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Ch. 12The Structure and Function of DNA
and RNA
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Interest Grabber
Chapter 12
DNA and RNA
Section 12-1
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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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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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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Figure 12-10 Chromosome Structure of Eukaryotes
Chromosome
Supercoils
Coils
Histones-proteins
DNA
double
helix
Section 12-2
Genes
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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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Hydrogen bonds
Nucleotide
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Figure 12–7 Structure of DNA
Section 12-1
•Hydrogen bonds can only form between certain nitrogenous bases.
Adenine-ThymineCytosine-Guanine
A-TC-G
This is called base pairing.
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Purines Pyrimidines
Adenine Guanine Cytosine Thymine
Phosphate group Deoxyribose
Figure 12–5 DNA Nucleotides
Section 12-1
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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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Interest Grabber
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.
Section 12-2
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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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Hydrogen bonds
Nucleotide
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Figure 12–7 Structure of DNA
Section 12-1
•Hydrogen bonds can only form between certain nitrogenous bases.
Adenine-ThymineCytosine-Guanine
A-TC-G
This is called base pairing.
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Figure 12–11 DNA Replication
Section 12-2
Growth
Growth
Replication fork
DNA polymerase
New strand
Original strand DNA
polymerase
Nitrogenous bases
Replication fork
Original strand
New strand
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Chromosome
E. coli bacterium
Bases on the chromosome
Prokaryotic Chromosome Structure
Section 12-2
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Figure 12-10 Chromosome Structure of Eukaryotes
Chromosome
Supercoils
Coils
Nucleosome
Histones
DNA
double
helix
Section 12-2
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Stop for DNA Replication Activity
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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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from to to make up
Three types of RNA
Section 12-3
also called which functions to also called also called which functions towhich functions to
can be
RNA
Messenger RNA Ribosomal RNA Transfer RNA
mRNA Carry instructions rRNACombine
with proteins tRNABring
amino acids toribosome
DNA Ribosome Ribosomes
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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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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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RNADNA
RNApolymerase
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)
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Figure 12–17 The Genetic Code
Section 12-3
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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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Figure 12–18 Translation
Section 12-3
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Figure 12–18 Translation (continued)
Section 12-3
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Mutations
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
Section 12-4
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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-catThe-dog-bit-the-car
Chromosomal mutations- change the number or structure of chromosomes.
Down syndrome- Extra 21st chromosome
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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
Section 12-4
Section Outline
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
Click the image to play the video segment.
Video 1
Griffith’s Experiment
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Video 2
DNA Replication
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Video 3
DNA Transcription
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Video 4
Protein Synthesis
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Video 5
Duplication and Deletion
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Video 6
Translocation and Inversion
Click the image to play the video segment.
Video 7
Point Mutations
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.
Go Online
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 eachnew 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-AAU-AUU-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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