Chapter 6

Properties of DNA

Genetics and DNA: Introduction

In, Chapter 5 we studied how traits are passed from parent to offspring (heredity).

In Chapter 6, we will study the form and structure of DNA as well as its properties.

Are DNA and heredity related? If so, how? On the next slide are a few questions to

gauge your understanding of DNA.

Genetics and DNA: Introduction

1) What is DNA? 2) What is genetics? 3) How are DNA and Genetics related? 4) Where is DNA located in cells? 5) Do all cells have DNA. If not, what type

of cells do have DNA?

Genetics and DNA: Introduction

6) How is DNA packaged differently in eukaryotes and prokaryotes?

7) What is the function of DNA? 8) How does DNA related to traits? 9) How is DNA related to chromosomes? 10) How to chromosomes relate to

heredity?

Complete the Following Cross: Review In beagles, short hair is dominant over

long hair. Cross a homozygous dominant beagle with a heterozygous beagle. Answer the following after your cross:Offspring Genotype (%):Offspring Phenotype (%):Offspring Ratio (%):

Complete the Following Cross: Review Pick any 2 offspring from the last slide and

complete a cross. Dominant and recessive traits remain the same.Offspring Genotype (%):Offspring Phenotype (%):Offspring Ratio (%):

Complete the Following Cross: Review In lilies, white flower color is dominant over

yellow flower color. Cross 2 heterozygous lilies. Answer the following after your cross:Offspring Genotype (%):Offspring Phenotype (%):Offspring Ratio (%):

Complete the Following Cross: Review Pick any 2 offspring from the last slide and

make a cross. Dominant and recessive traits remain the same.Offspring Genotype (%):Offspring Phenotype (%):Offspring Ratio (%):

Section 1: Objectives

List 3 important events that led to understanding the structure of DNA.

Describe the basic structure of a DNA molecule.

Explain Chargaff’s Rules for DNA.

Discovering DNA

For many years, DNA’s structure was a mystery.

It wasn’t until the 1950s that DNA’s structure was finally discovered.

These scientists later won the Nobel prize for this discovery.

Discovering DNA

Inherited characteristics are determined by genes.

Genes are passed from one generation to the next.

Genes are part of chromosomes, which are structures in the nucleus.

Chromosomes are made of proteins and DNA.

Discovering DNA

Scientists knew DNA must be able to:Give instructions for building/maintaining cellsBe copied

Why is it important for DNA to be copied each time a cell divides?

What is the name of this process?

Discovering DNA

DNA is made of subunits called nucleotides.

A nucleotide consists of:SugarPhosphate Base

Discovering DNA

The nucleotides are identical; except for the base.

The 4 bases are:Adenine (A)Guanine (G)Cytosine (C)Thymine (T)

Discovering DNA

In the 1950s, Edwin Chargaff did some research on DNA and nucleotides.

He found that the amount of (A) = (T) and (G) = (C).

At the time, no one knew the importance of these discoveries.

Later, they helped scientists discover the structure of DNA.

Discovering DNA

More clues about the structure of DNA came from Britain.

Rosalind Franklin was able to make images of DNA molecules.

She used a process called X-ray diffraction to do this.

Discovering DNA

After seeing, Franklin’s images, Watson and Crick concluded that DNA must be shaped like a twisted ladder.

They later built a model which was nicknamed the “double helix.”

This model eventually helped explain how DNA is copied and how it functions in the cell.

Chapter 6 Sec. 1 Pop Quiz

1) When was the structure of DNA discovered?

2) What are inherited characteristics determined by?

3) What 2 things did scientists know that DNA must be able to do?

Chapter 6 Sec. 1 Pop Quiz

4) What 3 things does a nucleotide consist of? 5) List the 4 bases of DNA. 6) What did Chargaff discover about DNA? 7)What contribution did Franklin make to the

discovery of DNA? 8) What did Watson and Crick nickname the

structure of DNA?

Section 1: Objectives

1) Describe the basic structure of DNA

2) Explain Chargaff’s Rules for DNA

DNA’s Double Helix

The 2 sides of the ladder are made up of alternating sugars and phosphates.

