Hydrogen bonds form between electronegative atoms such as nitrogen and hydrogen atoms on their complementary bases between the DNA backbones. Adenine and thymine make two hydrogen bonds, while cytosine and guanine made three hydrogen bonds. Phosphodiester bonds keep the DNA backbone bonded together. Ionic and covalent bonds are too strong to bond the two antiparallel strands together since the strands must be separated during DNA synthesis. Hydrogen bonds are the perfect bond since they are weak individually, but collectively very strong.

Promoters help the transcription machinery and associated proteins (like DNA helicase) find the correct spot to start transcription and facilitate opening of the DNA. When transcription takes place, DNA helicase must open up or "unzip" the double helix. Te fewer the hydrogen bonds the easier it is for DNA to be denatured. Adenine and thymine only have two hydrogen bonds between them, while cytosine and guanine have 3. Thymine and adenine are the best candidates for promoter sequences based on their fewer number of hydrogen bonds which is evidenced by a common promoter sequence called "TATA box".

Earth's early atmosphere contained carbon,  (methane),  (ammonia), and , but no oxygen. 

RNA stands for ribonucleic acid, and each RNA nucleotide contains one phosphate, one nitrogenous base (either adenine, uracil, cytosine, or guanine), and one ribose sugar. RNA does not contain a deoxyribose sugar as seen in DNA.

Nucleotides are linked together to form nucleic acids by bonds between the phosphate groups and ribose sugars. A phosphate group is bonded the 5' carbon of one ribose and the 3' carbon of the next ribose, leading to the 5' to 3 directionality of DNA.

A nucleotide is made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base.  Lipids consist of a glycerol and fatty acid chains

The lock and key model states that the active site of an enzyme precisely fits a specific substrate. The induced fit model states that the active site of an enzyme will undergo a conformational change when binding a substrate, to improve the fit. The induced fit model accounts for the broad specificity of enzymes as the active site is not rigid, but can undergo a conformational change to better fit the substrate binding.

The lock and key model states that the active site of an enzyme precisely fits a specific substrate. The induced fit model states that the active site of an enzyme will undergo a conformational change when binding a substrate, to improve the fit.

The lock and key model states that the active site of an enzyme precisely fits a specific substrate. The induced fit model states that the active site of an enzyme will undergo a conformational change when binding a substrate, to improve the fit.

The lock and key model states that the active site of an enzyme precisely fits a specific substrate. The induced fit model states that the active site of an enzyme will undergo a conformational change when binding a substrate, to improve the fit.