chapter 5 - j. falabella portfolio · are fluid mosaics of lipids and proteins with many functions...

PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth Edition REECE • TAYLOR • SIMON • DICKEY • HOGAN

Chapter 5

Lecture by Edward J. Zalisko

The Working Cell

© 2015 Pearson Education, Inc.

Introduction

• The plasma membrane and its proteins enable cells to

•  survive and •  function.

• Aquaporins are membrane proteins that function as water channels.


Introduction

• This chapter addresses how working cells use • membranes, •  energy, and •  enzymes.



Figure 5.0-1


Figure 5.0-2 Chapter 5: Big Ideas

Membrane Structure and Function

Energy and the Cell

How Enzymes Function

Cellular respiration

ATP ATP

MEMBRANE STRUCTURE AND FUNCTION


5.1 VISUALIZING THE CONCEPT: Membranes are fluid mosaics of lipids and proteins with many functions

• Biologists use the fluid mosaic model to describe a membrane’s structure, a patchwork of diverse protein molecules embedded in a phospholipid bilayer.

• The plasma membrane exhibits selective permeability.

• The proteins embedded in a membrane’s phospholipid bilayer perform various functions.


Animation: Overview of Cell Signaling


Animation: Signal Transduction Pathways



Figure 5.1

Phospholipid

Cholesterol

Membrane proteins

Microfilaments of cytoskeleton

Extracellular side of membrane

Fibers of extracellular matrices (ECM)

Cytoplasmic side of membrane

O2 CO2


Figure 5.1-1

Enzyme

Enzyme

O2 CO2

Diffusion of small nonpolar molecules

Attachment protein

Receptor protein

Channel protein

Active transport protein ATP

Junction protein

Glyco- protein

Junction protein


Figure 5.1-2


O2 CO2


Figure 5.1-3

Solute molecules

Channel protein

Active transport protein

Transport Proteins

ATP

•  Allow specific ions or molecules to enter or exit the cell


Figure 5.1-4

Enzymes

Initial reactant

Product of reaction

Enzymes •  Some membrane proteins are enzymes •  Enzymes may be grouped to carry out

sequential reactions


Figure 5.1-5

Extracellular matrix

Attachment protein


Attachment Proteins • Attach to the extracellular matrix and cytoskeleton • Help support the membrane • Can coordinate external and internal changes


Figure 5.1-6

Signaling molecule

Receptor protein

Receptor Proteins •  Signaling molecules bind to receptor proteins •  Receptor proteins relay the message by

activating other molecules inside the cell


Figure 5.1-7

Junction protein

Junction protein

Junction Proteins •  Form intercellular junctions that

attach adjacent cells


Figure 5.1-8

Attached sugars

Glycoprotein

Protein that recognizes neighboring cell

Glycoproteins •  Serve as ID tags •  May be recognized by membrane

proteins of other cells


Figure 5.1-9

Phospholipid

Cholesterol


Extracellular side of membrane

Fibers of extracellular matrices (ECM)

Cytoplasmic side of membrane

O2 CO2


Enzyme

Attachment protein

Receptor protein

Channel protein

Active transport protein ATP

Junction protein

Glyco- protein

Junction protein

Enzyme

5.2 EVOLUTION CONNECTION: The spontaneous formation of membranes was 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.



Figure 5.2

Water-filled bubble made of phospholipids

5.3 Passive transport is diffusion across a membrane with no energy investment

• Diffusion is the tendency of particles to spread out evenly in an available space.

•  Particles move from an area of more concentrated particles to an area where they are less concentrated.

•  This means that particles diffuse down their concentration gradient.

•  Eventually, the particles reach dynamic equilibrium, where there is no net change in concentration on either side of the membrane.



Figure 5.3a

Molecules of dye

Pores

Membrane

Net diffusion Net diffusion Equilibrium


Figure 5.3b



5.3 Passive transport is diffusion across a membrane with no energy investment

• Diffusion across a cell membrane does not require energy, so it is called passive transport.

• Diffusion down concentration gradients is the sole means by which oxygen enters your cells and carbon dioxide passes out of cells.


Animation: Diffusion


Animation: Membrane Selectivity


5.4 Osmosis is the diffusion of water across a membrane

• One of the most important substances that crosses membranes by passive transport is water.

