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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
Refer to the DNA handoutRefer to the DNA handout
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
Refer to the DNA handoutRefer to the DNA handout
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
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
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
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 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.
Types of RNATypes of RNA
Transfer RNA (tRNA)The anticodonanticodon that matches the codon found on mRNA.
It transfers an amino acid in order
to assemble a protein chain.
Types of RNATypes of RNA
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.