Transcript Macromolecules - Southgate Schools

CHAPTER 3
The Molecules of Life
PowerPoint® Lectures for
Essential Biology, Third Edition
– Neil Campbell, Jane Reece, and Eric Simon
Essential Biology with Physiology, Second Edition
– Neil Campbell, Jane Reece, and Eric Simon
Lectures by Chris C. Romero
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Biology and Society:
Does Thanksgiving Dinner Make You Sleepy?
• After finishing a huge Thanksgiving dinner,
– Many people feel especially lethargic and a few
even doze off.
• Many people think that turkey makes you sleepy.
– Is there a biological basis to this claim?
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• Turkey meat is high in tryptophan.
– Tryptophan is a molecule that is converted in your
body to serotonin, which promotes sleep.
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Figure 3.1
• However, there is little evidence
– That a turkey dinner encourages sleep more than
any other meal.
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Organic Molecules
• A cell is mostly water.
– The rest of the cell consists mostly of carbonbased molecules.
– Organic chemistry is the study of carbon
compounds.
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Carbon Chemistry
• Carbon is a versatile atom.
– It has four electrons in an outer shell that holds
eight.
– Carbon can share its electrons with other atoms to
form up to four covalent bonds.
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• Carbon can use its bonds to
– Attach to other carbons.
– Form an endless diversity of carbon skeletons.
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Figure 3.2
• The simplest organic compounds are hydrocarbons.
– These are organic molecules containing only
carbon and hydrogen atoms.
– The simplest hydrocarbon is methane.
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Figure 3.3
• Larger hydrocarbons
– Are the main molecules in the gasoline we burn in
our cars.
• The hydrocarbons of fat molecules provide energy
for our bodies.
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Figure 3.4
• Each type of organic molecule has a unique threedimensional shape that defines its function in an
organism.
– The molecules of your body recognize one
another based on their shapes.
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• The unique properties of an organic compound
depend not only on its carbon skeleton but also on
the atoms attached to the skeleton.
– These atoms are called functional groups.
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Figure 3.5
Giant Molecules from Smaller Building Blocks
• On a molecular scale, many of life’s molecules are
gigantic.
– Biologists call them macromolecules.
– Examples: DNA, carbohydrates
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• Most macromolecules are polymers.
– Polymers are made by stringing together many
smaller molecules called monomers.
– Cells link monomers by dehydration reactions.
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Figure 3.6a
• Organisms also have to break down
macromolecules.
– Cells do this by a process called hydrolysis.
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Figure 3.6b
Biological Molecules
• There are four categories of large molecules in
cells:
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
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Carbohydrates
• Carbohydrates include:
– Small sugar molecules in soft drinks
– Long starch molecules in pasta and potatoes
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Monosaccharides
• Monosaccharides are simple sugars.
– Glucose is found in sports drinks.
– Fructose is found in fruit.
• Honey contains both glucose and fructose.
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Figure 3.7
• The monosaccharides glucose and fructose are
isomers.
– They have the same formula, but their atoms are
arranged differently.
Isomers
L-Dopa
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Figure 3.8
• In aqueous solutions, monosaccharides form rings.
• Monosaccharides are the main fuel that cells use
for cellular work.
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Figure 3.9
Disaccharides
• A disaccharide is a double sugar.
– It is constructed from two monosaccharides.
• Disaccharides are joined through a dehydration
reaction.
Disaccharides
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Figure 3.10
• Lactose is another type of disaccharide.
– Some people have trouble digesting lactose, a
condition called lactose intolerance.
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Figure 3.11
• The most common disaccharide is sucrose,
common table sugar.
– It consists of a glucose linked to a fructose.
– Sucrose is extracted from sugar cane and the roots
of sugar beets.
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• The United States is one of the world’s leading
markets for sweeteners.
– The average American consumes about 64 kg of
sugar per year.
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Figure 3.12
Polysaccharides
• Complex carbohydrates are called polysaccharides.
– They are long chains of sugar units.
– They are polymers of monosaccharides.
Polysaccharides
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Figure 3.13
• One familiar example of a polysaccharide is starch.
– Plant cells store starch for energy.
– Potatoes and grains are major sources of starch in
the human diet.
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• Animals store excess sugar in the form of a
polysaccharide called glycogen.
– Glycogen is similar in structure to starch.
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• Cellulose is the most abundant organic compound
on Earth.
– It forms cable-like fibrils in the tough walls that
enclose plants.
– It is a major component of wood.
– It is also known as dietary fiber.
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• Most animals cannot derive nutrition from fiber.
