Bio (Protein synthesis)

protein synthesis

process by which proteins are made (turning DNA into functional protein)

proteins

large biological molecules made up of one or more amino acid chains

protein synthesis steps and which one comes first

translation and transcription, transcription comes first

transcription

to produce a mRNA molecule from the DNA in the nucleus so DNA doesn’t get damaged leaving the nucleus

translation

cellular process by which the ribosome moves along the single stranded mRNA molecule and reads the coded message used to link amino acids correctly to form a polypeptide chain. occurs in cytoplasm

triplet

a sequence of three bases along a DNA molecule

codon

a sequence of three consecutive bases on a mRNA molecule. a codon is complementary to a triplet on DNA

first step of transcription

initiation: RNA polymerase binds to the promoter sequence of the gene. It unwinds/separates the DNA so the gene can be copied.

second step of transcription

elongation: RNA polymerase moves along the DNA template (antisense) strand. It adds RNA nucleotides one at a time using complementary base pairing. In RNA, U (uracil) replaces T (thymine).

third step of transcription

termination: RNA polymerase reaches the termination sequence. RNA polymerase and the mRNA detach from the DNA.

what happens after the step of termination in transcription

introns are spliced out, exons and expressed. A 5′ cap and 3′ poly-A tail are added to protect the mRNA. DNA rewinds into original shape.

first step of translation

initiation: The mRNA is in the cytoplasm. A ribosome attaches to the start codon (AUG) on the mRNA. A tRNA brings the amino acid methionine (Met).

second step of translation

elongation: The ribosome reads the mRNA 3 bases at a time (codon). A tRNA has a matching anticodon that binds to the complementary codon on the mRNA. This happens inside the ribosome. The amino acids carried by the tRNAs are brought next to each other. A peptide bond/linkage forms between the amino acids and the ribosome then moves along the mRNA to the next codon. This repeats, adding more amino acids to the growing chain.

third step of translation

termination: This continues until the ribosome reaches a stop codon: UGA, UAA, UAG. The polypeptide (amino acid chain) is released. It then folds and is modified by endoplasmic reticulum (ER).