Transcript Nucleic Acids

Chapter 3
The Molecules of Life
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
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Biology and Society:
Got Lactose?
• Lactose is the main sugar found in milk.
• Some adults exhibit lactose intolerance, the inability to properly
digest lactose.
• Lactose-intolerant individuals are unable to digest lactose
properly.
• Lactose is broken down by bacteria in the large intestine
producing gas and discomfort. There is no treatment for the
underlying cause of lactose intolerance.
• Affected people must
– Avoid lactose-containing foods or
– Take the enzyme lactase when eating dairy products
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Evolution Connection:
Evolution and Lactose Intolerance in Humans
• Most people are lactose-intolerant as adults:
– African Americans and Native Americans — 80%
– Asian Americans — 90%
– But only 10% of Americans of northern European descent are
lactose-intolerant
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• Lactose tolerance appears to have evolved in northern European
cultures that relied upon dairy products.
• Ethnic groups in East Africa that rely upon dairy products are also
lactose tolerant.
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• Polymers are made by stringing together many smaller molecules
called monomers.
• A dehydration reaction
– Links two monomers together
– Removes a molecule of water
• Organisms also have to break down macromolecules.
• Hydrolysis
– Breaks bonds between monomers
– Adds a molecule of water
– Reverses the dehydration reaction
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LARGE BIOLOGICAL MOLECULES
• There are four categories of large molecules in cells:
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
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Carbohydrates
• Carbohydrates are sugars or sugar polymers. They include
– Small sugar molecules in soft drinks
– Long starch molecules in pasta and potatoes
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Monosaccharides & Disaccharides
• Monosaccharides are simple sugars that cannot be broken down
by hydrolysis into smaller sugars.
• Common examples are
– Glucose in sports drinks
– Fructose found in fruit
• A disaccharide is
– A double sugar
– Constructed from two monosaccharides
– Formed by a dehydration reaction
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• Disaccharides include
– Lactose in milk (see next slide)
– Maltose in beer, malted milk shakes, and malted milk ball candy
– Sucrose in table sugar
• Sucrose is
– The main carbohydrate in plant sap
– Rarely used as a sweetener in processed foods
• High-fructose corn syrup is made by a commercial process that
converts natural glucose in corn syrup to much sweeter fructose.
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Galactose
Glucose
Lactose
Figure 3.7
processed to extract
Starch
broken down into
Glucose
converted to sweeter
Fructose
added to foods as
high-fructose corn syrup
Ingredients: carbonated water,
high-fructose corn syrup,
caramel color, phosphoric acid,
natural flavors
Figure 3.8
Polysaccharides
• Polysaccharides are
– Complex carbohydrates
– Made of long chains of sugar units and polymers of
monosaccharides
– Examples include: starch, glycogen and cellulose
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Glucose
monomer
Starch granules
a Starch
Glycogen
granules
b Glycogen
Cellulose fibril
Cellulose
molecules
c Cellulose
Figure 3.9
• Starch is
– A familiar example of a polysaccharide
– Used by plant cells to store energy
• Potatoes and grains are major sources of starch in the human diet.
• Glycogen is
– Used by animals cells to store energy
– Converted to glucose when it is needed
• Cellulose
– Is the most abundant organic compound on Earth
– Forms cable-like fibers in the tough walls that enclose plants
– Cannot be broken apart by most animals
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Lipids
• Lipids are
–
Neither macromolecules nor polymers
–
Hydrophobic, unable to mix with water
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Oil (hydrophobic)
Vinegar (hydrophilic)
Figure 3.10
Fats
• A typical fat, or triglyceride, consists of a glycerol molecule
joined with three fatty acid molecules via a dehydration reaction.
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Fatty acid
Glycerol
(a) A dehydration reaction linking a fatty acid to glycerol
(b) A fat molecule with a glycerol “head” and three
energy-rich hydrocarbon fatty acid “tails”
Figure 3.11
• Fats perform essential functions in the human body including
– Energy storage
– Cushioning
– Insulation
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• Most animal fats
– Have a high proportion of saturated fatty acids
– Can easily stack, tending to be solid at room temperature
– Contribute to atherosclerosis, a condition in which lipidcontaining plaques build up within the walls of blood vessels
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• Most plant oils tend to be low in saturated fatty acids and liquid at
room temperature.
