Molecular Genetics (Chapters 11-15)

Nucleotide

Monomer (building block) of nucleic acids, consisting of a phosphate group, a 5-carbon sugar, and a nitrogenous base.

Helicase

Enzyme that unzips the DNA and forms the replication fork during replication.

Topoisomerase

Enzyme that prevents supercoiling ahead of the replication fork.

Single-strand binding proteins

Proteins that stabilize the separated strands of DNA during replication.

Primase

Enzyme that adds an RNA primer to give DNA synthesis a starting point.

DNA polymerase

Enzyme that adds new DNA nucleotides to the growing strand (only to the 3' end, in the 5' to 3' direction) and replaces mismatched bases.

DNA ligase

Enzyme that covalently links Okazaki fragments together.

Telomerase

Enzyme that adds repeated DNA sequences to the 3' end of chromosomes to prevent shortening.

Okazaki fragments

Short pieces of DNA made discontinuously on the lagging strand.

Origin of replication

An A-T rich site where DNA replication begins.

Semiconservative replication

The mechanism of DNA replication, proven by Meselson and Stahl, where each new DNA molecule consists of one original strand and one newly synthesized strand.

Leading strand

The DNA strand that is synthesized continuously in the same direction as the replication fork.

Histones

Proteins around which DNA wraps in eukaryotic cells.

Chromatin

The complex of DNA and proteins found in the eukaryotic nucleus.

Central dogma

The concept that genetic information flows from DNA to mRNA to amino acid sequence.

Transcription

The process of synthesizing RNA from a DNA template, occurring in the nucleus in eukaryotes.

Translation

The process where mRNA is decoded to produce a polypeptide, occurring in the cytoplasm on ribosomes.

mRNA

Messenger RNA that carries the genetic message in the form of codons.

tRNA

Transfer RNA that has an anticodon and carries specific amino acids to the ribosome.

rRNA

Ribosomal RNA that combines with proteins to form the ribosome.

Codon

A three-base sequence on mRNA that codes for an amino acid.

Anticodon

A three-base sequence on tRNA that pairs with a complementary codon on mRNA.

A site

The ribosomal binding site where a new incoming tRNA enters.

P site

The ribosomal binding site that holds the tRNA attached to the growing polypeptide chain.

E site

The ribosomal binding site where used, uncharged tRNA exits.

Promoter

The DNA sequence where RNA polymerase binds to start transcription.

Intron

A non-coding sequence removed from pre-mRNA during RNA splicing.

Exon

A coding sequence that remains in the mature mRNA after splicing.

Release factor

A protein that binds to a stop codon and terminates translation.

Gene regulation

The ability of cells to control their level of gene expression.

Constitutive genes

Unregulated genes that are constantly expressed at continuous, constant levels.

Operon

A set of genes controlled as a single unit, commonly found in bacteria.

trp operon

A repressible operon involved in biosynthetic processes; tryptophan binds the repressor, enabling it to bind the operator and block transcription.

lac operon

An inducible operon involved in catabolic processes; lactose binds the repressor to change its shape, freeing the operator so transcription can occur.

Activators

Proteins that increase the rate of transcription.

Repressors

Proteins that decrease or prevent transcription.

General transcription factors

Proteins that bind the TATA box and help form the transcription initiation complex.

Mediator

A protein complex that interacts with activators and repressors to modulate transcription.

Coactivators

Factors that increase the rate of transcription without directly binding to DNA.

Histone acetylation

An epigenetic modification that loosens DNA around histones, resulting in increased transcription.

DNA methylation

An epigenetic modification that tightens DNA around histones, resulting in decreased transcription.

Epigenetic

A change in gene expression that occurs without altering the underlying DNA sequence.

Alternative splicing