The Genetic Material
Is the structure and function of DNA
the same in almost all organisms?
Fredrick Griffith and
Hershey and Chase Show That
Genes Are Made of DNA
Structure of DNA
Nucleotides Are the Building Blocks.
• There are three components
to a nucleotide
– Sugar (5 carbon)
– Nitrogenous base
(adenine, quanine, thymine,
– Phosphate group
Semi-conservative Model of DNA
• Prokayotes • Eukaryotes
– One circular – Humans have 46
– 5 million base – 6 billion base pairs
pairs – Replicated in a
– Replicates in less few hours
than one hour – DNA is separated
from most of the
machinery by the
Both carry out replication very quickly and with
tremendous accuracy – 1 error /billion nucleotides.
The Bases Are Either Purines or
A always pairs with T and C always pairs with G. This
is because of the number of bonds formed between the
bases. Two hydrogen bonds form between A and T
and three between C and G.
Write the compliment for GGCTATTGGCA.
• Steps in replication
– DNA helix is unwound by helicase.
– The point where the DNA strands separate is
called the replication fork (Y)
– At the replication fork, the enzyme DNA
polymerase adds bases according to the base-
– Two new DNA helixes are formed.
Replication Begins at the Origin of Replication
• Prokaryotes have only one (1) origin of
• Eukaryotes have 100’s or 1000’s of origins
• Replication proceeds in both directions,
forming a replication bubble.
• At the ends of the replication bubble is the
replication fork – a” Y shaped” region.
• DNA polymerase has the
ability to proofread and
make corrections if an
error has been made.
After proofreading the
rate of errors is one per
• There are multiple DNA
replication forks in a
strand of linear DNA
multiple replication forks,
it would take 16 days to
copy one DNA molecule.)
What Is the Energy Source for
• The energy source is a
• This molecule is similar to
ATP except the sugar is
deoxyribose and the sugar
in ATP is ribose.
• The energy comes from
the hydrolysis of the
DNA Is Anti-parallel
Structure of A Gene
• Genes are DNA –encoded information that
specifies particular proteins; each gene is
made of a specific sequence of nucleotides.
• Genes are composed of coding and
– Coding sequences are exons (code for amino
– Noncoding sequences are introns (intervening)
• Telomeres are special
located at the end of
• They do not contain
genes but mutliple
repetitions of short
When the introns are removed, the resulting
fragments are stitched together to make a