3. TRANSCRIPTION (p. 242)
1. The DNA molecule unzips and the enzyme _______________
attaches to one side of the DNA (______________________),
attracted to a particular section of DNA by a special DNA base
sequence called a _________________________
2. A complimentary daughter strand is assembled using RNA
nucleotides
3. Once the RNA polymerase reaches a ____________________,
the new RNA strand, called the ________________________,
separates from the DNA strand, and the DNA zips back up
5. TRANSCRIPTION (cont’d)
4. Modifications are done to this primary transcript before it can leave
the nucleus:
5. The RNA strand, now called mRNA transcript , migrates out of
6. TRANSLATION (p. 250)
1. Once the mRNA strand is in the cytoplasm it
attaches onto the smaller subunit of the ribosome
2. A______, with the appropriate _________ binds to the
mRNA and the larger subunit of the ribosome attaches
to the smaller part, putting the tRNA in the _________
• the first ________ (group of 3 bases on the
mRNA) is always _______, which codes for the
amino acid _____________________
• the first _______________ (3 exposed bases of
the middle loop of tRNA) is ________
• there are _____________different codons
7.
8. TRANSLATION (cont’d)
3. A second _______ binds to the mRNA at the ______
of the ribosome, starting the __________________.
4. An enzyme, _______________________, attaches the
methionine to the amino acid of the tRNA in the A site,
forming a ____________________, and releases the
tRNA from the P site.
5. The ___________________three bases down the mRNA
strand, __________________________________, leaving
the A site for the next tRNA with the appropriate
anticodon.
9. TRANSLATION (cont’d)
6. Once the appropriate amino acid sequence
(________________) is made, the last codon on
the mRNA molecule codes for a _______________
• there are 3 _________________that code for
a _______________instead of an amino acid:
7. The release factor causes an _______ group to bind
to the last amino acid, completing the carboxyl
end, and causes the ________________________,
the ____________________and the ___________
to all come apart
6. The mRNA strand then finds another ribosome to
begin the sequence
13. Regulation of Protein Synthesis
Eukaryotic Cells: there are 4 levels of control of gene expression
a)Transcriptional: regulates which genes are transcribed
(housekeeping genes)
b)Post-transcriptional: capping and tailing, and excising
of introns
c)Translational: controls how often and how rapidly
mRNA transcripts will be translated
into proteins
d)Post-translational a number of control mechanisms
affect the rate at which a protein
becomes active and the time it
remains functional
14. Regulation of Protein Synthesis (cont’d)
Prokaryotic Cells: there are two types of control mechanisms
that these cells use: enzyme inducers and
enzyme repressors
• Operon is the general name of these control mechanisms
•Lac operon is an example of an inducer operon
•Trp operon is an example of a repressor operon
• Operons are made up of a cluster of genes under the
control of a promoter and an operator
15. LAC OPERON
– in bacteria, the LacZ, LacY, and LacA genes code for enzymes that
break down lactose
No lactose present
-The repressor molecule (Lacl protein) is
active and binds onto the operator site
-RNA polymerase cannot bind to the
operator
-The genes are not transcribed
(no lactose present, no need for protein that
breaks it down!)
Lactose present:
-Lactose binds to the lactose site on the
repressor, deactivating it
-mRNA polymerase can bind to the operator
-the genes are transcribed
The presence of lactose ACTIVATES it;
therefore, promoter operon
16. TRP OPERON
– in bacteria, there are 5 genes that code for enzymes necessary to
make the amino acid tryptophan
*Inhibitor; presence of the thing (trp) inhibits it
No tryptophan present:
-the repressor is inactive, and nRNA polymerase
can bind to the operator
-the genes that code for the making of more
trytophan are transcribed
Trytophan present
Tryptophan binds to the site on the repressor
molecule, activating it, causing it to bind to the
operator
-mRNA polymerase cannot bind to the operator
-the genes are not transcribed
Questions: Page 258
REALLY GOOD QUESTIONS!! Do them, faggot~
