DNA & RNA

Chapter 12

Page 287

12-1 DNA

All good scientists have questions.How do genes work?What are genes made out of?How do genes determine the characteristics

of organisms?

Scientists That Led to DNA’s Discovery 1928 Griffith

Wanted to learn how bacteria make people sick.

He tested mice with a harmless strand of bacteria. They lived!

He tested mice with disease causing pneumonia. They died!

Was it some sort of poison that the bacteria made that killed the mice?

Griffith Continued

He tested his hypothesis to see if the bacteria did secrete a toxic poison. He killed all of the bacteria with heat and injected it

into the mice. They lived! Conclusion: It wasn’t a toxin that killed the mice.

Next he tried mixing the heat killed bacteria and the harmless bacteria thinking the mice would live. They died! This led to the discovery of transformation.

Somehow the harmless bacteria had been transformed into the disease causing bacteria?!?!?!

Griffith’s Hypothesis

Some factor was transferred between the dead, disease causing bacteria and the live, harmless bacteria.

That factor must have contained information that could change harmless bacteria into harmful ones.

The ability to cause disease is inherited so the factor might be a gene!

1944 Avery

Repeated Griffith’s work to determine which molecule was require for transformation. Took heat killed bacteria and treaded it with enzymes

that destroyed everything but DNA. Transformation still occurred.

Repeated the experiment with an enzyme that destroyed DNA.

Transformation did not occur.

Conclusion

Avery discovered that DNA stores and transmits genetic

information from one generation to the next.

DNA

Now scientists wondered…How could DNA carry information from one

generation to the next?How does DNA put that information to work by

giving organisms their characteristics.How is DNA copied every time a cell divides?

Hhhhmmmmm……

Structure of DNA

DNA is a long molecule made up of nucleotides. A nucleotide is made of three basic components.

A sugar called deoxyribose. A phosphate group. A nitrogenous base (1 of 4 types)

Adenine (A) a large purine Guanine (G) a large purine Cytosine (C) a small pyrimidine Thymine (T) a small pyrimidine

You make one!

Gather 6 different colors of construction paper (one for each element of a DNA molecule).

Make 8 nucleotides by cutting, taping and labeling the parts of the molecule.

Once all 8 nucleotides are made call over Mrs. Haberman for approval before you proceed with connecting them into a strand of DNA. Turn to page 291 for a pattern to follow.

Chargaff’s Rule

He discovered that A=T and G=C in DNA molecules.

We call this base pairing. http://www.hhmi.org/biointeractive/dna/DN

Ai_chargaff_ratio.html

Add to your model.

Now create a corresponding chain of DNA to complement the one you’ve already made.

Start by making 8 nucleotides that will base pair A=T and G=C with the ones you’ve already made.

The Double Helix

Using Rosalind Franklin’s X-Ray image in the 1950’s, Watson and Crick discovered that DNA is in the shape of a double helix. A double helix is when 2 strands are wrapped around

each other. They also discovered that there are 2 hydrogen bonds

between A and T and three hydrogen bonds between G and C.

http://www.hhmi.org/biointeractive/dna/DNAi_watson_basepairing_anim.html

Using a line to represent the hydrogen bonds, connect the base pairs on your paper model.

12-2 Chromosome and DNA Replication Where is DNA found? How is it organized? Where are genes?

Where is DNA?

Prokaryotes lack a nucleus so the DNA is found in the cytoplasm.Usually a single circular DNA molecule.

Eukaryotes have a nucleus that contains the DNA.Can be unwound as chromatin or tightly coiled

as chromosomes.

How big is DNA?

Very long! See image on page 296.

The nucleus of a human cell contains more than 1 meter (3.3 feet) of DNA!

http://www.hhmi.org/biointeractive/dna/DNAi_packaging_vo2.html

DNA Extraction

Virtual Lab http://learn.genetics.utah.edu/content/labs/extraction/

See and touch real DNA!

http://learn.genetics.utah.edu/content/labs/extraction/howto/

DNA Replication

Watson and Crick realized that the double helix structure explained how DNA could be so easily copied or replicated. Each strand of DNA has the necessary information

needed to construct another strand by base pairing. The sites where separation and replication occur are

called replication forks. http://www.hhmi.org/biointeractive/dna/DNAi_replication_sch

ematic.html

Duplicating DNA

During DNA replication; The DNA molecule separates into 2 strands. Then it produces 2 new complementary strands by base pairing A=T

and G=C. Each strand serves as the template for the new strand being

created. EXAMPLE: strand TACGTT will make strand

ATGCAA Note that each DNA molecule contains one original strand and

one new strand! http://www.hhmi.org/biointeractive/dna/DNAi_replic

ation_vo1.html

Lets Review DNA!

What is DNA made of? How is it arranged?

Chapter 12-3 RNA & Protein

Gene Coded DNA instructions that control the making of

proteins within a cell. http://www.hhmi.org/biointeractive/dna/

DNAi_coding_sequences.html

So how do we decode these messages? The first step in decoding is to copy a sequence of

DNA and turn it into RNA. Ribonucleic acid.

The Structure of RNA

RNA is made up of a long chain of nucleotides.A ribose sugarA Phosphate And one of 4 bases (A, U, G, C)

DNA and RNA comparisons

DNA Deoxyribose sugar Made up of two

strands (double stranded).

Bases are A, T, G, C The master plan!

RNA Ribose sugar Made of one strand

(single stranded) Contains the base

uracil instead of thymine.

A, U, G, C

The blue prints!

