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Home , Adenine, Guanine, Thymine

Biology

Chapter 12 INTEREST GRABBER NOTEBOOK #1 Order! Order! are made of DNA, a large, complex molecule. DNA is composed of individual units called . Three of these units form a code. The order, or sequence, of a code and the type of code determine the meaning of the message. 1. On a sheet of paper, write the word cats. List the letters or units that make up the word cats. 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. 3. Did any of the codes you formed have the same meaning? 4. How do you think changing the order of the nucleotides in the DNA codon changes the codon’s message? DNA History

Griffith – Experimented on mice and observed some harmless strains of could change into harmful strains. He called this transformation. DNA History (continued)

• Avery – Discovered that DNA is the that stores and transmits the genetic information from one generation to the next.

• Hershey-Chase – Concluded that the genetic material in bacteria was DNA not

• Watson & Crick – created the double helix model for DNA. Prokaryotes and DNA

• In prokaryotes, DNA molecules are located in the cytoplasm of the cell.

• Most prokaryotic DNA is a single circular molecule that contains nearly all the cell’s genetic information. Eukaryotes & DNA

• Many eukaryotes have 1000 times as much DNA as prokaryotes.

• DNA is located in the nucleus in the form of chromosomes.

• Chromosomes consist of DNA wound tightly around proteins called histones. Percentage of bases in four

Source of DNA A T G C

Streptococcus 29.8 31.6 20.5 18.0

Yeast 31.3 32.9 18.7 17.1

Herring 27.8 27.5 22.2 22.6

Human 30.9 29.4 19.9 19.8 Structure of DNA

• DNA – deoxyribonucleic acid

• DNA is a long molecule made up of smaller units called nucleotides.

• Nucleotides are made of three parts:

1. 5-carbon sugar () 2. group

3. Nitrogen base Nucleotides- Nucleotides building blocks of DNA 4 bases:

- A - G - T - C - A, G C, T, U is found only in RNA Structure of DNA (continued) • Chargaff’s Rule - Chargaff discovered that the percentages of guanine and cytosine bases were almost equal in any sample of DNA.

• The same was true for adenine and thymine.

• A bonds only with T

• C bonds only with G Nucleotides- composed of a sugar, phosphate and base DNA Nucleotides

Purines Pyrimidines Adenine Guanine Cytosine Thymine Adenine – Thymine Guanine – Cytosine

-DNA nucleotides always bond A-T and C-G

Phosphate group Deoxyribose Structure of DNA- nucleotides are building blocks

Hydrogen bonds

Sugar- phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Rosalin Franklin Structure of DNA James Watson and won the Nobel Prize for discovering the structure of DNA Double Helix- shaped like a twisted ladder DNA structure (deoxyribonucleic acid) DNA Replication- zipper model DNA Replication

During DNA replication, the DNA molecule separates into two strands, then produces two new complimentary strands following the rules of base pairing (Chargaff’s Rule). Each strand of double helix of DNA serves as a template, or model, for the new strand.

DNA Replication (continued) • DNA replication is carried out by a series of .

• The enzymes unzip the DNA molecule creating two strands that serve as templates.

• Complimentary bases are added to the strands, for example a strand of DNA with the bases ATTCGAG would have a complimentary strand of TAAGCTC. DNA Replication (continued)

• Each new DNA molecule has one new strand and one strand from the original molecule.

• The DNA polymerase, the principal enzyme, “proofreads” the new DNA strands, helping to maximize the odds that each molecule is a perfect copy of the original. Role of DNA

DNA codes for specific proteins which make each unique Since both genes and proteins are unique, it is logical that genes may work by coding for proteins NOTEBOOK #2

1. What is a nucleotide? 2. What is a nucleotide composed of?

3. What bases bond during replication?

4. What bases are the purines? Pyrimidines?

5. What model is used to explain DNA replication? Interest Grabber

NOTEBOOK #3

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. Interest Grabber cont. 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? 3. Now, stack the papers, one on top of the other, and hold the papers up to the light. Are the lines the same? 4. How could you use the original paper to draw exact copies of the line without tracing it? 5. Why is it important that the copies of DNA that are given to new daughter cells be exact copies of the original? Prokaryotic Chromosome Structure

