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Ch.7 DNA Structure and Replication
Terms in this set (52)
You inherit half of your DNA (23 chromosomes) from your mother and half from your father.
Where does your DNA come from?
Deoxyribonucleic acid (DNA)
The molecule of heredity, common to all life forms, that is passed from parents to offspring.
A single, large DNA molecule wrapped around proteins. _______ are located in the nuclei of most eukaryotic cells.
The building blocks of DNA.
Sugar, a Phosphate and a Base.
The sequence (As, Cs, Gs, Ts) along a DNA strand is unique to each person.
The spiral structure formed by two strands of DNA nucleotides bound together.
Fitting together; two strands of DNA are said to be complementary in that A always pairs with T, and G always pairs with C.
The DNA in a cell is like a set of instructions. It has the information to make any protein in your body and provides the cell with instructions on how to develop and function.
In general terms, what is the function of DNA in all living cells?
DNA is located inside the nucleus of cells where proteins needed to be read and express.
The commands for cell growth and function typically come from within this organelle. DNA, however, is the element that is making the actual 'commands'.
Describe the location of DNA in the cell.
DNA and proteins.
What two kinds of molecules make up a chromosome?
Long strands of DNA are wrapped around the proteins in order to condense the DNA so it will fit inside the nucleus of the cell.
How DNA & proteins organized structurally to form a chromosome?
23 pairs = 46 chromosomes
How many pairs of chromosomes are in a typical human cell?
One comes from the mother and the other comes from the father.
Where do each of the two chromosomes in each pair come from?
a phosphate, a sugar and a base.
The three parts of a nucleotide are?
Adenine (A), Thymine (T), Guanine (G) and Cytosine (C).
List the name and abbreviation of each of the four nucleotides found in DNA.
Their bases are what differ one from another
Examine the close-up of the DNA double helix shown here and identify the nucleotides labeled "C" and "G". In which of their three components do these two nucleotides differ from one another? Is the same true of "A" and "T"?
The phosphate and sugar components.
The parts of each nucleotide shown in the bands on the outside of the double helix are referred to as the "DNA backbone." Which two parts of the nucleotides form the DNA backbone?
Covalent bonds are strong and hold the strand of nucleotides together.
If this bond were weak, the DNA would break and would likely become nonfunctional.
In this diagram, solid lines represent covalent bonds.
Are these bonds relatively strong or relatively weak?
Why might it be advantageous for the backbone of each DNA strand to be held together by covalent bonds?
Which component of each nucleotide forms the "rungs" linking the two DNA strands together?
Hydrogen bonds between the bases hold the two strands together.
What type of chemical bond (represented by the dashed lines) holds the two strands together?
Hydrogen bonds are relatively weak compared to covalent bonds.
Are hydrogen bonds relatively strong or relatively weak compared to covalent bonds?
A - T (in DNA) and U (in RNA)
T - A
G - C
C - G
According to the rules of complementary pairing, write each one the abbreviation of the nucleotide it can bond on the opposite strand to create a "rung" linking two DNA strands together:
A (in DNA) (in RNA)
The sequence of nucleotide bases in the strands of DNA.
If all DNA is built of the same building blocks and always forms a double helix, what feature of each individual's DNA structure is unique?
The natural process by which cells make an identical copy of a DNA molecule.
Fitting together; two strands of DNA are said to be _______ in that A always pairs with T, and G always pairs with C.
An enzyme that "reads" the sequence of a DNA strand and helps to add complementary nucleotides to form a new strand during DNA replication.
DNA replication is _______ because each newly made DNA molecule has one original and one new strand of DNA.
Polymerase Chain Reaction
A laboratory technique used to replicate, and thus amplify, a specific DNA segment.
Cells must replicate their DNA before they reproduce, otherwise the only one of the resulting cells (daughter cells) after the division would contain a full genome.
Why must cells replicate their DNA before they reproduce?
Replace old and nonfunctional cells
Promote growth of the body (like the liver or bones).
List at least three examples of why cells in your body must reproduce.
1. The DNA 'unzips' by breaking the hydrogen bonds between the base pairs of the two strands.
2. DNA polymerase attaches to one strand and 'reads' the nucleotide sequence and adds complementary new nucleotides to the growing strand.
List and briefly describe the two basic steps of DNA replication.
It 'reads' the DNA strand and adds on complementary nucleotides to the growing new strand.
During DNA replication, what does DNA polymerase do?
It uses the rules of complementary base pairing to pair an A with a T, and a G with a C.
Its important because it ensures that the sequence of nucleotides in DNA remains the same, coding for the same proteins.
Explain how DNA polymerase uses the rules of complementary base pairing to complete its task. Why is this important?
There are two strands that make up the original DNA molecule prior to replication. There are 4 strands (2 DNA molecules) present after DNA replication.
How many individual DNA strands make up the original DNA molecule prior to replication? How many individual DNA strands are present after replication?
