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CHAPTER 3
The Molecules of Life
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Did you know?
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Organic Molecules
• A cell is mostly water.
– The rest of the cell consists mostly of carbon-based molecules.
– Organic chemistry is the study of carbon compounds.
– An organic compound must contain Carbon! Note that there are some inorganic compounds that also contain carbon, but these lack hydrogen. An example is CO2. Another way to determine if a carbon containing compound is organic is to decide if it is found in living tissue.
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Carbon Chemistry
• Carbon is a versatile atom.
• Carbon has the atomic number of 6.
• How many valence electrons available for covalent bonding does it have______?
– Carbon can share its electrons with other atoms to form up to ________ covalent bonds.
• ___ single bond(s)
• ____ double bond(s)
• ___ triple bond(s)
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• Carbon can use its bonds to
– Attach to other carbons.
– Form an endless diversity of carbon skeletons in many shapes as shown below.
Carbon Chemistry
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• The simplest organic compounds are hydrocarbons.
– These are organic molecules containing only carbon and hydrogen atoms.
– The simplest hydrocarbon is methane (shown below)
Carbon Chemistry
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Carbon Chemistry
• Larger hydrocarbons are used in our bodies and elsewhere.
– 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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• Each type of organic molecule has a unique three-dimensional shape that defines its function in an organism.
– The molecules of your body recognize one another based on their shapes.
Carbon Chemistry
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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.
Hydroxyl: -OH alcoholsCarbonyl: -CO aldehydes & ketonesCarboxyl: -COOH aka carboxylic acidsAmino: -NH2 aminesPhosphate: -PO4 phosphates
Carbon Chemistry
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Memorize the names, chemical formula, where they are found and the structure of the parts.
Phosphate Group
Found in amino acids and used in energy storage in ATP!
-OH -CO
-COOH
-NH2-PO4
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Giant Molecules from Smaller Building Blocks
• On a molecular scale, many of life’s molecules are gigantic.
– Biologists call them macromolecules.
• macro = large
– Examples: carbohydrates, proteins, lipids, the nucleic acids - & RNA DNA
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Giant Molecules from Smaller Building Blocks
• Most macromolecules are polymers.
– Polymers are made by stringing together many smaller molecules called monomers.
– Cells link monomers to build polymers by dehydration reactions.
Note that water has been lost when the polymer is formed this is what makes it a “dehydration reaction”
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• Organisms also have to break down macromolecules.– Cells do this by a process called hydrolysis.
• Hydro = water, lysis = split/destroy
Note that water has been split to create break apart the polymer into smaller subunits such as monomers.
Breaking down large molecules
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Biological Molecules
• There are four categories of large molecules in cells:
1. Carbohydrates
2. Lipids
3. Proteins
4. 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.
– Examples:
• Glucose is found in sports drinks.
• Fructose is found in fruit.
• Honey contains both glucose and fructose.
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• The monosaccharides glucose, fructose and galactose are isomers.
– They have the same formula, but their atoms are arranged differently.
L-Dopa (watch and take notes!)
Isomers (watch and take notes!)
Monosaccharides
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• In aqueous solutions, monosaccharides form rings.
• Monosaccharides are the main fuel that cells use for cellular work.
Monosaccharides
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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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• Lactose is another type of disaccharide.
– Some people have trouble digesting lactose, a condition called lactose intolerance.
Disaccharides
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• 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.• The United States is one of
the world’s leading markets for sweeteners.
– The average American consumes about 64 kg of sugar per year.
Disaccharides
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Polysaccharides
• Complex carbohydrates are called polysaccharides.
– They are long chains of sugar units.
– They are polymers of monosaccharides.
Polysaccharides
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• 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.
Polysaccharides
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• Animals store excess sugar in the form of a polysaccharide called glycogen.
– Glycogen is similar in structure to starch.
• Cellulose is a structural component of plant cells and 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.
Polysaccharides
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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.
Polysaccharides
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• Simple sugars and double sugars dissolve readily in water.
– They are hydrophilic, or “water-loving.”
Polysaccharides
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Low-Carb Diets
• In recent years, “low-carb diets” and “no carb diets” have become popular.
– Are these diets healthy?
– But consumers need to be wary of products boasting that they are “low-carb” because they can 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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• Fats perform essential functions in the human body:
1. Energy storage
2. Cushioning
3. Insulation
Fats
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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.
Fats
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• 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
Fats
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• Not all fats are unhealthy.
– Fats perform important functions in the body and are essential to a healthy diet.
– Are no fat diets healthy?
Fats
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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
Steroids
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• Synthetic anabolic steroids are controversial.
– They are variants of testosterone.
• Some athletes use anabolic steroids to build up their muscles quickly.
– However, these substances can pose serious health risks.
– Testicle shrinkage, Addiction, Growth of Breasts (in men), Facial Hair (in women) Reduced Sexual Function, Baldness & Skin Conditions, Infertility, Halted Growth (in teens) High Blood Pressure, Liver Damage, Pain, Psycosis, Heart Attack, Death and more!
Steroids
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Proteins
• A protein is a polymer constructed from amino acid monomers.
• Proteins perform most of the tasks the body needs to function.
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Structural Proteins
Storage Proteins
Contractile Proteins
Transport Proteins
Defensive Proteins
Receptor Proteins
Enzymes
Hormonal Proteins
Sensory Proteins
Protein Videos
• Information on many important proteins below.
• I encourage you to watch those we do not get to in class online for more information!
Gene Regulatory Proteins
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The Monomers: Amino Acids
• All proteins are constructed from a common set of 20 kinds of amino acids.
• Each amino acid consists of
1. A central carbon atom bonded to four covalent partners.
2. A side group that is variable among all 20.
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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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• Your body has tens of thousands of different kinds of protein.
– The arrangement of amino acids makes each one different.
Proteins as Polymers
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• Primary structure
– The specific sequence of amino acids in a protein
Proteins
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• 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.
Proteins
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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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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.
• There are two types of nucleic acids:
– DNA, deoxyribonucleic acid
– RNA, ribonucleic acid DNA
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• The genetic instructions in DNA
– Must be translated from “nucleic acid language” to “protein language.”
Nucleic Acids
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• Nucleic acids are polymers of nucleotides.
Nucleic Acids
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• Each DNA nucleotide has one of the following bases:
– Adenine (A)
– Guanine (G)
– Thymine (T)
– Cytosine (C)
Nucleic Acids
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• 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
Nucleic Acids
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• Two strands of DNA join together to form a double helix.
Nucleic Acids
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• RNA, ribonucleic acid, is different from DNA.
– Its sugar ribosehas an extra OH group.
– It has the base uracil (U) instead of thymine (T).
Nucleic Acids
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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