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 in thin threads called_chromatin______. In the nucleus, we find the DNA in thin threads called_chromatin______. These thicken into larger rod-like structures called__chromosomes_______. These thicken into larger rod-like structures called__chromosomes_______. Humans have __23 pairs___ of chromosomes. Some Humans have __23 pairs___ of chromosomes. Some species have __more___, others _less___. species have __more___, others _less___.

DNA: The Genetic Material The instructions for inherited traits are called_genes_______. A gene is a small segment of deoxyribonucleic acid, or DNA, that is located in a chromosome. The instructions for inherited traits are called_genes_______. A gene is a small segment of deoxyribonucleic acid, or DNA, that is located in a chromosome. DNA is the primary material that causes _inheritable__characteristics in related groups of organisms. DNA is the primary material that causes _inheritable__characteristics in related groups of organisms. DNA is a simple molecule, composed of only DNA is a simple molecule, composed of only four different subunits.

DNA: The Genetic Material As early as 1900, scientists suspected _units of heredity____ were on chromosomes. As early as 1900, scientists suspected _units of heredity____ were on chromosomes. Most scientists thought _proteins____ not _nucleic __acids___ would control heredity. Most scientists thought _proteins____ not _nucleic __acids___ would control heredity. Since chromosomes are _50/50____ DNA and protein, this was not unreasonable. Since chromosomes are _50/50____ DNA and protein, this was not unreasonable.

Searching for the Genetic Material Three major _experiments__ led to the conclusion that DNA is the genetic material in cells. These experiments were performed by Griffith, Avery, and Hershey and Chase. Three major _experiments__ led to the conclusion that DNA is the genetic material in cells. These experiments were performed by Griffith, Avery, and Hershey and Chase. _Griffith_ worked with two related strains of bacteria which cause _pneumonia_in mice. _Griffith_ worked with two related strains of bacteria which cause _pneumonia_in mice. Griffith discovered that when harmless__live bacteria were mixed with heat-killed disease- causing bacteria and then injected into mice, the mice __died_. Griffith discovered that when harmless__live bacteria were mixed with heat-killed disease- causing bacteria and then injected into mice, the mice __died_.

Griffith’s Discovery of Transformation

Searching for the Genetic Material, continued These results led Griffith to discover_Transformation_. Transformation is a change in genotype that is caused when cells take up foreign genetic material. These results led Griffith to discover_Transformation_. Transformation is a change in genotype that is caused when cells take up foreign genetic material. Griffith’s experiments led to the conclusion that _hereditary__material could be transferred between cells. Griffith’s experiments led to the conclusion that _hereditary__material could be transferred between cells.

Searching for the Genetic Material, continued Avery wanted to determine whether the transforming agent in Griffith’s experiments was protein, RNA, or DNA. Avery wanted to determine whether the transforming agent in Griffith’s experiments was protein, RNA, or DNA. Avery used enzymes to destroy each of these molecules in heat-killed bacteria. Avery used enzymes to destroy each of these molecules in heat-killed bacteria. Avery’s experiments led to the conclusion that DNA is responsible for transformation in bacteria. Avery’s experiments led to the conclusion that DNA is responsible for transformation in bacteria.

Avery’s Experiment

Searching for the Genetic Material, continued Hershey and Chase studied bacteriophages. Bacteriophages are viruses that infect bacterial cells and cause the cells to produce viruses. Hershey and Chase studied bacteriophages. Bacteriophages are viruses that infect bacterial cells and cause the cells to produce viruses. By using radioactive isotopes, Hershey and Chase showed that DNA, not protein, is the genetic material in viruses. By using radioactive isotopes, Hershey and Chase showed that DNA, not protein, is the genetic material in viruses.

Hershey and Chase Bacteriophages are made of only __proteins_ and __nucleic_ __acids_. Bacteriophages are made of only __proteins_ and __nucleic_ __acids_. Hershey and Chase labeled the proteins with radioactive _sulfur______ and the nucleic acids with radioactive _phosphorous__. Hershey and Chase labeled the proteins with radioactive _sulfur______ and the nucleic acids with radioactive _phosphorous__.

Bacteriophage

Hershey and Chase

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

The Shape of DNA A DNA molecule is shaped like a spiral staircase and is composed of two parallel strands of linked subunits. A DNA molecule is shaped like a spiral staircase and is composed of two parallel strands of linked subunits. The spiral shape of DNA is known as a double helix. The spiral shape of DNA is known as a double helix. Each strand of DNA is made up of linked subunits called. Each strand of DNA is made up of linked subunits called nucleotides.

