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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 replication
Be 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
Be
Be
Be
Be
able to sequence the steps in protein synthesis
able to distinguish between different types of mutations
able to describe the effect of genetic mutations
able to describe the causes of mutations
familiar with how DNA is repaired.
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Cracking the Code of Life
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UNDERSTANDING DNA
History 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
Process by which
bacteria takes up foreign DNA
 Non-Virulent bacteria become
Virulent (disease causing)
 Descendents of the transformed
cells also virulent.

Transformation:
Transformed bacteria
1.Infected
with nonvirulent
2.
Mice
bacteria
infected
.
with live,
virulent
bacteria.
3. Mice
infected
with
heatkilled
bacteria.
4.Infected
with live,
nonvirulent
AND heatkilled
bacteria.
Mouse dies
FROM
TRANSFORMED
BACTERIA
.
Oswald Avery
(1944)
Protein or
DNA?
*DNA is the
Genetic
material.
Oswald Avery
 Protein
 Did
vs. DNA?
same type of experiments as Griffith,
but treated with protein and DNAdigesting enzymes.
 RESULTS: Treatment with proteindigesting enzymes-- bacteria still
transform
Treatment with DNA-digesting
enzymes-not able to transform
 Concluded that DNA, not protein,
transforms bacteria
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)
virus particle
labeled with 35S
virus particle
labeled with 32P
bacterial cell (cutaway view)
label
outside cell
label inside cell
Structure of the
Hereditary Material Still
Was a Mystery
1953
Nobel Prize
James 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
 The
like a coiled spring.
molecule coils into this
– shape as a result of the
– base bonding.
Rosalind Franklin’s
Work was Critical
Expert
DNA
in x-ray images
was some sort of helixlike a tightly coiled spring
Structure

DNA:polymer of nucleotides (4)
Nucleotides
Sugar (deoxyribose)
 Phosphate
 Nitrogen base

 Forms
2 long parallel chains
of nucleotides
covalently bonded (chains)
Sugar –to -phosphate
Phosphate-sugar-phosphate-sugarphosphate…..
 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 cytosine
T thymine
A adenine
G 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?

Base Pairing
or
or
one base pair
in-text, p. 195
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
– Color code:
and plain paper.
–
–
–
–
–
–
–
–
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:
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.
Semiconservative
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.
Relication preserves
the sequence of bases
in organism’s DNA.
new
old
old
new
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
 1.
result from:
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, hair
 Enzymes: 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.
What was (is) the
DNA
Contains instructions
for
molecular
cause of
making proteins.
Lorenzo’s disease?
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
RNA
Cytosine
Cytosine
Adenine
Adenine
Guanine
Thymine
Guanine
Uracil
An analogy:
DNA : Project Engineer
RNA’s: The workers.
Production
site:
.
ribosomes
Product: 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
steps
1.
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.
 ..\Bio
1\DNA\DNA animation
link.mht
GENE EXPRESSION
Transcription Translation
Transcription Practice
We’ll
DNA
make an mRNA from
---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
Universal
all 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 Practice
Directions: 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 Practice
Directions: 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:
GGUAUG CCU UCG GAG UUA ACA GCG UAA
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