Lecture 5 (recording 6)
Introduction to DNA Replication
Q. Is DNA replication conservative or semiconservative?
1. Conservative (both strands of parental conserved in one daughter cell, and both
strands are newly synthesized in one daughter cell)
2. Semiconservative (one strand is parental and other strand is newly synthesized in both
of 2 daughter cells---this can correct the error in newly synthesized strand)
Q. What is the direction of DNA replication?
3 possible models
-Unidirectional growth of single strands of two starting points (on both strands
at once 3’ to 5’)
ex) linear virus
-Unidirectional growth of two strands from one starting point (3’ to 5’ on one
strand and then 3’ to 5’ again on the partner strand)
ex) some plasmids
-Bidirectional growth from one starting point
ex) Eukaryotes and bacteria
When describing DNA replication, the newly synthesized strand is always made...
A. in the 5’ to 3’ direction
B. in an anti-parallel orientation to the template strand
C. by sequentially adding nucleotides to the 3’OH of the growing chain
D. Answers A and C are correct
E. Answers A, B and C are correct
Where does DNA replication start?
1. Always start from the same location on DNA
What are some of the characteristics of the sequences at replication origins?
- Easy to open, A-T rich - Recognized by and binding initiator proteins
2. Random start.
How many origins of replication?
*plasmid: a small circle of bacterial DNA that is independent of the main bacterial chromosome.
Plasmids often contain genes for drug resistances and can be transmitted between
bacteria of the same and different species: used in genetic engineering
*ARS: Autonomously Replicating Sequences
*yeast with ARS replicate even in the absence of histidine.