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