Biology Chapter 12 - Identifying the Substance of Genes
The principal enzyme involved in DNA replication is called ________________.
DNA polymerase
What was the significance of the radioactive isotopes Hershey and Chase chose?
Phosphorus is abundant in DNA, while sulfur is abundant in protein
Describe Watson and Crick's model of the DNA molecule.
Watson and Crick's model is composed of two antiparallel strands that are connected by hydrogen bonds between nitrogenous bases. Hydrogen bonds form between adenine and thymine and between cytosine and guanine.
What technique did Franklin use to study DNA?
X-ray diffraction
What are nucleic acids?
long, slightly acidic molecules originally identified in cell nucleic.
Nucleic acids are made up of _____________________ linked together to form long chains.
nucleotides
In most prokaryotes, DNA replication does not start until ___________________ bind to a single starting point on the chromosome. This triggers the beginning of DNA replication.
regulatory proteins
Before a cell divides, it duplicates its DNA in a copying process called __________________.
replication
The foremost job of DNA, as the molecule of heredity, is to ____________________.
store information
What are three key roles of DNA?
storing, copying, and transmitting information
What radioactive isotopes were used in the Hershey-Chase experiments?
sulfur-35 and phosphorus -32
base pairing
the nearly perfect fit between A-T and G-C nucleotides
Eukaryotic cells, can have up to _________________ more DNA.
1000 times.
What clues did bacterial transformation yield about the gene?
Avery and other scientists discovered that the nucleic acid DNA stores and transmits genetic information from one generation of bacteria to the next.
Describe the discoveries that led to the modeling of DNA.
Chargaff determined that, in a double-stranded DNA molecule, adenine and thymine are present in equal proportions and guanine and cytosine are present in equal proportions. Franklin's X-ray photographs of DNA revealed a spiral structure. Both of these findings helped Watson and Crick understand DNA's double helix and complementary base pairing.
What are the chemical components of DNA?
DNA is a nucleic acid made up of nucleotides joined into long stands or chains by covalent bonds.
Why did scientists have to use tools other than microscopes to solve the structure of DNA?
DNA is too small to be examined with a light microscope—the only kind of microscope available at the time.
the result of replication is two __________________ identical to each other and to the original molecule.
DNA molecules
Replication in most prokaryotic cells starts from a single point and proceeds in two directions until the entire chromosome is copied.
DNA replication in prokaryotic cells
Alfred Hershey
Determined that genetic DNA, not protein, was the genetic material using experiments about bacteriophages
___________________ discovered that the percentages of adenine and thymine bases are almost equal in any sample of DNA. The same thing is true for the other nucleotides, guanine and cytosine.
Erwin Chargaff
__________________ chromosomes are generally much bigger than those of prokaryotes.
Eukaryotic
List the conclusions Griffith, Avery, Hershey, and Chase drew from their experiments.
Griffith: He concluded that bacteria can transform other bacteria through the passing of genes, given to the offspring of the transformed bacteria. Avery: He discovered that DNA was the transforming factor, which is stored in nucleic acid and transmits genetic information from one generation of bacteria to the future generations.
What role did bacterial viruses play in identifying genetic material?
Hershey and Chase's experiment with bacteriophages convincing many scientists that DNA was the genetic material found in genes - not just in viruses and bacteria, but also in all living cells.
Why are hydrogen bonds so essential to the structure of DNA?
Hydrogen bonds hold the paired nitrogenous bases together. Because hydrogen bonds are weak bonds, the two strands of DNA are easily separated—a characteristic that is important to DNA's function.
At the same time as Franklin, ____________________, an American biologist, and Francis Crick, a British physicist, were also trying to understand the structure of DNA.
James Watson
Oswald Avery
Proved that DNA is the genetic material of bacteria.
What is the role of DNA in heredity?
The DNA that makes up genes must be capable of storing, copying, and transmitting the genetic information in a cell.
What clues helped scientists solve the structure of DNA?
The clues in Franklin's X-ray pattern enabled Watson and Crick to build a model that explained the specific structure and properties of DNA.
What does the double-helix model tell us about DNA?
The double-helix model explains Chargaff's rule of base pairing and how the two strands of DNA are held together.
What was the experimental variable that Avery used when he repeated Griffith's work?
The variable he used was using molecules from heat killed bacteria like Griffith did.
Why did Hershey and Chase grow viruses in cultures that contained both radioactive phosphorus and radioactive sulfur? What might have happened if they had used only one radioactive substance?
They used the two types because of the fact that phosphorus is very scarce in proteins, and sulfur isn't found in DNA. If they had only used one instead of the other, then the results wouldn't have been valid because the markers wouldn't have shown up on the results.
Why would the storage of genetic information in genes help explain why chromosomes are separated so carefully during mitosis?
They would be separated so carefully because one extra or one less chromosome more, and the cell would be completely changed and even destroyed.
What conclusion did Hershey and Chase draw from their experiments?
