Human Biology: Molecular Genetics, DNA Replication, and Gene Expression

A comprehensive vocabulary review of molecular biology concepts covering chromosome structures, DNA and RNA properties, enzymes of DNA replication, transcription, RNA processing, translation, the genetic code, and epigenetic regulation.

Diploid Organism

An organism whose cells contain two of each type of chromosome.

Nucleotide

The monomer building block of DNA and RNA, consisting of a nitrogenous base connected through a sugar and a phosphate group.

Nucleoid

The cytoplasmic region in a prokaryotic cell where its circular DNA genome is located.

Deoxyribonucleic Acid (DNA)

A double-stranded nucleic acid housed in the eukaryotic nucleus (or prokaryotic nucleoid) containing a sugar that lacks an oxygen and the bases cytosine, guanine, adenine, and thymine.

Ribonucleic Acid (RNA)

A single-stranded nucleic acid containing ribose sugar and the pyrimidine base uracil ($U$) in place of thymine ($T$).

Helicase

The enzyme responsible for unwinding the double helix strands of DNA during replication.

Primase

An enzyme that synthesizes and places primers on template strands to signal DNA polymerase where to initiate DNA synthesis.

DNA Polymerase

An enzyme that assembles new, complementary strands of DNA from free nucleotides using template strands; it requires a primer, adds bases to the new strand, and possesses proofreading abilities to correct replication mistakes.

DNA Ligase

An enzyme that seals gaps in the newly synthesized DNA strands to form a continuous strand.

Telomerase

An enzyme that assists in replicating the ends of chromosomes by using its own intrinsic RNA template to extend chromosome ends.

Mutation

Changes to the nucleotide sequence in a segment of DNA that codes for a protein, resulting from DNA polymerase replication errors or outside damaging factors.

Gene Expression

The flow of genetic information within a cell from DNA to RNA to protein.

Promoter

A specific region of DNA where RNA polymerase binds and transcription begins.

RNA Polymerase

The enzyme that carries out transcription by connecting complementary RNA bases to a DNA template strand to build a single-stranded mRNA molecule.

Messenger RNA (mRNA)

A single-stranded RNA transcript synthesized in the nucleus that carries genetic instructions based on DNA out to the cytoplasm to attach to ribosomes.

Exons

Portions of a eukaryotic pre-mRNA transcript that are kept and spliced together during RNA processing in the nucleus.

Introns

Non-coding portions of eukaryotic pre-mRNA that are excised and removed during RNA processing inside the nucleus.

Codon

A triplet sequence of three nucleotides on an mRNA strand; there are 61 codons that specify amino acids, as well as codons that signal termination.

Transfer RNA (tRNA)

The adapter molecule that executes the genetic code by carrying an amino acid on one end and a complementary anticodon on the other.

Anticodon

A group of three nucleotides located on a tRNA molecule that forms complementary base pairs with a specific mRNA codon (e.g., tRNA with anticodon U-A-C carries methionine).

Ribosomal RNA (rRNA)

The RNA component that combines with proteins to construct ribosomes, which assemble proteins during translation.

Translation

The process occurring in the cytoplasm or ER phase wherein ribosomes, mRNA, and amino acid-carrying tRNAs assemble a polypeptide chain joined by peptide bonds.

Stop Codon

A terminal mRNA codon that signals the ribosome to end translation; because tRNAs corresponding to stop codons do not carry an amino acid, no peptide bond can form.

Peptide Bond

The chemical covalent bond that links adjacent amino acids together into a growing polypeptide chain during translation.

DNA Methylation

An epigenetic mechanism involving the addition of a methyl group ($-\text{CH}_3$) to the C5 position of cytosine bases, which can be passed on to offspring.

Epigenetics

Heritable changes in gene expression and regulation, such as DNA methylation, that can be passed to offspring without altering the underlying nucleotide sequence.