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


Animation: Osmosis


5.4 Osmosis is the diffusion of water across a membrane

•  If a membrane, permeable to water but not to a solute, separates two solutions with different concentrations of solute, water will cross the membrane, moving down its own concentration gradient, until the solute concentration on both sides is equal.



Figure 5.4

Solute molecule

Selectively permeable membrane

Water molecule

Solute molecule with cluster of water molecules

Osmosis

H2O

Lower concentration

of solute

Higher concentration

of solute

More equal concentrations

of solute

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

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

• The tonicity of a solution mainly depends on its concentration of solutes relative to the concentration of solutes inside the cell.



• How will animal cells be affected when placed into solutions of various tonicities?

•  In an isotonic solution, the concentration of solute is the same on both sides of a membrane, and the cell volume will not change.

•  In a hypotonic solution, the solute concentration is lower outside the cell, water molecules move into the cell, and the cell will expand and may burst.

•  In a hypertonic solution, the solute concentration is higher outside the cell, water molecules move out of the cell, and the cell will shrink.



Figure 5.5

Animal cell

Plant cell

Hypotonic solution (lower solute levels)

Isotonic solution (equal solute levels)

Hypertonic solution (higher solute levels)

H2O

Lysed Normal Shriveled

Turgid (normal) Flaccid

Plasma membrane

Shriveled (plasmolyzed)

H2O H2O H2O

H2O H2O H2O


Figure 5.5

Animal cell




H2O

Lysed Normal Shriveled

H2O H2O H2O


• 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 of a plant cell exerts pressure that prevents the cell from taking in too much water and bursting when placed in a hypotonic environment.

•  But in a hypertonic environment, plant and animal cells both shrivel.


Video: Chlamydomonas


Video: Paramecium Vacuole


Video: Plasmolysis


Video: Turgid Elodea






Figure 5.5

Plant cell

Turgid (normal) Flaccid

Plasma membrane

Shriveled (plasmolyzed)

H2O H2O H2O

5.6 Transport proteins can facilitate diffusion across membranes

• Hydrophobic substances easily diffuse across a cell membrane.

• However, polar or charged substances do not easily cross cell membranes and, instead, move across membranes with the help of specific transport proteins in a process called facilitated diffusion, which

•  does not require energy and •  relies on the concentration gradient.



Figure 5.6

Solute molecule

Transport protein


• Some proteins function by becoming a hydrophilic tunnel for passage of ions or other molecules.

• Other proteins bind their passenger, change shape, and release their passenger on the other side.

•  In both cases, the transport protein helps a specific substance diffuse across the membrane down its concentration gradient and thus requires no input of energy.



• 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.


5.7 SCIENTIFIC THINKING: 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.

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



Figure 5.7

Time of rupture

RNA-injected eggs

Control eggs

Time (min)

Rel

ativ

e vo

lum

e of

repr

esen

tativ

e eg

gs

1.4

0 1 2 3 4 5

1.3

1.2

1.1

1.0

5.8 Cells expend energy in the active transport of a solute

•  In active transport, a cell must expend energy to move a solute against its concentration gradient.

• The energy molecule ATP supplies the energy for most active transport.

• The following figures show the four main stages of active transport.


Animation: Active Transport



Figure 5.8-1

Transport protein

Solute Solute binds to transport protein.

1


Figure 5.8-2

Transport protein

Solute ATP

Solute binds to transport protein.

ATP provides energy for change in protein shape.

1 2


Figure 5.8-3

Transport protein

Solute ATP

Solute binds to transport protein.

ATP provides energy for change in protein shape.

Protein returns to original shape and more solute can bind.

1 2 3

5.9 Exocytosis and endocytosis transport large molecules across membranes

• A cell uses two mechanisms to move large molecules across membranes.

1.  Exocytosis is used to export bulky molecules, such as proteins or polysaccharides.

2.  Endocytosis is used to take in large molecules. •  In both cases, material to be transported is

packaged within a vesicle that fuses with the membrane.


5.9 Exocytosis and endocytosis transport large molecules across membranes

• There are two kinds of endocytosis. 1.  Phagocytosis is the engulfment of a particle by

the cell wrapping cell membrane around it, forming a vacuole.

