The Working Cell

• Cells “work”by – Moving substance into and out of the cell.– Doing chemical reactions which utilize

enzymes.

CYTOPLASM

GlycoproteinATP

Membranes are fluid mosaics of lipids and proteins with many functions

Membranes are fluid mosaics of lipids and proteins with many functions

Membrane proteins perform many functions.

1. Some proteins help maintain cell shape and coordinate changes inside and outside the cell through their attachment to the cytoskeleton and extracellular matrix.

2. Some proteins function as receptors for chemical messengers from other cells.

3. Some membrane proteins function as enzymes.

Membranes are fluid mosaics of lipids and proteins with many functions

4. Some membrane glycoproteins are involved in cell-cell recognition.

5. Membrane proteins may participate in the intercellular junctions that attach adjacent cells to each other.

6. Membrane proteins transport substances across the membrane.

EVOLUTION CONNECTION: Membranes form spontaneously, a critical step in the origin of life

Phospholipids, the key ingredient of biological membranes, spontaneously self-assemble into simple membranes.

The formation of membrane-enclosed collections of molecules was a critical step in the evolution of the first cells.

Types of transportation possible across membrane….

Diffusion-

Simple diffusion-

Osmosis-

Facilitated Diffusion-

Active Transport-

Bulk Flow/Exocytosis/Endocytosis-

Molecules of dye Membrane

Pores

Net diffusion Net diffusion Equilibrium

Type of Transport

Passive or Energy

Concentration Gradient

Membrane Protein

Phospho

-lipids Examples

SimpleDiffusion

Osmosis

FacilitatedDiffusion

Active Transport

Exo/Endo-cytosis

Diffusion-overview• Substances move down the concentration

gradient• Passive, requires no energy• Speed dependent on:

– Concentration difference, steepness– Temperature– Size of molecules– Presence of electric charge– Pressure

Osmosis is the diffusion of water across a membrane

One of the most important substances that crosses membranes is water.

The diffusion of water across a selectively permeable membrane is called osmosis.

Osmosis

Solute moleculewith cluster ofwater molecules

Watermolecule

Selectivelypermeablemembrane

Solutemolecule

H2O

Lowerconcentration

of solute

Higherconcentration

of solute

Equalconcentrations

of solute

Water balance between cells and their surroundings is crucial to organisms

Tonicity is a term that describes the ability of a solution to cause a cell to gain or lose water.

Tonicity mostly depends on the concentration of a solute on both sides of the membrane.

– Hypotonic- _______________

– Hypertonic- _______________

– Isotonic- __________________

RBC

Most animal cells lack the ability to prevent lysis if placed in a hypotonic solution.Human cells are about 0.9% saline (salt water).

So cells are isotonic to a 0.9% saline solution. Ocean water is about 3.5 % salt.SO…now you know why you can’t drink salt water!

Water balance between cells and their surroundings is crucial to organisms

2% sucrose solution

1 liter of distilled water

1 liter of 10% sucrose

solution

1 liter of 2% sucrose

solution

HypotonicConditions

HypertonicConditions

IsotonicConditions

Water balance between cells and their surroundings is crucial to organisms

For an animal cell to survive in a hypotonic or hypertonic environment, it must engage in osmoregulation, the control of water balance.

The cell walls of plant cells, prokaryotes, and fungi make water balance issues somewhat different.

– The cell wall prevents the cell from taking in too much water but pressure builds up! This is called turgor pressure.

Turgor Pressure

Solutemolecule

Transportprotein

Membrane proteins can be channels or carriers (facilitated diffusion)

Transport proteins can facilitate diffusion across membranes

Example of

Facilitative Diffusion:

glucose transporter (channel)

SCIENTIFIC DISCOVERY: Research on another membrane protein led to the discovery of aquaporins

Dr. Peter Agre received the 2003 Nobel Prize in chemistry for his discovery of aquaporins.

– Because water is polar, its diffusion through a membrane’s hydrophobic interior is relatively slow.

– The very rapid diffusion of water into and out of certain cells is made possible by a protein channel called an aquaporin.

His research on the Rh protein used in blood typing led to this discovery.

Transportprotein

Solute ADPATP P P PProtein

changes shape.Phosphatedetaches.

Solute binding Phosphateattaching

Transport Proteinreversion

4321

Cells expend energy in the active transport of a solute

Example of Active Transport:

Calcium Pump

• Moves 2 kinds of ions in opposite directions.• Requires ATP• 3 Na+ move out of cell, 2 K+ ions move in• Important in nerve cell impulse transmissionExample of

ActiveTransport/

Pump/Cotransport:

Sodium-Potassium Pump

High

Concentrationgradient acrosscell membrane

Low

SimpleDiffusion of lipid-solubleSubstancesacross bilayer

Passive transport of water-soluble substancesthrough channel protein;no energy input needed

Active transportthrough ATPase;requires energyinput from ATP

ATP

aka Facilitated Diffusion

Move in response to gradient Uses energy to move against gradient

Exocytosis and endocytosis transport large molecules across membranes

There are three kinds of endocytosis.

1. Phagocytosis

2. Pinocytosis

3. Receptor-mediated endocytosis

Endocytosis (vesicles in)

Exocytosis (vesicles out)

Receptor-mediated Endocytosis

parasite macrophage

Type of WBC, defensive function

Proteins that will become part of the cell membrane are shipped in vesicles that fuse with the Golgi body. They are modified and sent off in other vesicles that fuse with the plasma membrane. In this way the cell membrane can be replaced and repaired as needed.

Membrane Cycling

Why is movement across a membrane important?

