➢ Nucleic Acids
- Contain carbon, hydrogen, oxygen, nitrogen, and phosphorous
- Structure
■ Nitrogenous base
■ Pentose sugar
■ Phosphate group
■ Portion of nucleotide w/o phosphate group is called nucleoside - Store, transmit, and help expres hereditary information
- monomer=nucleotides
- Amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene
■ Made up of DNA - Deoxyribonucleic acid (DNA)
● sugar=deoxyribose
● Contains genetic/hereditary information
● Provides directions for its own replication
● Directs synthesis of messenger RNA (mRNA), and through mRNA, controls protein synthesis - Occurs on ribosomes
- Ribonucleic acid (RNA)
● sugar=ribose
● Essential for protein synthesis - 2 families of nitrogenous bases
■ Pyrimidines
● Single 6-membered ring
● Ex. - Cytosine
- Thymine (only DNA
- Uracil (only RNA)
■ Purines
● 6-membered ring fused to a 5-membered ring
● Ex. - Adenine
- Guanine
- Nucleotide Polymers
■ Nucleotide polymers linked together to build a polynucleotide
■ Adjacent nucleotides are joined by covalent bonds that form between the$ -OH$ group on the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon on the next
● Links create a backbone of sugar-phosphate units with nitrogenous bases as appendages
■ RNA molecules usually exist as single polypeptide chains
■ DNA molecules have 2 polynucleotides spiraling around an imaginary axis, forming a double helix
● Two backbones run in opposite 5’→3’ directions from each other (antiparallel)
● One DNA molecule contains many genes
● Nitrogenous bases pair up and form hydrogen bonds - Adenine-Thymine
- Guanine-Cytosine
- Complementary base pairing
- In RNA, thymine is replaced by uracil, so A and U pair
F. Origins of the Earth
➢ Alexander Oparin and J. B. S. Haldane proposed that the primitive atmosphere contained the
following gases:
- Methane $(CH_4)$
- Ammonia $(NH_3)$
- Hydrogen $(H_2)$
- Water$ (H_2O)$
- No free oxygen$ (O_2)$
■ No oxidation/reduction
■ Rocks do not release oxygen through weathering - Gases collided, producing chemical reactions that eventually led to the organic molecules
we know today - Substantial support until 1953
➢ 1953, Stanley Miller and Harold Urey simulated the conditions of primitive Earth in a lab,
- Put theoried gases into flask, struck them with electrical charges to simulate lightning, and organic compounds similar to amino acids appeared
➢ Current theory of the origin of life suggests 4 main stages - 1. Formation of amino acids
- 2. Monomers form polymers
- 3. Enclosure of small organic molecules into larger ones
- 4. Self-replicating molecules that can direct synthesis of other organic substances
■ Energy sources for early organic synthesis
● Lightning
● Volcanic eruptions
➢ RNA world hypothesis - Original life-forms were simple molecules of RNA
■ RNA not restricted to double helix
■ RNA capable of replicating and passing genes Complex organic compounds must have formed via dehydration synthesis
■ Organic compounds then used as food by cells
● Simple cells evolved into complex cells
➢ Heterotrophs
- living organisms that rely on organic molecules for food Aka consumers
➢ Autotrophs
- Organisms that make their own food
■ Most commonly via photosynthesis - Aka producers