytosisPhagocytosis::

a- is the process by which bacteria and a- is the process by which bacteria and dead tissues are engulfed by cells.dead tissues are engulfed by cells.

b- is the process by which proteins and b- is the process by which proteins and peptides are secreted from the cells. peptides are secreted from the cells.

c- is the process during which the c- is the process during which the membrane fuses around the membrane fuses around the substance and moves it inside.substance and moves it inside.

d- is one of the active transport d- is one of the active transport mechanisms .mechanisms .

Write short notes onWrite short notes on::

1- Functions of cell membrane.1- Functions of cell membrane.2- Functions of membrane proteins.2- Functions of membrane proteins.3- Osmosis4- Facilitated diffusion.5- Compare and contrast:

a) Simple diffusion and active transport.b) Simple diffusion and facilitated diffusion.c) Endocytosis and exocytosis.

Which of the following is a way for Which of the following is a way for solutes in a aqueous solution to solutes in a aqueous solution to move from an area of high solute move from an area of high solute concentration to an area of low concentration to an area of low solute concentrationsolute concentration??

A.A.Facilitated diffusionFacilitated diffusionB.B.OsmosisOsmosisC.C.Active transportActive transportD.D.A and BA and BE.E.None of theseNone of these

Which of the following Which of the following defines the term specificitydefines the term specificity??

A. movement of molecules by the use of vesicles

B. the energy required to move molecules

C. a group of carrier proteins operating at their maximum rate

D. carrier transport of a group of closely related molecules

E. none of these

Water will always move from Water will always move from ___________ situations to _______ ___________ situations to _______ situationssituations..

A.A. Hyperosmotic, hyposmoticHyperosmotic, hyposmoticB.B. Hyposmotic, hyperosmoticHyposmotic, hyperosmoticC.C.Hyposmotic, isosmoticHyposmotic, isosmoticD.D.Hyperosmotic, isosmoticHyperosmotic, isosmotic

Which of the following pairs of Which of the following pairs of molecular characteristics favors molecular characteristics favors diffusion through the cell membranediffusion through the cell membrane??

A.A.Large, polarLarge, polarB.B.Large, non-polarLarge, non-polarC.C.Small, polarSmall, polarD.D.Small, non-polarSmall, non-polar

Which of the following is a way for Which of the following is a way for solutes in a aqueous solution to move solutes in a aqueous solution to move from an area of high solute from an area of high solute concentration to an area of low solute concentration to an area of low solute concentrationconcentration??

A.A.Facilitated diffusionFacilitated diffusionB.B.OsmosisOsmosisC.C.Active transportActive transportD.D.A and BA and BE.E.None of theseNone of these

،نسأل الله أن يعلمنا ما ينفعنا،وأن ينفعنا بما علمنا

وأن يزيدنا علما رمضان محمد احمد .د

[email protected]

وفي النهايةوفي النهاية