DNA Replication & Gene Expression

X-ray Crystallography

Method to discover DNA structure

Double Helix

DNA structure with 2 antiparallel strands

Antiparallel Strands

DNA strands run in opposite directions

Phosphate Backbone

Part of DNA structure with phosphate groups

Nitrogenous Bases

Adenine, guanine, cytosine, thymine in DNA

Watson-Crick Model

Specific base pairing in DNA

Chargaff's Rules

Amount of A=T, G=C in DNA

Semi-conservative Replication

New DNA has one parental strand

DNA Polymerases

Enzymes adding nucleotides in DNA replication

RNA Primer

Short RNA strand starting DNA replication

Primase

Enzyme starting RNA chain in DNA replication

Leading Strand

DNA strand synthesized continuously

Lagging Strand

DNA strand synthesized in Okazaki fragments

Replication Fork

Site of DNA unwinding in replication

Proofreading

DNA polymerase corrects incorrect nucleotides

Mismatch Repair

Enzymes correct DNA base pairing errors

Nucleotide Excision Repair

Damaged DNA stretches replaced by nuclease

Telomeres

Ends of eukaryotic chromosomes for replication

Telomerase

Enzyme elongating telomeres to prevent aging

Gene Expression

DNA directs protein synthesis

Transcription

DNA to RNA synthesis

Translation

RNA to protein synthesis

Central Dogma

DNA → RNA → protein flow

Template Strand

DNA strand used for RNA synthesis

Initiation (Transcription)

Start of RNA synthesis

Elongation (Transcription)

RNA polymerase adds nucleotides to RNA

Termination (Transcription)

End of RNA synthesis

RNA transcript

Product of transcription

Transcription initiation complex

Assembly of transcription factors at the promoter region

Termination of Transcription

Process where RNA polymerase stops transcription

Polyadenylation signal sequence

Sequence where eukaryotic RNA polymerase stops transcription

5′ Cap

Modified nucleotide at the 5′ end of mRNA

Poly-A tail

Sequence of adenine nucleotides at the 3′ end of mRNA

RNA splicing

Process of removing introns and joining exons in mRNA

Introns

Non-coding regions of pre-mRNA

Exons

Coding regions of pre-mRNA

Alternative RNA splicing

Process where different exons are spliced to generate diverse proteins

Codon

Three-base sequence on mRNA that codes for an amino acid

Genetic code

Set of rules relating nucleotide sequence to amino acid sequence

Aminoacyl-tRNA synthetase

Enzyme that attaches the correct amino acid to tRNA

Wobble

Flexible base pairing at the third position of a codon

Translation initiation complex

Assembly of mRNA, tRNA, and ribosomal subunits at the start codon

Elongation factors

Proteins involved in the stepwise addition of amino acids during translation

Release factor

Protein that triggers termination of translation by recognizing stop codons

Transfer RNA (tRNA)

RNA molecule that carries amino acids to the ribosome

Ribosome

Cellular machinery where translation occurs

Polypeptide

Chain of amino acids formed during translation

Silent mutations

Nucleotide substitutions that do not change the amino acid sequence

Missense mutations

Nucleotide substitutions that result in an incorrect amino acid

Nonsense mutations

Nucleotide substitutions that create a premature stop codon