They're conclusion was that DNA was the genetic material instead of genes because of the marker they had used to observe this.
Did Watson and Crick's model account for the equal amounts of thymine and adenine in DNA?
Watson and Crick's model depicted DNA as a double helix with adenine and thymine paired together. This pairing accounts for the equal amounts of thymine and adenine in DNA.
In the 1950s, Bristish scientist Rosalind Franklin used a technique called ___________________________ to get information about the structure of the DNA molecule.
X-ray diffraction
X-ray diffraction revealed an _______________________ showing that the strands of DNA are twisted around each other like the coils of a spring.
X-shaped pattern
In base pairing between DNA strands, hydrogen bonds are formed between what?
adenine and thymine
DNA has four kinds of nitgrogenous bases : ___________________, _____________________, ___________________, and _____________________.
adenine, guanine, cytosine, and thymine
These three functions (of storing, copying, and transmitting) are ___________________ to the way in which you might share a treasured book, as pictures in the figure.
analogous
The chromosomes separate from each other in _________________ of mitosis, producing two cells, each with a complete set of genes coded in the DNA.
anaphase
The kind of virus that infects bacteria is known as a _______________________ which means "bacteria eater".
bacteriophage
Each strand can be used to make the other strand, the strands are said to be ____________________.
complementary
The nucleotides in a strand of DNA are joined by _______________________ formed between their sugar and phosphate groups.
covalent bonds
How are nucleotides joined together to form the DNA chain?
deoxyribose molecules and phosphate groups
DNA's nucleotides are made up of three basic components : a 5-carbon sugar called _________________, a _______________________, and a ______________________.
deoxyribose, phosphate group, nitrogenous base
The viral genes act to produce may new bacteriophages, which gradually _____________ the bacterium.
destroy
Hershey-Chase Experiment
determined that DNA is the genetic material
Genes control patterns of _______________________, which means that the instructions that cause a single cell to develop into an oak tree, a sea urchin, or a dog must somehow be written into the DNA of each of these organisms.
development
DNA replication is carried out by a series of _______________.
enzymes
When a bacteriophage enters a bacterium, it attaches to the surface of the bacterial cell and injects its ______________________________ into it.
genetic information
When a cell divides, each daughter cell must receive a complete copy of the ________________________.
genetic information
If the base on the old strand is cytosine, then __________________ is added to the newly forming strand.
guanine
Watson and Crick discovered that ___________________ could form between certain nitrogenous bases, providing just enough force to hold the two DNA strands together.
hydrogen bonds
What role does DNA polymerase play in copying DNA?
it is an enzyme that joins individual nucleotides to produce a new strand of DNA.
Before a cell divides it must....
make a complete copy of every one of its genes, similar to the way that a book is copied.
Careful sorting is especially important during the formation of reproductive cells in ____________________.
meiosis
The double-helix arrangement enables the _________________________ on both strands to come into contact at the center of the molecule.
nitrogenous bases
List the chemical components of DNA
nucleic acid composed of nucleotides joined into long chains by covalent bonds.
DNA polymerase is an enzyme that joins individual ___________________ to produce a new strand of DNA.
nucleotides
Nearly all of the DNA of eukaryotic cells is found in the ________________________.
nucleus
In the double-helix model, the two strands of DNA are "antiparallel" - they run in ____________________________.
opposite directions
transformation
process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria
DNA polymerase also _______________ each new DNA strand, ensuring that each molecule is a perfect copy of the original.
proofreads
Two copies of DNA produced by replication in each chromosome remain closely associated until the cell enters ___________________ of mitosis.
prophase
All nucleotides contain each of the following except?
protein
The double-helix arrangement also allows each strand of the double helix to carry a ______________________________, arranged almost like letters in a four-letter alphabet.
sequence of nucleotides
An enzyme called ____________________ compensates for this problem by adding short, repeated DNA sequences to telomeres, lenghtening the chromosomes slightly and making it less likely that important gene sequences will be lost from the telomeres during replication.
telomerase
the tips of centromeres are known as _________________.
telomeres
Each strand of the double helix of DNA serves as __________________ or model, for the new strand.
template
During DNA replication, enzymes "unzip" a molecule of DNA by breaking __________________ between base pairs and unwinding the two strands of the molecule.
the hydrogen bonds
If the base on the old strands is adenine, then __________________ is added to the newly forming strand.
thymine
A double-helix looks like a _____________________.
twisted ladder
The angle of the X-shaped pattern suggested that there are ________________ in the structure.
two strands
the two strands of the double-helix separate or "_____________" , allowing two replication forks to form.
unzip
Hydrogen bonds are relatively ___________________ that allow two strands of the helix to separate.
weak chemical forces
Martha Chase
worked with Alfred Hershey and used radioactivity to study DNA
In eukaryotic cells, replication may be at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied.
DNA replication in eukaryotic cells
What did Hershey and Chase's experiment confirmed?
DNA was genetic material found in genes
