Mark Louie D. LopezDepartment of BiologyCollege of SciencePolytechnic University of the Philippines

CELL SIGNALLING and

MEMBRANE TRANSPORT

GENERIC SIGNALLING PATHWAY

ANIMAL PHYSIOLOGY

CELL RESPONSE TO SIGNALS

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CELL RESPONSE TO SIGNALS

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IMPORTANT CHARACTERS IN PATHWAYS

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Ligand

Receptors

Messengers

Kinase

Signal

Transduction

Pathway

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Assist in initiating eukaryotic transcription

Enhancers Promoter

Gene

DNA Activator

proteins

Other

proteins

Transcription

factors

RNA polymerase

Bending

of DNATranscription

TRANSCRIPTION FACTORS

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DNA

OFF OFF

Master control gene myoD Other muscle-specific genesNucleus

Embryonic

precursor cell

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DNA

OFF OFF

OFF

mRNA

MyoD protein

(transcription

factor)

Master control gene myoD

Determination. Signals from other

cells lead to activation of a master

regulatory gene called myoD, and

the cell makes MyoD protein, a

transcription factor. The cell, now

called a myoblast, is irreversibly

committed to becoming a skeletal

muscle cell.

1

Other muscle-specific genesNucleus

Myoblast

(determined)

Embryonic

precursor cell

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DNA

OFF OFF

OFF

mRNA

mRNA mRNA mRNA mRNA

Another

transcription

factor

MyoD

Muscle cell

(fully differentiated)

MyoD protein

(transcription

factor)Myoblast

(determined)

Embryonic

precursor cell

Myosin, other

muscle proteins,

and cell-cycle

blocking proteins

Other muscle-specific genesMaster control gene myoDNucleus

Determination. Signals from other

cells lead to activation of a master

regulatory gene called myoD, and

the cell makes MyoD protein, a

transcription factor. The cell, now

called a myoblast, is irreversibly

committed to becoming a skeletal

muscle cell.

1

Differentiation. MyoD protein stimulates

the myoD gene further, and activates

genes encoding other muscle-specific

transcription factors, which in turn

activate genes for muscle proteins. MyoD

also turns on genes that block the cell

cycle, thus stopping cell division. The

nondividing myoblasts fuse to become

mature multinucleate muscle cells, also

called muscle fibers.

2

Autocrine

Paracrine

Encdocrine

Neuroendocrine

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PATTERNS OF CELL COMMUNICATION

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AUTOCRINE

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PARACRINE

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ENDOCRINE

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NEUROENDOCRINE

NEED TO TRANSPORT

Cells maintain high K+ and low Na+

ICF

K+ - rich

ECF

Na+, Cl- - rich

Plasma & interstitial – similar solute composition but no

plasma proteins from the interstitium

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GRADIENT

Difference in concentration of substance on

one to to another

Chemical Gradient

Electrical Gradient

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Electric Potential

Chemical Concentration

Electrochemical gradient

GRADIENT

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GIBB-DONNAN’S EQUILIBRUIM

refers to the uneven distribution of charged

particles on one side of a semipermeable

membrane.

these particles are not able to evenly distribute

themselves by diffusion across both sides of the

membrane.

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DONNAN’S EQUILIBRUIM

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DONNAN’S EQUILIBRUIM

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MEMBRANE ELECTRIC POTENTIAL

Electrochemical equilibrium The state

at which the concentration gradient of an ion across a

membrane is precisely balanced by the electric potential

across the membrane.

Electrochemical potential The electrical

potential developed across a membrane due to a chemical

concentration gradient of an ion that can diffuse across the

membrane.

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NERNST EQUATION

The Nernst equation gives a formula that relates

the numerical values of the concentration

gradient to the electric gradient that balances it.

