1. 11-27-09 Notes
Next week – Class on Monday, Wednesday and Thursday.
Exam Monday December 7th, 1:30-4:30 pm
Chapter 10, page 195
Translating mRNA codons into amino acid sequence
DNA to RNA
Thymine – adenine
Adenine – uracil
Guanine – cytosine
Cytosine – guanine
Transfer RNA: tRNA
-mRNA – AUG
-tRNA met anti-codon – UAC
-must be “charged”, each tRNA must have the correct amino acid
attached. [“charged” meaning that enzyme + amino acid are attached
-Aminoacyl-tRNA synthetase [enzyme]
-each tRNA synthase is a separate translator, one piece at a time
Initiation of Transcription
-mRNA floating around, methianine tRNA anticodon that is complimentary
to AUG start codon.
-met codon = initiator tRNA
-tRNA with amino acid slots into the a-site
-amino end of polypeptide
-if ends do not match, hydrogen bonds cannot form, tRNA will not bond
-wrong anticodons will not work
Termination
-Stop codon (UAG, UAA, UGA)
-No anti-codons for these
-proteins, tRNA release, ribosomes come apart and float away
Polyribosomes => chains of ribosomes walking down mRNA strands
ER protein synthesis
-Ribosomes that make protein attached to ER start out as free ribosomes
-Attach when about to create protein to be exported
-Signal recognition protein attaches, allowing complex to attach
to cytoplasm side of ER
Point Mutations
-Point mutations can affect protein structure and function

2. -Types of point mutations
-Substitutions
-Insertions and Deletions (frameshift mutations)
-Mutagens
-Ex. Sickle Cell Anemia
-“sickle” shaped blood cells, as opposed to pudgy round
blood cells can block arteries and veins due to wrong-
shaped haemoglobin
-Several codons = same amino acid , so point mutations do
not always have an effect
Substitution
-one amino acid takes place of another
-Shape of enzyme can change as long as active site
does not change and enzyme’s function will not be affected.
“silent mutation”.
Frameshift mutation
-Extra letter [ex U] inserted.