DNA: The Genetic Material. Orientation On the top rail, the strand is said to be oriented 5′ to...

DNA: The Genetic Material

Orientation

On the top rail, the strand is said to be oriented 5′ to 3′.

The strand on the bottom runs in the opposite direction and is oriented 3′ to 5′.



Chromosome Structure DNA coils around histones to form nucleosomes,

which coil to form chromatin fibers. The chromatin fibers supercoil to form chromosomes

that are visible in the metaphase stage of mitosis.

Replication of DNA

Semiconservative Replication

Parental strands of DNA separate, serve as templates, and produce DNA molecules that have one strand of parental DNA andone strand of new DNA.

Unwinding

DNA helicase, an enzyme, is responsible for unwinding and unzipping the double helix.

RNA primase adds a short segment of RNA, called an RNA primer, on each DNA strand.

Replication of DNA

Base pairing

DNA polymerase continues adding appropriate nucleotides to the chain by adding to the 3′ end of the new DNA strand.

Replication of DNA

One strand is called the leading strand and is elongated as the DNA unwinds.

The other strand of DNA, called the lagging strand, elongates away from the replication fork.

The lagging strand is synthesized discontinuously into small segments, called Okazaki fragments.

Replication of DNA

Joining

DNA polymerase removes the RNA primer and fills in the place with DNA nucleotides.

DNA ligase links the two sections.

Replication of DNA

Replication of DNA

Comparing DNA Replication in Eukaryotes and Prokaryotes

Eukaryotic DNA unwinds in multiple areas as DNA is replicated.

In prokaryotes, the circular DNA strand is opened at one origin of replication.

DNA, RNA, and Protein

Central Dogma

RNA

Contains the sugar ribose and the base uracil

Usually is single stranded

Messenger RNA (mRNA) Long strands of RNA nucleotides that are

formed complementary to one strand of DNA

Ribosomal RNA (rRNA) Associates with proteins to form ribosomes

in the cytoplasm

Transfer RNA (tRNA) Smaller segments of RNA nucleotides that

transport amino acids to the ribosome


DNA is unzipped in the nucleus and RNA polymerase binds to a specific section where an mRNA will be synthesized.

Transcription

Through transcription, the DNA code is transferred to mRNA in the nucleus.


RNA Processing

The code on the DNA is interrupted periodically by sequences that are not in the final mRNA.

Intervening sequences are called introns.

Remaining pieces of DNA that serve as the coding sequences are called exons.


The Code

Experiments during the 1960s demonstrated that the DNA code was a three-base code.

The three-base code in DNA or mRNA is called a codon.


Translation In translation, tRNA

molecules act as the interpreters of the mRNA codon sequence.

At the middle of the folded strand, there is a three-base coding sequence called the anticodon.

Each anticodon is complementary to a codon on the mRNA.



One Gene—One Enzyme

The Beadle and Tatum experiment showed that one gene codes for one enzyme. We now know that one gene codes for one polypeptide.

Gene Regulation and Mutation

Prokaryote Gene Regulation Ability of an organism to control which genes

are transcribed in response to the environment An operon is a section of DNA that contains

the genes for the proteins needed for a specific metabolic pathway.

Operator Promoter Regulatory gene Genes coding for proteins

The Trp Operon


The Lac Operon


Eukaryote Gene Regulation

Controlling transcription

Transcription factors ensure that a gene is used at the right time and that proteins are made in the right amounts

The complex structure of eukaryotic DNA also regulates transcription.


Hox Genes

Hox genes are responsible for the general body pattern of most animals.


RNA Interference

RNA interference can stop the mRNA from translating its message.


Mutations

A permanent change that occurs in a cell’s DNA is called a mutation.

Types of mutations

Point mutation Insertion Deletion


Molecular GeneticsChapter 12

Protein Folding and Stability

Substitutions also can lead to genetic disorders.

Can change both the folding and stability of the protein


Causes of Mutation

Can occur spontaneously

Chemicals and radiation also can damage DNA.

High-energy forms of radiation, such as X rays and gamma rays, are highly mutagenic.


Body-cell v. Sex-cell Mutation

Somatic cell mutations are not passed on to the next generation.

Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.


1. A2. B3. C4. D

CDQ 1

A. Watson and Crick

B. Mendel

C. Hershey and Chase

D. Avery

Which scientist(s) definitively proved that DNA transfers genetic material?

Chapter Diagnostic Questions

1. A2. B3. C4. D

CDQ 2


A. ligase

B. Okazaki fragments

C. polymerase

D. helicase

Name the small segments of the lagging DNA strand.

1. A2. B3. C4. D

CDQ 3


A. It contains the

sugar ribose.

B. It contains the

base uracil.

C. It is single-stranded.

D. It contains a phosphate.

Which is not true of RNA?

