chapter 3 the molecules of cells
TRANSCRIPT
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Copyright © 2009 Pearson Education, Inc.
PowerPoint Lectures for
Biology: Concepts & Connections, Sixth Edition
Campbell, Reece, Taylor, Simon, and Dickey
Chapter 3 The Molecules of Cells
Lecture by Richard L. Myers
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Introduction: Got Lactose?
Most of the world’s population cannot digest milk-based foods
– They are lactose intolerant, because they lack the enzyme lactase
This illustrates the importance of biological molecules, such as lactase, to functioning living organisms
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INTRODUCTION TO ORGANIC COMPOUNDS
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3.1 Life’s molecular diversity is based on the properties of carbon
Diverse molecules found in cells are composed of carbon bonded to other elements
– Carbon-based molecules are called organic compounds
– By sharing electrons, carbon can bond to four other atoms
– By doing so, it can branch in up to four directions
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3.1 Life’s molecular diversity is based on the properties of carbon
Methane (CH4) is one of the simplest organic compounds
– Four covalent bonds link four hydrogen atoms to the carbon atom
– Each of the four lines in the formula for methane represents a pair of shared electrons
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Structuralformula
Ball-and-stickmodel
Space-fillingmodel
Methane
The four single bonds of carbon point to the cornersof a tetrahedron.
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3.1 Life’s molecular diversity is based on the properties of carbon
Methane and other compounds composed of only carbon and hydrogen are called hydrocarbons
– Carbon, with attached hydrogens, can bond together in chains of various lengths
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A chain of carbon atoms is called a carbon skeleton
– Carbon skeletons can be branched or unbranched
– Therefore, different compounds with the same molecular formula can be produced
– These structures are called isomers
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3.1 Life’s molecular diversity is based on the properties of carbon
Animation: Isomers
Animation: Carbon Skeletons
Animation: L-Dopa
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Carbon skeletons vary in length.
Branching. Skeletons may be unbranched or branched.
Butane Isobutane
PropaneEthane
Double bonds.
2-Butene
Skeletons may have double bonds,which can vary in location.
Cyclohexane
Length.
1-Butene
Benzene
Skeletons may be arranged in rings.Rings.
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Carbon skeletons vary in length.
PropaneEthane
Length.
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Skeletons may be unbranched or branched.
Butane Isobutane
Branching.
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Double bonds.
2-Butene
Skeletons may have double bonds,which can vary in location.
1-Butene
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Cyclohexane Benzene
Skeletons may be arranged in rings.Rings.
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3.2 Characteristic chemical groups help determine the properties of organic compounds
An organic compound has unique properties that depend upon
– The size and shape of the molecule and
– The groups of atoms (functional groups) attached to it
A functional group affects a biological molecule’s function in a characteristic way
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3.2 Characteristic chemical groups help determine the properties of organic compounds
Compounds containing functional groups are hydrophilic (water-loving)
– This means that they are soluble in water, which is a necessary prerequisite for their roles in water-based life
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3.2 Characteristic chemical groups help determine the properties of organic compounds
The functional groups are
– Hydroxyl group—consists of a hydrogen bonded to an oxygen
– Carbonyl group—a carbon linked by a double bond to an oxygen atom
– Carboxyl group—consists of a carbon double-bonded to both an oxygen and a hydroxyl group
– Amino group—composed of a nitrogen bonded to two hydrogen atoms and the carbon skeleton
– Phosphate group—consists of a phosphorus atom bonded to four oxygen atoms
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3.2 Characteristic chemical groups help determine the properties of organic compounds
An example of similar compounds that differ only in functional groups is sex hormones
– Male and female sex hormones differ only in functional groups
– The differences cause varied molecular actions
– The result is distinguishable features of males and females
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Estradiol
Male lionTestosterone
Female lion
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Estradiol
Female lion
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Male lionTestosterone
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3.3 Cells make a huge number of large molecules from a small set of small molecules
There are four classes of biological molecules
– Carbohydrates
– Proteins
– Lipids
– Nucleic acids
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3.3 Cells make a huge number of large molecules from a small set of small molecules
The four classes of biological molecules contain very large molecules
– They are often called macromolecules because of their large size
– They are also called polymers because they are made from identical building blocks strung together
– The building blocks are called monomers
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A cell makes a large number of polymers from a small group of monomers
