DNA: THE MOLECULE OF HEREDITY

CHAPTER 9

Big Idea

• The Big Idea!• The structure of DNA, the molecule of

heredity, enables the molecule to copy itself.•

Enduring Understanding

• Students will understand that:• -DNA carries the code for the building blocks

of a living organism.• -Mutations can lead to changes and there is

potential to changes those mutations.• -We have the technology to manipulate DNA:

Essential Questions

• What is DNA and where is it found?• How can knowledge of DNA help us to

understand the way organisms are related to each other?

• How and why does DNA copy itself?• How is the discovery of DNA an example of

cooperation, competition, and Intrnationalism?

Knowledge

• DNA is composed of nucleotides and is shaped like a double helix, with strands running antiparallel

• Bases always form complementary base pairs (adenine with thymine and cytosine with guanine)

• Complementary base pairing enables DNA to replicate, or copy itself

• DNA replication involves three steps and each step uses a specific enzyme

• There is a leading strand and a lagging strand for each replication fork

• The lagging strand is made from Okazaki fragments

Students know

• The “ tranforming principle” from the experiment conducted by Griffith.

• DNA is the genetic material• Watson and Crick model of DNA• DNA is composed of four types of nucleotides• Nucleotides always pair in the same way.• Replication copies the genetic information

Vocabulary

• Nucleotide • Adenine• Thymine• Cytosine

• Transformation• Replication• Chromosomes

Tour of the basics, from Learn.Genetics.

• http://learn.genetics.utah.edu/content/begin/tour/

• This is a very useful link which will enable you to learn about DNA, Chromosomes, gene, protein, trait, all at your own pace. Make sure you make best use of this link.

Griffith’s Experiment

http://www.youtube.com/watch?v=vQOdDGM5vSg

Griffith’s Experiment

• Transformed Bacteria

The DNA Song

http://www.youtube.com/watch?v=FUA6_Ucw3i4

History Behind The Discovery of DNA

• Internet Search Activity• DNA timeline• Make sure you post brief information and also

the picture of the scientists.

Prokaryotic and Eukaryotic DNA

Prokaryotic and Eukaryotic DNA• genetic material DNA in prokaryotes is not bound within a nucleus

whereas in Eukaryotes the genetic material DNA is bound within the nucleus.

• In prokaryotes, DNA is a single loop/arranged in a circular shape. In Eukaryotes, DNA is organized into chromosomes.

• Eukaryotic DNA is complexed with proteins called “histones” and is organized into chromosomes; prokaryotic DNA is “naked” meaning that it has no histones associated with it, and it is not formed into chromosomes.

• In prokaryotic DNA there is only one replication origin when replication starts. By contrast, in eukaryotic DNA there are as many as 1000 replication origins.

•

What is the Structure of DNA?

• How does DNA encode genetic information?• How is DNA duplicated so that information

can be accurately passed from one cell to its daughter cells?

• The secrets of DNA function, and therefore of heredity itself, can be found in the three dimensional structure of the DNA molecule.

Contribution made by Maurice Wilkins and Rosalind Franklin

• Wilkins and Franklin used X.ray diffraction to study DNA with X-rays recorded how the X-rays bounced off the DNA molecules.

• They deduced a lot of information about DNA from the pattern

• A molecule of DNA is long and thin, with a uniform diameter of 2 nanometers.

• DNA is helical; that is it is twisted like a corkscrew.• The DNA molecule consists of repeating subunits.• Based on this James Watson and Francis Crick proposed a

model for the structure of DNA

Structure of DNA

• DNA is composed of Four Nucleotides

DNA

• Structure of DNA

Structure of DNA• DNA is a double-helix: it has two strands that twist around

each other.• Each strand is a polymer of linked nucleotides.• Within each strand, the phosphate group of one nucleotide

bonds to the sugar of the next nucleotide in the strand.• This bonding pattern produces a “backbone” of alternating

covalently bonded sugars and phosphates.• Each strand is made of single units called nucleotides.• The nucleotide bases protrude from this sugar-phosphate

backbone.

-

• Each nucleotide in DNA consists of three parts: a phosphate group, a sugar called deoxyribose, and one of four possible nitrogen-containing bases – adenine (A), guanine (G), thymine (T), or cytosine (C).

• All of the nucleotides within a single DNA strand are oriented in the same direction. Therefore, the two ends of a DNA strand differ; ne end has a ‘free’ or unbonded sugar, and the other end has a “free” or unbonded phosphate

Nitrogenous Bases

Hydrogen Bonds Between Complementary Bases Hold the Two DNA Strands Together

• Watson and Crick proposed that two DNA strands are held together by hydrogen bonds that form between the two protruding bases of the individual DNA strands.