1. A2. B3. C4. D

FQ 1

A. carbohydrate

B. DNA

C. lipid

D. protein

The experiments of Avery, Hershey and Chase provided evidence that the carrier of genetic information is _______.

Formative Questions

1. A2. B3. C4. D

FQ 2

A. A—G and C—T

B. A—T and C—G

C. C—A and G—T

D. C—U and A—G

What is the base-pairing rule for purines and pyrimidines in the DNA molecule?

Formative Questions

1. A2. B3. C4. D

FQ 3

Formative Questions

A.chromatin and histones

B. DNA and protein

C. DNA and lipids

D. protein and centromeres

What are chromosomes composed of?

1. A

2. B

FQ 4

The work of Watson and Crick solved the mystery of how DNA works as a genetic code.

A. TrueB. False

Formative Questions

1. A2. B3. C4. D

FQ 5

Formative Questions

A. DNA ligase

B. DNA polymerase

C. hilicase

D. RNA primer

Which is not an enzyme involved in DNA replication?

1. A2. B3. C4. D

FQ 6

Which shows the basic chain of events in all organisms for reading and expressing genes?

A. DNA RNA protein

B. RNA DNA protein

C. mRNA rRNA tRNA

D. RNA processing

transcription translation

Formative Questions

1. A2. B3. C4. D

FQ 7

Formative Questions

In the RNA molecule, uracil replaces _______.

A. adenine

B. cytosine

C. purine

D. thymine

1. A2. B3. C4. D

FQ 8

Formative Questions

Which diagram shows messenger RNA (mRNA)?

A. B.

D.C

1. A2. B3. C4. D

FQ 9

Formative Questions

What characteristic of the mRNA molecule do scientists not yet understand?

A. intervening sequences in the mRNA molecule called introns

B. the original mRNA made in the nucleus called the pre-mRNA

C. how the sequence of bases in the mRNA molecule codes for amino acids

D. the function of many adenine nucleotides at the 5′ end called the poly-A tail

1. A2. B3. C4. D

FQ 10

Why do eukaryotic cells need a complex control system to regulate the expression of genes?

A. All of an organism’s cells transcribe the same genes.

B. Expression of incorrect genes can lead to mutations.

C. Certain genes are expressed more frequently than others are.

D. Different genes are expressed at different times in an organism’s lifetime.

Formative Questions

1. A2. B3. C4. D

FQ 11

Formative Questions

Which type of gene causes cells to become specialized in structure in function?

A. exon

B. Hox gene

C. intron

D. operon

1. A2. B3. C4. D

FQ 13

Formative Questions

Which is the most highly mutagenic?

A. chemicals in food

B. cigarette smoke

C. ultraviolet radiation

D. X rays

1. A2. B3. C4. D

CAQ 1

Look at the following figure. Identify the proteins that DNA first coils around.

Chapter Assessment Questions

A. chromatin fibers

B. chromosomes

C. histones

D. nucleosome

1. A2. B3. C4. D

CAQ 2


A. They determine size.

B. They determine body plan.

C. They determine sex.

D. They determine number

of body segments.

Explain how Hox genes affect an organism.

Explain the difference between body-cell and sex-cell mutation.


Answer: A mutagen in a body cell becomespart of the of the genetic sequence in that cell and in future daughter cells. The cell may die or simply not perform its normal function. These mutations are not passed on to the next generation. When mutations occur in sex cells, they will be present in every cell of the offspring.

CAQ 3

1. A2. B3. C4. D

STP 1

What does this diagram show about the replication of DNA in eukaryotic cells?

Standardized Test Practice

A. DNA is replicated only at certain places along the chromosome.

B. DNA replication is both semicontinuous and conservative.

C. Multiple areas of replication occur along the chromosome at the same time.

D. The leading DNA strand is synthesized discontinuously.

1. A2. B3. C4. D

STP 2


A. mRNA processing

B. protein synthesis

C. transcription

D. translation

What is this process called?

1. A2. B3. C4. D

STP 3


What type of mutation results in this change in the DNA sequence?

A. deletion

B. frameshift

C. insertion

D. substitution

TTCAGG TTCTGG

1. A2. B3. C4. D

STP 4


How could RNA interference be used to treat diseases such as cancer and diabetes?

A. by activating genes to produce proteins that can overcome the disease

B. by interfering with DNA replication in cells affected by the disease

C. by preventing the translation of mRNA into the genes associated with the disease

D. by shutting down protein synthesis

in the cells of diseased tissues

1. A

2. B

STP 5


The structure of a protein can be altered dramatically by the exchange of a single amino acid for another.

A. TrueB. False

DNA: The Genetic Material. Orientation On the top rail, the strand is said to be oriented 5′ to...

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