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Copyright Pearson Prentice Hall

12–1 DNA

Griffith and Transformation

In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused pneumonia.

He isolated two different strains of pneumonia bacteria from mice and grew them in his lab.

Griffith made two observations:

(1) The disease-causing strain of bacteria grew into smooth colonies on culture plates.

(2) The harmless strain grew into colonies with rough edges.

Griffith's Experiments

Griffith set up four individual experiments.

Experiment 1: Mice were injected with the disease-causing strain of bacteria. The mice developed pneumonia and died.

Experiment 2: Mice were injected with the harmless strain of bacteria. These mice didn’t get sick.

Harmless bacteria (rough colonies)

Experiment 3: Griffith heated the disease-causing bacteria. He then injected the heat-killed bacteria into the mice. The mice survived.

Heat-killed disease-causing bacteria (smooth colonies)

Experiment 4: Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria and injected the mixture into the mice. The mice developed pneumonia and died.

Live disease-causing bacteria(smooth colonies)

Dies of pneumonia

Griffith concluded that the heat-killed bacteria passed their disease-causing ability to the harmless strain.

Live disease-causing bacteria(smooth colonies)

Dies of pneumonia

Transformation

Griffith called this process transformation because one strain of bacteria (the harmless strain) had changed permanently into another (the disease-causing strain).

Griffith hypothesized that a factor must contain information that could change harmless bacteria into disease-causing ones.

Avery and DNA

Oswald Avery repeated Griffith’s work to determine which molecule was most important for transformation.

Avery and his colleagues made an extract from the heat-killed bacteria that they treated with enzymes.

Avery and DNA

The enzymes destroyed proteins, lipids, carbohydrates, and other molecules, including the nucleic acid RNA.

Transformation still occurred.

Avery and DNA

Avery and other scientists repeated the experiment using enzymes that would break down DNA.

When DNA was destroyed, transformation did not occur. Therefore, they concluded that DNA was the transforming factor.

Avery and DNA

Avery and other scientists discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next.

The Hershey-Chase Experiment

Alfred Hershey and Martha Chase studied viruses—nonliving particles smaller than a cell that can infect living organisms.

Bacteriophages

A virus that infects bacteria is known as a bacteriophage.

Bacteriophages are composed of a DNA or RNA core and a protein coat.

They grew viruses in cultures containing radioactive isotopes of phosphorus-32 (32P) and sulfur-35 (35S).

If 35S was found in the bacteria, it would mean that the viruses’ protein had been injected into the bacteria.

Bacteriophage withsuffur-35 in protein coat

Phage infects bacterium

No radioactivity inside bacterium

If 32P was found in the bacteria, then it was the DNA that had been injected.

Bacteriophage withphosphorus-32 in DNA

Phage infects bacterium

Radioactivity inside bacterium

Nearly all the radioactivity in the bacteria was from phosphorus (32P).

Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein.

The Components and Structure of DNA

DNA is made up of nucleotides.

A nucleotide is a monomer of nucleic acids made up of:

•Deoxyribose – 5-carbon Sugar

•Phosphate Group

•Nitrogenous Base

There are four kinds of bases in in DNA:

• adenine

• guanine

• cytosine

• thymine

Chargaff's Rules

Erwin Chargaff discovered that:

• The percentages of guanine [G] and cytosine [C] bases are almost equal in any sample of DNA.

• The percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA.

X-Ray Evidence

Rosalind Franklin used X-ray diffraction to get information about the structure of DNA.

She aimed an X-ray beam at concentrated DNA samples and recorded the scattering pattern of the X-rays on film.

The Double Helix

Using clues from Franklin’s pattern, James Watson and Francis Crick built a model that explained how DNA carried information and could be copied.

Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other.

DNA Double Helix

Watson and Crick discovered that hydrogen bonds can form only between certain base pairs—adenine and thymine, and guanine and cytosine.

This principle is called base pairing.

12–1

Avery and other scientists discovered that

a. DNA is found in a protein coat.

b. DNA stores and transmits genetic information from one generation to the next.

c. transformation does not affect bacteria.

d. proteins transmit genetic information from one generation to the next.

12–1

The Hershey-Chase experiment was based on the fact that

a. DNA has both sulfur and phosphorus in its structure.

b. protein has both sulfur and phosphorus in its structure.

c. both DNA and protein have no phosphorus or sulfur in their structure.

d. DNA has only phosphorus, while protein has only sulfur in its structure.

