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?