.Chapter 11:

Understanding DNA

CHAPTER 11: DNA AND GENES LEARNING OBJECTIVES

In addition to reading this material , you are expected to do all of the Section Assessment questions, as well as all of the Chapter 11 Assessment Questions, and the Standardized Test Practice in your textbook

We will do a project related to this chapter. You will research and prepare a brief biography for one individual who contributed to our current knowledge of DNA or Heredity. This will be due on Tuesday, Feb 27. To create a class Timeline of DNA Discoveries.

Be familiar with those scientists that largely contributed to discovering the structure and nature of DNA.Understand the structure of DNA, its components, bonds.Be able to describe DNA replicationBe able to describe the significance of the nucleotide sequence between organisms.Be able to describe ways that nucleotide sequencing is useful to scientists and you

Be able to sequence the steps in protein synthesisBe able to distinguish between different types of mutationsBe able to describe the effect of genetic mutationsBe able to describe the causes of mutationsBe familiar with how DNA is repaired.

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UNDERSTANDING DNAHistory of Research

Mendel 1860’s--traits passed parent to offspring

Others: set out to identify the substance responsible

Transformation-Genetic material could be transferred to another organism

1928 Fredrick Griffith Discovers that Genetic material could be

transferred to another organism Transformation: Process by which

bacteria takes up foreign DNANon-Virulent bacteria become

Virulent (disease causing)Descendents of the transformed

cells also virulent.

Transformed bacteria

.

1.Infected with non- virulent bacteria 2. Mice

infected with live, virulent bacteria.

3. Mice infected with heat-killed bacteria.

4.Infected with live, nonvirulent AND heat-killed bacteria. Mouse dies FROM TRANSFORMED BACTERIA

Oswald Avery (1944)

Protein or DNA?

*DNA is the Genetic material.

.

Oswald AveryProtein vs. DNA? Did same type of experiments as Griffith,

but treated with protein and DNA-digesting enzymes.

RESULTS: Treatment with protein-digesting enzymes-- bacteria still transform

Treatment with DNA-digesting enzymes-not able to transform

Concluded that DNA, not protein, transforms bacteria

virus particle labeled with 35S

virus particle labeled with 32P

bacterial cell (cutaway view)

label outside cell

label inside cell

1952: Hershey & Chase Reconfirm DNA is the Genetic Material.

They Infected bacteria with Labeled Viruses (radioisotopes of Sulfur and Phosphorous)(protein contains sulfur; DNA contains Phosphorous)

Structure of the Hereditary Material Still Was a Mystery

1953 Nobel PrizeJames Watson Francis Crick

Maurice Wilkins

Watson & Crick Developed Accurate Model

Double helix shape

Two strands of nucleotides

Like a spiral staircase

Watson-Crick Model

2 Strands of nucleotides

– Sugar and phosphates covalently bonded to

one another.

2 Strands held together by

hydrogen bonds between bases (rungs

on a ladder)

Shape of a double helix

Twisted like a coiled spring.

The molecule coils into this – shape as a result of the– base bonding.

Rosalind Franklin’s Work was Critical Expert in x-ray images

DNA was some sort of helix-like a tightly coiled spring

Structure DNA:polymer of nucleotides (4)

NucleotidesSugar (deoxyribose)PhosphateNitrogen base

Forms 2 long parallel chains of nucleotides covalently bonded (chains) Sugar –to -phosphate

Phosphate-sugar-phosphate-sugar-phosphate…..

The sugars and phosphates are held together by strong covalent bonds.

The bases hold the 2 strands together– The bases are held together by

HYDROGEN BONDS( WEAK).– They form the “rungs” of the

ladder-like shape.

DNA Structure

2 strands of nucleotides

Nucleotides bond (strong-covalent bonds) together to form 2 long chains

Each chain connected in the middle by (weak) hydrogen bonds

DNA-Made of 4 different. Nucleotides ( Nucleotides have 3 parts

–1 A sugar-deoxyribose–2. Phosphate Group–3. A Base (4 kinds)

–(draw and color in– your notes)

4 different nitrogeneous bases

C cytosineT thymineA adenineG guanine

Pattern of Base Pairing“Chargaff ‘s Rule” (1949)

–Amount of adenine always equals

amount of thymine and amount of

guanine always equals amount of

cytosine

A=T and G=C

Base Pairing

C with G

A with T

ALWAYS TRUE

DNA in cells

Where is it found? Does it leave? Why/why not?

Does a cell ever need to make more DNA?

Why? When?

one base pair

in-text, p. 195

or or

Base Pairing

The Importance of Nucleotide Sequences

All organisms DNA made of the same 4 bases

Vary in the– Sequence of the bases – Amount of DNA

The closer the relationship, the more similar the DNA sequences.

