What is the main purpose of Interphase of the cell cycle? Why is this a delicate process? What are the potential risks in copying DNA?

DNA Structure and Replication

A. DNA Discovery 1. DNA was gradually discovered through a series of experiments performed by different scientists from the early to mid 1900s. a. In 1923, Frederick Griffith found that dead bacteria could pass an “illness factor” to live bacteria and kill a mouse.

Griffith’s Experiment Scientist injects mouse with…   Results Meaning Mixture of living harmless and dead pneumonia Living, harmless bacteria Living pneumonia bacteria Dead pneumonia bacteria Mouse lives Mouse dies Mouse lives Mouse dies Harmless bacteria can’t kill a mouse Harmful bacteria can kill a mouse Dead harmful bacteria can’t kill a mouse Should not have killed the mouse

2. In 1953, scientists Watson and Crick interpreted X-ray pictures of DNA, discovering the DOUBLE HELIX shape. 3. This paved the way for exploration into understanding the structure and function of the DNA molecule.

Thinking question: What are some functions of DNA? Thinking question: What do you know about the structure of DNA?

B. DNA Function 1. DNA, or DEOXYRIBONUCLEIC ACID, is a molecule found in the cells of all living things. 2. It has three main functions: a. Store genetic information b. Copy genetic information during cell reproduction

c. Transmit genetic information from parent to offspring.

1. DNA is a NUCLEIC ACID, and is made up of repeating units called NUCLEOTIDES. Thinking question: What are the three parts of a NUCLEOTIDE? a. All NUCLEOTIDES contain a SUGAR, a PHOSPHATE GROUP and one NITROGENOUS BASE. C. DNA Structure

2. The specific sugar in a DNA NUCLEOTIDE is DEOXYRIBOSE 2. The specific sugar in a DNA NUCLEOTIDE is DEOXYRIBOSE. With the PHOSPHATE, they make up the “backbone” of the DNA strand (outside of the ladder).

3. DNA contains 4 bases: ADENINE, THYMINE, GUANINE and CYTOSINE. a. They form BASE PAIRS between the “backbones” of two DNA strands.

b. C and T are PYRIMIDINES, with a one-ring shape b. C and T are PYRIMIDINES, with a one-ring shape. G and A are PURINES, with a two ring shape. PURINES can only bond with a PYRIMIDINE.

c. A bonds with T, and C bonds with G. They attach by HYDROGEN BONDS.

4. Two strands of DNA with opposite bases are COMPLEMENTARY 4. Two strands of DNA with opposite bases are COMPLEMENTARY. The two strands are twisted into a DOUBLE HELIX (coil).

5. Each strand of DNA has a 3’ (3 PRIME) and 5’ (5 PRIME) end 5. Each strand of DNA has a 3’ (3 PRIME) and 5’ (5 PRIME) end. The two strands are oriented opposite of each other, this is known as ANTIPARALLEL orientation.

6. Every single cell in an organism has the EXACT SAME DNA 6. Every single cell in an organism has the EXACT SAME DNA. What makes cells different is their ability to turn genes “on” and “off”, based on their specific functions This is called CELL SPECIALIZATION

Chromosome Structure To fit into a cell, DNA coils around a group of beadlike proteins called histones. DNA + histones form a nucleosome, which group together into chromatin fibers, which supercoil to form a chromosome.

GUESS WHO?!?!?!

C G A T Where are your base pairs? G C T A ORANGE RED BLUE GREEN

Why do organisms copy their DNA? How does DNA prepare to be copied? Where do the resources to make new copies of DNA come from?

DNA Replication

A. Plant/ Animal Cell DNA Replication DNA replication focuses on the order of bases in a DNA strand. Occurs in 3 Stages: Unwinding, Base-Pairing, and Joining Thinking question: Where are the bases located in a DOUBLE HELIX? A. Plant/ Animal Cell DNA Replication

2. To begin replication, the DOUBLE HELIX unwinds and separates. a. The Enzyme DNA HELICASE unwinds DNA, then moves between strands, breaking weak hydrogen bonds between BASE PAIRS. Stage 1: Unwinding An ENZYME is a molecule that enables a chemical process.

b. DNA is now in two straight, single strands with BASES exposed.

c. The two strands become TEMPLATES -their BASES determine the BASES on the new strands.

3. The enzyme DNA POLYMERASE will add NUCLEOTIDES with COMPLEMENTARY BASES to the TEMPLATE strands (by HYDROGEN BONDS.) Stage 2: Base-Pairing

a. Because the TEMPLATE strands are ANTIPARALLEL, the two new strands are built in opposite directions at the same time.

b. The LEADING strand is build moving towards where HELICASE is opening DNA. The LAGGING strand is build moving away from HELICASE.

3. Replication occurs in fragments, called OKAZAKI FRAGMENTS, which are joined by an enzyme called DNA LIGASE. Right after new sections of DNA are built, they twist back into a HELIX. Stage 3: Joining

Thinking question: Why doesn’t the whole strand unzip and replicate at once?

a. In EUKARYOTIC (plant/animal) DNA, replication occurs at multiple points in a strand at once. To unzip the whole strand increases risk for errors.

4. DNA POLYMERASE is an enzyme that checks/corrects and errors before separating the two new identical DOUBLE HELIX strands.

5. DNA replication is SEMICONSERVATIVE 5. DNA replication is SEMICONSERVATIVE. This means that each new strand contains one of the TEMPLATES and one new strand.

Thinking question: Is bacteria DNA replication different than plant/animal DNA replication? Thinking question: Why?

B. Bacteria DNA Replication 1. PROKARYOTIC DNA (bacteria) is less complex. It is a DOUBLE HELIX shape, but its ends are connected in a circle. B. Bacteria DNA Replication

a. Replication only happens at one point, moving in opposite directions until complete. b. This keeps DNA organized without a NUCLEUS, which bacteria cells don’t have.

WE'RE BAAAAAAAAAACCCCCKKKKKK

https://www.youtube.com/watch?v=TNKWgcFPHqw