12.3 - RNA & Protein Synthesis

• Structure of RNA

  • Ribonucleic Acid differs from DNA in 3 ways
  • The sugar in the nucleotide is ribose (similar to DNA deoxyribose)
  • RNA is made up of one strand of nucleotides
  • RNA has the nit. base uracil instead of thymine
• RNA copied from DNA -> transcription

  RNA is then used to make proteins -> translation
• There are 3 types of RNA:

  These 3 kinds of RNA all "carry" the genetic code from DNA, but they all have slightly different jobs in the process of making proteins

  1. messenger RNA (mRNA): carries the genetic code for protein synthesis from DNA to the cytoplasm
  2. ribosomal RNA: makes up the structure of a ribosome (along with proteins) and reads the mRNA code
  3. transfer RNA: piece of RNA that transfers amino acids to the ribosome for assembly
• • DNA stores the code for how organism are made
  • RNA: made from DNA and is used to create the different phenotypes of organisms
  • Proteins are what make the phenotype of organisms
  • The process of making proteins is called protein synthesis
  • RNA is a copy of DNA (from the nucleus) and is used to make proteins in the cytoplasm of cells
• RNA Transcription

  • Transcription: RNA is made by copying a part of the DNA nucleotide sequence into one complementary strand of RNA

  1. RNA polymerase binds to DNA and separates the 2 DNA strands
  2. One DNA strand is used as a template to assemble RNA nucleotides into a strand of RNA
  3. The RNA polymerase binds to the DNA where the gene sequence is needed, at a point called the promoter ("to start")
  4. When the RNA strand is completed, it detaches from the DNA, will be edited, and moves to the cytoplasm
• Editing during Transcription

  When making RNA, the new RNA is edited and many pieces are "cut out" of the strand.

  • introns: pieces of RNA that are removed (exit) and unused to make a particular protein
  • exons: RNA pieces that will be used (stay in) to make that specific protein
• Editing during Transcription

  • Different introns can be spliced together to create the cast collection of proteins that exist
  • Much of the DNA is actually non-coding DNA - this means that it's not used to code for proteins
  • These sequences regulate gene expression by turning gene on and off for transcription and regulating which introns are to be transcribed and translated based on need
• Translation - Protein Synthesis

  • Translation: the process of decoding the genetic code from DNA and the RNA to make protein molecules
  • amino acids (peptide) -> protein (polypeptide)
• Remember!

  • transcription: DNA -> RNA
  • translation: RNA -> protein
• Translation

  • The building blocks of proteins (polypeptides) are amino acids
  • The order of amino acids gives the protein its properties and shape
  • There are a total fo 20 amino acids that make up proteins
  • The order of amino acids comes from the "genetic code" which is the sequence of A, U, G, C in RNA
• Translation

  • The code reads 3 nucleotides at a time along RNA called a codon
  • A codon codes for one single amino acid in a protein chain
  • The sequence of bases in DNA is used as a template for mRNA
  • The codons on mRNA specify the sequence of amino acids in a protein
  • There are 64 codon combos and all 20 amino acids have a few codon combos that code for that specific amino acid
  • AUG is the start codon & there are 3 other stop codons
• Steps to Protein Synthesis

  1. RNA is transcribed from DNA & goes to cytoplasm
  2. mRNA attaches to ribosome
  3. mRNA is moved through the ribosome (rRNA) & 3 bases (1 codon) are read at a time
  4. proper amino acid is brought to the ribosome by tRNA
  5. Each kind of tRNA carries only one kind of amino acid
  6. tRNA has a set of 3 bases called the anticodon, which complement the 3 base codon on mRNA
  7. Each amino acid forms a peptide bond with the next amino acid, making a polypeptide (protein) chain
  8. mRNA is read until the ribosome reaches a stop codon - the protein is released and translation is completed
• • Many proteins are enzymes, which catalyze and regulate chemical reactions
  • Proteins are each specifically designed to build or operate a component of a living cell