DNA and Heredity. DNA and Heredity DNA is found in the cell’s nucleus_. DNA is found in the cell’s nucleus_____. In the nucleus, we find the

DNA and HeredityDNA and Heredity

DNA and HeredityDNA and Heredity

DNA is found in the cell’s __nucleus_______.DNA is found in the cell’s __nucleus_______. In the nucleus, we find the DNA in thin In the nucleus, we find the DNA in thin

threads calledthreads called_chromatin______._chromatin______. These thicken into larger rod-like These thicken into larger rod-like

structures calledstructures called__chromosomes_______.__chromosomes_______. Humans have Humans have __23 pairs_____23 pairs___ of of

chromosomes. Somechromosomes. Some species have species have __more___,__more___, others others _less___._less___.

DNA: The Genetic MaterialDNA: The Genetic Material

The instructions for inherited traits are The instructions for inherited traits are calledcalled_genes_______._genes_______. A A genegene is a small is a small segment of deoxyribonucleic acid, or DNA, segment of deoxyribonucleic acid, or DNA, that is located in a chromosome.that is located in a chromosome.

DNADNA is the primary material that causes is the primary material that causes _inheritable___inheritable__characteristics in related characteristics in related groups of organisms.groups of organisms.

DNA is a simple molecule, composed of DNA is a simple molecule, composed of onlyonly four different subunits.

DNA: The Genetic MaterialDNA: The Genetic Material

As early as 1900, scientists As early as 1900, scientists suspected suspected _units of heredity_____units of heredity____ were on chromosomes.were on chromosomes.

Most scientists thought Most scientists thought _proteins_____proteins____ not not _nucleic _nucleic __acids_____acids___ would control heredity. would control heredity.

Since chromosomes are Since chromosomes are _50/50_____50/50____ DNA and protein, this was not DNA and protein, this was not unreasonable.unreasonable.

Searching for the Genetic Searching for the Genetic MaterialMaterial

Three major Three major _experiments___experiments__ led to the led to the conclusion that DNA is the genetic material conclusion that DNA is the genetic material in cells. These experiments were performed in cells. These experiments were performed by Griffith, Avery, and Hershey and Chase.by Griffith, Avery, and Hershey and Chase.

_Griffith__Griffith_ worked with two related strains of worked with two related strains of bacteria which cause bacteria which cause _pneumonia__pneumonia_in mice.in mice.

Griffith discovered that when Griffith discovered that when harmlessharmless__live bacteria were mixed with __live bacteria were mixed with heat-killed disease-causing bacteria and heat-killed disease-causing bacteria and then injected into mice, the mice then injected into mice, the mice __died_.__died_.

Griffith’s Discovery of Griffith’s Discovery of Transformation Transformation

Searching for the Genetic Searching for the Genetic Material, Material, continuedcontinued

These results led Griffith to These results led Griffith to discoverdiscover_Transformation_._Transformation_. TransformationTransformation is a change in genotype is a change in genotype that is caused when cells take up foreign that is caused when cells take up foreign genetic material.genetic material.

Griffith’s experiments led to the conclusion Griffith’s experiments led to the conclusion that that _hereditary___hereditary__material could be material could be transferred between cells.transferred between cells.


Avery wanted to determine whether the Avery wanted to determine whether the transforming agent in Griffith’s transforming agent in Griffith’s experiments was experiments was protein, RNA, or DNAprotein, RNA, or DNA..

Avery used Avery used enzymesenzymes to destroy each of to destroy each of these molecules in heat-killed bacteria.these molecules in heat-killed bacteria.

Avery’s experiments led to the conclusion Avery’s experiments led to the conclusion that that DNADNA is responsible for transformation is responsible for transformation in bacteria.in bacteria.

Avery’s ExperimentAvery’s Experiment


Hershey and Chase studied Hershey and Chase studied bacteriophagesbacteriophages. Bacteriophages are . Bacteriophages are virusesviruses that infect bacterial cells and that infect bacterial cells and cause the cells to produce viruses.cause the cells to produce viruses.

By using By using radioactive isotopesradioactive isotopes, Hershey , Hershey and Chase showed that DNA, not protein, and Chase showed that DNA, not protein, is the genetic material in viruses.is the genetic material in viruses.

Hershey and ChaseHershey and Chase

Bacteriophages are made of only Bacteriophages are made of only __proteins___proteins_ and and __nucleic___nucleic_ __acids_.__acids_.

Hershey and Chase labeled the Hershey and Chase labeled the proteins with radioactive proteins with radioactive _sulfur_______sulfur______ and the nucleic acids and the nucleic acids with radioactive with radioactive _phosphorous__._phosphorous__.

BacteriophageBacteriophage



Because the radioactive proteins Because the radioactive proteins were found in the were found in the solution and the radioactive DNA was found inside the bacteria, this was proof that DNA controlled heredity.

