Transcription is the process of copying a gene’s DNA sequence into RNA (mRNA).

Translation is the process where mRNA is decoded by ribosomes to synthesize a protein.

Input: DNA template strand; Output: RNA (pre-mRNA in eukaryotes).

Input: mRNA; Output: polypeptide (protein).

Template strand: DNA strand read by RNA polymerase to synthesize RNA. Coding strand: complementary to template strand, same sequence as RNA (except T → U).

5’ → 3’ direction.

RNA nucleotides (ribonucleotides: A, U, G, C); sugar is ribose (DNA has deoxyribose).

Phosphodiester bonds in sugar-phosphate backbone; hydrogen bonds between complementary bases in secondary structures.

RNA polymerase.

Primer.

Bacteria: 1; Eukaryotes: 3 main types (I, II, III).

Sigma factor binds RNA polymerase to help it recognize promoter sequences in bacteria.

RNA polymerase bound to promoter, correct sigma factor, DNA unwinding at start site.

Different sigma factors allow recognition of different sets of genes under varying conditions.

1. RNA polymerase holoenzyme binds promoter.
2. DNA unwinds near start site.
3. RNA polymerase positions first nucleotide.
4. RNA polymerase starts RNA synthesis.
5. Sigma factor may dissociate.

RNA polymerase continues synthesizing RNA.

RNA polymerase encounters a terminator sequence; RNA is released, polymerase detaches.

Eukaryotes: pre-mRNA is capped, spliced, polyadenylated; bacteria: transcription directly produces functional mRNA.

Initial transcript with introns; introns removed, cap and poly-A tail added to form functional mRNA.

Exon: coding region; Intron: non-coding region removed during RNA splicing.

Removal of introns from pre-mRNA; does not occur in bacteria.

Introns are removed; exons remain.

Bacteria: transcription & translation can occur simultaneously in cytoplasm; Eukaryotes: transcription in nucleus, translation in cytoplasm after mRNA processing.

tRNA carries amino acids to ribosome; has anticodon; mRNA carries codon sequence template.

Three nucleotides on tRNA complementary to mRNA codon; ensures correct amino acid incorporation.

Bacteria: cytoplasm; Eukaryotes: cytoplasm (ribosomes) or rough ER.

By peptide bonds to form polypeptide chain.

Made of rRNA + proteins; catalyzes translation, aligns mRNA and tRNAs, forms peptide bonds.

Ribosomal RNA, forms core of ribosome structure and catalyzes peptide bond formation.

Small subunit: binds mRNA and decodes codons; Large subunit: catalyzes peptide bond formation.

Initiation, elongation, termination.

1. Small ribosomal subunit binds mRNA.
2. Initiator tRNA binds start codon.
3. Large ribosomal subunit joins to form complete ribosome.

1. tRNA enters A site.
2. Peptide bond forms.
3. Ribosome translocates along mRNA.

1. Stop codon recognized.
2. Release factor binds and promotes polypeptide release.
3. Ribosomal subunits dissociate.