Chapter 5

Preview

Section 1 What Does DNA Look Like?

Section 2 How DNA Works

Genes and DNA

Concept Mapping

Chapter 5 Section 1 What Does DNA Look Like?

Bellringer

Can you explain the difference between traits andcharacteristics? Which is more closely associatedwith DNA and genes? Where do you think DNA andgenes are usually found?

Write your answers in your science journal.

Chapter 5

Objectives

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

• Describe the basic structure of a DNA molecule.

• Explain how DNA molecules can be copied.

Section 1 What Does DNA Look Like?

Chapter 5

The Pieces of the Puzzle

• DNA stands for deoxyribonucleic acid. DNA is the genetic material that determines inherited characteristics.

• Nucleotides: The Subunits of DNA DNA is made of subunits called nucleotides. A nucleotide consists of a sugar, a phosphate, and a base.

Section 1 What Does DNA Look Like?

Chapter 5

The Pieces of the Puzzle, continued

• Chargaff’s Rule Erwin Chargaff found that the amount of adenine in DNA always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine.

• Franklin’s Discovery Chemist Rosalind Franklin was able to make images of DNA molecules by using X-ray diffraction.

Section 1 What Does DNA Look Like?

Chapter 5

The Pieces of the Puzzle, continued

• Watson and Crick’s Model James Watson and Francis Crick used Chargaff’s and Franklin’s research to build a model of DNA.

• The model, which looked like a long, twisted ladder, eventually helped explain how DNA is copied and how it functions in the cell.

Section 1 What Does DNA Look Like?

Chapter 5

DNA’s Double Structure

• The Double Helix The shape of DNA is known as a double helix.

• The two sides of the ladder are made of alternating sugar parts and phosphate parts.

• The rungs of the ladder are made of a pair of bases.

Section 1 What Does DNA Look Like?

Chapter 5Chapter 5 Section 1 What Does DNA Look Like?

Chapter 5

Making Copies of DNA

• How Copies Are Made During replication, a DNA molecule is split down the middle, where the bases meet. The bases on each side of the molecule are used as a pattern for a new strand.

• When Copies Are Made DNA is copied every time a cell divides. Each new cell gets a complete copy of all the DNA.

Section 1 What Does DNA Look Like?

Chapter 5

Making Copies of DNA, continued

Section 1 What Does DNA Look Like?

Chapter 5

DNA Replication

Click below to watch the Visual Concept.

Visual Concept

Section 1 What Does DNA Look Like?

Chapter 5 Section 2 How DNA Works

Bellringer

Unscramble the following words:tpsoneirneesg

Now think of three words you associate with each of the above words and use them all in a paragraph that highlights what you know about DNA.

Write your paragraph in your science journal.

Chapter 5

Objectives

• Explain the relationship between DNA, genes, and proteins.

• Outline the basic steps in making a protein.

• Describe three types of mutations, and provide an example of a gene mutation.

• Describe two examples of uses of genetic knowledge.

Section 2 How DNA Works

Chapter 5

Unraveling DNA

• DNA is often wound around proteins, coiled into strands, and then bundled up even more. In a cell that has a nucleus, the strands of DNA and proteins are bundled into chromosomes.

• A gene consists of a string of nucleotides that give the cell information about how to make a specific trait.

Section 2 How DNA Works

Chapter 5Chapter 5 Section 2 How DNA Works

Chapter 5

Genes and Proteins

• Proteins and Traits Proteins act as chemical triggers for many of the processes within cells. Proteins help determine traits.

• Help from RNA Another type of molecule that helps make proteins is called RNA, or ribonucleic acid. RNA is so similar to DNA that RNA can serve as a temporary copy of a DNA sequence.

Section 2 How DNA Works

Chapter 5

Genes and Proteins, continued

• The Making of a Protein The first step in making a protein is to copy one side of the segment of DNA containing a gene. This copy is called messenger RNA (mRNA).

• A ribosome is a cell organelle composed of RNA and protein. A ribosome uses mRNA, transfer RNA (tRNA), and amino acids to make proteins.

• You can see the steps of protein production on the following two slides.

Section 2 How DNA Works

Chapter 5Chapter 5 Section 2 How DNA Works

Chapter 5Chapter 5 Section 2 How DNA Works

Chapter 5

Changes in Genes

• Mutations Changes in the number, type, or order of bases on a piece of DNA are known as mutations.

Section 2 How DNA Works

Chapter 5

Changes in Genes, continued

• Do Mutations Matter? There are three possible consequences to changes in DNA: an improved trait, no change, or a harmful trait.

• How Do Mutations Happen? Mutations happen regularly because of random errors when DNA is copied. Any physical or chemical agent that can cause a mutation in DNA is called a mutagen.

Section 2 How DNA Works

Chapter 5

Carcinogens and Mutagens

Click below to watch the Visual Concept.

Visual Concept

Section 2 How DNA Works

Chapter 5

An Example of Substitution

• A mutation, such as a substitution, can be harmful because it may cause a gene to produce the wrong protein.

• A simple change in an amino acid can cause a disease such as sickle cell anemia, as shown on the next slide.

Section 2 How DNA Works

Chapter 5Chapter 5 Section 2 How DNA Works

Chapter 5

Uses of Genetic Knowledge

• Genetic Engineering Scientists can manipulate individual genes within organisms. This kind of manipulation is called genetic engineering.

• Genetic Identification Your DNA is unique, so it can be used like a fingerprint to identify you. DNA fingerprinting identifies the unique patterns in an individual’s DNA.

Section 2 How DNA Works

Chapter 5 Genes and DNA

Concept Mapping

Use the terms below to complete the concept map on the next slide.

mutation genesamino acid guaninenucleotide proteinsDNA chromosomesadenine cytosine

Chapter 5Chapter 5 Genes and DNA

Chapter 5Chapter 5 Genes and DNA