The Shape of DNAThe Shape of DNA

A DNA molecule is shaped like a A DNA molecule is shaped like a spiral spiral staircasestaircase and is composed of two parallel and is composed of two parallel strands of linked subunits.strands of linked subunits.

The spiral shape of DNA is known as a The spiral shape of DNA is known as a double helix.double helix.

Each strand of DNA is made up of linked Each strand of DNA is made up of linked subunits called subunits called nucleotides..

The Shape of DNA, The Shape of DNA, continuedcontinued

A A nucleotidenucleotide is made up of three parts: is made up of three parts: a phosphate group, a five-carbon sugar group, and a nitrogen-containing base.

The phosphate groups and the sugar The phosphate groups and the sugar molecules of nucleotides link together to molecules of nucleotides link together to form a “form a “backbonebackbone” for the DNA strand.” for the DNA strand.

The five-carbon sugar in DNA is called The five-carbon sugar in DNA is called deoxyribose,deoxyribose, from which DNA gets its full from which DNA gets its full name, name, deoxyribonucleic acid.deoxyribonucleic acid.

DNADNA

nucleotideDOUBLEHELIX

Nitrogenbase

Sugarphosphate

The Information in DNAThe Information in DNA The information in DNA is contained in the The information in DNA is contained in the orderorder

of the bases, while the of the bases, while the base-pairing structure structure allows the information to be allows the information to be copiedcopied..

In DNA, each nucleotide has the same sugar In DNA, each nucleotide has the same sugar group and phosphate group, but each nucleotide group and phosphate group, but each nucleotide can have one of can have one of four nitrogenous basesfour nitrogenous bases..

The four kinds of bases are The four kinds of bases are adenineadenine (A), (A), guanineguanine (G), (G), thyminethymine (T), and (T), and cytosinecytosine (C). (C).

Bases A and G have a double-ring structure and Bases A and G have a double-ring structure and are classified as are classified as purinespurines..

The Information in DNA, The Information in DNA, continuedcontinued

Bases T and C have a single-ring structure and are Bases T and C have a single-ring structure and are classified as classified as pyrimidinespyrimidines..

A purine on one strand of a DNA molecule is A purine on one strand of a DNA molecule is always paired with a pyrimidine on the other always paired with a pyrimidine on the other strand. Specifically, strand. Specifically, adenine always pairs with always pairs with thymine, and , and guanine always pairs with always pairs with cytosine..

Base-pairing rulesBase-pairing rules are dictated by the chemical are dictated by the chemical structure of the bases.structure of the bases.

The The hydrogen bondshydrogen bonds between bases keep the between bases keep the two strands of DNA togethertwo strands of DNA together..

Discovering DNA’s StructureDiscovering DNA’s Structure

Watson and Crick used information from used information from experiments by Chargaff, Wilkins, and Franklin to experiments by Chargaff, Wilkins, and Franklin to determine the three-dimensional structure of determine the three-dimensional structure of DNA.DNA.

Chargaff showed that the amount of adenine showed that the amount of adenine always equaled the amount of thymine, and the always equaled the amount of thymine, and the amount of guanine always equaled the amount of amount of guanine always equaled the amount of cytosine.cytosine.

Franklin and WilkinsFranklin and Wilkins developed X-ray developed X-ray diffraction images of strands of DNA that diffraction images of strands of DNA that suggested the DNA molecule resembled a tightly suggested the DNA molecule resembled a tightly coiled helix.coiled helix.

X-Ray diffractionX-Ray diffraction

Discovering DNA’s Structure, Discovering DNA’s Structure, continuedcontinued

Watson and Crick used both Chargaff’s Watson and Crick used both Chargaff’s data and the X-ray diffraction studies to data and the X-ray diffraction studies to create a complete create a complete three-dimensional three-dimensional model ofmodel of DNA. DNA.

Their model showed a “spiral staircase” in Their model showed a “spiral staircase” in which two strands of nucleotides twisted which two strands of nucleotides twisted around a around a central axiscentral axis..

Watson and CrickWatson and Crick

DNA ReplicationDNA Replication Because DNA is made of two strands of Because DNA is made of two strands of

complementary base pairs, if the strands , if the strands are separated then each strand can serve as a are separated then each strand can serve as a pattern to make a new complementary strand.pattern to make a new complementary strand.

The process of making a copy of DNA is called The process of making a copy of DNA is called DNA replication..

In DNA replication, the DNA In DNA replication, the DNA molecule molecule unwindsunwinds, and the two sides split. Then, new , and the two sides split. Then, new bases are added to each side until two bases are added to each side until two identical sequences result.identical sequences result.

DNA Replication, DNA Replication, continuedcontinued As the double helix unwinds, the two As the double helix unwinds, the two

complementary strands of DNA separate from complementary strands of DNA separate from each other and form Y shapes. These Y-shaped each other and form Y shapes. These Y-shaped areas are called areas are called replication forks.replication forks.

At the replication fork, At the replication fork, new nucleotidesnew nucleotides are are added to each side and new base pairs are added to each side and new base pairs are formed according to the base-pairing rules.formed according to the base-pairing rules.

