Protein synthesis

• What is protein synthesis?

  The process of making proteins
• Protein synthesis occurs primarily on the ribosome
• Stages of protein synthesis

  1️⃣ Transcription

  2️⃣ Translation
• Where does transcription take place in the cell?

  Inside the nucleus
• During transcription, one of the strands of DNA is copied into mRNA
• DNA is too big to leave the nucleus directly.
• Why is DNA not allowed to leave the nucleus?

  Enzymes in cytoplasm could damage it
• The enzyme responsible for unwinding the DNA double helix during transcription is called DNA helicase
• Steps of transcription

  1️⃣ DNA double helix unwinds

  2️⃣ One DNA strand acts as a template

  3️⃣ RNA nucleotides align to complementary bases

  4️⃣ RNA polymerase joins nucleotides

  5️⃣ Pre-mRNA is formed

  6️⃣ Introns are spliced out

  7️⃣ Modified mRNA exits nucleus
• What is the role of RNA polymerase during transcription?

  Joins RNA nucleotides together
• The non-coding sequences in DNA are called introns
• Introns are removed from pre-mRNA before it leaves the nucleus.
• What protein removes introns from pre-mRNA?

  Spliceosome
• The coding regions of DNA that remain after splicing are called exons
• What is the first step of translation?

  mRNA attaches to ribosome
• The start codon on mRNA is complementary to the anticodon on tRNA
• Each tRNA molecule carries a specific amino acid determined by its anticodon.
• What is the role of the ribosome during translation?

  Holds mRNA and tRNA in place
• Peptide bonds between amino acids are formed by an enzyme and require ATP
• The stop codon signals the end of translation.
• Steps of translation

  1️⃣ mRNA attaches to ribosome

  2️⃣ tRNA brings complementary anticodon

  3️⃣ Peptide bond is formed

  4️⃣ Ribosome moves along mRNA

  5️⃣ Process repeats until stop codon

  6️⃣ Ribosome detaches from mRNA

  7️⃣ Polypeptide chain is released
• Which organelle does the polypeptide chain move to after translation for folding and modifications?

  Golgi body