AP Biology Life’s Beginnings on Earth according to science

FOUR STEPS FOR LIFE TO EMERGE ON EARLY EARTH

1. ABIOTIC SYNTHESIS OF AMINO ACIDS AND NUCLEIC ACIDS

Nucleic Acid Formation Nucleic acids- DNA and RNA Stores molecular information Transmits hereditary information. RNA is believed to have evolved first--- not as molecularly stable as DNA

Amino Acid Formation Monomers of proteins Account for 50% of biomass of cells.

Protein’s Natural Form Intricate 3D structure Based on amino acid chain Amino acid sequence determines the 3D structure.

2. MONOMERS MUST JOIN TOGETHER TO FORM MORE COMPLEX POLYMERS USING ENERGY FROM THE ENVIRONMENT

Monosaccharides Combining Monomer of carbohydrates– sugars. ex: glucose Monosaccharides combine to make polysaccharides– storage for cells and structure for cells. Dehydration reactions synthesize polysaccharides

Phospholipid Formation Combine to make phospholipid bilayer that forms cell membrane

Construction of mRNA from DNA DNA  RNA  Protein DNA in the nucleus programs protein production in the cytoplasm by dictating the synthesis of messenger RNA (mRNA)

Constructing Chromosomes Chromosomes used for information storage.

3. DNA/RNA ABLE TO REPRODUCE AND STABILIZE USING CHEMICAL BONDING AND COMPLIMENTARY BONDING

DNA Replicating Double stranded– sugar- phosphate backbone Nitrogenous bases hold strands together– Adenine with Thymine or Uracil Guanine with Cytosine Single strands held together by covalent bonds Double strands held together by hydrogen bonds

4. EVOLUTION OF A PROTOBIONT “First life form”

- Hydrophilic head Hydrophobic tail WATER Membrane Formation

Representation of a Protobionts Phospholipid membrane and proteins keep the “cell” intact

SCIENTIFIC SUPPORTING EVIDENCE- -- TESTABLE IN THE LAB

Stanley Miller 1953, set up a closed system to simulate conditions on early earth.

LE 26-2 Water vapor CH 4 NH 3 H2H2 Electrode Condenser Cold water Cooled water containing organic molecules Sample for chemical analysis H2OH2O ocean Volcano gases lightning

Early Earth Hydrogen gas (H2), methane CH4, ammonia (NH3) and water vapor

Energy Source