Chromosome

E. coli bacterium

Bases on the chromosome Chromosome Structure of Eukaryotes

Chromosome Nucleosome DNA double helix Coils

Supercoils

Histones DNA Replication Original strand New strand DNA polymerase

DNA Growth polymerase

Growth

Replication Replication fork fork

Original New strand strand Interest Grabber NOTEBOOK #4 Information, Please DNA contains the information that a cell needs to carry out all of its functions. In a way, DNA is like the cell’s encyclopedia. Suppose that you go to the library to do research for a science project. You find the information in an encyclopedia. You go to the desk to sign out the book, but the librarian informs you that this book is for reference only and may not be taken out. 1. Why do you think the library holds some books for reference only? 2. If you can’t borrow a book, how can you take home the information in it? 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? 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.

Section 3 Answers Concept Map RNA

can be

Messenger Ribosomal Transfer RNA RNA RNA

also called which functions to also called which functions to also called

Bring Carry Combine mRNA tRNA amino acids to instructions rRNA with proteins ribosome

from to to make up

DNA Ribosome Ribosomes RNA does not have Thymine, instead it has Uracil. When mRNA copies DNA Adenine bonds to Uracil. (A-U)

Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only)

RNA polymerase

DNA RNA Transcription Messenger RNA (mRNA) enter the nucleus The DNA unzips and the mRNA copies one strand of the DNA The transcribed mRNA leaves the nucleus and heads to a ribosome NOTEBOOK #5

1. What are the three kinds of RNA?

2. In what part of the cell are they found?

3. What is transcription?

4. In what part of the cell does transcription take place?

5. What nucleic acids are involved? Translation Translation cont. At a ribosome, the mRNA code is read by the Transfer RNA Translation (tRNA) The tRNA brings specific amino acids to the mRNA The tRNA has a 3 base group called an anticodon, and the mRNA is read in groups of 3 bases called the codon Amino Acids - Amino Acids- Genetic Code Synthesis NOTEBOOK #6

1. What is translation? 2. In what part of the cell does translation occur? 3. What organelle is necessary for translation? 4. What nucleic acids are involved in translation? 5. What is ultimately the product of protein synthesis? Expression of Genes

- changes in the genetic code Mutagen- agents that cause mutations

DNA found in chloroplasts and mitochondria is circular- also some codons on organelle DNA code for different amino acids than nuclear DNA Mutations (Silent )

DNA mutations that do not result in a change to the amino acid sequence of a protein.

Example: GCG codes for alanine. If a mutation occurred and the DNA was ACG, it would still code for the amino acid alanine.

Mutation (Silent Mutation) Mutation (Nonsense)

A nonsense mutation is a in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA. Mutation (nonsense) DNA: 5' - ATG ACT CAC CGA GCG CGA AGC TGA - 3'shut 3' - TAC TGA GTG GCT CGC GCT TCG ACT - 5’ mRNA: 5' - AUG ACU CAC CGA GCG CGA AGC UGA - 3' Protein: Met Thr His Arg Ala Arg Ser Stop

DNA: 5' - ATG ACT CAC TGA GCG CGA AGC TGA - 3' 3' - TAC TGA GTG ACT CGC GCT TCG ACT - 5’ mRNA: 5' - AUG ACU CAC UGA GCG CGU AGC UGA - 3' Protein: Met Thr His Stop Mutation (Nonsense) Mutation (Frameshift) A genetic mutation caused by the insertions or deletions of a number of nucleotides that is not evenly divisible by three from a DNA sequence. Mutation (Frameshift) NOTEBOOK #7

1. What is a mutation? 2. What is a mutagen? 3. What is a silent mutation? 4. What is a nonsense mutation? 5. What is a frameshift mutation?