The steps are made up of bases. Adenine pairs with thymine and guanine

pairs with cytosine. Watson and Crick based their model off

Chargaff’s observations. (A=T and C=G)

DNA’s Double Helix

Copying DNA is known as “replication.” Each base always bonds with its

“complimentary” base.For example: A will bond with T and C will

bond with G.What bases would bond with the following

DNA sequence: CGAC?

DNA’s Double Helix

During replication, DNA is split down the middle.

The bases on each side of the molecule serve as a pattern for the new strand.

New bases pair with the old bases. The end result is 2 DNA strands: 1 new

and 1 old.

DNA’s Double Helix

DNA is copied every time a cell divides. Each new cell gets a complete copy of all

DNA. Proteins in the cell play a major role in

DNA replication:UnwindingCopyingRe-winding

Applying Chargaff’s Rules

If a molecule of DNA contains 37% Guanine, what percent Cytosine will it contain?What percent Adenine will it contain?What percent Thymine will it contain?

Applying Chargaff’s Rules

If a molecule of DNA contains 42% Adenine, what percent Thymine will it contain?What percent Guanine will it contain?What percent Cytosine will it contain?

Thinking Outside the Box

You are a scientist working at Miracle Grow Laboratories. You have been assigned to create a new formula for a Miracle Grow additive that will increase vegetable growth in gardens. You have already designed 2 new additives but are unsure which will increase vegetable growth the most.

Thinking Outside the Box

Testable Question: Which additive will increase vegetable growth the most?

Hypothesis: Educated guess Ind. Variable: Changes each test Dep. Variable: What is being measured? Controls: What stays the same each test? Results: Bar graph, line graph, pie chart

Thinking Outside the Box

You are a marine biologist working off the Gulf coast. A new species of fish has been introduced to the area. This species feeds off of algae and plankton. Your job is to study the effects of this new species of fish on the other marine life that are native to the Gulf to ensure that this species has no negative effects on the food supply.

Thinking Outside the Box

Testable Question: Will the newly introduced species have a negative effect on the food supply in the Gulf?

Hypothesis: Educated guess Ind. Variable: Changes each test Dep. Variable: What is being measured? Controls: What stays the same each test? Results: Bar graph, line graph, pie chart

Section 2: Objectives

Explain the relationship between DNA, genes, and proteins.

Outline the basic steps in making a protein.

How DNA Is Packaged

Prokaryotes: Coiled in a loop

Eukaryotes: Chromosomes in the nucleus

The structure of DNA allows it to hold information.What information does DNA contain?

Genes

A gene consists of a string of nucleotides.

These gives cells information for how to express a specific trait.

Humans have at least 30,000 genes.

Genes and Proteins

The DNA code is read like a book.

The bases form the alphabet for the code.

Groups of 3 bases are codes for amino acids.

Amino acids make up proteins.

Proteins and Traits

Proteins are found throughout cells.

They act as chemical triggers for many cellular processes.

Proteins help determine traits.

RNA

RNA is similar to DNA.

It can temporarily serve as a copy of a DNA sequence.

Contains the following bases: C,G,A, and U (Uracil)

The Making of Proteins

Step 1: Copy 1 side of a DNA segment (mRNA)

Step 2: The mRNA is fed through an assembly line 3 bases at a time

Chapter 6 Notebook Quiz

1) Chromosomes are made of _____ and ______.

2)Scientists knew DNA must be able to _____ and ______.

3) A nucleotide consists of ____, ____, and _____.

4) Chargaff found that the amount of A = ____ and the amount of _____ = G.

5) If a strand of DNA contains 30% A, what percent C,G, and T will be present?

Chapter 6 Notebook Quiz

6) Rosalind Franklin was able to make ______ of DNA molecules.

7) Watson and Crick built a model which they nicknamed the “______ ______”

8) Copying DNA is known as ______. 9) What happens to DNA during replication? 10) DNA is copied each time a _____ _____.