Mrs. Stewart Biology I Honors

STANDARDS: CLE Investigate how genetic information is encoded in nucleic acids. CLE 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

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: 1. Phosphate group 2. sugar 3. Nitrogenous base

Nucleotides Phosphate Pentose Sugar Nitrogenous Base

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 A Adenine T Thymine G Guanine C Cytosine

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.

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.

G G A T T A A C T G C 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

DNA Structure To crack the genetic code found in DNA we need to look at the sequence of bases. The bases are arranged in triplets (sets of 3) called codons. A G G - C T C - A A G - T C C - T A G T C C - G A G - T T C - A G G - A T C

A gene is a section of DNA that codes for a protein. Each unique gene has a unique sequence of bases. This unique sequence of bases will code for the production of a unique protein. It is these proteins and combination of proteins that give us a unique phenotype.

Protein DNA Gene Trait

Your Task Draw a flow chart to show how to get from:

Mrs. Stewart Biology I Honors DNA Replication

STANDARDS: CLE Investigate how genetic information is encoded in nucleic acids. CLE 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

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”

Think – pair - share Why does DNA need to replicate itself?

DNA Replication DNA makes an exact copy of itself Occurs during the S stage of interphase

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

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 Uses “free-floating” nucleotides in the nucleus to build the complementary strand of DNA

5‘ to 3‘ direction The new DNA strands need to form in the 5 prime to 3 prime direction. Leading strand: forms continuously because it is forming in the 5’ to 3’ direction Lagging strand: forms in short segments called Okazaki fragments, so that it can also form in the 5’ to 3’ direction

Animation of replication #1 Animation of replication #2