12–1

DNA is a long molecule made of monomers called

a. nucleotides.

b. purines.

c. pyrimidines.

d. sugars.

12–1

Chargaff's rules state that the number of guanine nucleotides must equal the number of

a. cytosine nucleotides.

b. adenine nucleotides.

c. thymine nucleotides.

d. thymine plus adenine nucleotides.

12–1

In DNA, the following base pairs occur:

a. A with C, and G with T.

b. A with T, and C with G.

c. A with G, and C with T.

d. A with T, and C with T.

12-2 Chromosomes and DNA Replication12–2 Chromosomes and DNA Replication

DNA and

Chromosomes

DNA and Chromosomes

In prokaryotic cells, DNA is located in the cytoplasm.

Most prokaryotes have a single DNA molecule containing nearly all of the cell’s genetic information.

DNA and

Chromosomes

Chromosome

E. Coli Bacterium

Bases on the Chromosomes

DNA and

Chromosomes

Many eukaryotes have 1000 times the amount of DNA as prokaryotes.

Eukaryotic DNA is located in the cell nucleus inside chromosomes.

The number of chromosomes varies widely from one species to the next.

DNA and

Chromosomes

Chromosome Structure

Eukaryotic chromosomes contain DNA and protein, tightly packed together to form chromatin.

Chromatin consists of DNA tightly coiled around proteins called histones.

DNA and histone molecules form nucleosomes.

Nucleosomes pack together, forming a thick fiber.

DNA and

Chromosomes

Eukaryotic Chromosome Structure

Chromosome

Supercoils

Nucleosome

DNA double helix

Histones

DNA Replica

DNA Replication

Each strand of the DNA double helix has all the information needed to reconstruct the other half by the mechanism of base pairing.

In most prokaryotes, DNA replication begins at a single point and continues in two directions.

DNA Replica

In eukaryotic chromosomes, DNA replication occurs at hundreds of places. Replication proceeds in both directions until each chromosome is completely copied.

The sites where separation and replication occur are called replication forks.

DNA Replica

Duplicating DNA

Before a cell divides, it duplicates its DNA in a process called replication.

Replication ensures that each resulting cell will have a complete set of DNA.

DNA Replica

During DNA replication, the DNA molecule separates into two strands, then produces two new complementary strands following the rules of base pairing. Each strand of the double helix of DNA serves as a template for the new strand.

DNA Replica

Nitrogen Bases

Replication Fork

DNA Polymerase

Replication Fork

Original strandNew Strand

Growth

DNA Replica

tionHow Replication Occurs

DNA replication is carried out by enzymes that “unzip” a molecule of DNA.

Hydrogen bonds between base pairs are broken and the two strands of DNA unwind.

DNA Replica

Nitrogen Bases

Replication Fork

DNA Polymerase

Replication Fork

Original strandNew Strand

Growth

DNA Replica

The principal enzyme involved in DNA replication is DNA polymerase.

DNA polymerase joins individual nucleotides to produce a DNA molecule and then “proofreads” each new DNA strand.

12–2

In prokaryotic cells, DNA is found in the

a. cytoplasm.

b. nucleus.

c. ribosome.

d. cell membrane.

12–2

The first step in DNA replication is

a. producing two new strands.

b. separating the strands.

c. producing DNA polymerase.

d. correctly pairing bases.

12–2

A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand?

a. GCGAATTCG

b. CGCTTAAGC

c. TATCCGGAT

d. GATGGCCAG

12–2

In addition to carrying out the replication of DNA, the enzyme DNA polymerase also functions to

a. unzip the DNA molecule.

b. regulate the time copying occurs in the cell cycle.

c. “proofread” the new copies to minimize the number of mistakes.

d. wrap the new strands onto histone proteins.

12–2

The structure that may play a role in regulating how genes are “read” to make a protein is the

a. coil.

b. histone.

c. nucleosome.

d. chromatin.

12-3 RNA and Protein Synthesis

12–3 RNA and Protein Synthesis

12–3 RNA

and Protein

Synthe

sisGenes are coded DNA instructions that control the production of proteins.

Genetic messages can be decoded by copying part of the nucleotide sequence from DNA into RNA.

RNA contains coded information for making proteins.

