Chapter 12 DNA Structure and Replication
Transformation• Changes one form of bacteria into a different
or some cases toxic form of bacteriaEX: Griffith’s experiment with heat killed bacteria vs. a harmless strain
Hershey – Chase Experiment• Bacteriophages – virus
that infects bacteria by attaching to the surface and injecting its DNA into the cell.
-genes produces more copies of
bacteriophages and destroy the cell
Components of DNA
• Nucleotide is monomer of DNA consisting of a 5 carbon sugar, phosphate, and a nitrogen group
Purines vs. Pyrimidines
• Purines are structures with 2 rings
Ex: adenine & guanine• Pyrimidines have 1
ringEx: cytosine &
thymine
Base Pairing
Double Helix• DNA is a twisted ladder
or spiral staircase.-Sugar phosphate backbone forms outside braces to the ladder-Nitrogen base pairs are the steps held together by
hydrogen bonds.
Chromosomes• Prokaryotes – DNA is circular and fills most
internal space of organism, cytoplasm- no internal organelles
• Eukaryotes – nucleus holds DNA
• Length of DNA in both types of organisms is vast.
Eukaryotes have about 1000 times more base pairs.
Structure of ChromosomeChromatin is the structure formed from tightly coiled DNA and proteins
-consists of nucleosome (protein) that packs DNA around histones in a beadlike thread.
DNA Replication• What phase of cell cycle will DNA duplicate
itself?• During S phase DNA will separate and enzymes will aid in the
copying mechanism that give a complementary strand from each DNA template strand
Replication
• Steps of Replication:1. Enzymes unzip the DNA molecule and breaks
hydrogen bonds2. Each strand serves as a template for
complementary (matching) strands3. An enzyme joins and proofreads sequence4. Enzymes patch together any gaps in sequence
for new strand
DNA Replication
DNA Replication
Enzymes of Replication
• DNA Helicase is the enzyme responsible for untwisting the DNA• DNA Polymerase is the enzyme responsible for
base pairing and proofreading the complementary nucleotides in the new copied strands• DNA Ligase patches and connects all spaces
between sequences.
Antiparallel Recognition
• Antiparallel meaning sequences are matching in opposite directions, or oriented in different directions
Ex: 3’ GGTTAACCGATC 5’5’ CCAATTGGCTAG 3’
EXIT QUESTION
• What are the steps of DNA Replication?