Transcription vs Translation vs DNA Replication

DNA replication

copying DNA to make an identical DNA molecule (DNA → DNA)

helicase

enzyme that unwinds the DNA double helix by breaking hydrogen bonds

topoisomerase

enzyme that relieves twisting/supercoiling ahead of the replication fork

single-strand binding proteins (SSB)

proteins that stabilize separated DNA strands so they do not re-anneal

replication fork

Y-shaped region where DNA is unwound and new DNA is synthesized

primase

enzyme that synthesizes short RNA primers needed to start DNA synthesis

RNA primer

short RNA sequence that provides a free 3′-OH for DNA polymerase to extend

DNA polymerase

enzyme that synthesizes new DNA by adding nucleotides to the 3′ end (works 5′ → 3′)

leading strand

strand synthesized continuously toward the replication fork

lagging strand

strand synthesized discontinuously away from the fork in short segments

Okazaki fragments

short DNA segments formed on the lagging strand during replication

DNA ligase

enzyme that seals nicks and joins Okazaki fragments by forming phosphodiester bonds

proofreading

DNA polymerase function that removes mismatched nucleotides to reduce errors

transcription

making an RNA copy of a gene using DNA as a template (DNA → RNA)

template strand

DNA strand read by RNA polymerase to build complementary RNA

coding strand

DNA strand with the same sequence as mRNA (except T instead of U)

RNA polymerase

enzyme that synthesizes RNA from a DNA template (5′ → 3′)

promoter

DNA sequence where RNA polymerase binds to begin transcription

transcription factors

proteins that help RNA polymerase bind promoters and start transcription (mainly eukaryotes)

terminator

DNA/RNA signal that causes transcription to stop

mRNA

messenger RNA that carries coding information from DNA to ribosomes

translation

using mRNA to build a polypeptide (protein) (mRNA → protein)

ribosome

rRNA-protein complex that reads mRNA and catalyzes peptide bond formation

rRNA

ribosomal RNA that forms the core of ribosomes and performs the catalytic peptidyl transferase activity

tRNA

transfer RNA adaptor that matches codons and delivers specific amino acids to the ribosome

anticodon

3-base sequence on tRNA that base-pairs with an mRNA codon

codon

3-nucleotide sequence in mRNA that specifies an amino acid or stop signal

genetic code

mapping of 64 mRNA codons to 20 amino acids plus stop signals

start codon

AUG; codon that initiates translation and codes for methionine

methionine (Met)

amino acid specified by the start codon AUG; first amino acid in new proteins

stop codon

UAA, UAG, or UGA; codons that signal termination of translation

aminoacyl-tRNA synthetase

enzyme that attaches the correct amino acid to its corresponding tRNA (charging)

charged tRNA

tRNA with its specific amino acid attached and ready for translation

A site

ribosome site where the incoming charged tRNA enters (aminoacyl site)

P site

ribosome site holding the tRNA with the growing polypeptide chain (peptidyl site)

E site

ribosome site where the empty tRNA exits after transfer (exit site)

peptide bond

covalent bond linking amino acids in a growing polypeptide chain

translocation

movement of the ribosome along mRNA that shifts tRNAs A → P → E during elongation

release factor

protein that recognizes stop codons in the A site and triggers polypeptide release

GTP

energy molecule used during translation steps like initiation, elongation, and termination