Interest Grabber 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.

Section 12-3

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?

Figure 12-10 Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Section 12-2

1) DNA Replication Before cellular division the cell must double its DNA

Prokaryotes – DNA replication begins at a single point in the chromosome and proceeds in two directions until replicated.

Eukaryotes – DNA has two complementary strands wound up in the shape of double helix. The DNA polymerase unwinds the DNA and a new strand is copied. The new strand is a complementary copy of the original.

Complementary means that if the original DNA base is adenine the complementary base is thymine.

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Figure 12–7 Structure of DNA

Section 12-1

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

How do DNA genes work?

DNA is a specific set of instructions for what?

DNA (genes) code for the production of protein

How does DNA get out of the nucleus? The first step in decoding genes is to copy a

sequence of DNA onto RNA.

What is RNA?

RNA - Ribonucleic acid is usually single stranded and contains Uracil instead of thymine and it has ribose as it’s sugar.

There are three types of RNA

from to to make up

Concept MapSection 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

STEP ONE DNA to mRNA

DNA needs to be transcribed into m (messenger) RNA

How is this done? RNA polymerase (enzyme) unzips the DNA

molecule and RNA uses one strand of DNA to make an exact copy. A pairs with U and C pairs with G. Nucleotides (Phosphate+ base+ sugar) of mRNA are assembled into a strand of RNA. The mRNA leave the nucleus.

CODONS

RNA will bind only to specific sites along the DNA called promoters – they have specific base sequences that appear in triplets.

RNADNA

RNApolymerase

Figure 12–14 TranscriptionSection 12-3

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

Questions

How is DNA replicated? DNA is replicated with DNA polymerase in the

nucleus

What enzyme unzips DNA for RNA transcription?

RNA polymerase unzips DNA for transcription.

Step Two - Translation

mRNA has made a copy of DNA – a set of instructions to make protein.

mRNA leaves the nucleus and looks for a ribosome to attach to so translation of the mRNA can begin.

Each codon (three letter code of RNA) is read by the ribosome. The ribosome uses the codon as a set of instructions to make a protein. Each three unit codon is matched to its anitcodon – also called tRNA:

AUG is matched with UAC And the anti codon is attached to a specific amino acid

Figure 12–18 TranslationSection 12-3

Translation Continued

The ribosome also bonds each amino acid to the next amino acid. This is how polypeptide chains of amino acids are formed.

The ribosome also breaks the bonds between the amino acid and its anticodon.

The polypeptide chin continues to grow until the ribosome reaches a stop codon.

Figure 12–18 Translation (continued)Section 12-3

http://www.pbs.org/wgbh/aso/tryit/dna/#

Figure 12–17 The Genetic CodeSection 12-3

Interest Grabber

Determining the Sequence of a Gene

DNA contains the code of instructions for cells. Sometimes, an error occurs when the code is copied. Such errors are called mutations.

Section 12-4

Substitution InsertionDeletion

Gene Mutations: Substitution, Insertion, and DeletionSection 12-4

Deletion

Duplication

Inversion

Translocation

Figure 12–20 Chromosomal Mutations

Section 12-4

Interest Grabber

Regulation of Protein Synthesis

Every cell in your body, with the exception of gametes, or sex cells, contains a complete copy of your DNA. Why, then, are some cells nerve cells with dendrites and axons, while others are red blood cells that have lost their nuclei and are packed with hemoglobin? Why are cells so different in structure and function? If the characteristics of a cell depend upon the proteins that are synthesized, what does this tell you about protein synthesis? Work with a partner to discuss and answer the questions that follow.

Section 12-5

Interest Grabber continuedSection 12-5

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?

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?

3. What type(s) of organic compounds are most likely the ones that help to regulate protein synthesis? Justify your answer.