Mrs. Stewart Biology I Honors DNA Structure Mrs. Stewart Biology I Honors

STANDARDS: CLE 3210.4.1 Investigate how genetic information is encoded in nucleic acids. CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits.

OBJECTIVES: (today, I will…) Evaluate the structure of nucleic acids Determine how genetic information is “coded” in nucleic acids Create complementary DNA strands using Chargaff’s rule

Nucleic Acids Macromolecules containing : Carbon Hydrogen Oxygen Nitrogen Phosphorus Function: Store and transmit genetic/hereditary information

Two types of Nucleic Acids DNA RNA

Deoxyribonucleic Acid DNA Stands for: Deoxyribonucleic Acid

DNA Structure DNA is made up of two strands that are arranged into a twisted, ladder-like structure called a Double Helix. A strand of DNA is made up of millions of tiny subunits called Nucleotides. Each nucleotide consists of 3 parts: Phosphate group sugar Nitrogenous base

Nucleotides Phosphate Nitrogenous Base Pentose Sugar

DNA sugar The 5 carbon sugar for DNA is Deoxyribose That is where the name (Deoxyribo)nucleic acid comes from

Nucleotides The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”. There are four types of nitrogenous bases.

4 different Nitrogen bases Adenine T Thymine C Cytosine G Guanine

Purines A Adenine G Guanine

Pyrimidines T Thymine C Cytosine

Chargaff’s rule Erwin Chargaff observed that the percentage of adenine equals the percentage of thymine, and the percentage of cytosine equals the percentage of guanine. Example: in one strand of DNA the following amounts may be found: 15% Adenine 15% Thymine 35% Cytosine 35% Guanine

Complementary base pairing: Each base will only bond with one other specific base. (Chargaff’s rule) Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Form a base pair. Form a base pair.

Base Pairs: T Thymine A Adenine Hydrogen bonds C Cytosine G Guanine

DNA Double Helix Made of 2 strands of nucleotides These strands are joined together with the pairing of the Nitrogen bases (A, T, C, G) The bases are joined by Hydrogen bonds

Think – Pair - Share Look at the picture and try to figure out what “antiparallel” means. Did you notice that the strands of DNA run in “opposite directions”?

5’ and 3’ ends of DNA Refers to the orientation of the carbon atoms on the deoxyribose Strands run in opposite directions One strand is “upside down”

DNA Structure Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

A C T G G A T C

Practice: Complete the complementary DNA strand for the following sequence: G T A A C T C C T C A T A G A G G A C T C C T A A A C G A G G A T T T G T A G A A T G C C A T C T T A C G G

Bell Work Get one of each sheet on the front work desk (2 worksheets and a strip of DNA) Get plickers card

Mrs. Stewart Biology I Honors DNA Replication Mrs. Stewart Biology I Honors

Face Partners One of is you is Jim and the other is Dwight

STANDARDS: CLE 3210.4.1 Investigate how genetic information is encoded in nucleic acids. CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits.

OBJECTIVES: (today, I will…) Evaluate the structure of DNA and the need for replication Create complementary DNA strands to simulate replication

Central Dogma

Partners Think – Pair – Share Why does DNA need to replicate itself?

Review: When does DNA copy itself? Occurs during the S stage of interphase

DNA Replication DNA makes an exact copy of itself

Animation of replication #1

Semi-conservative Each strand of the double helix will serve as a template for the new strands that will form End result is two complete DNA double helixes – each containing one strand from the original molecule and one newly made complementary strand

Jim – explain to Dwight what semi conservative means.

Helicase Enzyme that “unzips” the DNA double helix by breaking the Hydrogen bonds between the bases to separate the strands in preparation for replication Creates a “replication fork”

DNA Polymerase Enzyme that builds the new strand of DNA using “free-floating” nucleotides in the nucleus

Dwight – Explain to Jim the role of Helicase in DNA replication

Jim – Explain to Dwight the role of DNA polymerase

5’ to 3’ direction DNA polymerase can only build DNA strands in the 5’ to 3’ direction. Leading strand: forms continuously because it is already running in the 5’ to 3’ direction Lagging strand: runs 3’ to 5’ so must form in short segments called Okazaki fragments that are joined together - this allows it to form in the 5’ to 3’ direction

Ligase Enzyme responsible for joining the Okazaki fragments together

Dwight – explain the difference between the leading and lagging strands

Jim – explain to Dwight what Ligase does

Animation of replication #1

COMPLETE REPLICATION ACTIVITY AND QUESTIONS