The "daughter molecules" are made up of one original DNA strand and one newly synthesized DNA strand. semi-conserved
The sequences of the original DNA molecule and the newly synthesized molecules are identical.
Describe the composition of the two newly formed DNA double helices ("daughter molecules") with respect to the two strands in the original DNA molecule. What about their sequences?
PCR amplification and DNA replication are similar in that they both involve separating the parent (or template) DNA strands, using DNA polymerase to add new complementary base pairs to the growing strand and, when finished, result in two daughter molecules of DNA that contain one strand of the template DNA and one strand of the newly synthesized DNA.
How is PCR amplification similar to DNA replication? Identify steps in each process that are the same.
The differences between that PCR occurs in a test tube (not a cell) and it only amplifies a specific region of DNA (not the whole chromosome).
Also, instead of enzymes separating the template strand for replication, PCR uses heat to separate the strands.
What are the differences between PCR and natural DNA replication?
1. Template DNA strand: this is the DNA that will be replicated.
2. Primers: these are short lengths of nucleotides that bind to a specific region of DNA and tell the DNA polymerase where to start replicating.
3. DNA Polymerase: the enzyme that reads the template strand and adds new complementary base pairs to the growing strand.
4. Nucleotides: are added as material for the DNA polymerase to use in order to create the new strands.
List the "ingredients" necessary for PCR and describe the function of each. The following "ingredients" are necessary for PCR:
1. All starting materials are added to the tube.
2. DNA is heated to cause it to separate.
3. Primers bind to the complementary region of DNA and act as a flag for the DNA polymerase to come and bind.
4. DNA polymerase binds to the primer/template DNA and starts replicating the DNA.
5. Once the DNA polymerase stops replicating, it dissociates from the template strand.
6. The tube is then cooled and the DNA strands come together and bind; one template strand with one newly synthesized strand. Now the process is ready to begin again!
List the steps of a single round of PCR in the correct order. Describe the roles of heating and cooling.
The PCR process can produce a large amount of DNA quickly because it is an exponential process. After one round of PCR, the template becomes two Now you have two templates in the tube. After the next round of PCR, each template becomes two again totaling in four. Four templates become eight, eight templates become 16 and so on and so forth.
In your own words, explain how the PCR process can produce such large amounts of DNA so quickly (in just a couple of hours).
A visual representation of a person's unique DNA sequence.
One complete set of genetic instructions encoded in the DNA of an organism.
Short Tandem Repeats
Sections of a chromosome in which DNA sequences are repeated.
A laboratory technique that separates fragments of DNA by size.
AGCT - 6
Assume that the nucleotides are color coded as follows: Yellow = A; Red = G; Green = C; Blue = T.
What is the STR that is repeated along that region?
How many times is the STR repeated along the maternal chromosome 7 of that individual?
PCR is used to amplify the DNA at multiple STR regions.
After DNA has been extracted from crime scene evidence, what is PCR used for?
Gel electrophoresis is used to separate fragments of DNA by length. The shorter the fragment of DNA, the quicker it moves through the gel.
Describe the process of gel electrophoresis. What determines how far each piece of DNA will travel through the gel?
STRs are a good source of DNA for DNA profiling because the DNA will be of varying length, depending on how many copies of the STR are present.
Explain what makes STRs good target regions for DNA profiling?
5; So 1 in ~ 3,200,000
10; So 1 in ~ 10,240,000,000,000
15; So 1 in ~ 327,690,000,000,000,000,000,000
What would the odds be of 2 people matching STR patterns at 5 sites? 10? 15?
The more STR sites included in the analysis, the less likely the chance that two people would match due to coincidence (or chance).
In your own words, explain why DNA profiling becomes more discriminating as more STR sites are included in the analysis.
Hair and bite mark samples are not conclusive enough evidence to identify a person.
Bite marks error rates of correctly identifying a person based on their bite pattern is as high as 91%. Hair samples only tell you characteristics about a person not positively identify one.
DNA evidence, on the other hand, is now the gold standard used to positively identify a perso
The original conviction rested, in part, on hair and bite mark samples taken from the crime scene. What's wrong with this evidence, and why should DNA evidence outweigh it?
PCR - Small amounts of DNA are amplified to very large amounts without changing the sequence of the DNA. The DNA analyzed by forensic scientists look at specific regions of the DNA STRs. Short Tandem Repeats are blocks of repeated DNA sequences. Which could be used by scientists to determine if a sample matches a suspect's DNA.
Prosecutors have argued that the amount of DNA obtained at the crime scene is minute. How can such a small sample be reliably used as evidence?
This could potentially happen if only one or two STR regions were studied. However, 15 STR regions are typically used in order to identify a person by their DNA. The odds of two people sharing the same 15 STR region characteristics is 1 in several quintillion.
We see people who share common traits all the time - even non-family members can have the same eye color, face shape, etc.
How do we know that two matching DNA profiles came from the same person if traits can be shared among people?
Couldn't the profiles come from two different people who just happen to share the profiles by chance?
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