Chapter 12

DNA & RNA

I.DNA

A. Griffith & TransformationFrederick Griffith was trying to figure out how bacteria

made people sick-how they cause a certain type of pneumonia.

He isolated 2 strains(types) from mice-both cultured well,but only one caused pneumonia.The culture of the disease causing bacteria were __________________colonies while the other was

rough.

smooth

1-Griffith’s experiments (1928) Mice injected w/ disease –causing strain got sick

and died and nothing happened if injected w/other strain…He wondered if the disease-causing type made a toxin…?

So he took some of disease strain and heated to kill bacteria and then injected into mice….mice survived suggesting it was not a toxin producing disease

Disease-causing bacteria (smooth

colonies)

Harmless bacteria (rough colonies)

Heat-killed, disease-causing bacteria (smooth colonies)

Control(no growth)

Heat-killed, disease-causing bacteria (smooth colonies)

Harmless bacteria (rough colonies)

Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

Dies of pneumonia

Section 12-1

Figure 12–2 Griffith’s Experiment

Disease-causing bacteria (smooth

colonies)

Harmless bacteria (rough colonies)

Heat-killed, disease-causing bacteria (smooth colonies)

Control(no growth)

Heat-killed, disease-causing bacteria (smooth colonies)

Harmless bacteria (rough colonies)

Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

Dies of pneumonia

Section 12-1

Figure 12–2 Griffith’s Experiment

2-Transformation He mixed his heat –killed w/ live harmless bacteria and

injected into mice…..________________________ Somehow the disease –causing strain passed their

disease capacity to harmless bacteria….. disease –causing strain found in lungs

He called this changing of one bacteria by the genes of another _____________________....Thus a factor(gene) from heat killed disease –causing strain was passed on.

Mice developed pneumonia transformation

B. Avery & DNA

Team of scientists lead by Avery in 1944 repeated Griffith’s experiment in order to determine which molecule was responsible for the transformation.

They made an extract from the heat-killed bacteria and treated it w/enzymes that kill proteins,lipids and other molecules,inc. RNA

Avery cont’d

____________________still occurred so the above molecules were not responsible for transformation

They repeated the experiment but used enzymes that kill____________, stopping transformation….

Therefore ________caused the transformation and thus stores and transmits genetic info

transformation

DNA

C. The Hershey –Chase Experiment

1952-Alfred Hershey and Martha Chase studied viruses-disease-causing particles smaller than a cell.

______________________-virus that infects bacteria.They have a DNA or RNA core and a protein coat…They attach to the surface of a bacterium and inject genetic info into cell.The viral genes act to produce many new bacteriophages and eventually destroy bacterial cell,w/_____________bursting out.

bacteriophageviruses

They grew viruses in cultures containing _________________________________,mixed them w/bacteria and waited a few min. for viruses to inject genetic material.

Then they separated the bacteria from the viruses and tested bacteria for radioactive marker…..nearly all the radioactivity was P-32-found in _________----thus concluding it was the genetic material was DNA !

Radioactive markers

DNA

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Figure 12–4 Hershey-Chase ExperimentSection 12-1

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Section 12-1

Figure 12–4 Hershey-Chase Experiment

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Section 12-1

Figure 12–4 Hershey-Chase Experiment

D. The Components and Structure of DNA

Scientists questioned how the DNA molecule could do three things 1)carry info from 1 generation to the next 2)putting that info to work and 3)could be easily copied

DNA is a long molecule made of units called ___________________________________________-

nucleotides

The nucleotide is made of 3 basic parts:______________________(sugar), a phosphate group and a_________________________________

deoxyribose Nitrogenous base

2 nitrogenous bases are purines(have 2 rings):___________________________(A)and_______(G)

2 other nitrogenous bases are pyrimidines (have 1 ring):____________________(C)and

____________________________(T)

Adenine ,guanine

Cytosine and thymine

--backbone made by sugar and phosphate w/ bases sticking out sideways

Purines Pyrimidines

Adenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

Figure 12–5 DNA Nucleotides

Section 12-1

1-_______________________Rules-discovered that %’s of Cytosine and guanine were almost equal in DNA and the same was true for adenine and thymine….Thus A pairs w/T and C w/ G-BASE PAIRING

Chargaff’s Rules

Percentage of Bases in Four OrganismsSection 12-1

Source of DNA A T G CSource 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

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

2- X-ray evidence-1950’s –Rosalind Franklin used X-ray diffraction to learn about DNA structure----The scattered X pattern seen begins to show the __________-partial TWISTED STRUCTURE of DNA

helix

3---Double helix_ Watson and Crick -2 strands wound around each

other---like the twisted ladder or spiral staircase Strands held together by H-bonds

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Figure 12–7 Structure of DNA

Section 12-1

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 & ChromosomesIn cytoplasm in prokaryotesIn _______________________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 codonRibosome 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

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 effectHarmful 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