Each double-stranded DNA helix is made of Each double-stranded DNA helix is made of one one new strandnew strand of DNA and of DNA and one original strandone original strand of of DNA.DNA.

DNA ReplicationDNA Replication

Replication ProteinsReplication Proteins The replication of DNA involves many The replication of DNA involves many proteins that that

form a machinelike complex of moving parts. Each form a machinelike complex of moving parts. Each protein has a specific function.protein has a specific function.

Proteins called Proteins called DNA helicases unwind the DNA unwind the DNA double helix during DNA replication. These proteins double helix during DNA replication. These proteins wedge themselves between the two strands of the wedge themselves between the two strands of the double helix and break the hydrogen bonds double helix and break the hydrogen bonds between the base pairs.between the base pairs.

Proteins called Proteins called DNA polymerases catalyze the catalyze the formation of the DNA molecule by moving along formation of the DNA molecule by moving along each strand and adding nucleotides that pair with each strand and adding nucleotides that pair with each base.each base.

Replication Proteins, Replication Proteins, continuedcontinued

DNA polymerases also have a DNA polymerases also have a “proofreading“proofreading” function.” function.

During DNA replication, During DNA replication, mutations mutations sometime occur and the wrong nucleotide is sometime occur and the wrong nucleotide is added to the new strand.added to the new strand.

If a mismatch occurs, the DNA polymerase If a mismatch occurs, the DNA polymerase can backtrack, remove the incorrect can backtrack, remove the incorrect nucleotide, and replace it with the correct nucleotide, and replace it with the correct one. This will correct one. This will correct 9,999 out of 10,000 errors..

Prokaryotic and Eukaryotic Prokaryotic and Eukaryotic ReplicationReplication

All cells have All cells have chromosomeschromosomes, but eukaryotes and , but eukaryotes and prokaryotes replicate their chromosomes differently.prokaryotes replicate their chromosomes differently.

In prokaryotic cells, replication starts at a In prokaryotic cells, replication starts at a single single sitesite. In eukaryotic cells, replication starts at many . In eukaryotic cells, replication starts at many sites along the chromosome.sites along the chromosome.

Prokaryotic cells usually have a Prokaryotic cells usually have a singlesingle chromosome chromosome which is a closed loop attached to the inner cell which is a closed loop attached to the inner cell membrane.membrane.

Replication in prokaryotes begins at one place along Replication in prokaryotes begins at one place along the loop. This site is called the the loop. This site is called the origin of origin of replicationreplication..

Prokaryotic and Eukaryotic Prokaryotic and Eukaryotic Replication, Replication, continuedcontinued

Two Two replication forks begin at the origin of begin at the origin of replication in prokaryotes.replication in prokaryotes.

Replication occurs in Replication occurs in oppositeopposite directions until directions until the forks meet on the opposite side of the loop.the forks meet on the opposite side of the loop.

Eukaryotic cells often have several chromosomes Eukaryotic cells often have several chromosomes which are which are linearlinear and contain both DNA and and contain both DNA and protein.protein.

Replication starts at Replication starts at many sites along the along the chromosome. This process allows eukaryotic cells chromosome. This process allows eukaryotic cells to replicate their DNA faster than prokaryotes.to replicate their DNA faster than prokaryotes.


Two distinct replication forks form at each Two distinct replication forks form at each start site, and replication occurs in start site, and replication occurs in opposite directions.opposite directions.

This process forms This process forms replication replication “bubbles”“bubbles” along the DNA molecule. along the DNA molecule.

Replication bubbles continue to get Replication bubbles continue to get largerlarger as more of the DNA is copied.as more of the DNA is copied.

Prokaryotic v. EukaryoticProkaryotic v. Eukaryotic


The smallest eukaryotic chromosomes are often The smallest eukaryotic chromosomes are often 10 10 timestimes the size of a prokaryotic chromosome. the size of a prokaryotic chromosome. Eukaryotic chromosomes are so long that it would Eukaryotic chromosomes are so long that it would take take 33 days33 days to replicate a typical human to replicate a typical human chromosome if there were only one origin of chromosome if there were only one origin of replication.replication.

Human chromosomes are replicated in about Human chromosomes are replicated in about 100 100 sectionssections that are 100,000 nucleotides long, each that are 100,000 nucleotides long, each section with its own starting point.section with its own starting point.

Because eukaryotic cells have multiple replication Because eukaryotic cells have multiple replication forks working at the same time, an entire human forks working at the same time, an entire human chromosome can be replicated in about chromosome can be replicated in about 8 hours8 hours..

Documents

DNA and Heredity. DNA and Heredity DNA is found in the cell’s __nucleus_______. DNA is found in the cell’s __nucleus_______. In the nucleus, we find the

DNA and Heredity. DNA and Heredity DNA is found in the cell’s nucleus_. DNA is found in the cell’s nucleus_____. In the nucleus, we find the