DNA synthesis

Central Dogma of biology:
- Information flows in one direction
DNA → RNA → Protein
involves three processes
- replication -- copies DNA
- Transcription -- converts DNA to RNA
- same “language” nucleic acid to nucleic acid
- Translation -- interprets RNA message into string of amino acids
- changes “language” nucleic acid to protein
In DNA: A, T, G, C
In RNA: A, U, G, C
DNA: Deoxyribose Nucleic Acid
RNA: Ribose Nucleic Acid
Transcription
- produces an RNA molecule from a DNA template
- Takes place in the nucleus
- Gene -- not entire DNA strand -- transcribed into RNA
- Catalyzed by RNA polymerase
- Enzyme that bonds nucleotides together
- Steps of Transcription
- \
  1. large transcription complex
  - RNA polymerase and other proteins
  - Unwinds segment of DNA
- \
  1. RNA polymerase uses one strand of DNA as a template
  - RNA nucleotides form complimentary base pairs with template
  - Same base pairing rules except $Uracil$ on RNA not Thymine
- \
  1. completed RNA strand separates from DNA
  - transcription complex falls apart
  - DNA zips back together
- AUG UGG CAA UAG CCC GAU
- AUG UAC GCC UAA UGA CAU
- Transcription makes three types of RNA
  - mRNA -- messenger RNA takes information for protein to be made from DNA to the ribosome
  - tRNA -- transfer RNA carries amino acids to ribosomes, lines them up in the correct order according to mRNA
  - rRNA ribosomal RNA makes up the structure of the ribosome
- Replication and Transcription both very similar processes
mRNA processing
- after transcription, mRNA is edited
- $Ex$ ons = gene that codes for protein ( $ex$ pressed) keep
- $In$ trons = part of DNA that does not code for a protein ( $in$ tervene) throw out
Translation
- translation = converting mRNA message into polypeptide
- “language” of nucleic acids -- A G C T (U)
- “language” of proteins " -- amino acids
- triplet codon
- codon = three nucleotide sequence that codes for amino acid
- $Special codons$
- stop codons -- 3 codons that signal the end of the protein: UGA, UAG, UAA
- start codons -- 1 codon (AUG) signals the start of translation -- also codes for amino acid methionine. ^^ALWAYS START AT AUG^^
- Reading the code
- mRNA codon, find the amino acid on the chart
- tRNA has “anti codons”
- Steps of translation
- \
  1. mRNA arrives at ribosome and attaches to small ribosomal unit
  2. tRNA with methionine binds to AUG codon – signals \n large subunit to attach
  3. mRNA pulled through ribosome one codon at a time
  4. exposed codon attracts complimentary tRNA carrying amino acid
  5. Ribosome forms peptide bond between 2 amino acids
  6. first tRNA is freed - leaves to pick up another amino acid
  7. Process continues with next exposed codon
  8. once stop codon is reached - no tRNA comes in and protein is released