Name ____________________________________________ Date __________ Period ______

PowerPoint Notes on Chapter 9 - DNA: The Genetic Ma terial

Griffith’s Discovery of Transformation

Section 2 The Structure of DNA

Objectives • Describe the three components of a nucleotide. • Develop a model of the structure of a DNA molecule. • Evaluate the contributions of Chargaff, Franklin, and Wilkins in helping Watson and Crick

determine the double-helical structure of DNA. • Relate the role of the base-pairing rules to the structure of DNA.

DNA Overview (Video clip)

DNA is made up of subunits called ____________________, each made of 3 parts: a _______,

a ______________ group, and a ______________base. In DNA, the sugar is _____________.

A Winding Staircase • Watson and Crick determined that a DNA molecule is a ____________________ — two

strands twisted around each other, like a winding staircase.

• _______________________ are the subunits that make up DNA. Each nucleotide is

made of three parts: a phosphate group, a five-carbon sugar molecule, and a nitrogen-

containing base.

• ______________________________________________________________________.

Double Helix (Video clip) To what do they compare DNA’s double helix? ______________

Nucleotides (Video clip) What portion of the ladder do the sugars and phosphate groups of

a nucleotide form? ____________ The nitrogen bases face each other and bond to form

what portion of the ladder? __________________

• The nitrogen base in a nucleotide can be either a bulky, _________________________,

or a smaller, _______________________________.

Structure of a Nucleotide Discovering DNA’s Structure:

Chargaff’s Observations • In 1949, Erwin Chargaff observed that for each organism he studied, _______________

______________________________________________________________________

• Likewise, ______________________________________________________________

• However, the amount of adenine and thymine and of guanine and cytosine __________

_______________________________________

Wilkins and Franklin’s Photographs • By analyzing the complex patterns on X-ray diffraction photo, scientists can determine

____________________________________________.

• In 1952, Maurice Wilkins and Rosalind Franklin developed high-quality X-ray diffraction

photographs of _____________________________.

• These photographs suggested that the DNA molecule ___________________________

______________________________________________________________________

Watson and Crick’s DNA Model • In 1953, _______________________________________________________________,

a “spiral staircase” of two strands of nucleotides twisting around a central axis.

• The double-helical model of DNA takes into account ____________________________

______________________________________________________________________

Pairing Between Bases • An adenine on one strand always pairs with a _______________ on the opposite strand,

and a guanine on one strand always pairs with a ____________ on the opposite strand.

• These __________________________ are supported by _____________ observations.

• The strictness of base-pairing results in ______________________________________

___________________________________________________

• The diagram of DNA below the helix makes it easier to visualize the base-pairing that

occurs between DNA strands.

(Video clip) Complementary Base Pairing What are the base pairing rules? ______________

____________________________________________________________________________

Section 3 The Replication of DNA Objectives

• Summarize the process of DNA replication. • Describe how errors are corrected during DNA replication. • Compare the number of replication forks in prokaryotic and eukaryotic DNA.

Roles of Enzymes in DNA Replication

• The complementary structure of DNA is used as a basis to ______________________

_________________________________________________

• The process of making a copy of DNA is called _________________________.

• DNA ____________________________________________________ of the cell cycle,

before a cell divides.

• DNA replication occurs in three steps:

o Step 1 _____________________________________________________________

that link the complementary nitrogen bases between the two strands. The ________

where the double helix separates are called _______________________________.

o Step 2 At the replication fork, ___________________________________________

_______________________. __________________________________________

to the exposed nitrogen bases, __________________________________________.

o Step 3 ________________________ that are __________________________ DNA

molecule.

(Video clip) DNA Replication What does the enzyme helicase do to DNA? ________________

_____________________________________________________________________________

What does the enzyme DNA polymerase do? _________________________________________

_____________________________________________________________________________

What is the end result of DNA replication? ___________________________________________

______________________________________________________________________________

Checking for Errors

• In the course of DNA replication, ____________________________________________

______________________________________________________________________.

• An important feature of DNA replication is that _________________________________

______________________________________________________________________

• This proofreading ____________________ in DNA replication to about _____________

______________________________________________________________________

The Rate of Replication

• Replication does not _________________ of the DNA molecule and _______________

• The _____________________ molecules found in __________________ usually have

______________________________________________________________________.

• The __________________________________________________________________

_______________________of the DNA circle.

• In ______________ cells, each chromosome contains __________________________.

• Each human chromosome is ______________________________________________

_____________________________________________________________________.

• With multiple replication forks working in concert, _______________________________

___________________________________________________.

Replication Forks Increase the Speed of Replication