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Principles of Biology Chapter 3
Chapter 3 Molecules of Life
• Carbon is essential to life
• Cells are mostly carbon molecules &
water
• Carbon is the basic building block of the
4 macromolecules
– Carbohydrates, lipids, proteins, DNA
• Carbon
– Can form very large molecules - 4 bonds
– Basis of Organic chemistry
Fig. 3.2
Carbon skeletons
• Can be very large and varied
– Linear or branched
– Bonded to carbon atoms or other molecules
• Hydrocarbon
– Simplest organic molecule
• Methane
• Gasoline
– Consists of carbon and hydrogen atoms
• Unique 3-D shape
Fig. 3.3
Fig. 3.5
Functional groups
• Attached to hydrocarbon skeleton
• Participate in chemical reactions
– OH - called hydroxyl or alcohol group
• Sugars and alcohols
– Carbonyl - O = C (double bond to carbon)
• Found in sugars
– NH3 - amino group found in proteins
– COOH - carboxyl group
• Found in amino acids, fatty acids and vitamins
Fig. 3.6
Synthesis and digestion
• Macromolecules - very large
• Polymers - many (repeating)parts
– Monomer - one unit
• Dehydration synthesis -builds
– Bonds monomers together
– Release water molecule
• Digestion - breaks
– Aka hydrolysis ( water breaking)
– Adds water ions to the broken ends
Carbohydrates
• Monosaccharides
– One sugar unit- molecular formula of CH2O
– Glucose - C6H12O6
– Fructose - C6H12O6
– Honey has both monosaccharides
• In aqueous solutions forms rings
• Main fuel for cellular work
– Can used to make other molecules
– Can be chained together
• Disaccharides - two sugar units
Fig. 3.9
Fig. 3.10
Fig. 3.11
Polysaccharides
• Complex sugars - many sugar units
• Starch
– Glucose chain molecules
– Energy storage in plants
• Glycogen
– Glucose chain molecule
– Energy storage in animals
• Cellulose
– Glucose chain molecule
– Structural molecule in plant cell walls
Lipids
• Hydrophobic
– Water hating
• Fats and steroids
• Fats
– Glycerol molecule and 3 fatty acids
– Triglyceride
– Store twice as much energy as carbs
– Cushion and insulate
– Saturated - no double bonds- all possible H
– Unsaturated- double bonds - fewer H atoms
Fig. 3.14
Steroids
• Lipids because they are hydrophobic
• Carbon chains form 4 fused rings
• Cholesterol
– Form other steroids from it
– Make into sex hormones
• Estrogen
• Testosterone
– Component of cell membranes
Fig. 3.15
Anabolic steroids
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Mimic testosterone
First used for anemia / muscle disease
Abused by athletes
Misuse can cause
– Facial bloating/acne
– Violent mood swings
– Liver damage
– Increase cholesterol levels
– Reduce sex drive and fertility
Phospholipids
• Two regions with opposite properties
• Phosphate ‘head’ is polar
– Hydrophillic water loving
• Fatty acid tails are non-polar
– Hydrophobic - water fearing
• Forms plasma membrane
– Phosphate group faces out
– Watery environment inside/outside cell
- Tails face each other
- Form barrier
Fig. 3.18
Proteins
•
•
•
•
Greek word meaning “first place”
Polymer of amino acids
Have thousands of proteins in us
Monomer
– Amino acid
•
•
•
•
•
Central carbon
Amine group
Carboxyl group
Hydrogen
“R” group - remainder - what differs from amino
acid to amino acid
Proteins
• Amino acids linked by peptide bonds
• Forming a polypeptide (aka protein)
– Chain of amino acids
– 100 or more
• Primary structure
– Order of amino acids
– 20 different amino acids
– Change in order can cause disease
• Sickle cell anemia
• One amino acid changed
Fig. 3.20
Fig. 3.21
Protein structure
• Secondary and tertiary structure
– Twisting and folding
– Bonding between different parts of
molecule
– 3-D shape
• Quaternary structure
– Interaction between more that one
polypeptide
• All this leads to a particular shape that
allows the protein to do its job
Fig. 3.19
Protein shape
• Must twist, fold, and coil correctly to
function
• Hydrophobic region inside
• Hydrophilic regions outside in watery
environment of cell
• 3-D shape is critical
• Denaturation
– Caused by change in pH or temperature
– Changes 3-D shape - non functional
• Shape determines function
Fig. 3.22
Enzymes
• Enzymes are a kind of protein
– Many different enzymes in our bodies
• Metabolism is the sum total of all
chemical reactions in an organism
– Most require a specific enzyme to happen
– Catalyst - stimulate a reaction to occur
• Reactions require a input of energy to
get started - activation energy
• Enzymes lower the energy required
• Result is that chem rxns are effective
How is structure determined?
• Order of amino acids specified by a gene
- recipe for a polypeptide
• Proteins include
– Structural
– Storage
– Contractile
– Transport
– Defensive
– Signal proteins
– ENZYMES!
Nucleic acids
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•
•
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DeoxyriboNucleic Acid - DNA
DNA is a recipe book for proteins
Genes direct the order of amino acids
Two types of nucleic acids
– DNA
– RNA - RiboNucleic Acid
• Chemical code
– Nucleic acid to protein language
– RNA helps with this process
Fig. 3.26
Nucleic acids
• Polymer
– Repeating unit is a nucleotide consisting of:
• Sugar
• Phosphate
• Base
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–
–
–
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Adenine - A
Cytosine - C
Guanine - G
Thymine - T (only in DNA)
Uracil - U (only in RNA)
• Dehydration synthesis makes the
polymer
Fig. 3.27
DNA
• One strand has 100’s to 1000’s of genes
• DNA double helix
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–
–
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2 strands
Bonded to each other by hydrogen bonds
A pairs with T, vice versa
C pairs with G, vice versa
• RNA is a single strand of nucleotides
• Replication (DNA copying)
– Strands separated
– New complementary nucleotides join
Fig. 3.29