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Deoxyribose is a five-carbon sugar that forms the backbone of DNA by linking phosphate groups together; its absence of a hydroxyl (-OH) group on the 2' carbon (compared to ribose) makes DNA chemically stable.

A nucleotide is the basic monomer unit of nucleic acids, consisting of a pentose sugar (ribose or deoxyribose), a phosphate group, and a nitrogenous base.

DNA strands have polarity defined by the carbon atoms of the deoxyribose sugar; the 3' end has a free hydroxyl (-OH) group on the 3' carbon, and the 5' end has a free phosphate group, giving DNA directional asymmetry.

Adenine pairs with thymine (A-T) via two hydrogen bonds, and guanine pairs with cytosine (G-C) via three hydrogen bonds; this ensures each strand is a complement of the other.

DNA contains deoxyribose sugar and thymine; RNA contains ribose sugar (with a hydroxyl group on the 2' carbon) and uracil instead of thymine; RNA is typically single-stranded while DNA is double-stranded.

A gene is a discrete unit of hereditary information, typically consisting of a DNA sequence that codes for a specific protein or functional RNA molecule, including regulatory sequences.

Transcription is the process by which RNA polymerase synthesizes messenger RNA (mRNA) using a DNA template strand, producing a complementary RNA copy of genetic information.

Initiation (RNA polymerase binds to promoter), elongation (mRNA chain extends as RNA polymerase moves along template), and termination (RNA polymerase releases completed mRNA at termination signals).

mRNA carries genetic information from DNA to ribosomes as a temporary copy; it contains codons that specify which amino acids are added during translation.

Translation is the process by which ribosomes synthesize proteins by reading mRNA codons and assembling amino acids in the correct sequence using tRNA as an intermediary.

A codon is a three-nucleotide sequence on mRNA that codes for a specific amino acid or a stop signal; there are 64 possible codons (61 code for amino acids, 3 are stop codons).

tRNA (transfer RNA) has two functional ends: one with an anticodon that pairs with mRNA codons, and the other that carries the corresponding amino acid; it brings amino acids to the ribosome in correct order.

A ribosome is a complex organelle composed of ribosomal RNA and proteins; it catalyses the formation of peptide bonds between amino acids and facilitates the reading of mRNA codons during translation.

A protein is a polymer of amino acids linked by peptide bonds; it folds into a three-dimensional structure and performs specific cellular functions including enzymatic, structural, and regulatory roles.

An enzyme is a protein catalyst that lowers the activation energy of biochemical reactions without being consumed; it does this by providing an optimal environment for substrate molecules to react.

The active site is the region of an enzyme where substrate molecules bind and where the catalytic reaction occurs; its specific three-dimensional shape and chemical environment are complementary to the substrate.

The lock-and-key model proposes that enzymes have rigid active sites shaped to fit specific substrates perfectly, like a key fitting a lock; substrate binds, reaction occurs, and product is released.

Higher temperatures increase enzyme activity by increasing molecular collisions until the enzyme denatures (optimal temperature varies); pH changes can denature the enzyme or alter its active site shape (each enzyme has optimal pH).

A cofactor is a non-protein chemical compound (often metal ions like Mg2+ or Zn2+) or a coenzyme (organic molecules like vitamins) required by some enzymes to function; they often participate directly in the catalytic mechanism.

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose, while releasing oxygen as a byproduct; it occurs in chloroplasts.