The Shape of DNA, continued A nucleotide is made up of three parts: A nucleotide 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 molecules of nucleotides link together to form a “backbone” for the DNA strand. The phosphate groups and the sugar molecules of nucleotides link together to form a “backbone” for the DNA strand. The five-carbon sugar in DNA is called deoxyribose, from which DNA gets its full name, deoxyribonucleic acid. The five-carbon sugar in DNA is called deoxyribose, from which DNA gets its full name, deoxyribonucleic acid.

DNA nucleotide DOUBLE HELIX Nitrogen base Sugar phosphate

The Information in DNA The information in DNA is contained in the order of the bases, while the structure allows the information to be copied. The information in DNA is contained in the order of the bases, while the base-pairing structure allows the information to be copied. In DNA, each nucleotide has the same sugar group and phosphate group, but each nucleotide can have one of four nitrogenous bases. In DNA, each nucleotide has the same sugar group and phosphate group, but each nucleotide can have one of four nitrogenous bases. The four kinds of bases are adenine (A), guanine (G), thymine (T), and cytosine (C). The four kinds of bases are adenine (A), guanine (G), thymine (T), and cytosine (C). Bases A and G have a double-ring structure and are classified as purines. Bases A and G have a double-ring structure and are classified as purines.

The Information in DNA, continued Bases T and C have a single-ring structure and are classified as pyrimidines. Bases T and C have a single-ring structure and are classified as pyrimidines. A purine on one strand of a DNA molecule is always paired with a pyrimidine on the other strand. Specifically, always pairs with, and always pairs with. A purine on one strand of a DNA molecule is always paired with a pyrimidine on the other strand. Specifically, adenine always pairs with thymine, and guanine always pairs with cytosine. Base-pairing rules are dictated by the chemical structure of the bases. Base-pairing rules are dictated by the chemical structure of the bases. The hydrogen bonds between bases keep the two strands of DNA together. The hydrogen bonds between bases keep the two strands of DNA together.

Discovering DNA’s Structure used information from experiments by Chargaff, Wilkins, and Franklin to determine the three-dimensional structure of DNA. Watson and Crick used information from experiments by Chargaff, Wilkins, and Franklin to determine the three-dimensional structure of DNA. showed that the amount of adenine always equaled the amount of thymine, and the amount of guanine always equaled the amount of cytosine. Chargaff showed that the amount of adenine always equaled the amount of thymine, and the amount of guanine always equaled the amount of cytosine. Franklin and Wilkins developed X-ray diffraction images of strands of DNA that suggested the DNA molecule resembled a tightly coiled helix. Franklin and Wilkins developed X-ray diffraction images of strands of DNA that suggested the DNA molecule resembled a tightly coiled helix.

X-Ray diffraction

Discovering DNA’s Structure, continued Watson and Crick used both Chargaff’s data and the X-ray diffraction studies to create a complete three-dimensional model of DNA. Watson and Crick used both Chargaff’s data and the X-ray diffraction studies to create a complete three-dimensional model of DNA. Their model showed a “spiral staircase” in which two strands of nucleotides twisted around a central axis. Their model showed a “spiral staircase” in which two strands of nucleotides twisted around a central axis.

Watson and Crick

DNA Replication Because DNA is made of two strands of, if the strands are separated then each strand can serve as a pattern to make a new complementary strand. Because DNA is made of two strands of complementary base pairs, if the strands are separated then each strand can serve as a 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 molecule unwinds, and the two sides split. Then, new bases are added to each side until two identical sequences result. In DNA replication, the DNA molecule unwinds, and the two sides split. Then, new bases are added to each side until two identical sequences result.

DNA Replication, continued As the double helix unwinds, the two complementary strands of DNA separate from each other and form Y shapes. These Y-shaped areas are called replication forks. As the double helix unwinds, the two complementary strands of DNA separate from each other and form Y shapes. These Y-shaped areas are called replication forks. At the replication fork, new nucleotides are added to each side and new base pairs are formed according to the base-pairing rules. At the replication fork, new nucleotides are added to each side and new base pairs are formed according to the base-pairing rules. Each double-stranded DNA helix is made of one new strand of DNA and one original strand of DNA. Each double-stranded DNA helix is made of one new strand of DNA and one original strand of DNA.

