CELL TRANSPORT

By: Dr. Tess Consulta

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Cell Membrane• Cell membrane helps organisms

maintain homeostasis by controlling what substances may enter or leave cells.

Watch the video discussing the cell membrane structure

https://www.youtube.com/watch?v=79QDkdpHgBk

Functions of the membrane components

PHOSPHOLIPIDS• constitute about 50% of the plasma

membrane of most animal cells. Removal/destroyed: • leads to cell death due to loss of

structural ability of the membrane.• cell loses the boundary that

regulates its interaction with its external environment.

CHOLESTEROL• reduces membrane fluidity at room

temperature but prevents the solidification of the membrane at room temperature.

If removed/destroyed: • increase membrane fluidity thus,

increasing membrane permeability. Cause cells to open more rapidly

• Membrane will instantly freeze at cold temperature

UNSATURATED HYDROCARBON TAILS IN THE PHOSPHOLIPID

• Prevents the phospholipid molecules from packing together, thus phospholipid can move laterally within the membrane increasing fluidity.

• Removal of this reduces permeability of the membrane, so normal exchange of materials between the cell and environment will be disrupted.

CARBOHYDRATE CHAINS

• Important in cell interaction or recognition

• Used as markers to distinguish cells from one another

• Removal cause breakdown in immune response since the body cannot distinguish its own cells from those of its pathogens

PROTEIN CHANNELS

• act as a passive pore. • Molecules will randomly

move through the opening in a process called diffusion.

• This requires no energy, molecules move from an area of high concentration to an area of low concentration

Two main components of the cell membrane

• 1. Lipids (cholesterol and phospholipid)

• 2. proteins

Two main functions of the cell membrane

1. Protects the cell from its outer environment.

2. Regulates the entrance and exit of substances in the cell

TYPES OF MEMBRANE PERMEABILITY

• Permeable – allows all substances to pass through

• Semi permeable – selects substances to pass through

• Impermeable – does not allow any substances to pass through

Summing upPHOSPHOLIPIDS• For the boundary and structural ability

of the membrane.

CHOLESTEROL• For membrane fluidity and prevents the

solidification of the membrane at room temperature.

Summing upUNSATURATED HYDROCARBON TAILS IN THE

PHOSPHOLIPID• Prevents the phospholipid molecules from

packing together

CARBOHYDRATE CHAINS• Important in cell interaction or recognition

PROTEIN CHANNELS• act as a passive pore.

PASSIVE TRANSPORT:DIFFUSION

• If you spray or apply a cologne or perfume to yourself, how come that the people surrounding you are also able to smell the fragrance?

• The perfume or cologne evaporates and diffuses out from the wearer

Passive Transport• A Process where substances can cross

the cell membrane without any input of energy by the cell.

Diffusion• Movement of molecules from an area of

higher to lower concentration.

Concentration Gradient•Concentration of molecules across a distance

Watch the video on Diffusion

https://www.youtube.com/watch?v=mlB7yU_uZNc

Simple Demonstration Result

Simple Demonstration Result

Simple Demonstration Explained

• Diffusion is driven by molecule energy and randomly travels on a straight line until they hit an object.

• In the absence of other influences, diffusion will eventually cause the molecules to be in equilibrium

Maintaining Equilibrium

• If the beaker of the water is left undisturbed, The concentration of the molecules will be the same throughout the space the molecule occupies

• The random molecules of many molecules in many directions balance one another and equilibrium is maintained

Diffusion Across a MembraneSimple Diffusion: •A molecule across a cell membrane depends on the size, type of the molecule and on chemical nature of the membrane.

Phospholipid bilayer and proteins form pores in the membrane:•Molecules that can dissolve in lipids can pass through the membrane.•Example Carbon and Oxygen (non polar)•Small Non polar molecules pass through the pores

What is the relationship of cell size to diffusion

• It is inversely proportional• As the size of the cell increases, the

rate of diffusion decreases.

What is the relationship of temperature to diffusion

• It is directly proportional• As the temperature increases, the rate

of diffusion increases.

What is the relationship of temperature to kinetic energy

of molecules

• It is directly proportional• As the temperature increases, the

kinetic energy of molecules increases.

Summing upPASSIVE TRANSPORT• substances can cross the cell membrane

without any input of energy by the cell.

DIFFUSION• Movement of molecules from an area of

higher to lower concentration

Summing upHow is Equilibrium achieved in the simple demonstration?•Diffusion is driven by molecule energy and randomly travels on a straight line until they hit an object. In the absence of other influences, diffusion will eventually cause the molecules to be in equilibrium

How do molecules maintain homeostasis?•The random molecules of many molecules in many directions balance one another and equilibrium is maintained

Summing upHow does simple diffusion happens?

• A molecule across a cell membrane depends on the size, type of the molecule and on chemical nature of the membrane.

