Unit 6 - Gene Expression and Regulation

Helicase

Unwinds the DNA double helix by breaking hydrogen bonds

Topoisomerase

Prevents supercoiling ahead of the replication fork

Single-Strand Binding Proteins

Prevent separated DNA strands from reannealing

Primase

Adds RNA primer to start DNA replication

DNA Polymerase III

Adds nucleotides to the new DNA strand (5’ to 3’)

DNA Polymerase I

Replaces RNA primers with DNA

Ligase

Seals gaps between Okazaki fragments

RNA Polymerase

Synthesizes mRNA from DNA template

Helicase (transcription)

Unwinds DNA to form transcription bubble

Spliceosome

Removes introns and joins exons

snRNPs

Help spliceosome cut out introns

Poly(A) Polymerase

Adds poly-A tail to mRNA’s 3’ end

Capping Enzymes

Add 5’ cap to mRNA

Ribosome

Assembles proteins by reading mRNA

DNA replication

The process by which a cell copies its DNA before cell division

Leading Strand

Continuous replication in the 5’ to 3’ direction

Lagging Strand

Discontinuous replication with Okazaki fragments

Conservative Replication

Original DNA stays intact, new molecule is fully new

Semi-Conservative Replication

Each DNA has one old strand and one new strand

Dispersive Replication

DNA is a mix of old and new fragments throughout both strands

Transcription

DNA is copied into mRNA in the nucleus

Translation

Ribosomes read mRNA to build proteins in the cytoplasm

Promoter

Region where RNA polymerase binds to start transcription

Operator

On/off switch that controls access to genes by binding repressors

Regulatory gene

Codes for repressor protein that controls the operon

Repressor

Protein that binds to the operator to block transcription

TATA box

A repeating DNA sequence in the promoter that helps position RNA polymerase for transcription

Transcription bubble

Opened section of DNA where RNA polymerase reads the template strand to make mRNA

Phosphodiester bonds

Strong covalent bonds that link nucleotides together in DNA and RNA strands.

Template strand

The DNA strand used as a guide to build mRNA during transcription

Alternative Splicing

Creates different mRNAs by including/excluding exons

Messenger RNA (mRNA)

Carries genetic instructions from DNA to ribosomes

Ribosomal RNA (rRNA)

Forms the ribosome and helps assemble proteins

Transfer RNA (tRNA)

Brings amino acids to the ribosome based on mRNA codons

5’ Cap

Added to mRNA to protect it and help ribosome binding

Poly-A Tail

Added to mRNA’s end to stabilize and export it from nucleus

A site

Holds incoming tRNA with an amino acid

P site

Holds tRNA with the growing polypeptide chain

E site

Where empty tRNA exits the ribosome

Codon

A 3-nucleotide sequence on mRNA that codes for a specific amino acid (e.g. AUG = start/methionine)

Anticodon

A 3-nucleotide sequence on tRNA that pairs with the mRNA codon to bring the correct amino acid

Retroviruses

Viruses that have RNA as their genetic material and use reverse transcriptase to convert RNA into DNA

Reverse Transcriptase

An enzyme that converts RNA into DNA

Operons

Clusters of genes in prokaryotes that work and are regulated together

Inducible Operon

An operon that is normally off but can be turned on by an inducer (e.g., lac operon)

Repressible Operon

An operon that is normally on but can be turned off by a repressor (e.g., trp operon)

Tryptophan

A type of amino acid used in the trp operon; its presence can turn off the operon

Euchromatin

Loosely packed chromatin that is active in gene expression.

Heterochromatin

Tightly packed chromatin that is usually inactive and not expressed

Histone Proteins

Proteins that help package DNA into a compact form

Epigenetics

Study of changes in gene expression without altering the DNA sequence

miRNA

Small RNA molecules that regulate gene expression by binding to mRNA and preventing translation.

siRNA

Small interfering RNA that helps degrade mRNA and prevents gene expression

Induction

The process by which one cell or tissue influences the development of another

Morphogenesis

The process by which cells and tissues develop into their correct shape and size

Transcriptional Co-repressors

Proteins that bind to repressors and help turn off gene transcription

Transcription Factors (TFs)

Proteins that help initiate or regulate gene transcription

Point Mutations

A change in a single nucleotide in the DNA sequence

Silent Mutation

A mutation that does not change the amino acid sequence

Missense Mutation

A mutation that changes one amino acid in the protein sequence

Nonsense Mutation

A mutation that introduces a premature stop codon, leading to a truncated protein

Insertions and Deletions

Mutations where nucleotides are added (insertion) or removed (deletion), which can cause frameshift mutations

Transformation

The process by which a cell takes up foreign DNA from its environment

Transduction

The process by which a virus transfers DNA between bacteria

Conjugation

The process by which bacteria transfer genetic material through direct contact

DNA Cloning

The process of making multiple copies of a specific DNA fragment

Gel Electrophoresis

A technique used to separate DNA, RNA, or proteins based on size and charge

PCR (Polymerase Chain Reaction)

A method to amplify (make many copies of) a specific DNA segment

Biopiracy

The unethical use of biological resources or traditional knowledge from indigenous communities without fair compensation