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DNAThe "Stuff" of Life
Its simplistic and
elegant, structure.
Note: Write down all
text information!!
DNA
DNA is the longest molecule found in the cell,
yet its structure is quite simple. The human
cell contains 5-6 feet of DNA in every cell
autosomal cell. The basic building block of
nucleic acids are the nucleotides. There are 3
billion base pairs or 6 billion nucleotides in a
human cell.
A nucleotide consist of:
1. A pentose sugar:
Deoxyribose for DNA and
Ribose for RNA
2. Phosphate groupThis is what makes the nucleic acid, acidic
3. Nitrogenous baseDNA- AGCT
RNA- AGCU
Nitrogenous bases
How is DNA analogous to a
ladder?
DNA is double stranded and analogous to a ladder. The
sides of the ladder are composed of alternating sugars
(deoxyribose) and phosphate groups that run
antiparallel (opposite direction) to one another. On the
left side the first carbon found on the strand is #5 and
the last carbon is carbon #3. This side is said to be 5'-3'.
What types of molecules make up
the backbone of the DNA
molecule made of?
Why is the other side of the
DNA molecule is upside down!
The opposite side is upside down
compared to the left side. On the right
side, the first carbon found on the
strand is #3 and moving on down the
last carbon is carbon # 5. This side is
said to be 3'-5'.
Why do the two sides run in
opposite directions?
What makes up the “rungs”
of the DNA molecule?
The nitrogenous bases form the rungs of the ladder. A
pyrimidine always base pairs with a purine. Thyamine will
base pair with adenine on the opposite side. This is a
double ring paired with a single ring. This will form 2
hydrogen bonds. Nitrogen bonding forms weak hydrogen
bonds. Hydrogen bonds are weak but millions of them
together will keep the two strands together.
What type of bond is between adenine
and thymine? How many bonds
between adenine and thymine?
Guanine pairs with? How many
bonds between this
complementary base pair?
Guanine will base pair with cytosine on the
opposite side. This is a single ring paired with a
double ring. This will form 3 instead of 2
hydrogen bonds.
Notice the direction of the
nucleotides on each side of the
DNA molecule.
This will continue for billions of base pairings
forming a molecule of DNA.
What is the direction of the left
side of the sugar phosphate back
bone? What is the direction of
the right side? What does this
mean?
This is how the
molecule may be
represented in a
book. Notice the
shapes of the
nitrogenous base
pairs.