Chapter 12: Molecular Genetics DNA structure DNA structure Replication Replication Protein synthesis...

Chapter 12: Chapter 12: Molecular GeneticsMolecular Genetics

• DNA structureDNA structure

• ReplicationReplication

• Protein synthesisProtein synthesis

DNA: The Genetic DNA: The Genetic MaterialMaterial

Section 1 – p. 329

The “OLD” people of DNA

1.Fredrick Griffith

2.Oswald Avery

3.Hershey and Chase

4.Erwin Chargaff

5.Watson and Crick

Fredrick Griffith-1928

In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused pneumonia.

He isolated two different strains of pneumonia bacteria from mice and grew them in his lab.

Performed the first major experiment that led to the discovery of DNA as the genetic material

So Griffith, Avery, Hershey and Chase all helped discover DNA and the importance that it plays in transferring Genes.

But what is DNA???

what is it made of???

what does it look like??????

What is DNA?1. A genetic code

2. A molecule made of subunits called nucleotidesnucleotides

3. A complex molecule that is arranged as a double helixdouble helix.

NUCLEOTIDES

are repeating subunits are repeating subunits (monomers) that include:(monomers) that include:

Phosphate group

5-Carbon sugar

Nitrogen base

NUCLEOTIDES

the smallest subunit of DNA

Two Kinds of bases in DNA

Pyrimidines are single ring bases.

Thymine & Cytosine

Purines are double ring bases.

Adenine & Guanine

Memory trick “Y” are you single?

A G C T

Erwin Chargraff-

Analyzed the amounts of A, C, T, and G in DNA; Discovered A=T & C=G

The Shape of DNA

DNA often is compared to a twisted ladder.

Rails of the ladder are represented by the alternating deoxyribose and phosphate.

The pairs of bases (cytosine–guanine or thymine–adenine) form the steps.

Watson and Crick

Built a model of the double helix that conformed to the others’ research

1. two outside strands consist of alternating deoxyribose and phosphate

2. cytosine and guanine bases pair to each other by three hydrogen bonds

3. thymine and adenine bases pair to each other by two hydrogen bonds

Watson and Crick

suggested the structure for DNA and Hypothesized a method of replication

Refer to the DNA handoutRefer to the DNA handout

1. Locate the Phosphate groupsPhosphate groups (small circles). Label each one with “PP”

2. Color all phosphate groups orangeorange

3. Locate the deoxyribose sugardeoxyribose sugar molecules (large pentagon shapes attached to the P’s). Label them by name.

4. Color all sugars blueblue


1.Locate the nitrogen bases. Label the first base by name and the others “NB”.

2.What do you notice about these molecules?

4 Nitrogen Bases4 Nitrogen BasesPurines are

larger basesPyrimidines are

smaller bases

Adenine Thymine

Guanine Cytosine


1. Locate the nitrogen bases – 2 large, 2 small

2. Label one of the large bases AdenineAdenine

3. Label the other large base GuanineGuanine

4. Label one of the smaller bases ThymineThymine

5. Label the other small base CytosineCytosine

6. Color each base a different color.

CHARGAFF’S BASECHARGAFF’S BASE PAIRING RULES

A binds with T

G binds with C

Hydrogen Bonds

Fig. 4. Adenine-Thymine base pair with two hydrogen bounds.

Fig. 5. Guanine-Cytosine base pair with three hydrogen bounds

C = Carbon = gray N = Nitrogen = blue O = Oxygen = red

3-D Animation of DNA

http://www.umass.edu/molvis/tutorials/dna/dnapairs.htm

Stop & ReviewStop & Review1. What is the smallest subunit of DNA?

2. List 3 parts to #1?

3. What are the side chains of DNA made of?

4. What are the “steps” of DNA made of?

5. What are the base pairing rules of DNA?

6. Describe the structure of DNA in 2 words.

ANSWERS

1.Nucleotide2.Sugar, phosphate and a

nitrogen base3.Sugar and phosphate4.Nitrogen base5.A=T, C=G6.Double Helix

How are genesgenes, chromosomes and DNA related?Genes are portions of DNA that are tightly packed into chromosomes and code for the manufacture of proteins.

How are genesgenes, chromosomes and DNA related?

Think of chromosomes as socks and genes as stripes on the socks.

Place in order from smallest to largest.

Gene

DNA

Chromosomes

Have Your DNA & eat it too!Have Your DNA & eat it too!

1.Collect materials

2.Follow instructions

*A (pinkpink) pairs with T (greengreen)

*C (orangeorange) pairs with G (yellowyellow)

Semi-conservative Semi-conservative replicationreplication

Part 2

Essential Questions

What is replicationreplication and how is it done?

What’s the role of the enzymes helicasehelicase and DNA polymeraseDNA polymerase?