• The DNA strands are not straight, they are twisted about each other to form a double helix.

• The two strands in a DNA double helix are oriented in opposite direction.• Complementary Base Pairs:• Adenine forms hydrogen bonds only with thymine and that guanine forms

hydrogen bonds only with cytosine.• The presence of complementary base pairs expalians Chargaff’s results-

that the DNA of a given species contains equal amounts of adenine and thymine, as well a equal amounts of cytosine and guanine.

• Within a DNA strand, the four types of bases can be arranged in any linear order, and this sequence is wht encodes genetic information.

Complementary Base Pairs:

• Adenine forms hydrogen bonds only with thymine and that guanine forms hydrogen bonds only with cytosine.

• The presence of complementary base pairs expalains Chargaff’s results-that the DNA of a given species contains equal amounts of adenine and thymine, as well a equal amounts of cytosine and guanine.

• Within a DNA strand, the four types of bases can be arranged in any linear order, and this sequence is what encodes genetic information.

• All of the nucleotides within a single DNA strand are oriented in the same direction. Therefore, the two ends of a DNA strand differ; ne end has a ‘free’ or unbonded sugar, and the other end has a “free” or unbonded phosphate

Nitrogenous bases

• Nitrogenous bases are of two typesPurines and Pyramidines• Purines – Adenine (A) and guanine (G)• Pyramidines - thymine (T) and Cytosine ( C)

How to extract your own DNA?

• http://m.gizmodo.com/5889997/how-to-extract-your-own-dna-using-household-items

• I am sure you will have fun.• Watch the video and the demonstration and

follow the steps carefully and extract your own DNA.

• Awesome to watch your own DNA!!!!.

The order of Nucleotides in DNA can Encode vast amounts of Information

• Consider the many characteristics of just one organism.• How can the color of a bird’s feathers, the size and

shape of its beak, the ability to make a nest, its song, and its ability to migrate all be determined by a molecule with just four simple parts?

• It’s not the number of different subunits but their sequence that’s important.

• Within a DNA strand, the four types of bases can be arranged in any linear order, and this sequence is what encodes genetic information.

The Discovery of the Double Helix

• Read page number 154 in your text book and you can also refer to other Biology text book and form a time line for the discovery of DNA.

Differences between DNA and RNADNA RNA

a double- stranded molecule with a long chain of nucleotides

A single-stranded molecule and has a shorter chain of nucleotides

A-T(Adenine-Thymine), G-C(Guanine-Cytosine)

A-U(Adenine-Uracil), G-C(Guanine-Cytosine)

Found in nucleus Found in nucleus and cytoplasm

Sugar is deoxyribose. nitrogenous bases are A,T,C,G

Sugar is ribose. Nitrogenous bases are A,U,C,G

Transmission of hereditary material The main job of RNA is to transfer the genetic code need for the creation of proteins from the nucleus to the ribosome

DNA REPLICATION

• Key concept• DNA replication copies the genetic

information of a cell.• Replication copies the genetic information• Proteins carry out the process of replication• Replication is fast and accurate

The Replication of DNA is a critical event in a cell’s life

• Nearly every cell of our body contains identical genetic information-the same genetic information present in the fertilized egg.

• During the process of cell division, two daughter cells are formed from a single parent cell. Each daughter cell receives a nearly perfect copy of the parent cell’s genetic information.

• As a result, the parent cell must synthesize two exact copies of its DNA through a process known as DNA Replication.

• DNA replication produces two identical double helices, one of which will be passed to each of the new daughter cells.

Replication Process

1. Enzymes called DNA helicases begin to unzip the double helix at numerous places along the chromosomes called origins of replication. That is, the hydrogen bonds connecting base pairs are broken, the original molecules separates, and the bases on each strand are exposed.

-

• 2. now DNA strands complimentary to the two parental strands must be synthesized. One by one, free nucleotides pair with the bases exposed nucleotide pair in the template strand.

• DNA polymerases bond the nucleotides together and form new strands complementary to each template.

• DNA polymerase also connects these free nucleotides with one another to form two new DNA strands, each complementary to one of the parental DNA strands.

-

• When replication is complete, one parental DNA strand and its newly synthesized, complementary daughter DNA strand wind together into one double helix. At the same time, the other parental strand and its daughter strand wind together into a second double helix.

• In forming a new double helix, the process of DNA replication conserves one parental DNA strand and produces one newly synthesized strand. Hence, the process is called semiconservative replication

Semiconservative DNA Replication

http://www.mcb.harvard.edu/losick/images/trombonefinald.swf