– Proteins are made from only 20 different amino acids, and DNA is built from just four kinds of nucleotides
The monomers used to make polymers are universal
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3.3 Cells make a huge number of large molecules from a small set of small molecules
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3.3 Cells make a huge number of large molecules from a small set of small molecules
Monomers are linked together to form polymers through dehydration reactions, which remove water
Polymers are broken apart by hydrolysis, the addition of water
All biological reactions of this sort are mediated by enzymes, which speed up chemical reactions in cells
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Animation: Polymers
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Unlinkedmonomer
Short polymer
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Unlinkedmonomer
Short polymer
Longer polymer
Dehydrationreaction
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Hydrolysis
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CARBOHYDRATES
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3.4 Monosaccharides are the simplest carbohydrates
Carbohydrates range from small sugar molecules (monomers) to large polysaccharides
– Sugar monomers are monosaccharides, such as glucose and fructose
– These can be hooked together to form the polysaccharides
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3.4 Monosaccharides are the simplest carbohydrates
The carbon skeletons of monosaccharides vary in length
– Glucose and fructose are six carbons long
– Others have three to seven carbon atoms
Monosaccharides are the main fuels for cellular work
– Monosaccharides are also used as raw materials to manufacture other organic molecules
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Glucose
(an aldose)
Fructose
(a ketose)
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Structuralformula
Abbreviatedstructure
Simplifiedstructure
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3.5 Cells link two single sugars to form disaccharides
Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reaction
– An example is a glucose monomer bonding to a fructose monomer to form sucrose, a common disaccharide
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Animation: Disaccharides
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Glucose Glucose
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Glucose Glucose
Maltose
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3.6 CONNECTION: What is high-fructose corn syrup and is it to blame for obesity?
When you drink a soda, you are probably consuming a sweetener called high-fructose corn syrup (HFCS)
Because fructose is sweeter than glucose, glucose atoms produced from starch are rearranged to make the glucose isomer, fructose
– This is used to sweeten sodas
– So, if you overconsume sweeteners as well as fat and do not exercise, you may experience weight gain
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3.7 Polysaccharides are long chains of sugar units
Polysaccharides are polymers of monosaccharides
– They can function in the cell as a storage molecule or as a structural compound
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3.7 Polysaccharides are long chains of sugar units
Starch is a storage polysaccharide composed of glucose monomers and found in plants
Glycogen is a storage polysaccharide composed of glucose, which is hydrolyzed by animals when glucose is needed
Cellulose is a polymer of glucose that forms plant cell walls
Chitin is a polysaccharide used by insects and crustaceans to build an exoskeleton
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3.7 Polysaccharides are long chains of sugar units
Polysaccharides are hydrophilic (water-loving)
– Cotton fibers, such as those in bath towels, are water absorbent
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Animation: Polysaccharides
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Starch granules inpotato tuber cells
Glycogengranulesin muscletissue
Cellulose fibrils ina plant cell wall
Cellulosemolecules
Glucosemonomer
GLYCOGEN
CELLULOSE
Hydrogen bonds
STARCH
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Starch granules inpotato tuber cells
Glucosemonomer
STARCH
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Glycogengranulesin muscletissue
GLYCOGEN
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Cellulose fibrils ina plant cell wall
Cellulosemolecules
CELLULOSE
Hydrogen bonds
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LIPIDS
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3.8 Fats are lipids that are mostly energy-storage molecules
Lipids are water insoluble (hydrophobic, or water fearing) compounds that are important in energy storage
– They contain twice as much energy as a polysaccharide
Fats are lipids made from glycerol and fatty acids
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3.8 Fats are lipids that are mostly energy-storage molecules
Fatty acids link to glycerol by a dehydration reaction
– A fat contains one glycerol linked to three fatty acids
– Fats are often called triglycerides because of their structure
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Fatty acid
Glycerol
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3.8 Fats are lipids that are mostly energy-storage molecules
Some fatty acids contain double bonds
– This causes kinks or bends in the carbon chain because the maximum number of hydrogen atoms cannot bond to the carbons at the double bond
– These compounds are called unsaturated fats because they have fewer than the maximum number of hydrogens
– Fats with the maximum number of hydrogens are called saturated fats
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3.9 Phospholipids and steroids are important lipids with a variety of functions