ReplicationReplicationA complete copy of the

DNA is made

The DNA code is in the middle of the helix, so how does it get copied if it’s obscured by the side chains and twist of the helix shape?

Replication

DNA replication is an important part of the cell division process.

Before a cell divides, it first duplicates its DNA so that the new cell will have the same genetic information.

The specific base pair matching during replication ensures that exact DNA copies are made.

The DNA code is in the middle of the helix, so how does it get copied if it’s obscured by the side chains and twist of the helix shape?

Replication1. Enzymes (helicasehelicase) will “unzip” or

unwind the double helix by weakening H-bonds creating a replication fork replication fork where the two chains separate

2.2. DNA polymeraseDNA polymerase assembles new DNA using each original strand as a template

3. The replicated DNA is proofread and mistakes are edited

Replication

ReplicationReplication forkfork

Boring person explaining

Replication is discontinuousReplication is discontinuous

Short fragments of DNA called Okazaki fragmentsOkazaki fragments are added near the replication fork

Then gaps are filled in by DNA DNA polymerasepolymerase

Bases are added following the base pairing rules (A-T, C-G)

* The lengths of Okazaki fragments are between 1,000 to 2,000 nucleotides long in bacteria and are generally between 100 to 200 nucleotides long in eukaryotes.

Copy the following sequence to your foldable.

T--T--

A--A--

C--C--

A--A--

A--A--

A--A--

C--C--

T--T--

T--T--

A--A--

C--C--

T--T--

--A--A

--T--T

--G--G

--T--T

--T--T

--T--T

--G--G

--A--A

--A--A

--T--T

--G--G

--A--A

Remember that H-bonds hold complementary bases together

Unzip sequence to your foldable.

TT

AA

CC

AA

AA

AA

CC

TT

TT

AA

CC

TT

AA

TT

GG

TT

TT

TT

GG

AA

AA

TT

GG

AA

Step 1: HelicaseHelicase enzyme “unzips” double helix by weakening H-bonds

Using the original DNA sequence on the foldable make a copy.

TT

AA

CC

AA

AA

AA

CC

TT

TT

AA

CC

TT

AA

TT

GG

TT

TT

TT

GG

AA

AA

TT

GG

AA

Step 2: DNA DNA polymerase polymerase enzyme adds DNA bases to the exposed nucleotides on the leading strand

AA

TT

GG

TT

TT

TT

GG

AA

AA

TT

GG

AA


TT

AA

CC

AA

AA

AA

CC

TT

TT

AA

CC

TT

AA

TT

GG

TT

TT

TT

GG

AA

AA

TT

GG

AA

While Okazaki Okazaki fragmentsfragments are added on the lagging strand

AA

TT

GG

TT

TT

TT

GG

AA

AA

TT

GG

AA

AA

CC

AA

AA

CC

AA

CC

TT


TT

AA

CC

AA

AA

AA

CC

TT

TT

AA

CC

TT

AA

TT

GG

TT

TT

TT

GG

AA

AA

TT

GG

AA

Step 3: Polymerase Polymerase also proofreads and edits any gaps

AA

TT

GG

TT

TT

TT

GG

AA

AA

TT

GG

AA

T T

AA

CC

AA

A A

AA

CC

T T

TT

AA

CC

TT

RESULTS

TWO strands of identical DNA

DNA replication is known as semiconservative meaning each DNA molecule contained one original strand an one new strand.

Have Your DNA & eat it too!

1.Now replicate the DNA, using 2 more pieces of licorice but use black sticks

3-2-13 steps cells undergo in replication

2 words meaning the structure of DNA

1 word for duplicating cell DNA

Protein synthesisProtein synthesisPart 3

Warm-Up Quiz: DNA Warm-Up Quiz: DNA 101101

1. DNA is a double stranded sequence of ___________ (smallest unit of DNA).

2. DNA is a code of instructions for building ___________ (molecule).

3. DNA is stored in the _________ (control center of the cell).

4. The DNA code must be transmitted to the ___________ where proteins are built. Today we’ll see how this happens.

Essential Questions

7. What is the primary function of DNA?

8. How do RNA and DNA compare?

9. What are the three main types of RNA? What are their roles?

10. How do the base-pairing rules for RNA compare to the rules for DNA?

11. Describe the roles of DNA and RNA in the overall process of protein synthesis.

The role of DNA is to store and transmit genetic information

How do DNA & RNA compare?How do DNA & RNA compare?

RNA

Ribose sugar & phosphate “backbone”

URACIL replaces thymine

Single-stranded, globular, hairpin (huh? Hairpin???)

DNA

Deoxyribose sugar & phosphate “backbone”

N-bases: A, C, G, T

Double helix

Check your understanding…Decide with your partner whether the following describes DNA or RNA:

1. Master Plan

2. Blueprint copy

3. Stays in nucleus

4. Goes to ribosome

5. Involves Thymine

6. Involves Uracil

7. Single-stranded

8. Double-stranded

9. Involves codons

10.Polymerase

Types of RNATypes of RNA

Messenger RNA

(mRNA)The original DNA

code is transcribed then carried from the nucleus to the

ribosome.

mRNA is written in the form of

codonscodons.