• Molecules that can dissolve in lipids can pass through the membrane while Small polar molecules pass through the pores

OsmosisObjectives:1.Distinguish between diffusion and Osmosis2.Differentiate hypotonic, hypertonic and isotonic solution3.Elucidate on how cells deal with osmosis

Osmosis• What is the reason why fruit and

vegetable vendors would occasionally sprinkle water on the fruits and vegetables?

- to maintain the crispiness of the fruits and vegetables

SolutionA solution is composed of a solute dissolved in a solvent.

Sugar water Demo:Solute – the one’s being dissolved. Ex. sugarSolvent – The one’s dissolving solutes. Ex. water

OSMOSIS• diffusion of water across a semi-

permeable (or differentially permeable or selectively permeable) membrane

• Still no energy is required • Net direction of osmosis depends on

the relative concentration of solutes on the two sides of the membrane

DIRECTION OF OSMOSIS• Hypotonic – the concentration of solute

molecules outside the cell is lower than the concentration in the cytosol (water diffuses into the cell until equilibrium is achieved)

DIRECTION OF OSMOSIS• Hypertonic– the concentration of solute

molecules outside the cell is higher than the concentration in the cytosol (water diffuses out of the cell until equilibrium is achieved).

DIRECTION OF OSMOSIS• Isotonic– the concentration of solute

molecules outside and inside the cell is equal. Water diffuses inside and outside of the cell at equal rates

Types of osmotic solutions

Effects of Osmosis in cells

Summary of OsmosisDescription Movement of

waterEffects on cells

Example

Hypotonic concentration of solute molecules outside the cell is lower than inside the cell

Water moves inside the cell

Swelling and bursting of cells

Turgor pressure

Sprinkling water on fresh vegetables to maintain its crispiness

Hypertonic concentration of solute molecules outside the cell is higher than inside the cell

Water moves outside the cell

Shrinking of cells (plasmolysis)

Food preservation with salt or sugar

Isotonic concentration of solute molecules outside and inside the cell is equal

Water moves equally inside and outside the cell

The cell remains the same

Isotonic IV solution to prevent patient’s dehydration

Practical Applications of Osmosis

Watch this videohttps://www.youtube.com/watch?

v=Br4_SAbRE4w

HOW A PARAMECIUM DEALS WITH OSMOSIS

• http://www.sabah.edu.my/csm07010/form%204/osmosis3.htm

SIMPLE SORE THROAT REMEDY• swelling of the throat tissues due to the

accumulation of extra cellular fluid. • Salt water has a higher solute concentration that this

extracellular fluid, so water moves by osmosis from the throat tissues into the salt water decreasing the swelling and relieving some of the pain.

• The salt water also may kill bacteria it contacts.

AGRICULTURE: OSMOSIS AND CHERRIES

• Pure rain-water on a ripe, sugar filled cherry will begin to diffuse inward, causing the cherry to swell and split, and ruin the fruit.

• Orchardists sprays the water soaked cherry trees with calcium chloride

• This nontoxic substance increases the concentration of the solute outside the cherry, reducing inward diffusion.

KIDNEY DIALYSIS• In 1938, a Dutch Physician Willem Kolff invented a

machine that is known today as kidney dialysis

FOOD PRESERVATION BY PIONEERS

• When American pioneers moved west in the 19th century, they often preserved food, especially meat by burying it in casks of salt.

• Bacteria that would land on the salt would quickly die because water would move out of them by osmosis.

Objectives1. To explain how substances cross the cell membrane through facilitated diffusion.

2. Explain how ion channels assist the diffusion of ions across the cell membrane

Watch this video on facilitated diffusion

https://www.youtube.com/watch?v=IX-kLh34KcQ

https://www.youtube.com/watch?v=LsTo73joO0U

Facilitated diffusion- Still a form of passive transport- Used for molecules that cannot readily diffuse to cell membranes (because these molecules cannot dissolve in lipids or too large to pass on membrane pores)

Two properties of facilitated diffusion

Transport of Glucose1.Facilitated diffusion can help substances move in and out of the cell depending on the concentration gradient

(when the level of glucose is higher inside a cell than the outside, facilitated diffusion speeds the diffusion of glucose out of the cell)

Two properties of facilitated diffusion

Transport of Glucose2. Carrier proteins involved in facilitated diffusion are each specific for one type of molecule

Example: The carrier proteins that helps in the diffusion of glucose and sugars does not assist with the diffusion of amino acids

Diffusion Through Ion Channels

• Ion channels – transport ions such as sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-)

• Some ion channels are always open

Diffusion Through Ion Channels

• Some have “gates” that open and close in response to:

Stretching of the cell membraneElectrical signalsChemicals in the cell or external environment

How far have you learned?

Open your book on page 101 – 102. Answer the following questions below in your copy book.