Phospholipids are structurally similar to fats and are an important component of all cells
– For example, they are a major part of cell membranes, in which they cluster into a bilayer of phospholipids
– The hydrophilic heads are in contact with the water of the environment and the internal part of the cell
– The hydrophobic tails band in the center of the bilayer
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Water
Hydrophobictails
Hydrophilicheads
Water
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3.9 Phospholipids and steroids are important lipids with a variety of functions
Steroids are lipids composed of fused ring structures
– Cholesterol is an example of a steroid that plays a significant role in the structure of the cell membrane
– In addition, cholesterol is the compound from which we synthesize sex hormones
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3.10 CONNECTION: Anabolic steroids pose health risks
Anabolic steroids are synthetic variants of testosterone that can cause a buildup of muscle and bone mass
– They can be sold as prescription drugs and used to treat certain diseases
– They may also be abused with serious consequences, such as liver damage that can lead to cancer
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PROTEINS
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3.11 Proteins are essential to the structures and functions of life
A protein is a polymer built from various combinations of 20 amino acid monomers
– Proteins have unique structures that are directly related to their functions
– Enzymes, proteins that serve as metabolic catalysts, regulate the chemical reactions within cells
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3.11 Proteins are essential to the structures and functions of life
Structural proteins provide associations between body parts and contractile proteins are found within muscle
Defensive proteins include antibodies of the immune system, and signal proteins are best exemplified by the hormones
Receptor proteins serve as antenna for outside signals, and transport proteins carry oxygen
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3.12 Proteins are made from amino acids linked by peptide bonds
Amino acids, the building blocks of proteins, have an amino group and a carboxyl group
– Both of these are covalently bonded to a central carbon atom
– Also bonded to the central carbon is a hydrogen atom and some other chemical group symbolized by R
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Carboxylgroup
Aminogroup
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3.12 Proteins are made from amino acids linked by peptide bonds
Amino acids are classified as hydrophobic or hydrophilic
– Some amino acids have a nonpolar R group and are hydrophobic
– Others have a polar R group and are hydrophilic, which means they easily dissolve in aqueous solutions
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Leucine (Leu)
Hydrophobic
Serine (Ser)
Hydrophilic
Aspartic acid (Asp)
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3.12 Proteins are made from amino acids linked by peptide bonds
Amino acid monomers are linked together to form polymeric proteins
– This is accomplished by an enzyme-mediated dehydration reaction
– This links the carboxyl group of one amino acid to the amino group of the next amino acid
– The covalent linkage resulting is called a peptide bond
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Carboxylgroup
Amino acid
Aminogroup
Amino acid
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Carboxylgroup
Amino acid
Aminogroup
Amino acid
Peptidebond
Dipeptide
Dehydrationreaction
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3.13 A protein’s specific shape determines its function
A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bonds
– The amino acid sequence causes the polypeptide to assume a particular shape
– The shape of a protein determines its specific function
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Groove
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Groove
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3.13 A protein’s specific shape determines its function
If for some reason a protein’s shape is altered, it can no longer function
– Denaturation will cause polypeptide chains to unravel and lose their shape and, thus, their function
– Proteins can be denatured by changes in salt concentration and pH
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3.14 A protein’s shape depends on four levels of structure
A protein can have four levels of structure
– Primary structure
– Secondary structure
– Tertiary structure
– Quaternary structure
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3.14 A protein’s shape depends on four levels of structure
The primary structure of a protein is its unique amino acid sequence
– The correct amino acid sequence is determined by the cell’s genetic information
– The slightest change in this sequence affects the protein’s ability to function
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3.14 A protein’s shape depends on four levels of structure
Protein secondary structure results from coiling or folding of the polypeptide
– Coiling results in a helical structure called an alpha helix
– Folding may lead to a structure called a pleated sheet
– Coiling and folding result from hydrogen bonding between certain areas of the polypeptide chain
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Collagen
Polypeptide
chain
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3.14 A protein’s shape depends on four levels of structure
The overall three-dimensional shape of a protein is called its tertiary structure
– Tertiary structure generally results from interactions between the R groups of the various amino acids
– Disulfide bridges are covalent bonds that further strengthen the protein’s shape