The Structu

re of RNA

The Structure of RNA

There are three main differences between RNA and DNA:

a. The sugar in RNA is ribose instead of deoxyribose.

b. RNA is generally single-stranded.

c. RNA contains uracil in place of thymine.

Types of RNA

There are three main types of RNA:

a. messenger RNA

b. ribosomal RNA

c. transfer RNA

Types of RNA

Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins.

Types of RNA

Ribosomes are made up of proteins and ribosomal RNA (rRNA).

Ribosome

Ribosomal RNA

Protein Synthe

DNADNAmoleculemolecule

DNA strandDNA strand(template)(template)

TRANSCRIPTIONTRANSCRIPTION

CodonCodon

mRNAmRNA

TRANSLATIONTRANSLATION

ProteinProtein

Amino acidAmino acid

Transcription

DNA is copied in the form of RNA

This first process is called transcription.

The process begins at a section of DNA called a promoter.

Transcription

RNA polymerase

RNA Editing

Some DNA within a gene is not needed to produce a protein. These areas are called introns.

The DNA sequences that code for proteins are called exons.

RNA Editing

The introns are cut out of RNA molecules.

The exons are the spliced together to form mRNA.

Exon IntronDNA

Pre-mRNA

Cap Tail

The Genetic

The Genetic Code

The genetic code is the “language” of mRNA instructions.

The code is written using four “letters” (the bases: A, U, C, and G).

The Genetic

A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.

The Genetic

Nucleus

mRNACopyright Pearson Prentice Hall

Translation

Translation is the decoding of an mRNA message into a polypeptide chain (protein).

Translation takes place on ribosomes.

During translation, the cell uses information from messenger RNA to produce proteins.

Translation

LysinetRNAPhenylalanine

Methionine

Ribosome

mRNAStart codon

The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA.

Translation

Protein SynthesistRNA

Ribosome

Lysine

Translation direction

Translation

The process continues until the ribosome reaches a stop codon.

Polypeptide

Ribosome

Genes and

Proteins

Protein

CodonCodon Codon

Codon Codon Codon

Alanine Arginine Leucine

Amino acids within a polypeptide

Single strand of DNA

12–3

The role of a master plan in a building is similar to the role of which molecule?

a. messenger RNA

b. DNA

c. transfer RNA

d. ribosomal RNA

12–3

A base that is present in RNA but NOT in DNA is

a. thymine.

b. uracil.

c. cytosine.

d. adenine.

12–3

The nucleic acid responsible for bringing individual amino acids to the ribosome is

a. transfer RNA.

b. DNA.

c. messenger RNA.

d. ribosomal RNA.

12–3

A region of a DNA molecule that indicates to an enzyme where to bind to make RNA is the

a. intron.

b. exon.

c. promoter.

d. codon.

A codon typically carries sufficient information to specify a(an)

a. single base pair in RNA.

b. single amino acid.

c. entire protein.

d. single base pair in DNA.

12–3

12-4 Mutations

12–4 Mutations

12-4 Mutati

Mutations are changes in the genetic material.

Kinds of Mutations

Mutations that produce changes in a single gene are known as gene mutations.

Mutations that produce changes in whole chromosomes are known as chromosomal mutations.

Kinds of Mutations

Gene Mutations

Gene mutations involving a change in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence.

Point mutations include substitutions, insertions, and deletions.

Kinds of Mutations

Substitutions usually affect no more than a single amino acid.

Kinds of Mutations

The effects of insertions or deletions are more dramatic.

The addition or deletion of a nucleotide causes a shift in the grouping of codons.

Changes like these are called frameshift mutations.

Kinds of Mutations

In an insertion, an extra base is inserted into a base sequence.

Kinds of Mutations

In a deletion, the loss of a single base is deleted and the reading frame is shifted.

Kinds of Mutations

Chromosomal Mutations

Chromosomal mutations involve changes in the number or structure of chromosomes.

Chromosomal mutations include deletions, duplications, inversions, and translocations.

Kinds of Mutations

Deletions involve the loss of all or part of a chromosome.

Kinds of Mutations

Duplications produce extra copies of parts of a chromosome.

Kinds of Mutations

Inversions reverse the direction of parts of chromosomes.

Kinds of Mutations

Translocations occurs when part of one chromosome breaks off and attaches to another.

Significance of Mutations

Many mutations have little or no effect on gene expression.

Some mutations are the cause of genetic disorders.