1.What is the similarity between simple diffusion and facilitated diffusion?2.What is the difference between simple and facilitated diffusion?3.What role do carrier proteins play in facilitated diffusion?4.What are the substances that ion channels transport into the cell?5.Make a schematic diagram tracing the process of facilitated diffusion.6.How is facilitated diffusion similar to diffusion through ion channels?7.What types of stimuli can cause the gates on ion channels to open or close?

What role do carrier proteins play in facilitated diffusion?

• Carrier proteins bind to molecules to one side of the cell membrane, the proteins change shape, and then the proteins release the molecules on the other side of the membrane.

How is facilitated diffusion similar to diffusion through ion

channels?

• Both processes can help move down their concentration gradients from one side of the cell membrane to the other, without an input of energy by cells.

• Both processes involves membrane proteins.

What is the similarity between simple diffusion and facilitated diffusion?

• Both are passive transport• Both do not require energy• Both of their molecules from higher to

lower concentration• Both are involve in movement of

materials in and out of the cell• Both involves membrane proteins

What are the substances that ion channels transport into the cell?

• transport ions such as sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-)

What is the difference between simple and facilitated diffusion?

• Simple diffusion occurs when small molecules pass through the lipid bilayer of a cell membrane.

• Facilitated diffusion depends on carrier proteins embedded in the membrane to allow specific substances to pass through that might not be able to diffuse through the cell membrane.

What types of stimuli can cause the gates on ion channels to open or

close?

Stretching of the cell membraneElectrical signalsChemicals in the cell or external environment

HomeworkRead the short article on eco-connection page 102 in your book.•Answer the following questions in your copy book:1.Does Osmosis requires energy expenditure by a cell? Explain.2.Does reverse osmosis require energy expenditure? Why?3.If reverse osmosis occurred in cell, What kind of transport would it be?

Reinforcement ActivityAnswer questions # 1 to 8 on passive transport (page 102) in your copy book. Write your answers on your copy book. Submit your copy book to your instructor at the end of the period.

ObjectivesTo evaluate the learning outcome of students.

Objectives

Chapter 5: Lesson 2(Active Transport)

1.To distinguish between passive transport and active transport2.To explain how the sodium-potassium pump operates3.Compare endocytosis and Exocytosis

ACTIVE TRANSPORT• Movement of materials from lower

concentration to higher concentration (“up” their concentration gradient)

• Requires energy from the cell

CELL MEMBRANE PUMPS• Sodium-Potassium Pump

• transports Na+ and K+ ions up their concentration gradients

VIDEO: https://www.youtube.com/watch?v=MRKgbwl8vCY

Steps of the Sodium-Potassium Pump1. Three Na+ ions from the

inside of the cell bind to the carrier protein

2. A phosphate group is removed from ATP and bound to the carrier protein

3. The carrier protein changes shape, allowing three Na+ ions to be released to the outside of the cell

Steps of the Sodium-Potassium Pump4. Two K+ ions from the

outside of the cell bind to the carrier protein

5. The phosphate group is released and the carrier protein goes back to its original shape

6. The two K+ ions are released to the inside of the cell and the cycle is ready to repeat

Importance of the Sodium-Potassium Pump• The ion exchange creates an electrical gradient

across the cell membrane– Outside becomes positively charged– Inside becomes negatively charged

• This difference in charge is important for the conduction of electrical impulses along nerve cells

Summing upSodium-Potassium pump

Sodium ions Potassium Ions

Pumps three Pumps two

Out of the cell into the cell

• Used for:– Substances that are too large to pass through the

cell membrane– Transporting large amounts of small molecules into

or out of cells at the same timeVideo: https://www.youtube.com/watch?v=DuDmvlbpjHQ

Movement in Vesicles

Latin word: Vesicula (bladder or sac)

Endocytosis• Process in which cells ingest external

fluid, macromolecules, and large particles, including other cells

• Two types of endocytosis:– Pinocytosis – transport of solutes or fluids

(cell drinking)– Phagocytosis – transport of large particles

or whole cells (cell eating)

Endocytosis

1. The cell folds around the food or liquid and forms a small pouch.

2. the pouch pinches off from the cell membrane to become a vesicle.

Exocytosis• Process by which a substance is released

from the cell through a vesicle that transports the substance to the cell surface and then fuses with the membrane to let the substance out of the cell

Exocytosis

1. Vesicle moves through the cell membrane2. fuses with the cell membrane3. releases it content to the outside cell.

Examples include the transport of insulin and cholesterol into animal cells.

Reinforcement ActivityAnswer questions # 1 to 9 on passive transport (page 106) in your copy book. Write your answers on your copy book. Submit your copy book to your instructor at the end of the period.

ObjectivesTo evaluate the learning outcome of students.

Watch this video as a summary of all the topics

discussed

https://www.youtube.com/watch?v=dPKvHrD1eS4

Concept map summary