1. Chapter 5
The Working Cell

2. Chapter 5: Concepts Energy : Kinetic, Potential, chemical and Entropy
ATP: How we get energy out of it
Enzymes: Activation energy, importance of shape
Membrane function: Active and Passive transport plus cell signaling
Osmosis
Exocytosis and Endocytosis

3. Biology and Society: Natural Nanotechnology
Cells control their chemical environment using
Energy
Enzymes
The plasma membrane
Cell-based nanotechnology may be used to power microscopic robots.
© 2010 Pearson Education, Inc.
All living processes depend on energy which is supplied by the cell through a process called glycolysis. The energy is released by the breakdown of food molecules using enzymes. In this chapter we will study how a cell uses energy, enzymes and PM to carry out the work of controlling its internal chemical environment.

4. SOME BASIC ENERGY CONCEPT
Energy makes the world go round. All organisms require energy to stay alive
Energy is defined as the capacity to perform work.
Whenever something moves against an opposing force, work is performed
Some forms of energy are used to perform work.
Energy is the ability to rearrange a collection of matter.
Energy primarily come into two different types
Kinetic energy is the energy of motion.
Potential energy is stored energy. It is energy that an object has because of its location or structure.
Energy is defined as the capacity to perform work and it makes the world go around. Work is performed whenever an object is moved against an opposing force. Work must be performed when you climb up stairs to overcome the force of gravity.
Potential energy is energy that an object has because of its location or structure such as water stored in dam or in a compressed spring.

5. Energy conversions during a dive
In living systems, energy is converted in an energy cycle from kinetic to potential energy and back
Climbing the steps converts
Kinetic energy of muscle
movement to potential energy.
On the platform,
the diver has more
potential energy.
Diving converts
potential energy
to kinetic energy.
In the water, the
diver has less
Figure 5.1Energy conversions during a dive

6. Conservation of Energy
Machines and organisms can transform kinetic energy to potential energy and vice versa.
In all such energy transformations, total energy is conserved.
First law of Thermodynamics
Energy can be changed from one form to another
Energy cannot be created or destroyed, only converted primarily into heat
This is the principle of conservation of energy
Energy is defined as the capacity to perform work and it makes the world go around. Work is performed whenever an object is moved against an opposing force. Work must be performed when you climb up stairs to overcome the force of gravity.
Potential energy is energy that an object has because of its location or structure such as water stored in dam or in a compressed spring.

7. For example, the chemical energy (=potential energy) in the covalent bonds of gasoline molecules is converted to kinetic energy to move the car

8. Heat
Every energy conversion releases some randomized energy in the form of heat.
Heat is a
a type of kinetic energy contained in the random motion of atoms and molecules
a product of all energy conversions
If energy is not destroyed where it has gone when the diver hits the water? It has been converted to heat in the air and then in water which is produced by the friction between the body and its surroundings.

9. Entropy
Scientists use the term entropy as a measure of disorder, or randomness in a system.
All energy conversions increase the entropy of the universe
This is because some energy is always “lost” as heat
No energy conversion is ever perfectly 100% efficient
Example: food web trophic levels
This is the second law
of Thermodynamic
If energy is not destroyed where it has gone when the diver hits the water? It has been converted to heat in the air and then in water which is produced by the friction between the body and its surroundings.

10. Chemical Energy
Molecules store varying amounts of potential energy in the arrangement of their atoms.
Organic compounds are relatively rich in such chemical energy.
Is found in food, gasoline and other fuels
Living cells and automobile engines use the same basic process to make chemical energy do work.
Cellular respiration is the energy-releasing chemical breakdown of fuel molecules that provides energy for cells to do work.
Humans convert about 40% of the energy in food to useful work, such as the contraction of muscles.
Carbs, fats and gasoline have structures that makes them especially rich in chemical energy. Whether it is a living cells or automobile engines, they use the same basic process to make chemical energy do work. They breakdown the organic fuel molecules thereby releasing the energy for cells to do work.
About 60% of energy released generates the body heat.

11. Energy conversions in a car and a cell
Fuel rich in
chemical
energy
Energy conversion
Waste products
poor in chemical
Gasoline 
Oxygen
Carbon dioxide
Water
Energy conversion in a car
Energy for cellular work
Energy conversion in a cell
Heat
Food
Combustion
Cellular
respiration
Kinetic energy
of movement
ATP
Figure 5.2 Energy conversions in a car and a cell
In both car and a cell, the chemical energy of organic fuel is harvested using oxygen. This chemical breakdown releases energy stored in the fuel molecules and produces CO2 and H2O. The released energy can be used to perform work.

