How DNA Makes Protein / Protein Synthesis

1
How DNA Makes Protein / Protein Synthesis

• Starting Facts
• A section of DNA that codes for a polypeptide (a
  gene) has its bases in the correct order.
• Aas are in the body because we have eaten
  protein and after digestion, the aas were
  absorbed from the small intestine into our blood.
  Cells that needed them took them in.
• 3 stages
• Transcription, aa activation, translation

2

• Transcription
• The order of bases in a gene is changed into a
  mRNA molecule
• Where ? In nucleus
• How ?
• DNA unwinds and unzips (H bonds between
  complementary bases break).
• In the nucleus there are free mRNA bases floating
  around. With the help of RNA polymerase they
  come in and temporarily complementary base pair
  with the exposed DNA bases. (N.B an exposed A
  on the DNA will have U (uracil) pair with it).
• When the gene has been transcribed, the
  temporary H bonds break. mRNA moves away and out
  through the nuclear pores and into the cytoplasm.
• The DNA zips up and winds up (to protect itself)
  

3
(No Transcript)
4

• Aa activation
• This is when tRNA becomes loaded /activated
  with its correct aa.
• Where ? - in the cytoplasm
• How ?
• Its correct aa matches the 3 bases at the
  bottom of the tRNA, its anticodon.
• This is all catalysed by a specific enzyme and
  ATP energy is used.

5
(No Transcript)
6

• 3) Translation
• This converts the mRNA into a line of aas that
  are in the correct order.
• Where ? In the cytoplasm
• How ?
• a) The first 3 bases, codon, of mRNA is held by
  a ribosome.
• b) The correct tRNA, carrying the correct aa
  comes along and temporarily forms H bonds during
  complementary base pairing.
• c) The ribosome is also holding the second
  codon, its complementary tRNA comes along and
  the anticodon forms H bonds with its codon,
  during cbp.
• d) The first aa detaches from its tRNA and goes
  and bonds to the 2nd aa.
• The ribosome moves along and this process
  continues until the whole mRNA has been
  translated.
• After each tRNA has left its aa there to join
  the aa line, it goes away and will get activated
  /loaded up again with another aa that is correct.
  

7
This powerpoint was kindly donated to
www.worldofteaching.com http//www.worldofteac
hing.com is home to over a thousand powerpoints
submitted by teachers. This is a completely free
site and requires no registration. Please visit
and I hope it will help in your teaching.
Free Powerpoint Presentations
7