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.

(AT & GC)

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 Replication1. 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.