everything in protein synthesis

• Second phase of protein synthesis:

  • Uses the mRNA strand as a template to produce an amino acid sequence
  • Takes place in the ribosome
• Amino acids:

  • Building blocks of proteins
  • There are a total of 20 amino acids
• Codon (root word: code):

  • Equivalent to an amino acid
  • A triplet (made up of three nitrogenous bases/mRNA nucleotides) found in the mRNA
  • There are 64 codons
• Start Codon:

  • Code that starts translation
  • Made up of the triplet AUG which always equals the amino acid met (methionine)
  • 61 codons code for 20 amino acids
• Stop Codon:

  • Made up of 3 possible codons: UAA, UAG, and UGA
  • There are 3 stop codons
  • No amino acids are associated with stop codons
• mRNA (messenger RNA):

  • Contains the "codons" or information to make proteins
• tRNA (transfer RNA):

  • Contains the "anticodons" complementary to the codon and transfers the amino acid
  • Freely floats in the cytoplasm waiting to be activated
• rRNA (ribosomal RNA):

  • Component of the ribosome made up of the large ribosomal subunit (LRS) and small ribosomal subunit (SRS)
• Genetic Code Table:

  • Shows how mRNA is translated into an amino acid sequence
  • Demonstrates the relationship between amino acids and codons
• Steps in Translation:

  Initiation:

  • mRNA transcript attaches to the ribosome (rRNA), specifically SRS
  • SRS reads the transcript and finds the start codon AUG
  • Met is carried to the ribosome

  Elongation:

  • Ribosome reads the succeeding codons in the mRNA sequence
  • Different tRNAs deliver the corresponding amino acids

  Termination:

  • Ribosome moves until a stop codon (UAA, UGA, UAG) is reached
  • mRNA, tRNA, and ribosome separate, releasing the protein (polypeptide)
• Protein synthesis is the process of cells producing proteins and consists of two phases: transcription and translation
• Transcription is the process where information from DNA is copied into an mRNA
• Translation is the process where the mRNA is decoded to produce proteins
• Central Dogma: DNA (replication) - RNA (transcription) - PROTEIN (translation)
• Transcription, also known as RNA synthesis:

  • Takes place in the nucleus
  • Uses the DNA strand as a template to produce an mRNA transcript
  • Results in a single-stranded RNA molecule containing information from the DNA
• In transcription, the two strands in double-stranded DNA are the template and coding strands

  • The template strand is used for transcription, read from 3’ to 5’
  • DNA is read from 3’ to 5’ during transcription
• Steps/Phases in Transcription:

  Initiation:

  • DNA unwinds and unzips with the help of enzyme HELICASE
  • RNA polymerase binds to the DNA and recognizes the promoter (tata box) region
• Elongation:

  • RNA polymerase adds free RNA nucleotides to the growing mRNA strand
  • The DNA template is read from 3’ to 5’ as the mRNA transcript is synthesized in the 5’ to 3’ direction
• Termination:

  • RNA polymerase reaches the termination region and stops copying
  • The mRNA detaches from the DNA template and moves to the cytoplasm