2.  Receptor-mediated endocytosis uses membrane receptors for specific solutes. The region of the membrane with receptors pinches inward to form a vesicle. •  Receptor-mediated endocytosis is used to take in

cholesterol from the blood.


Animation: Exocytosis and Endocytosis Introduction


Animation: Exocytosis


Animation: Pinocytosis


Animation: Phagocytosis


Animation: Receptor-Mediated Endocytosis



Figure 5.9-0 Phagocytosis

Pseudopodium

EXTRACELLULAR FLUID

CYTOPLASM

“Food” or other particle

Food vacuole

Receptor-mediated endocytosis Coat protein

Receptor

Specific molecule

Coated pit

Coated vesicle


Figure 5.9-1

Phagocytosis

Pseudopodium

EXTRACELLULAR FLUID

CYTOPLASM

“Food” or other particle

Food vacuole


Figure 5.9-2

Receptor-mediated endocytosis Coat protein

Receptor

Specific molecule

Coated pit

Coated vesicle


ENERGY AND THE CELL

5.10 Cells transform energy as they perform work

• Cells are miniature chemical factories, housing thousands of chemical reactions.

• Some of these chemical reactions release energy, and others require energy.



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

• There are two basic forms of energy. 1.  Kinetic energy is the energy of motion. 2.  Potential energy is energy that matter

possesses as a result of its location or structure.



• Thermal energy is a type of kinetic energy associated with the random movement of atoms or molecules.

• Thermal energy in transfer from one object to another is called heat.

• Light is also a type of kinetic energy; it can be harnessed to power photosynthesis.



• Chemical energy is the •  potential energy available for release in a chemical

reaction and •  the most important type of energy for living

organisms to power the work of the cell.


Animation: Energy Concepts



• Thermodynamics is the study of energy transformations that occur in a collection of matter.

•  The word system is used for the matter under study. •  The word surroundings is used for everything

outside the system; the rest of the universe.



• Two laws govern energy transformations in organisms.

•  Per the first law of thermodynamics (also known as the law of energy conservation), energy in the universe is constant.

•  Per the second law of thermodynamics, energy conversions increase the disorder of the universe.

• Entropy is the measure of disorder or randomness.



• Automobile engines and cells use the same basic process to make the chemical energy of their fuel available for work.

•  In the car and cells, the waste products are carbon dioxide and water.

• Cells use oxygen in reactions that release energy from fuel molecules.

•  In cellular respiration, the chemical energy stored in organic molecules is used to produce ATP, which the cell can use to perform work.



Figure 5.10-0

Fuel Energy conversion Waste products

Gasoline

Oxygen

Heat energy

Combustion Kinetic energy of movement

Carbon dioxide

Water

Energy conversion in a car

+ +

Glucose

Oxygen

Carbon dioxide

Water

+ +

Heat energy

Energy conversion in a cell

ATP

Energy for cellular work

ATP



Figure 5.10-1


Gasoline

Oxygen

Heat energy

Combustion Kinetic energy of movement

Carbon dioxide

Water

Energy conversion in a car

+ +


Figure 5.10-2


Glucose

Oxygen

Carbon dioxide

Water

+ +

Heat energy

Energy conversion in a cell

ATP

Energy for cellular work

ATP


5.11 Chemical reactions either release or store energy

• Chemical reactions either •  release energy (exergonic reactions) or •  require an input of energy and store energy

(endergonic reactions).



• Exergonic reactions release energy. •  These reactions release the energy in covalent

bonds of the reactants. •  Burning wood releases the energy in glucose as

heat and light. • Cellular respiration

•  involves many steps, •  releases energy slowly, and •  uses some of the released energy to produce ATP.



Figure 5.11a

Reactants

Energy Products

Amount of energy released

Pote

ntia

l ene

rgy


• An endergonic reaction •  requires an input of energy and •  yields products rich in potential energy.

• Endergonic reactions •  start with reactant molecules that contain relatively

little potential energy but •  end with products that contain more chemical

energy.



