Cohesion Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion...

Cohesion

• Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion

• Cohesion helps the transport of water against gravity in plants

• Adhesion is an attraction between different substances, for example, between water and plant cell walls

Animation: Water TransportAnimation: Water Transport

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings1

Fig. 3-3

Water-conductingcells

Adhesion

Cohesion150 µm

Directionof watermovement

2

Universal Solvent

• A solution is a liquid that is a homogeneous mixture of substances

• A solvent is the dissolving agent of a solution• The solute is the substance that is dissolved• An aqueous solution is one in which water is

the solvent


Fig. 3-7

Cl–

Na

Cl–

+

+

+

+

+

+

++

–

–

–

–

–

–

––

Na +

–

––

+

4

The Formation of Bonds with Carbon

• With four valence electrons, carbon can form four covalent bonds with a variety of atoms

• This tetravalence makes large, complex molecules possible

• In molecules with multiple carbons, each carbon bonded to four other atoms has a tetrahedral shape

• However, when two carbon atoms are joined by a double bond, the molecule has a flat shape


Fig. 4-3

NameMolecular Formula

Structural Formula

Ball-and-StickModel

Space-FillingModel

(a) Methane

(b) Ethane

(c) Ethene (ethylene)

6

ATP: An Important Source of Energy for Cellular Processes

• One phosphate molecule, adenosine triphosphate (ATP), is the primary energy-transferring molecule in the cell

• ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups


Fig. 4-UN4

P P P P i P PAdenosine Adenosine Energy

ADPATP Inorganic phosphate

Reacts with H2O

8

Carbohydrates serve as fuel and building material

• Carbohydrates include sugars and the polymers of sugars

• The simplest carbohydrates are monosaccharides, or single sugars

• Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks


• Starch Plants store surplus starch as granules within chloroplasts and other plastids

• Cellulose is a major component of the tough wall of plant cells

• Chitin provides structural support for the cell walls of many fungi


Concept 5.3: Lipids are a diverse group of hydrophobic molecules

• Lipids store energy and maintain membranes• Lipids are hydrophobic becausethey consist

mostly of hydrocarbons, which form nonpolar covalent bonds


• Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds

• Unsaturated fatty acids have one or more double bonds

Animation: FatsAnimation: Fats


Four Levels of Protein Structure

• The primary structure of a protein is its unique sequence of amino acids

• Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain

• Tertiary structure is determined by interactions among various side chains (R groups)

• Quaternary structure results when a protein consists of multiple polypeptide chains

Animation: Protein Structure IntroductionAnimation: Protein Structure Introduction


Fig. 5-22

Primarystructure

Secondaryand tertiarystructures

Quaternarystructure

Normalhemoglobin(top view)

Primarystructure


Quaternarystructure

Function Function

subunit

Molecules donot associatewith oneanother; eachcarries oxygen.

Red bloodcell shape

Normal red bloodcells are full ofindividualhemoglobinmoledules, eachcarrying oxygen.

10 µm

Normal hemoglobin

1 2 3 4 5 6 7Val His Leu Thr Pro Glu Glu

Red bloodcell shape

subunit

Exposedhydrophobicregion

Sickle-cellhemoglobin

Moleculesinteract withone another andcrystallize intoa fiber; capacityto carry oxygenis greatly reduced.

Fibers of abnormalhemoglobin deformred blood cell intosickle shape.

10 µm

Sickle-cell hemoglobin

GluProThrLeuHisVal Val

1 2 3 4 5 6 7

14

The Roles of Nucleic Acids

• There are two types of nucleic acids:–Deoxyribonucleic acid (DNA) directs

synthesis of messenger RNA –Ribonucleic acid (RNA) controls

protein synthesis


Fig. 5-26-3

mRNA

Synthesis ofmRNA in thenucleus

DNA

NUCLEUS

mRNA

CYTOPLASM

Movement ofmRNA into cytoplasmvia nuclear pore

Ribosome

AminoacidsPolypeptide

Synthesisof protein

1

2

3

16

Concept 5.2: Carbohydrates serve as fuel and building material

• Carbohydrates include sugars and the polymers of sugars

• The simplest carbohydrates are monosaccharides, or single sugars

• Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks


• Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods

• Chitin also provides structural support for the cell walls of many fungi


Concept 5.3: Lipids are a diverse group of hydrophobic molecules

• Lipids are the one class of large biological molecules that do not form polymers

• The unifying feature of lipids is having little or no affinity for water

• Lipids are hydrophobic becausethey consist mostly of hydrocarbons, which form nonpolar covalent bonds

• The most biologically important lipids are fats, phospholipids, and steroids


• Fatty acids vary in length (number of carbons) and in the number and locations of double bonds

• Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds

• Unsaturated fatty acids have one or more double bonds

Animation: FatsAnimation: Fats


Four Levels of Protein Structure

• The primary structure of a protein is its unique sequence of amino acids

• Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain

• Tertiary structure is determined by interactions among various side chains (R groups)

• Quaternary structure results when a protein consists of multiple polypeptide chains

Animation: Protein Structure IntroductionAnimation: Protein Structure Introduction


Fig. 5-22

Primarystructure


Quaternarystructure

Normalhemoglobin(top view)

Primarystructure


Quaternarystructure

Function Function

subunit

Molecules donot associatewith oneanother; eachcarries oxygen.

Red bloodcell shape

Normal red bloodcells are full ofindividualhemoglobinmoledules, eachcarrying oxygen.

10 µm

Normal hemoglobin

1 2 3 4 5 6 7

Val His Leu Thr Pro Glu Glu

Red bloodcell shape

subunit

Exposedhydrophobicregion

Sickle-cellhemoglobin

Moleculesinteract withone another andcrystallize intoa fiber; capacityto carry oxygenis greatly reduced.

Fibers of abnormalhemoglobin deformred blood cell intosickle shape.

10 µm

Sickle-cell hemoglobin

GluProThrLeuHisVal Val

1 2 3 4 5 6 7

22

What Determines Protein Structure?

• In addition to primary structure, physical and chemical conditions can affect structure

• Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel

• This loss of a protein’s native structure is called denaturation

• A denatured protein is biologically inactive


Fig. 5-23

Normal protein Denatured protein

Denaturation

Renaturation

24

The Roles of Nucleic Acids

• There are two types of nucleic acids:– Deoxyribonucleic acid (DNA)– Ribonucleic acid (RNA)

• DNA provides directions for its own replication• DNA directs synthesis of messenger RNA

(mRNA) and, through mRNA, controls protein synthesis

• Protein synthesis occurs in ribosomes


Fig. 5-26-3

mRNA

Synthesis ofmRNA in thenucleus

DNA

NUCLEUS

mRNA

CYTOPLASM

Movement ofmRNA into cytoplasmvia nuclear pore

Ribosome

AminoacidsPolypeptide

Synthesisof protein

1

2

3

26

Cohesion Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion...

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