Chapter 12

DNA & RNA

Interest GrabberOrder! Order!

Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. 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.

Section 12-1

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 eachnew 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?

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

I

Section 12-2

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?

II. Chromosomes & DNA Replication

A-DNA & Chromosomes In cytoplasm in prokaryotes In _______________________found in cell

nucleus in the form of a number of chromosomes(46 humans,8 Drosophilia and 22 Sequoia trees)

eukaryotes

1--DNA length 1.6 mm in E.coli(has 4,639,221 base pairs)---

obviously it must be tightly folded

2-Chromosome Structure Eukaryotic cells have about 1000 times as many

base pairs of DNA than a bacterium Humans cells have ~ 1 m DNA Eukaryotic chromosomes contain DNA and a

protein ,which together make _____________________-consisting of DNA tightly packed around proteins called histones

chromatin

DNA and histone together make beadlike_____________________________

Nucleosomes pack together to make thick fibers,drawn together during mitosis…also separating

Role of nucleosomes-fold great lengths of DNA into tiny spaces

nucleosomes

Chromosome

E. coli bacterium

Bases on the chromosome

Prokaryotic Chromosome StructureSection 12-2

Figure 12-10 Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Section 12-2

B. DNA Replication

Each strand of DNA double helix has all the info to___________________________by base pairing

Strands are complementary In prokaryotes,this begins @single point and

proceeds-often in 2 directions In Eukaryotes,DNA replication begins @ 100’s of

places,going both directions until complete __________________________is where replication

occurs

Reconstruct the other half

Replication fork

1-Duplicating DNA __________________________or duplication of

DNA happens before cell division---ensuring each cell has a complete set of DNA molecules

Each strand of a double helix serves as a _____________________or model for new strand

A pairs w/ T and C w/ G

replication

template

2-How Replication Occurs Carried out by a series of enzymes that unzip a

molecule ____________________________________ joins

individual nucleotides to make a DNA molecule….also proof reads the new strands

DNA polymerase

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

III. RNA & Protein Synthesis

The double helix structure explains how DNA is copied,but not how a gene works-_______________are coded DNA instructions that control the production of protein in the cell.

A) The structure of RNA Long chain of nucleotides 3 main differences between DNA & RNA:

1--Sugar is _________________ 2---Generally single-stranded 3---RNA contains ________________(U) in

place of thymine (T)

genes

uracil ribose

B. Types of RNA

Main job=_________________-ie the assembly of amino acids into proteins

3 Types: ____________________(mRNA)-carry copies for

instructions from DNA to rest of cell ____________________(rRNA)-type of RNA that helps

make up ribosomes,where proteins assembled ________________(tRNA)transfers each amino acid to

the ribosome as it is coded for on mRNA.

Protein synthesis

messenger

ribosomal Transfer

from to to make up

Concept MapSection 12-3

also called which functions to

also called also called which functions to

which functions to

can be

RNA

Messenger RNA Ribosomal RNA Transfer RNA

mRNA Carry instructions rRNACombine

with proteins tRNABring

amino acids toribosome

DNA Ribosome Ribosomes

C. Transcription-produces RNA molecules by copying part of nucleotide sequence of DNA into a complementary sequence in RNA

Requires enzyme known as _______________________________________-binds to DNA and separates DNA strands.Then uses one strand as template to make RNA

The enzyme only binds to areas known as promoters-signals that indicate where to make RNA.Similar signals tell where to stop

RNA-polymerase

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)

D. RNA editing

________________________ in eukaryotic genes ,sequences of nucleotides that ARE NOT involved in coding for proteins

_______________________-DNA sequence that does code for protein

introns

exons

E. Genetic Code

______________________-chain of amino acids=proteins

_________________-3 consecutive nucleotides that specify a specific amino acid

Example –UCGCACGGU reads UCG_CAC_GGU and codes for Serine-Histidine-Glycine

polypeptide

codon

 The Genetic Code

Section 12-3

Universal code64 possible 3 base codonsAUG can specify methionine or start

codon3 stop codons that do not code for an

amino acid

F. Translation ______________________reads the instructions for

the order in which amino acids should be joined by reading mRNA

____________________________is the decoding of an mRNA message into a polypeptide(protein)

Before translation occurs,mRNA is transcribed from DNA and released into __________________________.

Translation begins when mRNA molecule in cytoplasm attaches to a _____________________.

ribosome

translation

cytoplasm

ribosome

As each codon of the mRNA moves through the moves through the ribosome,_____________brings in the proper,indicated amino acid and transferred to polypeptide chain

Each tRNA carries one kind of amino acid __________________ is a group of 3 bases on a

tRNA that are complementary to a mRNA codon Ribosome forms a _________________bond

between amino acids and breaks tRNA bond releasing it

Protein keeps growing until ribosome reaches stop codon on mRNA

tRNA

anticodonpeptide

Figure 12–18 TranslationSection 12-3

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

IV.Mutations=________________________

A.---Kinds of Mutations 1) ________________________________-changes in a

single gene _____________________________________-changes in 1 or

a few nucleotides-@ a single point in DNA-includes substitutions,insertions and deletions

Substitutions usually affect no more than 1 amino acid ____________________________________-insertions or

deletions where the reading frame of the codon message is changed-can VERY much alter or even stop the function of a protein

Changes in genetic material

Point mutation

Frameshift mutation

Gene mutation

2)Chromosomal Mutations-change in the # or structure of chromosomes-can change the location of genes on chromosomes and /or number of copies of some genes.

4 types-1)Deletions-loss of all or part of a chromosome

2)__________________-extra copies of a part of a chromosome

3)________________reverse directions of parts of chromosomes

4)____________-part of one chromosome breaks off and attaches to another

duplication

inversions

translocations

Substitution InsertionDeletion

Gene Mutations: Substitution, Insertion, and Deletion

Section 12-4

Deletion

Duplication

Inversion

Translocation

Figure 12–20 Chromosomal Mutations

Section 12-4

B. Significance of Mutations

Many have no effect Harmful effects include genetic disorders and cancer ________________________-contains extra set of

chromosomes-bad in most cases but often helpful in PLANTS.

polyploidy

V. Gene Regulation

Only a fraction of a gene expressed at one time ___________________-group of genes that

operate together ________________-where repressor binds operon

(when it)is turned off Operons not usually found in eukaryotes-these

genes are usually controlled individually and regulation more complex---mainly because of cell specialization

Hox genes-control differentiation of cells and tissues in the embryo

operon

operator

Regulatory sites

Promoter(RNA polymerase binding site)

Start transcription

DNA strand

Stop transcription

Typical Gene StructureSection 12-5

Karyotypes