lecture 28 Flashcards
DNA
genetic material
what happened in the early 20th century:
the identification of the molecules of inheritance loomed as a major challenge to biologists
Genetic alphabet
T,A,C,G
DNA has directionality from
the sugars
Carbons join from the
3’ end and the 5’ end
‘=prime
5’ connects to the
phosphate
3’ connects to
nitrogenous bases
Maurice Wilkins and Rosalind Franklin were using a technique called
x-ray crystallography to study molecular structure
franklin produced a pic of the DNA molecules using this technique
Franklin’s x-ray crystallographic images of DNA enabled Watson to ..
deduce that DNA was helical and the width of the helix and the spacing of the nitrogenous bases
The width suggested that the DNA molecule was
made up of 2 strands, forming a double helix
5’ and 3’ run________to each other
antiparallel
Chargaff’s rule states:
many species there is an equal number of A and T bases, and an equal number of G + C bases
there are two antiparallel sugar-phosphate backbones…
with the nitrogenous bases paired in the molecules interior
Adenine (A) paired only with
thymine (T)
Guanine (G) paired only with
Cytosine (C)
the Watson-crick model explains Chargaff’s rules
in any organism the amount of A=T and G=C
A+G=2 rings
T+C=1 ring
parental
2 strands that are identical
the relationship between the structure + function is
manifest in the double helix
Watson and crick notes that the specific base pairing suggested a
possible copying mechanism for genetic material
Since the two strands of DNA are complementary,
each strand acts as a template fore building a new strand in replication
in DNA replication…
the parent molecules unwinds and 2 new daughter strands are built based on base-pairing rules
the copying of DNA is remarkable in its
speed and accuracy
more than a dozen enzymes and other proteins participate in ..
DNA replication
Replication begins at special sites called
organisms of replication, where the two DNA strands are separated, opening up a replication “bubble”
replication proceeds in both directions from each origin, unit…
the entire molecule is copied
at the end of each replication bubble is a
replication fork, a y shaped region where new DNA strands are elongating
DNA polymerases cannot initiate synthesis or a polypeptide, they can only
add nucleotides to the 3’ end.
the initial nucleotide strand is a short..
RNA primer
the primer is short__________, and the 3’ end serves as the starting point for the _______.
(5-10 nucleotides long)
new DNA strand
Enzymes called DNA polymerases catalyze the elongation of the new DNA at a
replication fork
Most DNA polymerases require a primer and a
DNA template strand
The rate of elongation is about ___________ in human cells
50 per second