12. Food Calories A calorie is a unit of energy
the amount of energy that raises the temperature of 1 gram of water by 1 degree Celsius (°C).

13. Food Calories Food Calories are kilocalories, equal to 1,000 calories.
The energy of calories in food is burned off by many activities.
(a) Food Calories (kilocalories) in
various foods
(b) Food Calories (kilocalories) we
burn in various activities
Cheeseburger
Spaghetti with sauce (1 cup)
Pizza with pepperoni (1 slice)
Peanuts (1 ounce)
Apple
Bean burrito
Fried chicken (drumstick)
Garden salad (2 cups)
Popcorn (plain, 1 cup)
Broccoli (1 cup)
Baked potato (plain, with skin)
Food Calories
Food
295
241
220
193
181
166 81 56
189 31 25
Activity
Food Calories consumed per
hour by a 150-pound person*
979
510
490
408
204 73 61
245 28
Running (7min/mi)
Sitting (writing)
Driving a car
Playing the piano
Dancing (slow)
Walking (3 mph)
Bicycling (10 mph)
Swimming (2 mph)
Dancing (fast)
*Not including energy necessary for basic functions, such
as breathing and heartbeat
Figure 5.3 Some caloric accounting

14. ATP AND CELLULAR WORK
Chemical energy of organic molecules is released by the breakdown of organic molecules during cellular respiration and used to generate molecules of ATP
ATP
Acts like an energy shuttle
Stores energy obtained from food
Releases it later as needed

15. Blast Animation: Structure of ATP
The Structure of ATP
ATP (adenosine triphosphate)
consists of adenosine plus a tail of three phosphate groups
ATP is broken down to ADP and a phosphate group, releasing energy
Triphosphate
Diphosphate
Adenosine
Energy
ATP
ADP P
Phosphate
(transferred to
another molecule)
Blast Animation: Structure of ATP
Figure 5.4 ATP power

16. Phosphate Transfer
ATP
ADP P X Y
(a) Motor protein performing mechanical work
(b) Transport protein performing transport work
(c) Chemical reactants performing chemical work
Solute
Solute transported
Protein moved
Product made
Reactants
Transport
protein
Motor
ATP can energizes other molecules by transferring phosphate groups.
This energy helps cells perform
Mechanical work
Transport work
Chemical work
Figure 5.5 How ATP drives cellular work
Each type of work shown here is powered when enzymes transfer phosphate from ATP to a recipient molecule.
Chemical work: the transport of ions prepares the brain cells to transmit signals to muscles and other tissues.
All these types of work occur when target molecules accept a phosphate group from ATP.

17. The ATP Cycle Cellular work spends ATP.
ATP is recycled from ADP and a phosphate group through cellular respiration.
A working muscle cell spends and recycles about 10 million ATP molecules per second.
Cellular respiration:
chemical energy
harvested from
fuel molecules
Energy for
cellular work
ATP
ADP P
Figure 5.6 The ATP cycle

18. Enzymes and Activation Energy
Metabolism is defined as the total of all chemical reactions in an organism.
Most metabolic reactions require the assistance of enzymes, proteins that speed up chemical reactions.
Activation energy
Is the energy needed to cause a reaction to occur
Activates the reactants
Triggers a chemical reaction
Enzymes lower the activation energy for chemical reactions.
For a reaction to begin the chemical bonds between the reactants must be broken which requires the molecules to absorb energy from their surroundings. This energy is caller Activation energy because it activates the reactants and triggers a chemical reaction.
Enzymes lower the activation energy required to break the bonds of reactant molecules. It does so by bindng to reactant molecules and putting them under physical or chemical stress, making it easier to break their bonds and start a reaction.

19. Enzymes and activation energy
A protein catalyst called an enzyme can lower the energy
activation and therefore decrease the energy barrier
Reactant = sucrose
Products = glucose and fructose
Activation
energy barrier
Activation
energy barrier
reduced by
enzyme
Enzyme
Reactant
Reactant
Energy level
Energy level
Products
Products
(a) Without enzyme
(b) With enzyme
Figure 5.7 Enzymes and activation energy

20. Induced Fit
Every enzyme is very selective, catalyzing a specific reaction.
Each enzyme recognizes a substrate, a specific reactant molecule.
The active site fits to the substrate, and the enzyme changes shape slightly.
This interaction is called induced fit because the entry of the substrate induces the enzyme to change shape slightly.
Enzymes can function over and over again, a key characteristic of enzymes.
Many enzymes are named for their substrates, but with an –ase ending (e.g., dehydrogenase)
The ability of the enzyme to recognize and bind to its specific substrate depends on the enzyme’s shape. The enzyme’s active site has a shape and chemistry that fit the substrate molecule.

