DNA Replication and Repair
DNA contains cell information Complete cell DNA sequence = genome Genome of bacteria usually circular (Can be linear) Bacterial genome = 0.6 – 9.4 million bp Human genome = 4 billion bp 1000× as large as E. coli But 8× genes: 30,000 (us) vs. 4,000 (E. coli) E. coli genes use less DNA sequence • About 1000 bases in typical bacterial gene • 3000 to 2.4 million in human gene
Nucleic acids structure (Deoxy) Ribose (A sugar) 3 phosphate groups on 5’ carbon 5’ phosphate of one nucleotide links to 3’ OH of previous nucleotide Base attached to sugar
B-type DNA Helix DNA not a perfectly linear helix Contains major and minor grooves Gives regulatory proteins access to internal bases Must be able to recognize sequence
DNA double helix is a right-handed helix Thumb points from bottom to top Strands coil in the same direction as the fingers
Chromosomes vs Genes A chromosome constitutes an entire DNA molecule + protein • Protein = histones • Supercoiled DNA in nucleosomes • Humans contain 46 such molecules (23 pairs) • 44 somatic chromosomes • 2 sex chromosomes (X +Y)
• Genes constitute distinct regions on the chromosome • Each gene codes for a protein product • DNA -> RNA-> protein • Differences in proteins brings about differences between individuals and species Chromosomes vs Genes
The cell cycle
DNA replication • Transfer of genetic information from generation to generation requires the faithful reproduction of the parental DNA. DNA reproduction produces two identical copies of the original DNA in a process termed DNA replication. • DNA replication results in new DNA duplex molecules in which one strand is from the parent duplex and the other is completely new. This mode of DNA replication is referred to as semi-conservative
April 25, 1953 Watson and Crick: "It has not escaped our notice that the specific (base) pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." The mechanism: Strand separation, followed by copying of each strand. Each separated strand acts as a template for the synthesis of a new complementary strand. DNA Replication