DNA, Genes, ChromosomesChapter 6 & 9The structure and function of DNA

BiologyFall 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

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