MBIO*1220 Class 9: The Blueprint of Life & Bacterial Genetics

Vocabulary flashcards covering the Central Dogma of molecular biology, DNA replication, transcription, translation, mutations, plasmids, and horizontal gene transfer in bacteria.

Genome

The total DNA contained within a cell, consisting of the chromosome(s) and any plasmids.

Gene

A specific section of DNA that codes for a functional product.

Nucleotide (DNA)

The building block macromolecule of DNA consisting of a nitrogenous base (A, T, G, or C), a 5-carbon deoxyribose sugar numbered $1'$ to $5'$, and a phosphate group.

Antiparallel Strands

The arrangement of double-stranded DNA where two complementary strands run in opposite directions (one in the $5' \rightarrow 3'$ direction and the other in the $3' \rightarrow 5'$ direction), joined by covalent phosphodiester bonds.

DNA Polymerase

The enzyme that reads nucleotides on a template strand in the $3' \rightarrow 5'$ direction to synthesize a complementary new DNA strand in the $5' \rightarrow 3'$ direction.

Primase

An enzyme that synthesizes a short RNA primer to serve as an initial starting site for DNA polymerase to assemble nucleotides into a new strand.

Leading Strand

The new DNA strand synthesized continuously in the $5' \rightarrow 3'$ direction, moving in the same direction as the unwinding replication fork.

Lagging Strand

The new DNA strand synthesized discontinuously in short fragments away from the replication fork due to DNA polymerase's requirement to synthesize in the $5' \rightarrow 3'$ direction.

Okazaki Fragments

Short discontinuous segments of DNA synthesized in the $5' \rightarrow 3'$ direction on the lagging strand during DNA replication.

DNA Ligase

The enzyme responsible for covalently joining Okazaki fragments together after RNA primers are removed during DNA replication.

Transcription

The process of synthesizing RNA complementary to a DNA template strand, replacing thymine (T) with uracil (U).

Messenger RNA (mRNA)

A type of RNA that carries encoded instructions from DNA to direct the synthesis of a specific protein during translation.

Ribosomal RNA (rRNA)

A functional class of RNA molecules that forms an essential structural and catalytic part of the ribosome.

Transfer RNA (tRNA)

An adaptor RNA molecule that carries specific amino acids to the ribosome for incorporation into a growing polypeptide chain during translation.

Promoter

A specific sequence of DNA where RNA polymerase binds and melts a short stretch of double-stranded DNA to initiate transcription.

Terminator

A specific sequence at the end of a gene causing RNA polymerase to fall off the template DNA and release the newly synthesized RNA.

Codon

A triplet sequence of three nucleotides in mRNA that specifies a particular amino acid or a signal to stop translation.

Stop Codons

The three codons ($\text{UAA}$, $\text{UAG}$, and $\text{UGA}$) that do not code for any amino acid and signal the termination of protein synthesis.

Translation

The biological process in which ribosomes decode the codon sequence carried by mRNA to synthesize a polypeptide chain.

Formyl-methionine (f-Met)

The initiating amino acid carried by tRNA that enters the ribosomal P site to base-pair with the start codon during bacterial translation initiation.

Mutation

A stable change in the nucleotide sequence of DNA that is passed to progeny and may alter the function of an encoded protein.

Base Substitution (Point Mutation)

A mutation in which a single nucleotide in the DNA sequence is replaced by another nucleotide.

Missense Mutation

A mutation resulting from a base substitution that alters a codon so that it specifies a different amino acid in the resulting protein.

Nonsense Mutation

A mutation that changes a codon to a premature stop codon, generating a truncated and typically nonfunctional protein.

Silent Mutation

A base substitution mutation that changes a codon without changing the encoded amino acid, preserving normal protein structure and function.

Frameshift Mutation

The insertion or deletion of one or two nucleotides in a gene, shifting the mRNA reading frame and nearly always producing a nonfunctional protein downstream.

Plasmid

A self-replicating, double-stranded circular DNA molecule physically separate from the bacterial chromosome that carries non-essential genes.

F Plasmid (Fertility Factor)

A circular plasmid containing genes necessary for pilus synthesis and the initiation of genetic transfer during conjugation.

F Pilus (Sex Pilus)

A proteinaceous filament produced by a donor ($\text{F}^+$) bacterial cell to attach to a recipient ($\text{F}^-$) cell and bring them together for conjugation.

R Plasmid

A resistance plasmid carrying genes that confer resistance to specific antibiotics, such as carbenicillin, chloramphenicol, and tetracycline.

Horizontal Gene Transfer

The transmission of genetic information from one living cell to another of the same generation via transformation, transduction, or conjugation.

Transformation

A mechanism of horizontal gene transfer wherein competent bacterial cells take up naked environmental DNA fragments and incorporate them into their chromosome via homologous recombination.

Transduction

A form of horizontal gene transfer in bacteria where bacterial chromosomal DNA fragments are transferred from a donor to a recipient cell via a bacteriophage.

Transducing Particle

A defective bacteriophage that mistakenly encapsulates host bacterial DNA instead of viral DNA during viral assembly.

Conjugation

A process of horizontal gene transfer requiring direct cell-to-cell contact through an F pilus to transfer a single strand of plasmid DNA from a donor ($\text{F}^+$) to a recipient ($\text{F}^-$) cell.