Polyploidy is the condition in which an organism has extra sets of chromosomes.

12–4

A mutation in which all or part of a chromosome is lost is called a(an)

a. duplication.

b. deletion.

c. inversion.

d. point mutation.

12–4

A mutation that affects every amino acid following an insertion or deletion is called a(an)

a. frameshift mutation.

b. point mutation.

c. chromosomal mutation.

d. inversion.

12–4

A mutation in which a segment of a chromosome is repeated is called a(an)

a. deletion.

b. inversion.

c. duplication.

d. point mutation.

12–4

The type of point mutation that usually affects only a single amino acid is called

a. a deletion.

b. a frameshift mutation.

c. an insertion.

d. a substitution.

12–4

When two different chromosomes exchange some of their material, the mutation is called a(an)

a. inversion.

b. deletion.

c. substitution.

d. translocation.

12-5 Gene Regulation

• 12-5 Gene Regulation

Fruit fly chromosome

Fruit fly embryo

Adult fruit fly

Mouse chromosomes

Mouse embryo

Adult mouse

Gene Regulation: An Example

• Gene Regulation: An Example

a. E. coli provides an example of how gene expression can be regulated.

b. An operon is a group of genes that operate together.

c. In E. coli, these genes must be turned on so the bacterium can use lactose as food.

d. Therefore, they are called the lac operon.

–How are lac genes turned off and on?

–The lac genes are turned off by repressors and turned on by the presence of lactose.

–On one side of the operon's three genes are two regulatory regions.

a. In the promoter (P) region, RNA polymerase binds and then begins transcription.

a. The other region is the operator (O).

–When the lac repressor binds to the O region, transcription is not possible.

• When lactose is added, sugar binds to the repressor proteins.

• The repressor protein changes shape and falls off the operator and transcription is made possible.

• Many genes are regulated by repressor proteins.

• Some genes use proteins that speed transcription.

• Sometimes regulation occurs at the level of protein synthesis.

Eukaryotic Gene Regulation

–How are most eukaryotic genes controlled?

• Eukaryotic Gene Regulation

–Operons are generally not found in eukaryotes.

–Most eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon.

• Many eukaryotic genes have a sequence called the TATA box.

Promotersequences

Upstreamenhancer

TATAbox Introns

Direction of transcription

• The TATA box seems to help position RNA polymerase.

Promotersequences

Upstreamenhancer

TATAbox

Introns

• Eukaryotic promoters are usually found just before the TATA box, and consist of short DNA sequences.

Promotersequences

Upstreamenhancer

TATAbox

Introns

• Genes are regulated in a variety of ways by enhancer sequences.

• Many proteins can bind to different enhancer sequences.

• Some DNA-binding proteins enhance transcription by:

a. opening up tightly packed chromatin

b. helping to attract RNA polymerase

c. blocking access to genes.

Development and Differentiation

• Development and Differentiation

a. As cells grow and divide, they undergo differentiation, meaning they become specialized in structure and function.

b. Hox genes control the differentiation of cells and tissues in the embryo.

• Careful control of expression in hox genes is essential for normal development.

• All hox genes are descended from the genes of common ancestors.

• Hox Genes

Fruit fly chromosome

Fruit fly embryo

Adult fruit fly

Mouse chromosomes

Mouse embryo

Adult mouse

12–5

–Which sequence shows the typical organization of a single gene site on a DNA strand?

a. start codon, regulatory site, promoter, stop codon

b. regulatory site, promoter, start codon, stop codon

c. start codon, promoter, regulatory site, stop codon

d. promoter, regulatory site, start codon, stop codon

12–5

– A group of genes that operates together is a(an)

a. promoter.

b. operon.

c. operator.

d. intron.

12–5

– Repressors function to

a. turn genes off.

b. produce lactose.

c. turn genes on.

d. slow cell division.

12–5

–Which of the following is unique to the regulation of eukaryotic genes?

a. promoter sequences

b. TATA box

c. different start codons

d. regulatory proteins

12–5

–Organs and tissues that develop in various parts of embryos are controlled by

a. regulation sites.

b. RNA polymerase.

c. hox genes.

d. DNA polymerase.

copyright pearson prentice hall 12–1 dna. copyright pearson prentice hall griffith and...

harmless strain of bacteria

certain types of bacteria

diseasecausing ones

diseasecausing ability

mice didnt

rough edges

dnathe enzymes

process transformation

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