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3.14 A protein’s shape depends on four levels of structure
Two or more polypeptide chains (subunits) associate providing quaternary structure
– Collagen is an example of a protein with quaternary structure
– Its triple helix gives great strength to connective tissue, bone, tendons, and ligaments
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Animation: Secondary Protein Structure
Animation: Quaternary Protein Structure
Animation: Tertiary Protein Structure
Animation: Protein Structure Introduction
Animation: Primary Protein Structure
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Four Levels of Protein Structure
Amino acids
Primary structure
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Four Levels of Protein Structure
Amino acids
Primary structure
Alpha helix
Hydrogenbond
Secondary structure
Pleated sheet
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Four Levels of Protein Structure
Amino acids
Primary structure
Alpha helix
Hydrogenbond
Secondary structure
Pleated sheet
Polypeptide(single subunitof transthyretin)
Tertiary structure
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Four Levels of Protein Structure
Amino acids
Primary structure
Alpha helix
Hydrogenbond
Secondary structure
Pleated sheet
Polypeptide(single subunitof transthyretin)
Tertiary structure
Transthyretin, withfour identicalpolypeptide subunits
Quaternary structure
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Amino acids
Primary structure
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Amino acids
Alpha helix
Hydrogenbond
Secondary structure
Pleated sheet
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Polypeptide(single subunitof transthyretin)
Tertiary structure
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Transthyretin, withfour identicalpolypeptide subunits
Quaternary structure
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3.15 TALKING ABOUT SCIENCE: Linus Pauling contributed to our understanding of the chemistry of life
After winning a Nobel Prize in Chemistry, Pauling spent considerable time studying biological molecules
– He discovered an oxygen attachment to hemoglobin as well as the cause of sickle-cell disease
– Pauling also discovered the alpha helix and pleated sheet of proteins
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NUCLEIC ACIDS
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3.16 Nucleic acids are information-rich polymers of nucleotides
DNA (deoxyribonucleic acid) and RNA(ribonucleic acid) are composed of monomers called nucleotides
– Nucleotides have three parts
– A five-carbon sugar called ribose in RNA and deoxyribose in DNA
– A phosphate group
– A nitrogenous base
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Phosphategroup
Nitrogenousbase
(adenine)
Sugar
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3.16 Nucleic acids are information-rich polymers of nucleotides
DNA nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G)
– RNA also has A, C, and G, but instead of T, it has uracil (U)
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3.16 Nucleic acids are information-rich polymers of nucleotides
A nucleic acid polymer, a polynucleotide, forms from the nucleotide monomers when the phosphate of one nucleotide bonds to the sugar of the next nucleotide
– The result is a repeating sugar-phosphate backbone with protruding nitrogenous bases
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Sugar-phosphatebackbone
Nucleotide
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3.16 Nucleic acids are information-rich polymers of nucleotides
Two polynucleotide strands wrap around each other to form a DNA double helix
– The two strands are associated because particular bases always hydrogen bond to one another
– A pairs with T, and C pairs with G, producing base pairs
RNA is usually a single polynucleotide strand
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Basepair
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3.16 Nucleic acids are information-rich polymers of nucleotides
A particular nucleotide sequence that can instruct the formation of a polypeptide is called a gene
– Most DNA molecules consist of millions of base pairs and, consequently, many genes
– These genes, many of which are unique to the species, determine the structure of proteins and, thus, life’s structures and functions
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3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human evolution
Mutations are alterations in bases or the sequence of bases in DNA
– Lactose tolerance is the result of mutations
– In many people, the gene that dictates lactose utilization is turned off in adulthood
– Apparently, mutations occurred over time that prevented the gene from turning off
– This is an excellent example of human evolution
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Short polymer MonomerHydrolysis
Dehydration
Longer polymer
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Sucrose
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Temperature (°C)
0 20
Rate
of
rea
cti
on
Enzyme A
100
Enzyme B
40 60 80
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You should now be able to
1. Discuss the importance of carbon to life’s molecular diversity
2. Describe the chemical groups that are important to life
3. Explain how a cell can make a variety of large molecules from a small set of molecules
4. Define monosaccharides, disaccharides, and polysaccharides and explain their functions
5. Define lipids, phospholipids, and steroids and explain their functions
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You should now be able to
6. Describe the chemical structure of proteins and their importance to cells
7. Describe the chemical structure of nucleic acids and how they relate to inheritance
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