• Cells need raw materials– _____________________– _____________________– _____________________

• Cells need to get rid of waste:– ____________________– ____________________

• Cells need to maintain water balance:– __________________________– __________________________– ___________________

Cystic Fibrosis

• CFTR is a protein

channel which allow

for the movement of Cl-,

followed by water• Thin, slippery film is

produced on surface of cell/tissue• Single amino acid change in

protein causes the CFTR to be

destroyed before reaching cell membrane• No film causes mucus to dry out and become sticky

Internet sites

Diffusion, Osmosis, and Movement Across a Membrane: Summary Info

• http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect09.htm

The Working Cell

• Cells “work”by – Moving substance into and out of the cell.– Doing chemical reactions which utilize

enzymes.

Energy Flows• Energy is not created or destroyed, there is a finite

amount of energy in the universe

(1st law of thermodynamics)

• Energy is converted from one form to another. It flows in one direction, spontaneously, from a concentrated (ordered) form to a less concentrated form. Energy disperses.

(2nd law of thermodynamics)

– Example: photosynthesis converts solar energy to chemical energy

Cells transform energy as they perform work

Cells are small units, a chemical factory, housing thousands of chemical reactions.

Cells use these chemical reactions for

– cell maintenance,

– manufacture of cellular parts, and

– cell replication.

Cells transform energy as they perform work

Energy is the capacity to cause change or to perform work.

There are two kinds of energy.

1. Kinetic energy is the energy of motion.

2. Potential energy is energy that matter possesses or stores as a result of its location or structure.

Fuel Energy conversion Waste products

Gasoline

Oxygen

Oxygen

Glucose

Heatenergy

CombustionKinetic energyof movement

Energy conversion in a car

Energy conversion in a cell

Energy for cellular work

Cellular respiration

ATP ATP

Heatenergy

Carbon dioxide

Carbon dioxide

Water

Water

Chemical reactions are either:•Endergonic

– Requires input of energy– Products are high in potential energy– Ex. Photosynthesis

•Exergonic– Releases energy– More energy in reactants than products– Ex. Cellular Respiration

Cells transform energy as they perform work

Chemical reactions either release or store energy

Photosynthesis is a type of endergonic process.

– Energy-poor reactants, carbon dioxide, and water are used.

– Energy is absorbed from sunlight.

– Energy-rich sugar molecules are produced.

ATP, adenosine triphosphate, powers nearly all forms of cellular work.

ATP consists of

– __________________________,

– ___________________________,

– ________________________.

ATP drives cellular work by coupling exergonic and endergonic reactions

ATP drives cellular work by coupling exergonic and endergonic reactions

Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule in a process called phosphorylation.

Most cellular work depends on ATP energizing molecules by phosphorylating them.

ADP: Adenosine Diphosphate

P P P Energy

H2OHydrolysis

Ribose

AdenineP P P

Phosphategroup

ATP: Adenosine Triphosphate

Enzymes speed up the cell’s chemical reactions by lowering energy barriers

Although biological molecules possess much potential energy, it is not released spontaneously.

– An energy barrier must be overcome before a chemical reaction can begin.

– This energy is called the activation energy (EA).

Role of ENZYMES…• ENZYMES ARE PROTEINS

• Shape determines function, Specific• Lowers activation energy (energy needed to run a reaction)

• Catalysts (make enzymes occur faster, millions of times faster)

Energy “in”

Energy “out”

This reaction is binding A and B

together

• Larger than substrates ( reactants that bind to the enzyme)

• Take reactants apart OR put reactants together

A specific enzyme catalyzes each cellular reaction

Binding of substrate to enzyme is…• Temporary

• Weak

• Changes the enzyme’s shape very slightly (induced-fit)

4

3

2

1

Products arereleased

Fructose

Glucose

Enzyme(sucrase)

Active site

Enzyme availablewith empty activesite

Substrate(sucrose)

Substrate bindsto enzyme withinduced fit

Substrate isconverted toproducts

H2O

A specific enzyme catalyzes each cellular reaction

Enzyme activity is affected by:

– Temperature

– pH

– Cofactors (inorganic)

– Coenzymes (organic)

– Competitive inhibitors

– Noncompetitive inhibitors

Substrate

Enzyme

Allosteric site

Active site

Normal binding of substrate

Competitiveinhibitor

Noncompetitiveinhibitor

Enzyme inhibition

Enzyme inhibitors can regulate enzyme activity in a cell

Enzyme inhibitors can regulate enzyme activity in a cell

Enzyme inhibitors are important in regulating cell metabolism.

Enzyme

Biology Place Enzyme Catalysis

http://www.phschool.com/science/biology_place/labbench/lab2/concepts.html

Enzyme Activity (other useful animations too)

http://www.lpscience.fatcow.com/jwanamaker/animations.htm

1. Describe the fluid mosaic structure of cell membranes.

2. Describe the diverse functions of membrane proteins.

3. Define diffusion and describe the process of passive transport.

4. Explain how osmosis can be defined as the diffusion of water across a membrane.

5. Distinguish between hypertonic, hypotonic, and isotonic solutions.

You should now be able to

6. Explain how transport proteins facilitate diffusion.

7. Describe movement of molecules across the membrane by active transport.

8. Distinguish between exocytosis/endocytosis, phagocytosis/pinocytosis, and receptor-mediated endocytosis.

9. Define and compare kinetic energy, potential energy, chemical energy, and heat.

10.Define the two laws of thermodynamics and explain how they relate to biological systems.

You should now be able to

11. Define and compare endergonic and exergonic reactions.

12. Explain how ATP functions as an energy shuttle.

13. Explain how enzymes speed up chemical reactions.

14. Explain how competitive and noncompetitive inhibitors alter an enzyme’s activity.

You should now be able to