DNA, Genes, Chromosomes Chapter 6 & 9 The structure and function of DNA Biology Fall 2012

Bell Ringer  How is the structure of DNA similar to a ladder, how is it different?

Bell Ringer- Answers

Objectives  Big Picture:  Differentiate between a gene, a DNA molecule, a chromosome  Today:  Describe the structure of DNA  Describe the function of DNA

A Winding Staircase  The ___________________ of DNA’s structure was important because it clarified how DNA could serve as the _________________ ______________________  DNA’s ___________________ is to store genetic information used in the _____________________ and ______________ of living organisms

A Winding Staircase  _________________________ : two strands twisted around each other, like a winding staircase  _________________: subunits that make up DNA  Each made up of 3 parts: ___________________, 5-carbon _________________ molecule, and a nitrogen containing ___________________  _________________________: 5-carbon sugar molecule in DNA nucleotides

 DNA picture A Winding Staircase

 Sugar molecule and phosphate group are the same for each _________________________  Nitrogen base may be any of 1 of 4 different kinds  Draw a nucleotide:

A Winding Staircase  Nitrogen bases: 1. _______________________ (A) 2. _______________________ (G) 3. _______________________ (T) 4. _______________________ (C)

A Winding Staircase  _______________________ : adenine and guanine  Made of 2 rings of carbon and nitrogen atoms  __________________________ : thymine and cytosine  Made up of a single ring of carbon and nitrogen atoms  Nitrogen bases ________ up and face each other  Are held together by weak _________________ bonds  _______ + ________

Discovering DNA’s Structure  Data (Chargaff) shows that for each organism, the __________ of adenine always ___________ the amount of thymine (__ = __)  Also the amount of ______________ always equals the amount of _____________ (G = C)  The amount of adenine and thymine and of guanine and cytosine varies between ____________________ organisms

Discovering DNA’s Structure  ___________________ and ____________:  1953  Used previous knowledge along with their knowledge of chemical bonding to determine 3-D ______________ of __________  __________________________________________  Two strands of __________________________ twisting around a central axis

Discovering DNA’s Structure  DNA model:

Pairing Between Bases  ______________ on one strand of DNA is always paired with a __________________________ on the opposite strand  ___________________ pairs with thymine  Guanine pairs with ____________________________

Pairing Between Bases  _________________________ rules : rules saying that cytosine pairs with guanine and adenine pairs with thymine in DNA  Supported by Chargaff’s experiment  Adenine forms 2 hydrogen bonds with ____________  ____________ forms 3 hydrogen bonds with guanine

Pairing Between Bases:  ___________________________ base pairs : sequence of bases on one strand determines the sequence of bases on the other strand

Review  What are the complementary base pairings to this strand of DNA: T C G A A C T  What are the complementary base pairings to this strand of DNA: C A T A C T G G C A