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NERNST EQUATION

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R= gas constant/ gas

constant, which is 8.31 (volt-

coulomb)/(mol-K)

T= absolute temperature

F= faraday’s constant/

96500 coulombs/mol

NERNST EQUATION EXAMPLE

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NERNST EQUATION EXAMPLE

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TYPES OF TRANSPORTATION

Passive Transport

allow water soluble substances (small polar molecules

and ions) to pass through the membrane without any

energy cost

Active Transport

The cell expends energy to transport water

soluble substances against their

concentration gradient

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PASSIVE TRANSPORT

Solute moves down

its electrochemical

gradient

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PASSIVE TRANSPORT

Requirements

– Membrane should be permeable

– Driving force – electrochemical gradient or

electrochemical potential energy difference

– Concentration gradient of solute

– Chemical potential energy difference

– Difference in voltage

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PASSIVE TRANSPORTFick’s Law of Diffusion describes diffusion and can

be used to solve for the diffusion coefficient

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FICK’S LAW

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OSMOSIS

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Process of net movement of water caused by a

concentration difference

From a higher to a lower water concentration

OSMOTIC PRESSURE

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OSMOTIC PRESSURE

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OSMOTIC PRESSURE

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OSMOLALITY

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Osmolality Concentration of a solution in terms of the

number of particles

OSMOLALITY COMPUTATION

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TONICITY

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TONICITY

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HemolysisCrenation

PASSIVE TRANSPORT

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• Substances cross membrane thru Intrinsic

membrane proteins

• Pores

• Channels

• Carriers

PORES

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• Always open

• Non-gated channel

• Can allow molecules <45kDa

• Examples

• Porins

• Perforin

• NPC

• Aquaporin

PORES

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Dalton is the unit for atomic

mass

PORES

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CHANNELS

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• Alternately open and close

• With movable barrier or gate

• Gated pore

• Undergo conformational

transition between open and

closed states

CHANNELS

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CARRIERS

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Facilitated passive diffusion of small solutes (eg. Glucose)

Mediate only downhill or passive transport

Do not hydrolyze ATP or couple to ETC

Each carrier protein has specific affinity for binding solutes

Fixed number of carriers to transport X

CARRIERS

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PASSIVE TRASPORT

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ACTIVE TRANSPORT

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Process that can transfer a solute uphill

across a membrane, against its

electrochemical gradient

Primary active transport (Direct)

Secondary active transport (Indirect)

ACTIVE TRASPORT

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PRIMARY ACTIVE TRASPORT

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Direct active transport

Driving force needed for the net transfer of

solute comes from the energy change

associated with ATP hydrolysis

Example: Na-K pump

Na-K PUMP

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In plasma membrane

Each cycle:

extrusion of 3Na+ and uptake of 2K+

with 1 ATP

Na-K PUMP

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SECONDARY ACTIVE TRANSPORT

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Indirect active transport

Co-transporter or Symport

Exchanger or Antiport

Driving force is provided by coupling the uphill

movement of one solute to the downhill movement

of another solute for which a favorable

electrochemical gradient exists

CO-TRANSPORTER

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Symports

Generally driven by

energy of inward directed

Na gradient

Driven solute moves in

the same direction as the

driving solute

CO-TRANSPORTER

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EXCHANGER

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Antiporters

Driven solute moves in

opposite direction of the

driving solute

Exchange cations for

cations, anions for anions

BULK FLOW

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ENDOCYTOSIS

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Process of ingestion of substances by the cell

membrane

Requires energy supplied by ATP

Requires Ca++

Lysosomes

Hydrolases

Digestive vesicle

PINOCYTOSIS

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Ingestion of small globules of extracellular

fluid

Occurs continuously

Pinocytic vesicle

100-200 nm

The only means by which most large

macromolecules esp proteins can enter cell

PINOCYTOSIS

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PINOCYTOSIS

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PHAGOCYTOSIS

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Ingestion of large particles (bacteria, cells,

degenerating tissue)

Only certain cells have this capability

Tissue macrophages

Some WBC’s

Initiated when a particle binds with the receptors

on the surface of the phagocyte

PHAGOCYTOSIS

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PHAGOCYTOSIS

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EXOCYTOSIS

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Process of excretion of undigestible

substances by the cell membrane

Opposite of endocytosis

Example

Release of neurotransmitters from the

presynaptic nerve endings

Release of pancreatic enzyme from

acinar cells of pancreas

EXOCYTOSIS

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EXOCYTOSIS

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2nd reviewReview

Present a summary of the original article regarding

the fluid-mosaic model of cell membrane

Limit your presentation to 10 slides. The slide must

include important aspect of the paper

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