Bellringer Please turn in your Banana DNA Lab to the tray at the front of the room if you have not already. Answer the following on the provided bellringer sheet: Where is DNA located in our cells? How does DNA fit into our cells and form chromosomes?
Learning Targets: Please write down the learning targets at the top of your DNA notes: Describe general structure and specific forms of DNA nucleotides. Explain the structure of DNA double helix and rules for base pairing between DNA strands.
DNA Model Project Groups of no more than 3 people. Provide your own materials for building. Will have class time on block day and Friday next week to work on model. MAKE SURE TO BRING YOUR SUPPLIES THOSE DAYS! Model will be due Tuesday, Jan. 17th Bonus points will be awarded to most creative and best overall model!
DNA
Definition Deoxyribonucleic acid (DNA) – molecule that contains genetic information that directs the activities of cells. DNA contains the instructions cells use to make proteins. Helps make bones, muscle, new cells, etc.
History Rosalind Franklin - took x-ray pictures of DNA molecules which helped to determine its shape.
History James Watson and Francis Crick - built the first DNA model and are usually given credit for determining its shape.
Structure Monomers called NUCLEOTIDES. 3 parts: sugar (deoxyribose) phosphate nitrogen base
Structure There are four different DNA nitrogen bases: Purines - adenine and guanine (double rings) Pyrimidines - cytosine and thymine (single rings)
Structure The nitrogen bases always bond to the deoxyribose molecule (sugar) of the nucleotide. Purines Pyrimidines Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose
Structure Nucleotides bond together to form a double stranded DNA molecule. DNA’s structure looks like a twisted ladder This structure is called the double helix. The deoxyribose and phosphate form the “rails,” of the ladder. Nitrogen bases bond together to form the “rungs,” of the ladder.
Structure Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)
Chargaff’s Rule Chargaff's Rule: Adenine (A) = Thymine (T) Guanine (G) = Cytosine (C)
Nitrogen Base Pairing Rules Nitrogen Base Pairing Rules ADENINE always bonds to THYMINE- Double Bond CYTOSINE always bonds to GUANINE-Triple Bond
Chemical Structure The nitrogen bases are bonded with weak hydrogen bonds to hold the two DNA strands together. The structure and shape of the nitrogen bases allows them to always bond to their complement
Scientist Check Point The picture to the right shows an x-ray diffraction of DNA. The x-ray diffraction of DNA led to the idea that DNA — What Scientist Took this picture? Why are Watson and Crick famous?
The Genetic Code The order of the nucleotides in creates a code used to make proteins. The arrangement of nitrogen bases (A-T-G-C) determines the amino acids used to construct proteins Like the alphabet makes words
How Does It All Fit??? All your DNA (end-to-end, from one cell) is about 2 meters long! One cell’s nucleus is about 2 micrometers in diameter! So, how can 2m of DNA fit into 2μm of space?
Supercoiling! DNA wraps around histone proteins DNA + histone = nucleosome Nucleosomes form a coil
Supercoiling! Coils coil again … This is a SUPERCOIL!
A Chromosome Is Supercoiled DNA Supercoiling! A Chromosome Is Supercoiled DNA
A chromosome is supercoiled DNA
Draw 2 strands, four nucleotides each: Remember, each nucleotide consists of sugar, phosphate, base! Label the sugars “S”, and the phosphates “P” … notice a pattern Notice: opposite directions! ? ? ? ?