RNA is…

A disposable copy of a segment of DNA. A working copy of a single gene. Responsible for making proteins.

Proteins are made by assembling amino acids.

Amino acids are the building blocks of proteins.

Types of RNA Messenger RNA mRNA

Carries the coded copy of a gene from the DNA inside the nucleus to a ribosome in the cytoplasm.

The blueprint of the master copy. Ribosomal RNA rRNA

This is where the proteins are put together. The construction site.

Transfer RNA tRNA Brings the amino acids to the ribosome.

It knows which amino acid to drop of from the coded message on the mRNA.

The construction workers that put the building together.

Let’s see what you remember

Activity time http://www.indiana.edu/~ensiweb/connections/

genetics/diy.dna.html

DNA base pair practice

On a piece of paper I want you to base pair the following DNA sequence.

TTAGCATCCGAT

_______________

How did you do?

Did you get

AATCGTAGGCTA

One more time…

Base pair

ACGTATCTGCTAGG

__________________

Now how did you do?

Did you get

TGCATAGACGATCC

Transcription

Transcription When a DNA code is turned into a

complementary strand of mRNA. Requires an enzyme known as RNA polymerase.

RNA polymerase separates the DNA strands where there is a “start” code.

http://www.hhmi.org/biointeractive/dna/DNAi_transcription_vo2.html

RNA base pairs

Remember that RNA does NOT have a T as a base. So when you transcribe DNA into mRNA it will look like this.

Transcription example

DNA = ATTAAACGTTGA

mRNA = UAAUUUGCAACU

Now you try

Transcribe the following DNA strand into mRNA.

DNA = ATTGCATGACATCAmRNA = __________________________

How’d you do?

Did you get

UAACGUACUGUAGU

One more time…

Transcribe

DNA = TTAGCGATTACGmRNA= _______________________

Now how did you do?

Did you get

AAUCGCUAAUGC

Proteins

Proteins are made by joining amino acids into long chains called a polypeptide.

The type of protein that’s made is determined by the order of the amino acids.

The Genetic Code

The “language” of mRNA instructions is called the genetic code.The code is written using 4 letters; A, U, G, C

How can a code with only 4 letters carry instructions for 20 amino acids?

http://www.hhmi.org/biointeractive/dna/DNAi_triplet_code.html

A Codon

The genetic code is written 3 letters at a time.

Each 3 letter “word” in in mRNA is known as a codon.Each codon (three consecutive nucleotides)

specifies a single amino acid.UCGCACGGU is read UCG-CAC-GGU (3 codons) Practice using the code wheel on page 303.

Translation

The instructions of mRNA must be “read” and put to use. This happens on a ribosome.

Decoding a mRNA message into a protein is called translation. Translation takes place on ribosomes.

Translation example

mRNA = CAUGCUUAGUCG Will be read by its codons

CAU-GCU-UAG-UCG

tRNA anticodons GUA-CGA-AUC-AGC

would be

Protein Synthesis Steps pg. 304

First, mRNA is transcribed in the nucleus from our DNA. The mRNA leaves the nucleus to find a ribosome in the cytoplasm. The mRNA moves through the ribosome one codon at a time. A tRNA drops off the amino acid it’s instructed to by base pairing

with their anticodons. The three letter code on a tRNA.

The polypeptide chain continues to grow until it reaches a stop codon.

The completed protein is then released. http://www.hhmi.org/biointeractive/dna/DNAi_translation_vo2.html

Let’s put the story together!

Now you will make a protein synthesis story book, song, skit, etc.

You make work alone or in a small group for the skit or a team of two for the song.

Make your story complete and be sure to tell the whole story. From transcription to translation.

You will be graded on creativity, ability to hold the interest of your audience, thoroughness and accuracy.

Protein Synthesis Game

Race the cellhttp://nature.ca/genome/04/041/041_e.cfm

So what do proteins have to do with me? Everything!

Many proteins are enzymes which regulate chemical reactions.

A gene that codes for an enzyme to produce pigment can control the color of a flower.

Genes for certain proteins regulate the rate and pattern of growth, controlling its size and shape.

Proteins are microscopic tools, each specifically designed to build or operate a component of a living cell.

Chapter 12-4 pg. 307

MutationWhen a cell makes a mistake copying its

DNA, inserting an incorrect base, or skiping a base.

Two types, gene and chromosomal.

Gene Mutations (humans have thousands of genes) Point mutations

When a base at a single point is changed in a gene.

Substitutions (one base is changed to another) Usually only affects a single amino acid.

Insertions (an extra based is added) Deletions (a base is left out)

Insertions and deletions are much more dramatic!

Gene Mutations con’t

Frameshift mutations Insertions and deletions shift the “reading

frame” around the codons.This can change EVERY amino acid after the

mutation. This can alter a protein so much that its unable to

perform its normal function.

See page 307 for examples

Chromosomal Mutations

Involve changes in the number OR structure of chromosomes.Humans have a total of 46 chromosomes.

See page 308 for examples

Significance of Mutations Most mutations are neutral.

Have little or no effect on the genes expression.

Some are harmful when they produce defective proteins.

Can cause human genetic disorders. Associated with different types of cancer.

Helpful mutations are the key to evolution. They help an organism survive in its environment.

Video clip (mutations)

http://www.powermediaplus.com/streaming/digitalVideoDetail.asp?videoID=6540&mode=browse&sections=all&searchFor=mutations&type=streaming&theSubjectID=736

Mutation Game

http://nature.ca/genome/04/0413_e.cfm