Chapter 12: Molecular Biology of the Gene

Vocabulary study cards covering DNA structure, base pairing rules, replication enzymes, the Central Dogma, transcription, RNA types, and translation stages.

Nucleotide

The basic building block of DNA consisting of three parts: a deoxyribose sugar (5-carbon pentose sugar), a phosphate group, and a nitrogenous base.

Double Helix Model

Model formulated by Watson & Crick describing DNA as two polynucleotide strands twisted into a spiral, with sugar-phosphate backbones on the outside and hydrogen-bonded nitrogenous bases on the inside.

Antiparallel Strands

The structural arrangement of DNA where the two complementary strands run in opposite directions, with one running $5'$ to $3'$ and the other running $3'$ to $5'$.

Complementary Base Pairing Rules

The specific pairing in DNA where a purine always bonds with a pyrimidine via hydrogen bonds: Adenine (A) pairs with Thymine (T) via 2 H-bonds, and Guanine (G) pairs with Cytosine (C) via 3 H-bonds.

Chargaff's Rule

The principle stating that while base amounts vary between species, within any given species the amount of adenine equals thymine ($\%A = \%T$) and guanine equals cytosine ($\%G = \%C$).

Semiconservative Replication

The mechanism of DNA replication in which the parent double helix separates, each parental strand acts as a template, and each resulting daughter DNA molecule consists of one old parental strand and one newly synthesized daughter strand.

DNA Helicase

An enzyme that unwinds and unzips parental double-stranded DNA by breaking the hydrogen bonds between complementary base pairs, creating a replication fork.

DNA Polymerase

An enzyme that synthesizes a new DNA strand in the $5'$ to $3'$ direction by matching complementary incoming nucleotides to the template strand, and also proofreads new strands for errors.

DNA to DNA replication

Use the base pair rules to make the other DNA strand (A=T) (C=G)

Central Dogma

The framework describing the directional flow of genetic information inside biological systems: DNA transcribes to mRNA in the nucleus, which then translates into protein at ribosomes.

Central Dogma Equation

Transcription Translation

DNA ————-——> RNA —————→ Proteins

Transcription

The synthesis of an RNA messenger molecule (mRNA) from a DNA gene template inside the nucleus of eukaryotic cells.

RNA Polymerase

The primary enzyme of transcription that opens the DNA helix and links complementary RNA nucleotides along the DNA template strand in a $5'$ to $3'$ direction.

Promoter

A specific sequence of DNA nucleotides located at the beginning of a gene where RNA polymerase binds to initiate transcription and determines which strand serves as the template.

Terminator

A specific DNA sequence signaling the end of a gene that prompts RNA polymerase to release the newly synthesized mRNA transcript and detach from the DNA.

mRNA (Messenger RNA)

A linear, single-stranded transcript produced during transcription that carries genetic information from nuclear DNA to the cytoplasm, organized into 3-nucleotide sequences called codons.

tRNA (Transfer RNA)

A cloverleaf-shaped RNA molecule containing an anticodon loop at one end and an amino acid binding site at the other, responsible for transferring specific amino acids from the cytoplasm to the ribosome.

rRNA (Ribosomal RNA)

The structural RNA component of the large and small ribosomal subunits that combines with proteins to form ribosomes and catalyzes peptide bond formation between adjacent amino acids.

Codon

A sequence of three consecutive nucleotides on an mRNA strand that codes for a single specific amino acid or acts as a stop signal.

Start Codon (AUG)

The mRNA triplet code (AUG) encoding Methionine (Met) that establishes the reading frame and marks where translation begins; any sequence preceding it is ignored by the ribosome.

Degenerate Genetic Code

A characteristic of the genetic code meaning it is redundant, having 64 total codons encoding 20 amino acids, such that most amino acids are specified by more than one codon.

Unambiguous Genetic Code

A property of the genetic code stating that each individual, specific codon codes for one and only one amino acid.

Universal Genetic Code

A feature of the genetic code stating that virtually all living organisms utilize the exact same codon-to-amino-acid assignments.

Translation

The cellular process carried out by ribosomes in the cytoplasm where the genetic message in mRNA codons is converted into a specific polypeptide or protein sequence.

Translation Initiation

The assembly phase of translation where the small ribosomal subunit binds mRNA near the $5'$ end, initiator tRNA with anticodon $3'\text{-UAC-}5'$ binds the AUG start codon, and the large subunit joins so the initiator tRNA occupies the P site.

Translation Elongation

The phase of translation where incoming tRNAs enter the A site, peptide bonds form transferring the growing polypeptide from the P site to the A site, and the ribosome translocates one codon downstream so the empty tRNA exits via the E site.

Release Factor

A protein that binds directly to a stop codon (UAA, UAG, or UGA) in the ribosomal A site during termination, hydrolyzing the bond to release the completed polypeptide and disassemble the ribosomal complex.