• Hydrogenation
– Adds hydrogen
– Converts unsaturated fats to saturated fats
– Makes liquid fats solid at room temperature
– Creates trans fat, a type of unsaturated fat that is even less healthy
than saturated fats
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TYPES OF FATS
Saturated Fats
Unsaturated Fats
Margarine
INGREDIENTS: SOYBEAN OIL, FULLY HYDROGENATED
COTTONSEED OIL, PARTIALLY HYDROGENATED
COTTONSEED OIL AND SOYBEAN OILS, MONO AND
DIGLYCERIDES, TBHO AND CITRIC ACID
Plant oils
Trans fats
ANTIOXIDANTS
Omega-3 fats
Figure 3.12
Steroids
• Steroids are very different from fats in structure and function.
– The carbon skeleton is bent to form four fused rings.
• Cholesterol is
– A key component of cell membranes
– The “base steroid” from which your body produces other steroids,
such as estrogen and testosterone
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Cholesterol
Testosterone
A type of estrogen
Figure 3.13
• Synthetic anabolic steroids
– Resemble testosterone
– Mimic some of its effects
– Can cause serious physical and mental problems
– Are abused by athletes to enhance performance
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Proteins
• Proteins
– Are polymers constructed from amino acid monomers
– Perform most of the tasks the body needs to function
– Form enzymes, chemicals that change the rate of a chemical
reaction without being changed in the process
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MAJOR TYPES OF PROTEINS
Structural Proteins
Storage Proteins
Contractile Proteins
Transport Proteins
Enzymes
Figure 3.15
Proteins as Polymers
• Cells link amino acids together by dehydration reactions, forming
peptide bonds and creating long chains of amino acids called
polypeptides.
• The specific sequence of amino acids in a protein is its primary
structure.
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Amino
acids
b Secondary structure
c Tertiary
structure
d Quaternary
structure
a Primary
structure
Pleated sheet
Protein with
four polypeptides
Polypeptide
Alpha helix
Figure 3.20-4
What Determines Protein Shape?
• A protein’s shape is sensitive to the surrounding environment.
• Unfavorable temperature and pH changes can cause
denaturation of a protein, in which it unravels and loses its
shape.
• High fevers (above 104º F) in humans can cause some proteins to
denature.
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• Misfolded proteins are associated with
– Alzheimer’s disease
– Mad cow disease
– Parkinson’s disease
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Nucleic Acids
• Nucleic acids
– Are macromolecules that provide the directions for building
proteins
– Include DNA and RNA
– Are the genetic material that organisms inherit from their parents
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• DNA resides in cells in long fibers called chromosomes.
• A gene is a specific stretch of DNA that programs the amino acid
sequence of a polypeptide.
• The chemical code of DNA must be translated from “nucleic acid
language” to “protein language.”
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Gene
DNA
Nucleic acids
RNA
Amino acid
Protein
Figure 3.22
•
Nucleic acids are polymers of nucleotides.
•
Each nucleotide has three parts:
–
A five-carbon sugar
–
A phosphate group
–
A nitrogenous base
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• Each DNA nucleotide has one of the following bases:
– Adenine (A)
– Guanine (G)
– Thymine (T)
– Cytosine (C)
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Base
pair
Hydrogen
bond
b Double helix
two polynucleotide strands
Figure 3.25b
• Two strands of DNA join together to form a double helix.
• Bases along one DNA strand hydrogen-bond to bases along the
other strand.
• The functional groups hanging off the base determine which bases
pair up:
– A only pairs with T.
– G can only pair with C.
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• RNA, ribonucleic acid, is different from DNA.
– RNA is usually single-stranded but DNA usually exists as a double
helix.
– RNA uses the sugar ribose and the base uracil (U) instead of
thymine (T).
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Large biological
molecules
Carbohydrates
Functions
Components
Examples
Monosaccharides:
glucose, fructose
Disaccharides:
lactose, sucrose
Polysaccharides:
starch, cellulose
Dietary energy;
storage; plant
structure
Monosaccharide
Lipids
Long-term
energy storage
fats;
hormones
steroids
Fatty acid
Glycerol
Components of
a triglyceride
Amino
group
Proteins
Enzymes, structure,
storage, contraction,
transport, and others
Fats triglycerides;
Steroids
testosterone,
estrogen
Carboxyl
group
Side
group
Lactase
an enzyme,
hemoglobin
a transport protein
Amino acid
Phosphate
Base
Nucleic acids
Information
storage
DNA, RNA
Sugar
Nucleotide
Figure UN3-2