Useful:– Determine evolutionary relationships– Determine whether 2 people are related– Crime scene investigation

NAME:______________ DNA QUIZ 1. What is Chargoff’s rule?_____________________________________ 2. Who constructed the first accurate model of DNA?___________________________ 1. List the three parts of a DNA nucleotide

1.2.3.

4. Nucleotides are the ________from which the Nucleic Acid polymers DNA and RNA are Made.

5. Nucleotides link together to form 2 sides of the DNA molecule ( like 2 sides of a ladder). The sugars and phosphates are held together by strong _____________bonds.

6. The bases hold the 2 strands together. The bases are held together by weak ________________bonds.

7. Why did use radioactive phosphate in their research to confirm that DNA and not protein was the “material of transformation & inheritance”?

____________________________________________________________

8. _______________is the process by which bacteria takes up foreign DNA 9. _________________are viruses that infect bacteria. 10. How does the DNA in YOU differ from the DNA in a tomato plant? (choose a or b)

– A) in tomato plants there are different nucleotides– B) In tomato plants, the nucleotides are assembled in a different way, but using

the same 4 nucleotides as in people

Problem Solving Lab 11.1 page 283

WE WILL BEGIN CONSTRUCTING A DNA MOLECULE-need 8 different colored pencils and plain paper.– Color code:

– Phosphate = yellow– Sugar= pink– Covalent Bonds=purple – Hydrogen Bonds =pencil– Adenine=green– Thymine=red– Guanine= orange– Cytosine=blue

Make 2 chains of P-S-P-S (20/each long)– (covalent bonds).

Leave 2 inches between the 2 strands.

Replication of DNA

DNA in cells

Where is it found? Does it leave? Why/why not?

Does a cell ever need to make more DNA?

Why? When?

Discussion questions

What if DNA was not replicated BEFORE MITOSIS?

What if DNA was not replicated BEFORE MEIOSIS?

Look at Figure 11.4 When a DNA molecule replicates, 2

molecules are formed.– DNA replication produces _____ molecules

from one. Each molecule has one original strand,

and one new strand. Please draw the first 2 steps of fig 11.4 in

your notes—use 2 colors. Why are you using 2 colors??

DNA REPLICATION-THE PROCESS OF COPYING DNA

Preserves the sequence of bases in an organism’s DNA

There are basically 2 steps…

HOW DNA IS COPIED

First Step:First Step:

Replication bubble forms: An enzyme breaks the hydrogen bonds between bases.

Unzips a section of the double helix, exposing the bases.

.

Step Second :

DNA polymerase (an enzyme) moves along the 2 strands, pairing complementary bases to the exposed nucleotides

one parent DNA strand

.

This process continues until the entire DNA molecule has unzipped and been copied.

WHY MUST DNA BE UNZIPPED BEFORE IT CAN BE COPIED?

DNA REPLICATION

Result is 2 identical DNA molecules.

Semi-conservative

Replication-recap

The 2 original strands serve as templates for 2 new strands.

Follow base-pairing of Chargaff’s rule.

Two complete DNA molecules result from replication.

newnew old old

Relication preserves

the sequence of bases

in organism’s DNA.

Problem to do:

If the sequence of nitrogenous bases on one strand of a DNA molecule is :

CCGAATGATTTG

What would be the sequence of bases on the complimentary strand?

Take out the DNA strand you began constructing earlier.

Mutation-An alteration in DNA structure

May result from: 1. Errors during replication

– OR 2. Mutagens: an environmental agent

Section 11.2 DNA to Protein

DNA controls cells HOW?

– Encoding instructions for making proteins

– Proteins and their functions:Structural: muscles, hairEnzymes: control chemical reactions

in organisms– Cellular respiration, photosynthesis,

digesting food, controlling cell cycle

Genes

Segment of DNA that controls protein production.

The specific nucleotide sequence is a “recipe” for a particular protein.

Using DNA

What was (is) the molecular cause of Lorenzo’s disease?

DNA Contains instructions for making proteins.

Recall that proteins are built on __________IN THE CYTOPLASM.

So how can we accomplish the protein building task?

RNA is the link (let’s make a double bubble using RNA and DNA)

A nucleic acid Single stranded molecule Sugar is RIBOSE Polymer

– Monomers are nucleotides– C, U, A, G

U=Uracil—it replaces Thymine– U base pairs with _________

3 kinds of RNA Carry out the job of protein

assembly

Nucleotide Base Comparison

DNA

CytosineGuanineAdenineThymine

RNA

CytosineGuanineAdenineUracil

An analogy: DNA : Project

EngineerRNA’s: The workers.Production site:

ribosomesProduct: proteins

.

