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
• 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
• 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
– 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– 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