Protein Synthesis
Protein or Polypeptide chain
Transcription – Copying the
DNA in RNA language. The
resulting mRNA moves out to
the cytoplasm.
Translation – At the
ribosome, the information
encoded in the mRNA is used
to assemble a chain of amino
acids or protein.
Comparing DNA and RNA
RNA
DNA
Ribose sugar
Uracil instead of Thymine
Single stranded
Deoxyribose sugar
Thymine
Double stranded
Transcription
• RNA polymerase copies the DNA strand,
adding the complimentary RNA bases to form
the mRNA
The mRNA moves to a ribosome for
translation into a protein.
The Triplet Code
• There are four DNA bases
• They code for 20 amino acids
• If two bases coded for one amino acid, there
wouldn’t be enough, only 16
• Three bases coding for each amino acid is just
right, 64 possible combinations.
• A set of 3 DNA bases that code for one amino acid is
referred to as a codon.
mRNA genetic code library
There are Three Forms of RNA
• mRNA – messenger RNA carries the
information for synthesis of protein
• rRNA – ribosomal RNA makes up ribosomes
• tRNA – brings the amino acids to the
ribosome for protein synthesis
• The triplet code in tRNA is called the anticodon
• Each tRNA and its anticodon is specific for one
amino acid
Translation
• mRNA binds to the ribosome
• tRNA arrives, binding to the ribosome
• A 2nd tRNA arrives, their amino acids bond
and the 1st tRNA leaves
• More tRNA arrive until the mRNA is
completely translated into protein
Mutations
• Mutation – a permanent alteration of a DNA base
sequence
• Most have no effect on an organism. Some have a
deadly effect, only a slight few have a positive effect.
• Point mutation
• When a single base pair is changed.
• Whole chromosome mutations
• See chapter 12
• Most mutations happen in somatic cells and
are of little or no importance.
• Melanoma or skin cancer
• Mutations that happen in gametes can be
passed from generation to generation.
A Pedigree of Hemophilia in the Royal Families of Europe
Selected members of the pedigree
I-1 = King George III
III-1 and III-2 = Prince Albert and Queen Victoria
IV-5 and IV-6 = Alice of Hesse and Ludwig IV of Hesse
V-13 and V-14 = Alix and Nicholas II (Tsar of Russia)
VI-16 = Alexei