Transcription and translation

key words: "central dogma" of molecular biology, transcription, translation, codon, anticodon, mRNA, tRNA, rRNA

  1. review "central dogma"
    1. DNA > messenger RNA > protein
  2. a protein is a molecule made of amino acids
    1. proteins are the only direct product of the translation of the DNA genetic code  
      1. proteins then construct other molecules such as fats, sugars, and DNA and RNA
  3. Transcription is the process of copying DNA into messenger RNA (mRNA)
    1. like DNA synthesis, it only occurs in one direction
    2. special regions of DNA "upstream" from a gene identify where a gene is
    3. only one strand of the DNA is transcribed
    4. the genetic code includes "start" and "stop" codons
  4. Eukaryotic vs. Prokaryotic transcription
    1. in eukaryotic cells (those with nuclear membranes), transcription takes place inside the nucleus
    2. eukaryotic genes occur in pieces
      1. introns = non-coding stretches
      2. exons = coding stretches 
    3. the mRNA is cut and spliced before leaving the nucleus
  5. Translation is the process of decoding mRNA and synthesizing a protein
    1. in eukaryotes and prokaryotes, this occurs at the ribosomes, small organelles (fig. 5.2 page 92, fig 5.3 pg 94)
    2. in prokaryotes, translation may occur immediately after transcription
    3. the matching of amino acids to mRNA codons occurs via transfer RNA molecules (tRNA)
      1. anticodon on the tRNA matches the codon of the mRNA
    4. ribosomes also are composed largely of RNA (rRNA of various types)
  6. Figure 13.19 (pg. 267) summarizes protein synthesis
  7. Proteins of many types are often processed after synthesis before they are functiona.
Study questions

1.  Using the figure 11.10 (pg 226):  Why could a point mutation in the third place of the codons UAU or UAC be particularly deterimental?  

2. The "start" and "stop" codons are used to initiate and stop transcription.  What would the RNA polymerase read on the DNA strand?

3.  Why is the genetic code presented in figure 11.10 (pg 226) given as ribonuleotides not deoxyribonucleotides?

  1. because transcription uses RNA
  2. because translation uses RNA
  3. it doesn't matter, because the DNA and the RNA codons will be identical (except substituting T for U)

4.  Trace the synthesis of a small protein (polypeptide) Alanine, Valine, Serine backwards through the anticodon, mRNA codon, to the DNA sequence.

5. Digestive enzymes, those that break down molecules into their component parts, are often synthesized in an inactive form.  Why might this be important?

Answers