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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 4Chapter 4
Carbon and the Molecular Diversity of Life
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Carbon—The Backbone of Biological Molecules
• Although cells are 70–95% water, the rest consists mostly of carbon-based compounds
• Carbon is unparalleled in its ability to form large, complex, and diverse molecules
• Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 4.1: Organic chemistry is the study of carbon compounds
• Organic compounds range from simple molecules to colossal ones
• Most organic compounds contain hydrogen atoms in addition to carbon atoms
• Vitalism, the idea that organic compounds arise only in organisms, was disproved when chemists synthesized the compounds
• Mechanism is the view that all natural phenomena are governed by physical and chemical laws
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 4.2: Carbon atoms can form diverse molecules by bonding to four other atoms
• Electron configuration is the key to an atom’s characteristics
• Electron configuration determines the kinds and number of bonds an atom will form with other atoms
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
LE 4-3
MolecularFormula
StructuralFormula
Ball-and-StickModel
Space-FillingModel
Methane
Ethane
Ethene (ethylene)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The electron configuration of carbon gives it covalent compatibility with many different elements
• The valences of carbon and its most frequent partners (hydrogen, oxygen, and nitrogen) are the “building code” that governs the architecture of living molecules
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Molecular Diversity Arising from Carbon Skeleton Variation
• Carbon chains form the skeletons of most organic molecules
• Carbon chains vary in length and shape
Animation: Carbon SkeletonsAnimation: Carbon Skeletons
LE 4-5
LengthEthane Propane
Butane 2-methylpropane(commonly called isobutane)
Branching
Double bonds
Rings
1-Butene 2-Butene
Cyclohexane Benzene
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Hydrocarbons
• Hydrocarbons are organic molecules consisting of only carbon and hydrogen
• Many organic molecules, such as fats, have hydrocarbon components
• Hydrocarbons can undergo reactions that release a large amount of energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Isomers
• Isomers are compounds with the same molecular formula but different structures and properties:
– Structural isomers have different covalent arrangements of their atoms
– Geometric isomers have the same covalent arrangements but differ in spatial arrangements
– Enantiomers are isomers that are mirror images of each other
Animation: IsomersAnimation: Isomers
LE 4-7
Structural isomers differ in covalent partners, as shown in this example of two isomers of pentane.
Geometric isomers differ in arrangement about a dou ble bond. In these diagrams, X represents an atom or gr oup of atoms attached to a double-bonded carbon.
cis isomer: The two Xsare on the same side.
trans isomer: The two Xsare on opposite sides.
L isomer D isomer
Enantiomers differ in spatial arrangement around an asymmetric carbon, resulting in molecules that are mirror images, like left and right hands. The two isomers are designated the L and D isomers from the Latin for l eft and right ( levo and dextro). Enantiomers cannot be superimposed on each other.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Enantiomers are important in the pharmaceutical industry
• Two enantiomers of a drug may have different effects
• Differing effects of enantiomers demonstrate that organisms are sensitive to even subtle variations in molecules
Animation: LAnimation: L --DopaDopa
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 4.3: Functional groups are the parts of molecules involved in chemical reactions
• Distinctive properties of organic molecules depend not only on the carbon skeleton but also on the molecular components attached to it
• Certain groups of atoms are often attached to skeletons of organic molecules
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Functional Groups Most Important in the Chemistry of Life
• Functional groups are the components of organic molecules that are most commonly involved in chemical reactions
• The number and arrangement of functional groups give each molecule its unique properties
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The six functional groups that are most important in the chemistry of life:
– Hydroxyl group
– Carbonyl group
– Carboxyl group
– Amino group
– Sulfhydryl group
– Phosphate group
LE 4-10aa
STRUCTURE
(may be written HO—)
NAME OF COMPOUNDS
Alcohols (their specific namesusually end in -ol)
Ethanol, the alcohol present inalcoholic beverages
FUNCTIONAL PROPERTIES
Is polar as a result of theelectronegative oxygen atomdrawing electrons toward itself.
Attracts water molecules, helpingdissolve organic compounds suchas sugars (see Figure 5.3).
LE 4-10ab
STRUCTURE
NAME OF COMPOUNDS
Ketones if the carbonyl group iswithin a carbon skeleton
EXAMPLE
Acetone, the simplest ketone
A ketone and an aldehyde maybe structural isomers withdifferent properties, as is the casefor acetone and propanal.
Aldehydes if the carbonyl group isat the end of the carbon skeleton
Acetone, the simplest ketone
Propanal, an aldehyde
FUNCTIONAL PROPERTIES
LE 4-10ac
STRUCTURE
NAME OF COMPOUNDS
Carboxylic acids, or organic acids
EXAMPLE
Has acidic properties because it isa source of hydrogen ions.
Acetic acid, which gives vinegarits sour taste
FUNCTIONAL PROPERTIES
The covalent bond betweenoxygen and hydrogen is so polarthat hydrogen ions (H +) tend todissociate reversibly; for example,
Acetic acid Acetate ion
In cells, found in the ionic form,which is called a carboxylate group.
LE 4-10ba
STRUCTURE
NAME OF COMPOUNDS
Amine
EXAMPLE
Because it also has a carboxylgroup, glycine is both an amine anda carboxylic acid; compounds withboth groups are called amino acids.
FUNCTIONAL PROPERTIES
Acts as a base; can pick up aproton from the surroundingsolution:
(nonionized)
Ionized, with a charge of 1+,under cellular conditions
Glycine
(ionized)
LE 4-10bb
STRUCTURE
(may be written HS—)
NAME OF COMPOUNDS
Thiols
EXAMPLE
Ethanethiol
FUNCTIONAL PROPERTIES
Two sulfhydryl groups caninteract to help stabilize proteinstructure (see Figure 5.20).
LE 4-10bc
STRUCTURE
NAME OF COMPOUNDS
Organic phosphates
EXAMPLE
Glycerol phosphate
FUNCTIONAL PROPERTIES
Makes the molecule of which itis a part an anion (negativelycharged ion).
Can transfer energy between organic molecules.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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