Bio 12
What is a replication fork?
A replication fork is a point in a DNA molecule where the two strands separate during replication.
If a species has 35 percent adenine in its DNA, what is the percentage of the other three bases?
35% thymine and 15% each of guanine and cytosine
List the chemical components of DNA.
5 carbon sugar molecules, phosphate groups, four different nitrogenous bases
How do the bases bond together
A bonds T and G bonds with C
DNA polymerase
principle enzyme involved in DNA replication
Base pairings
principle that bonds in DNA can form only between adenine and thymine and between guanine and cytosine
Replication
process of copying DNA prior to cell division
Nucleotides
subunit of which nucleic acids are composed; made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base
What enzyme makes it less likely that DNA will be lost from telomeres during replication?
telomerase
Describe the structure of DNA
It's a double helix with anti parallel strands. Bases pair together with hydrogen bonds. Phosphate groups and sugars are at the end with covalent bonds.
Amount of DNA-Prokaryotes
Less than eukaryotes
Location of DNA-Eukaryotes
Packaged in chro- mosomes in the nucleus
What are the sides of the DNA ladder made of
Phosphate, sugar groups
What are telomeres? Why are they important?
Repetitive DNA at the end of a eukaryotic chromosome. They make the DNA easier to replicate.
Nucleic acid
long, slightly acidic molecules originally identi ed in cell nuclei
Why are the strands of a DNA molecule said to be complementary?
Because each strand can be used to make the other strand.
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 Xray photo graphs of DNA revealed a spiral structure. Both of these findings helped Watson and Crick understand DNA's double helix and complementary base pairing.
The nucleotides in DNA are joined by what
Covalent bonds
Describe the structure of a nucleotide of DNA
DNA is made up of nucleotides, each with a deoxyribose molecule, a phosphate group, and a nitrogen-containing base. The four bases are adenine (A), guanine (G), cytosine (C), and thymine (T).
Where and in what form is prokaryotic DNA found? Where is eukaryotic DNA found?
DNA in prokaryotic cells is found in the form of a single circular chromosome in the cytoplasm; DNA in eukaryotic cells is found in the nucleus, packaged into big ger, individual chromosomes.
Starting Point(s) for Replication-Eukaryotes
Dozens or hundreds
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 micro scope available at the time.
What enzyme joins individual nucleotides to produce the new strand of DNA?
DNA polymerase
What is the role of DNA polymerase in DNA replication?
DNA polymerase joins individual nucleo tides to produce a new strand of DNA and proofreads each new strand so each molecule is a near perfect copy.
In your own words, describe the process of DNA replication.
DNA separates into two strands and produces two new complementary strands by the rules of base pairing.
Write out the full name of DNA
Deoxyribonucleic acid
What is the name of the sugar found in DNA
Deoxyribose
What is the shape of DNA
Double helix (ladder)
How is DNA unzipped at the replication fork
Enzymes break the hydrogen bonds between base pairs and unwinds the two strands of the molecule.
What are weak bonds that hold the two strands of DNA together at the nitrogenous bases, but also allow the DNA to separate and replicate called?
Hydrogen bonds
Why are hydrogen bonds so essential to the struc- ture of DNA?
Hydrogen bonds hold the paired nitrogen ous 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.
What could be the result of damaged DNA being replicated?
If damaged DNA is replicated, the cell that receives it may have altered genes, which could lead to serious consequences.
How does this enzyme work?
It adds short, repeated DNA sequences to telomeres.
The energy from UV light can excite electrons in the absorbing substance to the point where the electrons cause chemical changes. What chemical changes might occur in the nitrogenous bases of DNA?
It could change the bonds with the molecules.
Why is DNA called the blueprint of life
It holds all the genetic information
In what way is DNA like a book?
Like DNA, a book contains coded instructions for a cell to carry out important biological processes, such as how to move or transport ions. The book, like DNA, can also be copied and passed along to the next generation. These three tasks— storing, copying, and transmitting information—are also the three main functions of DNA.
What are the stairs of the DNA ladder made of
Nitrogenous bases
Is DNA replication always a foolproof process? Explain your answer.
No. Although many proteins check the DNA for damage or errors, damaged regions can still be replicated. This may result in gene alterations and serious complications for the organism.
Does DNA replication take place in the same direction along both strands of the DNA molecule that is being replicated? Explain your answer.
No. DNA replication proceeds in opposite directions between replication forks.
DNA is made of repeating units of building blocks called what
Nucleotides
In DNA what can be joined in any order
Nucleotides
DNA can be found in what main organelle
Nucleus
Where in the cell are chromosomes located
Nucleus
How does DNA replication differ in prokaryotic cells and eukaryotic cells?
Replication in most prokaryotic cells starts from a single point and proceeds in two directions until the entire chromosome is copied. In eukaryotic cells, replication may begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied.
Which scientists made X-ray diffraction photos of DNA?
Rosalind Franklin
What is a gene
Sequence of DNA that codes for a protein and thus determines a trait
Starting Point(s) for Replication-Prokaryotes
Single
Location of DNA-Prokaryotes
Singular, circular molecule in the cytoplasm
How is DNA replicated?
The DNA molecule separates into two strands at the replication fork. Each indi vidual strand is then used as a template for the attachment of complementary bases.
How might UV-induced chemical changes in bases affect the process of DNA replication?
The UV induced chemical change might cause enzymes not to work right during DNA replication causing the replication to happen wrong.
Our skin cells are exposed to UV light whenever they are in direct sunlight. How might this exposure affect base pairing in the DNA of our skin cells?
The UV light might weaken the bonds between the base pairing.
If the base sequence on a separated DNA strand is CGTAGG, what will the base sequence on its complementary strand be?
The complementary strand will be GCATCC.
Why is the pairing of bases during replication essential for the transmission of inherited traits from parent to offspring?
The match is (nearly always) perfect between A and T and G and C, so that the code is copied correctly every time. Offspring get the same sequence of bases their parents had.
What makes the new DNA strand complementary to the original strand?
The new DNA strand is complementary to the original strand because its base sequence is determined by the rules of base pairing. (Each strand can be used to make the other)
What is the first step in eukaryotic DNA replication?
The strands of the double helix separate, or unzip.
Amount of DNA-Eukaryotes
Up to 1000 times more than prokaryotes
What two scientists establish the structure of DNA
Watson & Crick
Did Watson and Crick's model account for the equal amounts of thymine and adenine in DNA? Explain.
Watson and Crick's model depicted DNA as a double helix with adenine and thymine paired together. This pair ing accounts for the equal amounts of thymine and adenine in DNA.
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 cyto sine and guanine.
Nitrogenous base
bases that contain nitrogen/DNA has four kinds of nitrogenous bases: adenine (ad uh neen), guanine (gwah neen), cyto- sine (sy tuh zeen), and thymine (thy meen)
Covalent bond
type of bond between atoms in which the electrons are shared