Figure 5.11b

Reactants

Energy

Products

Amount of energy required

Pote

ntia

l ene

rgy


• Photosynthesis is a type of endergonic process. •  In photosynthesis,

•  energy-poor reactants (carbon dioxide and water) are used,

•  energy is absorbed from sunlight, and •  energy-rich sugar molecules are produced.



• A living organism carries out thousands of endergonic and exergonic chemical reactions.

• The total of an organism’s chemical reactions is called metabolism.

• A metabolic pathway is a series of chemical reactions that either

•  builds a complex molecule or •  breaks down a complex molecule into simpler

compounds.



• Energy coupling uses the energy released from exergonic reactions to drive endergonic reactions, typically using the energy stored in ATP molecules.


5.12 ATP drives cellular work by coupling exergonic and endergonic reactions

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

• ATP consists of •  adenosine and •  a triphosphate tail of three phosphate groups.



• 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.



Figure 5.12a-1

Triphosphate

Adenosine P

ATP

P P


Figure 5.12a-2

Triphosphate

Adenosine P

ATP

H2O Diphosphate

ADP Phosphate

Energy

P P

P P P Adenosine


• There are three main types of cellular work: 1.  chemical, 2.  mechanical, and 3.  transport.

• ATP drives all three of these types of work.



Figure 5.12b Chemical work

ATP P

Reactants Product formed

ADP +

P

P

ATP

P ADP +

P

P

ATP P ADP + P P

Transport work

Transport protein Solute transported

Mechanical work

Motor protein Protein filament moved


• A cell uses and regenerates ATP continuously. •  In the ATP cycle, energy released in an exergonic

reaction, such as the breakdown of glucose during cellular respiration, is used in an endergonic reaction to generate ATP from ADP.



Figure 5.12c

ATP synthesis is endergonic

ATP hydrolysis is exergonic

Energy from cellular respiration (exergonic)

Energy for cellular work (endergonic)

ATP

ADP + P


HOW ENZYMES FUNCTION

5.13 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 (because it activates the reactants).



• We can think of activation energy as the amount of energy needed for a reactant molecule to move “uphill” to a higher-energy but an unstable state so that the “downhill” part of the reaction can begin.

• One way to speed up a reaction is to add heat, which agitates atoms so that bonds break more easily and reactions can proceed, but too much heat will kill a cell.



• Enzymes •  function as biological catalysts, •  increase the rate of a reaction without being

consumed by the reaction, and •  are usually proteins (although some RNA molecules

can function as enzymes). • Enzymes speed up a reaction by lowering the

activation energy needed for a reaction to begin.


Animation: How Enzymes Work



Figure 5.13-0

Reactants

Progress of the reaction Products

a

b

c

Reactant

Products

Reactant

Products

Ener

gy

Activation energy barrier

Without enzyme

Enzyme

Ener

gy

Activation energy barrier reduced by enzyme

With enzyme

Ener

gy


Figure 5.13-1

Reactant

Products

Reactant

Products

Ener

gy


Without enzyme

Enzyme

Ener

gy


With enzyme


Figure 5.13-2

Products

Reactant

Ener

gy


Without enzyme


Figure 5.13-3

Reactant

Products

Enzyme En

ergy


With enzyme


Figure 5.13-4

Reactants

Progress of the reaction Products

a

b

c Ener

gy

5.14 A specific enzyme catalyzes each cellular reaction

• An enzyme •  is very selective in the reaction it catalyzes and •  has a shape that determines the enzyme’s

specificity. • The specific reactant that an enzyme acts on is

called the enzyme’s substrate. • A substrate fits into a region of the enzyme called

the active site. • Enzymes are specific because only specific

substrate molecules fit into their active site. © 2015 Pearson Education, Inc.


• The following figure illustrates the catalytic cycle of an enzyme.



Figure 5.14-1

Enzyme (sucrase)

Active site

The enzyme available with an empty active site

1


Figure 5.14-2

Enzyme (sucrase)

Substrate binds to enzyme with induced fit.

Substrate (sucrose)

Active site


1

2


Figure 5.14-3

The substrate is converted to products

H2O

Enzyme (sucrase)


Substrate (sucrose)

Active site


1

2

3


Figure 5.14-4

Glucose

Fructose

The products are released

The substrate is converted to products

H2O

Enzyme (sucrase)


Substrate (sucrose)

Active site


1

2

3

4


• For every enzyme, there are optimal conditions under which it is most effective.

