The Working Cell Cells workby Moving substance into

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

Membranes are fluid mosaics of lipids and proteins with many functions ATP Glycoprotein CYTOPLASM

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 Equilibrium

Type of Transport Simple Diffusion Osmosis Facilitated Diffusion Active Transport Exo/Endocytosis Passive or Energy Concentration Gradient Membrane Protein Phospholipids Examples

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.

Lower Higher concentration of solute Solute molecule Equal concentrations of solute H 2 O Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Osmosis

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- _________

Water balance between cells and their surroundings is crucial to organisms 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!

2% sucrose solution 1 liter of distilled water 1 liter of 10% sucrose solution Hypotonic Conditions Hypertonic Conditions 1 liter of 2% sucrose solution Isotonic Conditions

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

Transport proteins can facilitate diffusion across membranes Solute molecule Transport protein Membrane proteins can be channels or carriers (facilitated diffusion)

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.

Cells expend energy in the active transport of a solute Transport protein Solute 1 Solute binding 2 P ATP ADP Phosphate attaching P Protein changes shape. 3 Transport Phosphate P detaches. 4 Protein reversion

Example of Active Transport: Calcium Pump

Example of Active. Transport/ Pump/Cotransport: Sodium-Potassium 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 transmission

Move in response to gradient Uses energy to move against gradient High Concentration gradient across cell membrane ATP Simple. Diffusion of lipid-soluble Substances across bilayer Passive transport of watersoluble substances through channel protein; no energy input needed aka Facilitated Diffusion Active transport through ATPase; requires energy input from ATP Low

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

Type of WBC, defensive function parasite macrophage

Membrane Cycling 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.

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 100/le cturesf 04 am/lect 09. 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 (1 st 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. (2 nd 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.

Energy conversion Fuel Waste products Heat energy Carbon dioxide Gasoline Combustion Kinetic energy of movement Water Oxygen Energy conversion in a car Heat energy Glucose Oxygen Cellular respiration ATP Energy for cellular work Energy conversion in a cell Carbon dioxide Water

Cells transform energy as they perform work 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

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 drives cellular work by coupling exergonic and endergonic reactions § ATP, adenosine triphosphate, powers nearly all forms of cellular work. § ATP consists of – __________________________, – _____________.

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.

ATP: Adenosine Triphosphate Phosphate group P P Adenine P Ribose Hydrolysis P ADP: H 2 O P Adenosine Diphosphate P Energy

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” This reaction is binding A and B together Energy “out”

A specific enzyme catalyzes each cellular reaction • Larger than substrates ( reactants that bind to the enzyme) • Take reactants apart OR put reactants together

Binding of substrate to enzyme is… • Temporary • Weak • Changes the enzyme’s shape very slightly (induced-fit)

1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Glucose Substrate binds to enzyme with induced fit Enzyme (sucrase) Fructose H 2 O 4 Products are released 3 Substrate is converted to products

A specific enzyme catalyzes each cellular reaction § Enzyme activity is affected by: – Temperature – p. H – Cofactors (inorganic) – Coenzymes (organic) – Competitive inhibitors – Noncompetitive inhibitors

Enzyme inhibitors can regulate enzyme activity in a cell Substrate Active site Enzyme Allosteric site Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Enzyme inhibition

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_pla ce/labbench/lab 2/concepts. html Enzyme Activity (other useful animations too) http: //www. lpscience. fatcow. com/jwanamaker/animations. htm

You should now be able to 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.