DNA Replication

Replication Proteins The replication of DNA involves many that form a machinelike complex of moving parts. Each protein has a specific function. The replication of DNA involves many proteins that form a machinelike complex of moving parts. Each protein has a specific function. Proteins called unwind the DNA double helix during DNA replication. These proteins wedge themselves between the two strands of the double helix and break the hydrogen bonds between the base pairs. Proteins called DNA helicases unwind the DNA double helix during DNA replication. These proteins wedge themselves between the two strands of the double helix and break the hydrogen bonds between the base pairs. Proteins called catalyze the formation of the DNA molecule by moving along each strand and adding nucleotides that pair with each base. Proteins called DNA polymerases catalyze the formation of the DNA molecule by moving along each strand and adding nucleotides that pair with each base.

Replication Proteins, continued DNA polymerases also have a “proofreading” function. DNA polymerases also have a “proofreading” function. During DNA replication, mutations sometime occur and the wrong nucleotide is added to the new strand. During DNA replication, mutations sometime occur and the wrong nucleotide is added to the new strand. If a mismatch occurs, the DNA polymerase can backtrack, remove the incorrect nucleotide, and replace it with the correct one. This will correct. If a mismatch occurs, the DNA polymerase can backtrack, remove the incorrect nucleotide, and replace it with the correct one. This will correct 9,999 out of 10,000 errors.

Prokaryotic and Eukaryotic Replication All cells have chromosomes, but eukaryotes and prokaryotes replicate their chromosomes differently. All cells have chromosomes, but eukaryotes and prokaryotes replicate their chromosomes differently. In prokaryotic cells, replication starts at a single site. In eukaryotic cells, replication starts at many sites along the chromosome. In prokaryotic cells, replication starts at a single site. In eukaryotic cells, replication starts at many sites along the chromosome. Prokaryotic cells usually have a single chromosome which is a closed loop attached to the inner cell membrane. Prokaryotic cells usually have a single chromosome which is a closed loop attached to the inner cell membrane. Replication in prokaryotes begins at one place along the loop. This site is called the origin of replication. Replication in prokaryotes begins at one place along the loop. This site is called the origin of replication.

Prokaryotic and Eukaryotic Replication, continued Two begin at the origin of replication in prokaryotes. Two replication forks begin at the origin of replication in prokaryotes. Replication occurs in opposite directions until the forks meet on the opposite side of the loop. Replication occurs in opposite directions until the forks meet on the opposite side of the loop. Eukaryotic cells often have several chromosomes which are linear and contain both DNA and protein. Eukaryotic cells often have several chromosomes which are linear and contain both DNA and protein. Replication starts at along the chromosome. This process allows eukaryotic cells to replicate their DNA faster than prokaryotes. Replication starts at many sites along the chromosome. This process allows eukaryotic cells to replicate their DNA faster than prokaryotes.

Prokaryotic and Eukaryotic Replication, continued Two distinct replication forks form at each start site, and replication occurs in opposite directions. Two distinct replication forks form at each start site, and replication occurs in opposite directions. This process forms replication “bubbles” along the DNA molecule. This process forms replication “bubbles” along the DNA molecule. Replication bubbles continue to get larger as more of the DNA is copied. Replication bubbles continue to get larger as more of the DNA is copied.

Prokaryotic v. Eukaryotic

Prokaryotic and Eukaryotic Replication, continued The smallest eukaryotic chromosomes are often 10 times the size of a prokaryotic chromosome. Eukaryotic chromosomes are so long that it would take 33 days to replicate a typical human chromosome if there were only one origin of replication. The smallest eukaryotic chromosomes are often 10 times the size of a prokaryotic chromosome. Eukaryotic chromosomes are so long that it would take 33 days to replicate a typical human chromosome if there were only one origin of replication. Human chromosomes are replicated in about 100 sections that are 100,000 nucleotides long, each section with its own starting point. Human chromosomes are replicated in about 100 sections that are 100,000 nucleotides long, each section with its own starting point. Because eukaryotic cells have multiple replication forks working at the same time, an entire human chromosome can be replicated in about 8 hours. Because eukaryotic cells have multiple replication forks working at the same time, an entire human chromosome can be replicated in about 8 hours.