21. How an enzyme works
Enzymes are used multiple times because they are catalysts
Substrate (sucrose)
Sucrase can accept a
molecule of its substrate.
Active site
Substrate binds
to the enzyme.
Enzyme
(sucrase)
Fructose
H2O
Glucose
The products
are released.
The enzyme
catalyzes the
chemical reaction.
Figure 5.9 How an enzyme works (Step 4)

22. Enzyme Inhibitors
Enzyme activity is influenced by temperature, salt concentration and pH
Enzyme inhibitors can prevent metabolic reactions by binding to the active site.
near the active site, resulting in changes to the enzyme’s shape so that the active site no longer accepts the substrate.
Other enzyme inhibitors
Bind at a remote site
Change the enzyme’s shape
Prevent the enzyme from binding to its substrate

23. Enzyme inhibitors Substrate (a) Enzyme and substrate Active site
binding normally
(b) Enzyme inhibition by
a substrate imposter
(c) Enzyme inhibition by a
molecule that causes the
active site to change shape
Figure 5.10 Enzyme inhibitors

24. Feedback regulation
Some products of a reaction may inhibit the enzyme required for its production.
This is called feedback regulation.
It prevents the cell from wasting resources.
Many antibiotics work by inhibiting enzymes of disease- causing bacteria.
Penicillin blocks the active site of an enzyme that bacteria use in making cell walls.
Ibuprofen inhibits an enzyme involved in sending pain signals.
Many cancer drugs inhibit enzymes that promote cell division.
In some cases, the binding is reversible, enabling certain inhibitors to regulate metabolism. For example, if metabolism is producing more of a certain product than a cell needs, that product may eversible inhibit an enzyme required for its production. This is called feedback regulation which prevents the cell from wasting resources.
Antibiotics – penicillin
Cancer drugs- cell division
Nerve gas – nerve impulse
pesticides

25. MEMBRANE FUNCTION
Working cells must control the flow of materials to and from the environment.
Membrane proteins perform many functions.
Transport proteins
Are located in membranes
Regulate the passage of materials into and out of the cell
So far we learned about how cells control the flow of energy and the pace of chemical ractions. They also must control the flow of materials to and from the environment

26. Intercellular joining Cell-cell recognition
Cell signaling
Enzymatic activity
Cytoplasm
Fibers of
extracellular
matrix
Cytoskeleton
Cytoplasm
Intercellular
joining
Attachment to the cytoskeleton
and extracellular matrix
Transport
Cell-cell
recognition
Figure 5.11
Figure 5.11 Primary functions of membrane proteins

27. Passive Transport: Diffusion across Membranes
Molecules contain heat energy that causes them to vibrate and wander randomly.
Diffusion is the tendency for molecules of any substance to spread out into the available space (example of passive transport)
Passive transport is the diffusion of a substance across a membrane without the input of energy (O2 and CO2).
Cell membranes are selectively permeable, allowing only certain substances to pass.
Substances diffuse down their concentration gradient, a region in which the substance’s density changes.

28. Passive transport: diffusion across a membrane
Molecules of dye
Membrane
(a) Passive transport of one type of molecule
(b) Passive transport of two types of molecules
Net diffusion
Equilibrium
Figure 5.12 Passive transport: diffusion across a membrane
A substance will diffuse from where it is more concentrated to where it is less concentrated which mean substances diffuse down their concentration gradient.
Passive transport of two types of molecules” each will diffuse down its own concentratrion gradient.

29. Animation: How Diffusion works

30. Passive transport: diffusion across a membrane
Some substances do not cross membranes spontaneously.
These substances can be transported via facilitated diffusion.
Specific transport proteins act as selective corridors.
No energy input is needed.

31. Osmosis and Water Balance
Compared to another solution,
A hypertonic solution has a higher concentration of solute than the cell (hyper=Gr. high).
A hypotonic solution has a lower concentration of solute than the cell (hypo=Gr. low).
An isotonic solution has an equal concentration of solute than the cell.

