Topic 2; The Chemical Building Blocks of Life

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Building blocks of life

• Carbon based: organic molecules
• Carbohydrates: CHO
• Lipids: CHO, water insoluble
• Proteins: CHONS, structure/function in cells
• Nucleic acids: CHONP, hereditary (genetic) information

Carbon

• Can make 4 covalent bonds1
• Chains
• Straight
• Branched
• Ring
• Hydrocarbons2 (C, H): store energy
• Functional groups
• Attach to carbon
• Alter chemical properties
• Form macromolecules
• Sapoteton

 Carbohydrates

• Principally CHO (rare N, S and P)      

• 1C:2H:1O ratio
• Energy rich (many C-H bonds)
• Monosaccharides (principal: glucose3)
• Simple sugars
• Principle formula: C6H12O6
• Form rings in water solution
• Disaccharides (sucrose, lactose)          
• Polysaccharides (starch, glycogen, cellulose, chitin)



fig 1.sources of carbohydrates

Stereoisomers

• Bond angles of carbon point to corners of a tetrahedron
• When 4 different groups are attached to a carbon, it is asymmetric, leading to various
types of isomerism
• Stereoisomers: (D, L)
• Same chemical properties
• Different biological properties
• D sugars, L amino acids

Lipids

• C-H bonds (nonpolar) instead of C-OH bonds as in carbohydrates
• High energy
• Hydrophobic (insoluble in water)
• Categories
• Fats: glycerol and three fatty acids
• Phospholipids: primary component of membranes
• Prostaglandins: chemical messengers (hormones)
• Steroids: membrane component; hormones
• Terpenes: pigments; structure

 Fatty acids

• Hydrocarbon chain
• Even number of C, 14->20
• Terminates in carboxyl group
• Saturated: contain maximum number of hydrogens (all single bonds); maximum energy
• Unsaturated: one or more double bonds
• Usually higher melting point
• Many common oils are polyunsaturated
fig3. fatty acid

Proteins

• Polymer of amino acids
• 21 different amino acids found in proteins
• Sequence of amino acids determined by gene
• Amino acid sequence determines shape of molecule
• Linked by peptide bond (covalent)
• Functions
• regulate chemical reactions and cell processes [enzymes]
• form bone and muscle; various other tissues
• facilitate transport across cell membrane [carrier proteins
• fight disease [antibodies]
• Motifs: folding patterns of secondary structure
• Domains: structural, functional part of protein often independent of another part; often








encoded by different exons
• Shape determines protein's function 

Amino acids

• 21 commonly found in proteins
• 21st is selenocysteine, not mentioned in text
• Common structure
• Amino group: NH2
• Carboxyl group: COOH
• R group- 4 different kinds of R groups
• acidic
• basic
• hydrophilic (polar)
• hydrophobic (nonpolar)
• Confer individual properties on amino acids
• List of amino acids4

 Structure

• Primary structure: the amino acid sequence
• Determines higher orders of structure
• Critical for structure and function of protein
• Secondary: stabilized by intramolecular hydrogen bonding
• helix
• sheet
• Tertiary: folding, stabilized by ionic bonds (between R groups), hydrogen bonding, van
der Waal's forces, hydrophobic interactions
• Quaternary: _2 polypeptides
fig 5.amino acid

 Function

• Requires proper folding, cofactors, pH, temperature, etc.
• Proteins are often modified after synthesis
• Chemical modification
• Addition of heme groups (hemoglobin, cytochrome)
• Denatured proteins can not function properly
• Proteins are degraded by proteosome as part of constant turnover of cell components

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