Download DNA

Ch. 12
The Structure and Function of DNA
and RNA
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Section:
Interest Grabber
Section 12-1
Chapter 12
DNA and RNA
Check your knowledge….
1.
What organelle is the control center of the cell?
2.
What are the “X” shaped structures found in the nucleus called?
3.
What are located on chromosomes “also called factors”?
4.
How do genes and chromosomes control the activity of the cell?
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Section:
DNA
Deoxyribonucleic acid (DNA) is a nucleic acid that contains the
genetic instructions used in the development and function of all
known living organisms.
•Found in the nucleus of eukaryotic cells
•Responsible for storing and transmitting genetic information (instructions)
•Allows the transmission of genetic information from generation to
generation
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Section:
DNA
Where is DNA located?
1. The nucleus contains chromosomes (look like “X’s”).
2. Chromosomes contain a nucleic acid called DNA.
3. DNA portions make genes (look like “bands”)..
Large to small 
Nucleus Chromosomes DNA Genes
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Section:
Figure 12-10 Chromosome Structure
of Eukaryotes
Section 12-2
Chromosome
DNA
double
helix
Coils
Genes
Supercoils
Histonesproteins
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Section:
Structure of DNA
In 1953 James Watson and Francis Crick made a model
of DNA called a double helix, in which two strands
wound around each other.
This was important because it shed light on how DNA
carries information and how the information can be
copied during cell division.
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Section:
Figure 12–7 Structure of DNA
Section 12-1
•Hydrogen bonds
can only form
between certain
nitrogenous
bases.
Adenine-Thymine
Cytosine-Guanine
A-T
C-G
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
This is called base
pairing.
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Section:
Cytosine (C)
Guanine (G)
Figure 12–5 DNA Nucleotides
Section 12-1
Purines
Adenine
Guanine
Phosphate
group
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Section:
Pyrimidines
Cytosine
Thymine
Deoxyribose
Replication
Problem:
I need to get my grades to the front office for Mrs. Morton. If I do not
get my grades down to the office report cards can’t go home. How
can I get the information down to the office?
• I cannot leave the room because I have to supervise the class.
•My gradebook is the master copy and it must not leave the room.
•My computer is not working so I cannot email the grades.
•Mrs. Morton is having eye problems and cannot read handwriting
easily.
What should we do?
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Section:
Interest Grabber
Section 12-2
A Perfect Copy
When a cell divides, each daughter cell receives a
complete set of chromosomes. This means that each
new cell has a complete set of the DNA code. Before a
cell can divide, the DNA must be copied so that there
are two sets ready to be distributed to the new cells.
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Section:
DNA Replication
DNA Replication
During DNA replication , the DNA molecule separates
into two strands, then produces two new
complementary strands according to the rules of base
pairing. Each strand serves as a template for a new
strand.
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Section:
Figure 12–7 Structure of DNA
Section 12-1
•Hydrogen bonds
can only form
between certain
nitrogenous
bases.
Adenine-Thymine
Cytosine-Guanine
A-T
C-G
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
This is called base
pairing.
Go to
Section:
Cytosine (C)
Guanine (G)
Figure 12–11 DNA Replication
Section 12-2
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
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Section:
Original
strand
Nitrogenous
bases
Prokaryotic Chromosome Structure
Section 12-2
Chromosome
E. coli bacterium
Bases on the chromosome
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Section:
Figure 12-10 Chromosome Structure
of Eukaryotes
Section 12-2
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
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Section:
Stop for DNA Replication
Activity
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Section:
RNA
Problem…
DNA cannot leave the nucleus but it must get
coded instructions outside of the cell to help
produce proteins.
Ribonucleic acid (RNA) will help solve this
problem.
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Section:
Three types of RNA
Section 12-3
RNA
can be
Messenger RNA
also called
Ribosomal RNA
which functions to
mRNA
Carry instructions
from
to
DNA
Ribosome
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Section:
also called
which functions to
rRNA
Combine
with proteins
to make up
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
Three types of RNA
Messenger RNA (mRNA) - RNA molecules that carry copies of
instructions to other parts of the cell. They serve as “messengers
from DNA to the rest of the cell.
Ribosomal RNA (rRNA) – RNA molecules that along with proteins,
make up ribosomes. Ribosomes are important because they make
proteins.
Transfer RNA (tRNA)- RNA molecule that transfers amino acids to
the ribosome. It performs this action according to the directions it
gets from DNA. Proteins are made up of amino acids. There are a
total of 20 different amino acids. The type of protein made depends
on the order of the amino acids.
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Section:
Transcription
Transcription- a process in which RNA binds to DNA and
uses one strand as a “template” in order to make a copy of
instructions (genetic code) so it can leave the nucleus.
A,U,C,G- thymine is replaced by uracil in RNA.
Polypetide- long chains of amino acids that make up
proteins.
Codon- three consecutive nucleotides that specify a single
amino acid to be added to the polypeptide chain.
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Section:
Figure 12–14 Transcription
Section 12-3
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
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Section:
Figure 12–17 The Genetic Code
Section 12-3
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Section:
Translation
Translation- the process in which the code is translated
in the ribosomes so the transfer RNA can help the
ribosome produce proteins.
Each t(RNA) molecule carries one amino acid to the
protein building site.
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Section:
Figure 12–18 Translation
Section 12-3
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Section:
Figure 12–18 Translation (continued)
Section 12-3
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Section:
Mutations
Section 12-4
Mutations
DNA contains the code of instructions for cells. Sometimes, an
error occurs when the code is copied. Such errors are called
mutations.