32. Osmosis and Water Balance
The diffusion of water across a selectively permeable membrane is osmosis (special kind of passive transport).
Hypotonic solution
Hypertonic solution
Sugar
molecule
Selectively
permeable
membrane
Osmosis
Isotonic solutions
People can take the advantage of osmosis to preserve foods.

33. Animation: How Osmosis works

34. Water Balance in Animal and Plant Cells
Osmoregulation is the control of water balance within a cell or organism.
Most animal cells require an isotonic environment
Plant have rigid cell walls.
Plant cells require a hypotonic environment, which keeps these walled cells turgid.
The survival of a cell depends on its ability to balance water uptake and loss. Most animal cells require an isotonic environment. For them to survive a hypotonic or hypertonic environment, they must have a way to balance an excessive uptake or excessive loss of water.

35. The behavior of animal and plant cells in different osmotic environments
Animal cell
Plant cell
Normal
Flaccid (wilts)
Lysing
Turgid
Shriveled
Plasma
membrane
H2O
Isotonic solution
H2O in = H2O out
(b) Hypotonic solution
H2O in > H2O out
(c) Hypertonic solution
H2O in < H2O out
Figure 5.14 The behavior of animal and plant cells in different osmotic environments

36. Water Balance in Plant Cells
As a plant cell loses water,
it shrivels and
its plasma membrane may pull away from the cell wall in the process of plasmolysis, which usually kills the cell.
Figure 5.15 Plant turgor

37. Active Transport: The Pumping of Molecules Across Membranes
Active transport requires energy to move molecules across a membrane.
Lower solute concentration
Higher solute concentration
ATP
Solute
Blast Animation: Active Transport: Sodium-Potassium Pump
Animation: Active Transport
© 2010 Pearson Education, Inc.
AT enables the cells to maintain internal concentration of solutes that differ from environmental concentrations – the nerve cell has to maintain higher K conc and lower Na conc which is vital for the propagation of nerve signals. The PM helps maintain these differences by pumping Na out of the cell and K into the cell.

38. Blast Animation: Active Transport: Sodium-Potassium Pump

39. Exocytosis and Endocytosis: Traffic of Large Molecules
Exocytosis is the secretion of large molecules within vesicles.
Outside of cell
Cytoplasm
Plasma
membrane
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The movement of larger molecules into and out of the cell depends on the ability of the membrane to form sacs, thereby packaging the larger moleucules into sacs.

40. Exocytosis and Endocytosis: Traffic of Large Molecules
Endocytosis takes material into a cell within vesicles that bud inward from the plasma membrane.

41. Summary: exocytosis and endocytosis
Figure UN4 Summary: exocytosis and endocytosis

42. Exocytosis and Endocytosis: Traffic of Large Molecules
There are three types of endocytosis:
Phagocytosis (“cellular eating”); a cell engulfs a particle and packages it within a food vacuole
Pinocytosis (“cellular drinking”); a cell “gulps” droplets of fluid by forming tiny vesicles
Receptor-mediated endocytosis; a cell takes in very specific molecules

43. The Role of Membranes in Cell Signaling
The plasma membrane helps convey signals between
cells and
between cells and their environment
Receptors on a cell surface trigger signal transduction pathways that
relay the signal and
convert it to chemical forms that can function within the cell

44. An example of cell signaling
Outside of cell
Cytoplasm
Reception
Transduction
Response
Receptor
protein
Epinephrine
(adrenaline)
from adrenal glands
Plasma membrane
Proteins of signal transduction
pathway
Hydrolysis
of glycogen
releases
glucose for
energy
Figure 5.19 An example of cell signaling (detail)
Communication begins when a receptor protein receives a stimulus from the outside environment or from a signaling molecule, hormone.
This stimulus triggers a chain reaction in one or more molecules that function in transduction that relay the signal and convert it to chemical forms that can function within the cell.
This signal leads to various response.

45. Evolution Connection: The Origin of Membranes
Phospholipids
are key ingredients of membranes,
were probably among the first organic compounds that formed from chemical reactions on early Earth, and
self-assemble into simple membranes.
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46. Facilitated diffusion Osmosis Higher solute concentration
MEMBRANE TRANSPORT
Passive Transport
(requires no energy)
Active Transport
(requires energy)
Diffusion
Facilitated diffusion
Osmosis
Higher solute concentration
Higher water concentration
(lower solute concentration)
Higher solute
concentration
Solute
Solute
Solute
Water
Solute
ATP
Lower solute concentration
Lower water concentration
(higher solute concentration)
Lower solute
concentration
Figure UN3 Summary: membrane transport