– Grazing animals survive on a diet of cellulose
because they have prokaryotes in their digestive
tracts that can break down cellulose.
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Figure 3.14
• Simple sugars and double sugars dissolve readily in
water.
– They are hydrophilic, or “water-loving.”
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Low-Carb Diets
• In recent years, “low-carb diets” have become
popular.
– But consumers need to be wary of products
boasting that they are “low-carb” because they
can sometimes be unhealthy.
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Lipids
• Lipids are hydrophobic.
– They do not mix with water.
– Examples: fats and steroids
Fats
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Fats
• Dietary fat consists largely of the molecule
triglyceride.
– Triglyceride is a combination of glycerol and
three fatty acids.
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Figure 3.15a
• Fats perform essential functions in the human
body:
– Energy storage
– Cushioning
– Insulation
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• Unsaturated fatty acids
– Have less than the maximum number of
hydrogens bonded to the carbons.
• Saturated fatty acids
– Have the maximum number of hydrogens bonded
to the carbons.
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Figure 3.15b
• Most animal fats have a high proportion of
saturated fatty acids, which can be unhealthy.
– Example: butter
• Most plant oils tend to be low in saturated fatty
acids.
– Example: corn oil
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• Not all fats are unhealthy.
– Some fats perform important functions in the
body and are essential to a healthy diet.
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Figure 3.16
Steroids
• Steroids are very different from fats in structure
and function.
– The carbon skeleton is bent to form four fused
rings.
• Cholesterol is the “base steroid” from which your
body produces other steroids.
– Example: sex hormones
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Figure 3.17
• Synthetic anabolic steroids are controversial.
– They are variants of testosterone.
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• Some athletes use anabolic steroids to build up
their muscles quickly.
– However, these substances can pose serious
health risks.
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Figure 3.18
Proteins
• A protein is a polymer constructed from amino acid
monomers.
• Proteins perform most of the tasks the body needs
to function.
Structural Proteins
Receptor Proteins
Storage Proteins
Enzymes
Contractile Proteins
Hormonal Proteins
Transport Proteins
Sensory Proteins
Defensive Proteins
Gene Regulatory
Proteins
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Figure 3.19
The Monomers: Amino Acids
• All proteins are constructed from a common set of
20 kinds of amino acids.
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• Each amino acid consists of
– A central carbon atom bonded to four covalent
partners.
– A side group that is variable among all 20.
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Figure 3.20
Proteins as Polymers
• Cells link amino acids together by dehydration
reactions.
– The resulting bond between them is called a
peptide bond.
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Figure 3.21
• Your body has tens of thousands of different kinds
of protein.
– The arrangement of amino acids makes each one
different.
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• Primary structure
– The specific sequence of amino acids in a protein
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Figure 3.22
• A slight change in the primary structure of a
protein affects its ability to function.
– The substitution of one amino acid for another in
hemoglobin causes sickle-cell disease.
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Figure 3.23
Protein Shape
• Proteins have four levels of structure.
Protein Structure Introduction
Primary Protein Structure
Secondary Protein Structure
Tertiary Protein Structure
Quaternary Protein Structure
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Figure 3.24
What Determines Protein Structure?
• A protein’s shape is sensitive to the surrounding
environment.
– Unfavorable temperature and pH changes can
cause a protein to unravel and lose its shape.
– This is called denaturation.
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Nucleic Acids
• Nucleic acids are information storage molecules.
– They provide the directions for building proteins.
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• There are two types of nucleic acids:
– DNA, deoxyribonucleic acid
– RNA, ribonucleic acid
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• The genetic instructions in DNA
– Must be translated from “nucleic acid language”
to “protein language.”
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Figure 3.25
• Nucleic acids are polymers of nucleotides.
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Figure 3.26
• Each DNA nucleotide has one of the following
bases:
– Adenine (A)
– Guanine (G)
– Thymine (T)
– Cytosine (C)
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Figure 3.27
• Nucleotide monomers are linked into long chains.
– These chains are called polynucleotides, or DNA
strands.
– A sugar-phosphate backbone joins them together.
DNA and RNA Structure
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Figure 3.28a
• Two strands of DNA join together to form a double
helix.
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Figure 3.28b
• RNA, ribonucleic acid, is different from DNA.
– Its sugar has an extra OH group.
– It has the base uracil (U) instead of thymine (T).
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Figure 3.29
Evolution Connection:
DNA and Proteins as Evolutionary Tape Measures
• Evolutionary relationships between organisms can
be assessed.
– Molecular genealogy extends to relationships
between species.
– Biologists use molecular analysis of DNA and
protein sequences for testing evolutionary
hypotheses.
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Figure 3.30