Unit 6: RNA & protein synthesis

• Central Dogma of Molecular Biology

  Each gene in the DNA molecule carries the information needed to construct one protein, which, acting as an enzyme, controls one chemical reaction in the cell
• Differences between DNA and RNA

  • The sugar in RNA is ribose, instead of deoxyribose
  • RNA is single stranded, and DNA is double stranded
  • RNA contains uracil, DNA contains thymine
• Why make a message (RNA), instead of just sending DNA?

  DNA is precious. If it gets damaged, then all subsequent information received from it may be damaged, causing changes in all further proteins made from the damaged DNA. However, if the DNA sends a blueprint of itself out (RNA), the DNA can stay protected in the nucleus.
• RNA

  Ribonucleic acid. RNA has one goal: code for the information needed to make a protein. RNA is just a segment of DNA that has the information needed to make a protein
• Types of RNA

  • mRNA (messenger RNA)
  • rRNA (ribosomal RNA)
  • tRNA (transfer RNA)
• mRNA


  Carries information for the necessary protein from the nucleus to the cytoplasm
• rRNA

  Makes up the two subunits that are a ribosome
• tRNA

  Carries amino acids to the ribosome where they can be attached in the proper order according to the mRNA
• Transcription


  1. RNA polymerase binds to the DNA strand at a specific sequence of the gene called a promoter

  2. Unwinds and unlinks the two strands of DNA

  3. Uses one of the DNA strands as a guide or template

  4. Matches new nucleotides with their complements on the DNA strand (G with C, A with U)

  5. Binds these new RNA nucleotides together to form a complementary copy of the DNA strand (mRNA)

  6. Stops when it encounters a termination sequence of bases (stop codon)
• Promoter


  Specific gene sequence that shows RNA polymerase where to begin transcription
• Termination sequence

  Area of the gene that tells RNA polymerase to stop RNA synthesis and unbind from DNA
• mRNA builds in the 5' to 3' direction. If it built in either direction, then it would be possible to place the wrong codon in place and code for the wrong amino acid.
• Translation#1


  1. Ribosome attaches to mRNA molecule in the cytoplasm.As each codon passes through the ribosom, tRNA bring the proper amino acids into the ribosomes.

  2.one at a time,the ribosomes attaches amino acids to the growing chain

  (Each tRNA molecule carries just one kind of amino acid. In addition, each tRNA molecule has three unpaired bases.Collectively those three tRNA bases are called anticodons. Each anticodon complements its mRNA codon.)3.
• Anticodon

  Three unpaired bases on a tRNA molecule that complement the mRNA codon
• What happens to the tRNA after it drops off its amino acid?

  The tRNA breaks off of the amino acid and returns to the cytoplasm to find a new amino acid to pick up.

  After that

  ●The amino acid chain continues until a “stop” codon is reached in the mRNA strand. Once it reaches the stop codon, the ribosome unbinds from the amino acid chain, and your protein is formed.
• Where does transcription take place ?

  prokaryotes: cytoplasm

  eukaryotes: nucleus
• Transcription is the process of what? 


  process of taking a section of DNA and turning it into RNA.
• Translation is the process of what ?

  • The decoding of an mRNA message into a protein
• What role does the ribosome play in assembling proteins?

  Ribosomes use the sequence of codons in mRNA to assemble amino acids into polypeptide chains.
• translation overview

  Translation is carried out by taking the product of transcription (mRNA) and creating the necessary protein from that information. Translation is performed in the cytoplasm.
• Translation#2

  3.Like an assembly-line worker who attaches one part to another, the ribosome forms a polypeptide bond between the first and second amino acids.

  4.After the bond is formed, the ribosome moves down the mRNA and continues attaching amino acids to each other.
• Ribosome forming a polypeptide bond

  1. Attaches first and second amino acids

  2. Moves down the mRNA

  3. Continues attaching amino acids to each other
• What happens to the tRNA after it drops off its amino acid

  1. tRNA breaks off of the amino acid

  2. Returns to the cytoplasm to find a new amino acid to pick up
• Amino acid chain formation

  1. Continues until a "stop" codon is reached in the mRNA strand

  2. Ribosome unbinds from the amino acid chain

  3. Protein is formed