General Biology/Getting Started/Chemical Building Blocks of Life

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 bonds
- Chains
  - Straight
  - Branched
  - Ring
- Hydrocarbons (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: glucose)
- Simple sugars
- Principle formula: C₆H₁₂O₆
- Form rings in water solution
Disaccharides (sucrose, lactose)
Polysaccharides (starch, glycogen, cellulose, chitin)

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

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 acids

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

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

Hereditary (Genetic) information

Nucleic acids
- DNA: deoxyribonucleic acid
Hereditary information of all cells
Hereditary information for many viruses
- RNA: ribonucleic acid
Hereditary information of certain viruses (HIV)
Intermediate in gene expression
Composed of nucleotides
- Ribonucleotides
- Deoxyribonucleotides

RNA DNA origin

Which came first?
Paradox: DNA encodes protein necessary for its own replication
Discovery of catalytic RNA by Cech and Altman suggested that RNA might have been first self-replicating molecule
DNA evolved as more stable type of storage molecule

Proteins: Their building block is amino acids. The bond connecting 2 of the amino acids together are called peptide bonds. One of these bonds makes a monopeptide, two a dipeptide, and any more than that makes a polypeptide.

References

This text is based on notes very generously donated by Dr. Paul Doerder, Ph.D., of the Cleveland State University.