Sept 15, 2009
Cis-acting Elements and Trans-acting Factors
-Refer to fig 2.16 Genes IX
-All genes have a control site followed by a coding region. The gene needs to be
activated by the control region before proteins can be made (refer also to fig. 2.17
There are 2 copies of each gene (alleles) in the cell and each one has a minute
nucleotide difference in order to differentiate the two.
-If a mutation occurs at one of the control site that causes the control region to be
blocked from the regulatory protein then that allele becomes unviable.
-Cis-acting element mutations affect only the DNA molecule to which it is
attached. In Trans-acting mutations prevents the expression of both alleles;
therefore it is said to be diffusible.
-Cis-acting molecules are within the DNA itself whereas Trans-acting molecules
are from the regulatory proteins that govern gene activity.
-The origin of replication would be the Cis elements whereas the elements needed
for replication would be the Trans factors.
Physical/Chemical Structure of DNA
-Refer to fig. 1.2 Singer & Burk
-The lack of the 2’ OH-group makes the DNA molecule more stable than the
other possible information storage molecules
-The purines are adenine (A) and guanine (G) made of dual cyclic structures, the
two pyrimidines are thymine (T) and cytosine (C) made of a single ring.
-Base + sugar = nucleoside. Phosphate + base = sugar = nucleotide; the names of
the bases also change.
-Refer to fig. 1.3 Singer & Burk
-the order of the carbons that the phosphates that bind to DNA give it
directionality (5’ 3’)
Double Helix Structure of DNA
-What are some of the attractive forces required for the replication of DNA?
-Hypothesized that it would require weak forces (ionic and hydrogen bonds, Van
der Waals bonds, hydrophobic interactions) not covalent bonds so that the
molecule can be separated; a covalent bond would require too much energy.
-Hydrophobic forces work by excluding polar molecules as they come together.
-On an individual basis these forces are weak but when with the sum of all the
weak forces there is sufficient energy for the structure to be held together.
-Daughter DNA that is created is always complimentary to the template strand,