3 types of RNA

1. mRNA: messenger RNA– Copies a segment of DNA, brings

it to ribosome 2. rRNA: part of the ribosome

– binds to rRNA, reads it. 2. tRNA: transfers amino acids

to ribosome for assembly.

How Proteins are made

Gene Expression– Using the genetic information in DNA to make proteins.

Gene Expression-2 steps1. Transcription: Copying a

portion of DNA to form an mRNA (using RNA Nucleotides)

2. Translation: 3 kinds of RNA work together to assemble amino acids into a protein molecule.

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GENE EXPRESSIONTranscription Translation

Transcription PracticeWe’ll make an mRNA from DNA

---afterward, we will learn about the UNIVERSAL GENETIC CODE” AND

Then “translation”

Transcription: page 290

1. enzymes unzip the DNA in the region of the gene to be transcribed.

2. Free nucleotides complimentary base pair with one strand of the DNA.

THE rRNA strand breaks away & the DNA zips back up.

rRNA leave nucleus, goes to cytoplasm.

Plan for Today

Demonstrate proficiency in translation (step 2 of protein synthesis).

Do this by completing activity following instruction.

15-20 minutes of Lorenzo’s oil. Watch for effects of treatment with monounsaturated fats.

The Genetic Code-Secret codes for amino acids.

Nearly Universalall organisms use the

same code

CODON = each mRNA triplet

“The Central Dogma of Biology”

DNA mRNA Protein

Protein Synthesis: Part 2. Translation

Translating the mRNA into a sequence of amino acids to form a protein.

All three RNA’s take part.

ROLES OF RNA’S IN TRANSLATION

mRNA has the codon

tRNA carries the amino acids & translates the codon– 20 different kinds– 20 different amino acids– Has a nucleotide sequence

complimentary to mRNA called an ANTICODON

rRNA is part of the ribosome

tRNA

Each kind of tRNA carries only _____type of _________.

Amino acid carried at one end.

Three- base ANTICODON.

This pairs up with an mRNA codon during translation.

Now, theTRANSLATION STEPS

1. A ribosome attaches to an mRNA strand.

2. Amino acids brought to the ribosome by tRNA.

The codon AUG codes for Methionine and signals the “start” to translation.

The tRNA carrying Methionine attaches to the ribosome, translates with its Anticodon _____.

3. The ribosome slides over the mRNA to the next codon.

4. A new tRNA attached next on the mRNA, translates with its anticodon, releases its corresponding amino acid which bonds to Methionine.

4. Translation continues until a “stop” codon is reached.

5. Complete protein detaches from ribosome.

4. mRNA disassembles , so nucleotides can be reused.

Translation PracticeDirections: Underline the codons beginning with the start codon. Identify the corresponding anticodon and amino acid. Join the amino acids into a chain.

Amino acid

anticodon

mRNA: G G U A U G C C U UC G G A G U U A A C A G C G UA A

Translation PracticeDirections: Underline the codons beginning with the start codon. Identify the corresponding anticodon and amino acid. Join the amino acids into a chain.

Amino acid-------Met Proline Serine Glut Phen Threo Alanine Stop

Anticodon C C A U A C G G A A G C C U C A A U U G U C G C A U U

mRNA: G G U A U G C C U U C G G A G U U A A C A G C G U A A

.

On bottom end, is an anticodon - a nucleotide sequence complimentary to mRNA.

tRNA base pairs with a mRNA codon

On top is the corresponding Amino Acid.

.

,

Section 11.3 Genetic Changes

Mutations: change in ________ sequence

Cuused by – Errors in relpication– Errors in transcription– Errors in cell division– External egents

Mutations in reproductive cells

Passed on to offspring if mutations occur in ________or __________cells

Rarely have a positive effect

– Important in evolution-if it permits enhanced survival capability in its environment.

Mutations in body cells

Not passed on to _____________> But may cause problems for the

individual. Passed on in cell division. If genes controlling cell division

are affected, may lead to _______.

Point Mutations

A change in a single ____ ____.

May change the structure of a protein & its function.

THE DOG BIT THE CAT THE DOG BIT THE CAR

Frameshift Mutation

The addition or ________ of a single base .

Each codon after this would be affected—shifted.

It shifts the reading codons.

More harmful than point mutations.

WHY???

Practice Problems

Figure 11.1; answer question and prepare explanations.

Problem Solving Lab 11.3 p. 299.

Problem Solving Lab 11.2 p. 300.

Figure 11.3

Review

Structure of nucleotide Structure of DNA Where are Hydrogen bonds

found in DNA molecules. All the other bonds are

Covalent Bonds.

GENE EXPRESSION