• Temperature affects molecular motion. •  An enzyme’s optimal temperature produces the

highest rate of contact between the reactants and the enzyme’s active site.

• Most human enzymes work best at 35–40°C. • The optimal pH for most enzymes is near

neutrality.



• Many enzymes require nonprotein helpers called cofactors, which

•  bind to the active site and •  function in catalysis.

• Some cofactors are inorganic, such as the ions of zinc, iron, or copper.

•  If a cofactor is an organic molecule, such as most vitamins, it is called a coenzyme.


5.15 Enzyme inhibition can regulate enzyme activity in a cell

• A chemical that interferes with an enzyme’s activity is called an inhibitor.

• Competitive inhibitors •  block substrates from entering the active site and •  reduce an enzyme’s productivity.



• Noncompetitive inhibitors •  bind to the enzyme somewhere other than the

active site, •  change the shape of the active site, and •  prevent the substrate from binding.



Figure 5.15a

Substrate

Enzyme

Active site

Normal binding of substrate

Competitive inhibitor

Noncompetitive inhibitor

Enzyme inhibition


• Enzyme inhibitors are important in regulating cell metabolism.

•  In some reactions, the product may act as an inhibitor of one of the enzymes in the pathway that produced it. This is called feedback inhibition.



Figure 5.15b

Feedback inhibition

Enzyme 1

Reaction 1 A

Starting molecule

Product

–

Enzyme 2

Reaction 2 B

Enzyme 3

Reaction 3 C D

5.16 CONNECTION: Many drugs, pesticides, and poisons are enzyme inhibitors

• Many beneficial drugs act as enzyme inhibitors, including

•  ibuprofen, which inhibits an enzyme involved in the production of prostaglandins (messenger molecules that increase the sensation of pain and inflammation),

•  some blood pressure medicines, •  some antidepressants, • many antibiotics, and •  protease inhibitors used to fight HIV.



Figure 5.16

5.16 CONNECTION: Many drugs, pesticides, and poisons are enzyme inhibitors

• Enzyme inhibitors have also been developed as •  pesticides and •  deadly poisons for chemical warfare.


You should now be able to

1.  Describe the fluid mosaic structure of cell membranes.

2.  Describe the diverse functions of membrane proteins.

3.  Relate the structure of phospholipid molecules to the structure and properties of cell membranes.

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



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

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

7.  Explain how transport proteins facilitate diffusion. 8.  Distinguish between exocytosis, endocytosis,

phagocytosis, 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.

11. Define and compare endergonic and exergonic reactions.

12. Explain how cells use cellular respiration and energy coupling to survive.



13. Explain how ATP functions as an energy shuttle. 14. Explain how enzymes speed up chemical

reactions. 15. Explain how competitive and noncompetitive

inhibitors alter an enzyme’s activity. 16. Explain how certain drugs, pesticides, and

poisons can affect enzymes.



Figure 5.UN01

Passive transport (requires no energy)

Active transport (requires energy)

Diffusion Facilitated diffusion

Higher solute concentration

Lower solute concentration

Osmosis

Higher free water concentration

Solute

Water

Lower free water concentration

Higher solute concentration

ATP

Lower solute concentration


Figure 5.UN02

Molecules cross cell membranes

by

passive transport (a)

may be moving down

moving against

requires

(b) ATP

diffusion (d)

uses

(e)

(c) polar molecules and ions

of of

uses

by

P


Figure 5.UN03

b. c.

a.

d.

f.

e.


Figure 5.UN04

Oocytes in buffer

Oocytes in low HgCl2

Oocytes in high HgCl2

Oocytes in low HgCl2 and ME

Wat

er p

erm

eabi

lity

(rat

e of

osm

otic

sw

ellin

g)

Data from G. M. Preston et al., Appearance of water channels in Xenopus oocytes expressing red cell CHIP28 protein, Science 256: 3385–7 (1992).


Figure 5.UN05

chapter 5 - j. falabella portfolio · are fluid mosaics of lipids and proteins with many functions...

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