DNA Structure & replication Flashcards
What kind of bonds join individual nucleotides to their neighbors in a single strand of DNA?
Are these strong bonds, yes or no?
Covalent, yes
What kind of bonds join bases to hold two strands of DNA together?
Are these strong bonds, yes or no?
Hydrogen, no
In DNA, the bases are paired in specific combinations.
What are these pairings?
A goes with T and C goes with G
What does it mean to say that the two strands in a DNA molecule are “antiparallel”?
if they run parallel to each other but with opposite directionality (alignments)
What does it mean to say that the process of DNA replication is “semi-conservative”?
This means the new strands formed during DNA replication will consist of one strand from the original double helix and one of the newly synthesized
List the four steps in DNA replication and briefly describe what happens in each step.
- Unwind: Helicase unwinds strands. SSBP stabilizes unwound DNA.
- Priming: Primase synthesizes short sections of RNA (RNA primers)
- Synthesis: DNA polymerase (Pol III) adds nucleotides to the 3’ end of the RNA primer. Pol I replaces RNA primers with DNA.
- Ligate: Ligase forms covalent bonds to seal gaps in the backbone.
List two key aspects of DNA polymerases
- Cannot add complementary nucleotides from scratch (NEED primer).
- Can only add bases to 3’ end of the primer.
What is the difference between the leading and the lagging strands during DNA replication?
The leading strand is replicated continuously, whereas the lagging strand is replicated discontinuously in short segments.
What is an Okazaki fragment?
Short sections of DNA formed by the lagging strand.
Explain why the telomeres get shorter every time a chromosome is copied.
The last RNA primer cannot be replaced because only the 5’ end is available (and Pol III cannot add nucleotides to the 5’ end). So, the end of the chromosome, aka the telomere, cannot be copied and is lost.