Mutations- changes (errors) in the genetic material
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Section:
Mutations
Types of Mutations
Gene mutations- mutations affecting genes
●Point mutation- mutations involving changes in only one or a few
nucleotides; they occur at a single point in the DNA sequence.
The-dog-bit-the-cat
The-dog-bit-the-car
Chromosomal mutations- change the number or structure of
chromosomes.
Down syndrome- Extra 21st chromosome
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Section:
Section Outline
Section 12-4
Mutagen- any agent that can cause a change in DNA
e.g.
Radiation- xrays, UV rays, and nuclear radiation
contain large amounts of energy that break apart
DNA and cause them to reconnect incorrectly
Chemicals- highly reactive compounds that cause
changes in the DNA molecule
High temperatures
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Section:
Videos
Click a hyperlink to choose a video.
Griffith’s Experiment
DNA Replication
DNA Transcription
Protein Synthesis
Duplication and Deletion
Translocation and Inversion
Point Mutations
Video 1
Griffith’s Experiment
Click the image to play the video segment.
Video 2
DNA Replication
Click the image to play the video segment.
Video 3
DNA Transcription
Click the image to play the video segment.
Video 4
Protein Synthesis
Click the image to play the video segment.
Video 5
Duplication and Deletion
Click the image to play the video segment.
Video 6
Translocation and Inversion
Click the image to play the video segment.
Video 7
Point Mutations
Click the image to play the video segment.
Go Online
Interactive test
Articles on genetics
For links on DNA, go to www.SciLinks.org and enter the Web Code as
follows: cbn-4121.
For links on DNA replication, go to www.SciLinks.org and enter Web
Code as follows: cbn-4122.
For links on protein synthesis, go to www.SciLinks.org and enter the
Web Code as follows: cbn-4123.
Interest Grabber Answers
1. On a sheet of paper, write the word cats. List the letters or units that make
up the word cats.
The units that make up cats are c, a, t, and s.
2. Try rearranging the units to form other words. Remember that each
new word can have only three units. Write each word on your paper, and
then add a definition for each word.
Student codes may include: Act; Sat; Cat
3. Did any of the codes you formed have the same meaning?
No
4. How do you think changing the order of the nucleotides in the DNA codon
changes the codon’s message?
Changing the order of the nucleotides changes the meaning of the codon.
Interest Grabber Answers
1. On a sheet of paper, draw a curving or zig-zagging line that divides the paper
into two halves. Vary the bends in the line as you draw it. Without tracing,
copy the line on a second sheet of paper.
2. Hold the papers side by side, and compare the lines. Do they look the same?
Lines will likely look similar.
3. Now, stack the papers, one on top of the other, and hold the papers up to the
light. Are the lines the same?
Overlaying the papers will show variations in the lines.
4. How could you use the original paper to draw exact copies of the line without
tracing it?
Possible answer: Cut along the line and use it as a template to draw the line
on another sheet of paper.
5. Why is it important that the copies of DNA that are given to new daughter
cells be exact copies of the original?
Each cell must have the correct DNA, or the cell will not
have the correct characteristics.
Interest Grabber Answers
1. Why do you think the library holds some books for reference only?
Possible answers: The books are too valuable to risk loss or damage to
them. The library wants to make sure the information is always available
and not tied up by one person.
2. If you can’t borrow a book, how can you take home the information in it?
Students may suggest making a photocopy or taking notes.
3. All of the parts of a cell are controlled by the information in DNA, yet DNA
does not leave the nucleus. How do you think the information in DNA might
get from the nucleus to the rest of the cell?
Students will likely say that the cell has some way to copy the information
without damaging the DNA.
Interest Grabber Answers
1. Copy the following information about Protein X: Methionine—Phenylalanine—
Tryptophan—Asparagine—Isoleucine—STOP.
2. Use Figure 12–17 on page 303 in your textbook to determine one possible sequence of
RNA to code for this information. Write this code below the description of Protein X.
Below this, write the DNA code that would produce this RNA sequence.
Sequences may vary. One example follows: Protein X: mRNA: AUG-UUU-UGG-AAUAUU-UGA; DNA: TAC-AAA-ACC-TTA-TAA-ACT
3. Now, cause a mutation in the gene sequence that you just determined by deleting the
fourth base in the DNA sequence. Write this new sequence.
(with deletion of 4th base U) DNA: TAC-AAA-CCT-TAT-AAA-CT
4. Write the new RNA sequence that would be produced. Below that, write the amino acid
sequence that would result from this mutation in your gene. Call this Protein Y.
mRNA: AUG-UUU-GGA-AUA-UUU-GA Codes for amino acid sequence: Methionine—
Phenylalaine—Glycine—Isoleucine—Phenylalanine—?
5. Did this single deletion cause much change in your protein? Explain your answer.
Yes, Protein Y was entirely different from Protein X.
Interest Grabber Answers
1. Do you think that cells produce all the proteins for which the DNA (genes)
code? Why or why not? How do the proteins made affect the type and
function of cells?
Cells do not make all of the proteins for which they have genes (DNA).
The structure and function of each cell are determined by the types of
proteins present.
2. Consider what you now know about genes and protein synthesis. What
might be some ways that a cell has control over the proteins it produces?
There must be certain types of compounds that are involved in determining
what types of mRNA transcripts are made and when this mRNA translates
at the ribosome.
3. What type(s) of organic compounds are most likely the ones that help to
regulate protein synthesis? Justify your answer.
The type of compound responsible is probably a protein, specifically
enzymes, because these catalyze the chemical reactions
that take place.
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