CHEE-370 Homework Assi
1 base pair = 0.34 nm in length (from the textbook, "Size of a DNA molecule”)
2220 kbp x 1000 bp/kbp x 0.34 nm = 754.8 micrometers ~ 0.8 mm = 0.08 cm
85% of 2220 kbp = 1887 kbp
(open reading frames => protein-coding base pairs)
1,887,000 base pairs => 1,887,000 bases in each strand
1 amino acid produced per 1 codon (triplet base sequence)
1,887,000 bases / (3 bases/codon) = 629,000 amino acids
Subtracting start and stop codons - difference in the number of proteins would be negligible.
629,000 a.a. / (300 a.a./protein) = 2096.7 ~ 2096 protein-encoding genes
A computer can be employed to scan DNA base sequences for open reading frames, looking for start and stop
codons. Open reading frames long enough to encode realistically long proteins would be considered protein-
encoding genes; thus, the presence of an ORF in an unknown DNA piece would indicate its ability to encode a
protein. A shortcoming of this technique is that it would not allow identifying of shorter genes, such as those
corresponding to protein hormones or regulatory peptides.
Due to prokaryotes being free of non-coding DNA regions in their vast majority, the remaining 15% of the DNA
can be made up of transposable elements (“jumping genes”) and repeated sequences (inverted repeats).
Prior to synthesizing new DNA by DNA polymerase, the original double helix must be unwound to expose the
template strands. In prokaryotes (Bacteria), DNA synthesis starts at the
origin of replication
which is a specific DNA
sequence of approximately 250 bases recognized by specific initiation proteins, such as DnaA in particular. After DnaA
binds and opens up the double helix to separate the individual strands, replication begins on two single strands. This zone
of unwound DNA where the process occurs is called the
. In circular DNA of prokaryotes, two replication
forks can proceed independently of each other thus forming a
, resembling the Greek “ ” when viewed
from above. Single strand binding proteins, namely helicase (DnaB), are then attached to each strand facing opposite ways.
Behind them, two enzymes, primase and DNA polymerase, are loaded to initiate DNA replication on both strands. As the
process continues, the replication fork moves along the DNA.