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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