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A Closer Look at DNA
Review Questions
(Discuss the answers)
1. What are the 3 parts of a DNA
nucleotide?
2. What is the technical term for the
“twisted ladder” shape of the DNA
molecule?
3. What makes up the “legs” of the DNA
ladder?
4. What makes up the “rungs” of the
DNA ladder?
Answers
1. What are the 3 parts of a DNA
nucleotide?
1. phosphate group
2. deoxyribose sugar
3. nitrogen base
Answers
2. What is the technical term for the
“twisted ladder” shape of the DNA
molecule?
double helix
Answers
3. What makes up the “legs”
of the DNA ladder?
The deoxyribose sugars and
phosphate groups of the
nucleotides bond together to
form the “backbone” of the
DNA molecule.
Answers
4. What makes up the
“rungs” of the DNA
ladder?
Pairs of nitrogen bases
form the “rungs” of the
DNA molecule.
(AT & GC)
Review:
Patterns of Base Pairing
• Base pairs are formed by the hydrogen
bonding of A with T and G with C.
• This pattern is constant for all
organisms.
• The sequence of bases in a nucleotide
strand is different from one species to
the next.
A Closer Look at DNA:
Two Questions
1. How is DNA copied?
2. If a mistake occurs in the copy,
how is it repaired?
DNA Replication…
• …is the process by which DNA is
duplicated prior to cell division.
2 Steps of DNA Replication
1. The two strands of DNA unwind and
expose their bases.
2. Unattached nucleotides are paired
with exposed bases.
Replication Enzymes
• DNA helicase: unwinds the double helix
• DNA polymerase: assembles the
nucleotides into chains
• DNA ligase: seals sections of new DNA
into continuous strands
• http://www.johnkyrk.com/DNAreplication.html
“Semiconservative Replication”
• DNA replication results in DNA
molecules that consist of one “old”
strand and one “new” strand.
“Semiconservative Replication”
DNA Repair…
• …is the process by which enzymes
remove and replace altered parts of
the base sequence in one strand of
DNA.
• DNA polymerases, DNA ligases, and
other enzymes are also involved in
DNA repair.
Genes
• Genes are portions of the DNA
strand that tell the body what
proteins to make.
• These proteins help carry out the
functions of the cell.