Transfer RNA (tRNA)The anticodonanticodon that matches the codon found on mRNA.

It transfers an amino acid in order

to assemble a protein chain.


RibosomalRNA

(rRNA)RNA &

proteins that make up

ribosomes where

proteins are made.

Base Pairing in DNA vs. RNABase Pairing in DNA vs. RNA

RNA

A - Uracil

C - G

DNA

A - T

C - G

PROTEIN PROTEIN SYNTHESIS SYNTHESIS

Step 1 Transcription

Step 2 Translation

Step 1: TRANSCRIPTION DNA is changed into a different form

of nucleic acid called RNA (ribonucleic acid)

The new code is “read” 3 nucleotides at a time called a codoncodon

Occurs in the nucleus

Why? Because mRNA can leave the nucleus whereas DNA cannot.

TRANSCRIPTIOTRANSCRIPTIONN1. Enzymes unzip helix

2.2. RNA polymerase RNA polymerase assembles mRNA nucleotides but base pairing rules changes slightlya. Thymine in DNA pairs with Adenine

b. Adenine in DNA pairs with UracilUracilc. Cytosine still pairs with Guanine

T - -

A - -

C - -

A - -

A - -

A - -

C - -

T - -

T - -

T - -

G - -

A - -

DNA

U

A

C

A

A

A

C

U

U

U

G

A

mRNA

A

T

G

T

T

T

G

A

A

A

C

TCo

py

the

foll

ow

ing

DN

A s

equ

ence

.

Write th

e com

plem

entary n

ucleo

tide seq

uen

ce.

Slide

- - A

- - T

- - G

- - T

- - T

- - T

- - G

- - A

- - A

- - A

- - C

- - TWri

te t

he

com

ple

men

tary

co

do

n s

equ

ence

.

Step 1: HelicaseHelicase enzyme “unzips”

double helix by weakening

H-bonds

Step 2: RNA RNA polymerase polymerase

enzyme forms complementary mRNA strand

Step 2: Step 2: TRANSLATIONTRANSLATION The language of DNA is

translated into the language of amino acids

Occurs in the cytoplasm on a ribosome

TRANSLATIONTRANSLATION

1. The mRNA travels to the ribosome where each codon is read

2. The codon of mRNA matches an anticodonanticodon on tRNA

3. When the codon and anticodon match the amino acid being carried by the tRNA is transferred to a growing protein chain.

Let’s use your foldable from before.A

T

G

T

T

T

G

A

A

A

C

T

DNA

U

A

C

A

A

A

C

U

U

U

G

A

mRNA

Open the foldable and translate the mRNA code into the correct amino acid sequence.

The translation…A

T

G

T

T

T

G

A

A

A

C

T

DNA

U

A

C

A

A

A

C

U

U

U

G

A

mRNA

LeucineLeucine

LysineLysine

TyrosineTyrosine

STOPSTOP

Central Dogma of BiologyCentral Dogma of Biology

DNA codes for RNA, which guides the synthesis of proteins.DNA RNA Protein1.DNA is unzipped

2.RNA polymerase uses DNA as a template for making mRNA (Uracil is incorporated instead of thymine)

3.mRNA moves out of nucleus to ribosome

4.tRNA carries amino acids to ribosome where they are assembled into a peptide chain

5.Upon reading a STOP codon, the complete protein chain is released

Now consider this…

1. On a sheet of paper, write the word CATS.

2. Try rearranging the letters to form as many 3-letter words as you can.

3. Write each word on your paper, and then add a definition for each word.

4. Did any of the codes you formed have the same meaning?

The DNA AlphabetThe DNA Alphabet

• Like CATS, there are only 4 nitrogen bases in the DNA alphabet.

• Like the CATS activity, DNA “words” are only 3-letters. These triplet base sequences are called codonscodons.

How many codons can be made using the four letters of the four different bases? Hint: A codon is made up of 3 nucleotides. So there are 3 spots and a possibility of 4

bases in each.4 bases x 4 bases x 4 bases

= 64 possible codon combinations.

Since the nitrogen base is the only unit to change, the sequence of bases makes up the

code.

BRAIN TEASERBRAIN TEASER

How is DNA How is DNA like Morse like Morse code?code?

How is DNA How is DNA like Morse like Morse code?code?

It is a series of single repeating units (sounds or symbols) that make up a message. The repeating units are the nucleotides of the DNA molecule. The message is the final protein that is produced. Proteins can be structural, enzymatic, hormones, etc.

Chapter 12: Molecular Genetics DNA structure DNA structure Replication Replication Protein synthesis...

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