Microbiology: DNA Replication, Gene Expression, Operons, and Mutations

Vocabulary flashcards generated from the lecture covering DNA replication enzymes, eukaryotic vs prokaryotic gene expression, TRP and lac operons, DNA mutation types, repair pathways, and HIV infection dynamics.

Semi-Conservative Replication

A mechanism of DNA replication in which each resulting double-stranded DNA molecule consists of one original parental strand and one newly synthesized daughter strand.

DNA Gyrase

An enzyme (known as topoisomerase in human cells) that relieves supercoils created during DNA replication by cutting, unwinding, and re-ligating phosphodiester bonds.

Single-Stranded Binding Proteins (SSBPs)

Proteins that bind to separated single stranded parental DNA to prevent complementary nitrogenous bases from reforming hydrogen bonds.

Primase

An enzyme that lays down an RNA primer to provide a free $3'$ hydroxyl group for DNA polymerase to work off of.

DNA Polymerase III

The main enzyme responsible for synthesizing new DNA by adding nucleotides onto a free $3'$ hydroxyl end.

Okazaki Fragments

Short fragments of DNA and RNA primers formed on the lagging strand during DNA replication, named after Doctor Okazaki.

DNA Polymerase I

The enzyme that chews out RNA primers from Okazaki fragments on the lagging strand and replaces them with DNA nucleotides.

DNA Ligase

An enzyme that joins DNA fragments by making phosphodiester bonds between adjacent $3'$ hydroxyl and $5'$ phosphate ends without adding new nucleotides.

Gene Expression

The process of using a gene's DNA information to synthesize proteins via transcription and translation, also known as the Central Dogma of Microbiology.

RNA Polymerase

The single enzyme that performs transcription by unwinding DNA and synthesizing mRNA in a $5'$ to $3'$ direction from a $3'$ to $5'$ DNA template strand.

Promoter

A specific sequence of DNA that binds RNA polymerase to initiate transcription immediately after at the $+1$ start site.

Enhancer Sequence

A eukaryotic DNA sequence that binds activator proteins, which grab RNA polymerase and put it onto the promoter to increase gene expression.

Silencer Sequence

A eukaryotic DNA sequence that binds repressor proteins, which block RNA polymerase from accessing the promoter and decrease gene expression.

Operon

A genetic regulatory structure in prokaryotes where multiple functional genes are controlled under a single promoter and an operator sequence.

Repressible Operon

An operon (such as the TRP operon) that is active by default but becomes repressed when its end product binds to a repressor protein, enabling it to attach to the operator.

Inducible Operon

An operon (such as the lac operon) that is normally off but becomes induced when a metabolite (such as lactose) binds to the repressor protein and removes it from the operator.

CAP-cAMP Complex

A complex formed by cyclic AMP and the metabolite activator protein (CAP) when glucose is low; it holds RNA polymerase onto a weak promoter to enable transcription.

Monocistronic mRNA

A mRNA structure characteristic of eukaryotic cells where one promoter controls one gene to produce a single protein sequence.

Polycistronic mRNA

A mRNA structure characteristic of prokaryotes where one promoter controls multiple genes, producing a single mRNA that codes for multiple proteins.

Silent Mutation

A point mutation that changes a nucleotide base in a codon without altering the resulting amino acid sequence.

Missense Mutation

A point mutation that changes a base within a codon, causing a different amino acid to be placed in the protein chain.

Nonsense Mutation

A point mutation that changes an amino acid codon into an early stop codon, preventing the full protein from being synthesized.

Frameshift Mutation

A mutation caused by the insertion or deletion of bases in DNA, shifting the frame of codon threes read by the ribosome and resulting in multiple missense mutations.

Thymine Dimer

A DNA mutation caused by UV light exposure that leads to adjacent thymine bases forming covalent bonds with each other instead of hydrogen bonding to complementary adenines.

Nucleotide Excision Repair (NER)

An enzyme-mediated repair pathway that cuts out thymine dimers and surrounding nucleotides, replacing them with the correct DNA sequence.

Xeroderma Pigmentosum (XP)

A genetic condition caused by mutated NER genes, rendering individuals incapable of repairing thymine dimers and making them highly susceptible to UV-induced skin cancer.

gp120

The glycoprotein spike on the HIV surface that binds to the CD4 receptor on host T helper cells.

CCR5 Delta 32

A 32-base deletion mutation in the CCR5 co-receptor gene that produces a shortened co-receptor protein, preventing HIV strain r5 from achieving membrane fusion and infecting T helper cells.