D1.1 DNA Replication Flashcards
State that DNA replication is the production of exact copies of DNA with identical base sequences.
DNA replication → production of exact copies of DNA with identical base sequences
Outline the purposes of DNA replication.
Growth and tissue replacement in multicellular organisms
Reproduction
Explain the role of complementary base pairing in DNA replication.
Due to complementary base pairing, DNA replication is highly accurate due to complementary base pairing
Describe the meaning of “semi conservative” in relation to DNA replication.
Both new strands have a parent strand from original DNA and one newly synthesized strand
State why DNA strands must be separated prior to replication.
Allow the primer and polymerase to attach to the single strand
Outline the role of helicase in DNA replication.
Unwinds the DNA double helix by breaking hydrogen bonds between complementary nucleotides.
Outline the role of DNA polymerases in DNA replication.
Moves along each strand of DNA linking nucleotides to form a growing chain of nucleotides using pre-existing strand as a template
State that there are separate DNA polymerases for each stand of template DNA.
Each strand of DNA has its own DNA polymerase
State the function of the PCR.
Amplify a DNA sequence from a small sample
Outline the process of the PCR, including the use of primers, temperature changes and Taq polymerase.
Denaturation : DNA sample heated to 95 C to break h - bonds and separate two DNA strands
Annealing : Temperature reduced to 54 C allows DNA primers to bind to both strands of DNA, next to the sequence that needs copied
Temperature increased to 72 C allowing Taq DNA polymerase to replicate both strands, starting at the primer, producing two identical double stranded DNA molecules.
Steps 1-3 repeated to produce many more copies of DNA
Outline the procedure for DNA electrophoresis.
Restriction enzymes cut DNA at specific sequences
Due to different individuals having different DNA, the location of restriction sites varies
Meaning each individual will have different sized fragments.
The fragments is then in wells in an agarose gel
Gel is located in a buffer filled chamber with a positive and negative side. DNA is located on the negative side
When the chamber is turned on DNA fragments will move to the positive side, at different speeds, smaller fragments moving faster and further within a given time
Describe how and why DNA fragments separate during electrophoresis.
Because the DNA fragments vary in size the smaller fragments moving faster and thus farther within a given time.
List applications of the PCR.
Forensic investigations
Paternity testing
Outline the use of the PCR in testing for viral infection.
Can be used to detect viral infections
Discuss advantages and disadvantages of using the PCR test for viral infections.
Advantages
High sensitivity and specificity
Multiplexing multiple viruses can be detected per test.
Disadvantagess
Long turnaround times for results
False positives can be yielded if samples aren’t collected at right times
Outline the process of DNA profiling.
Collect: Obtain DNA sample.
Amplify: Use PCR to copy DNA.
Separate: Analyze DNA fragments by size using gel electrophoresis
Count: Determine repeat units.
Match: Compare for identification.
List applications of DNA profiling.
Used to determine paternity
State that DNA polymerases can only add free nucleotides to an existing DNA strand.
DNA polymerase can only add free nucleotides to existing DNA strands
List example sources of DNA that can be used in DNA profiling.
Hair, Blood, Saliva, Semen
State that DNA polymerases can only add the 5’ phosphate of a free nucleotide to the 3’ deoxyribose of the elongating strand.
DNA polymerases can only add the 5’ phosphate of a free nucleotide to the 3’ deoxyribose of the elongating strand.
Explain why replication is different on the leading and lagging strands of DNA.
Because the polymerase on the lagging strand moves away from the replication fork
Compare the pace and direction of replication on the leading and lagging strands of DNA.
The leading strand’s DNA replication is continuous and the lagging strand is discontinuous
The leading strand’s DNA replicates towards the replication fork
The lagging strand moves away from the replication form
Outline the formation of Okazaki fragments on the lagging strand.
Due to the lagging strand polymerase moving away from the replication fork, the lagging strand has multiple fragments of DNA called Okazaki fragments.
Explain the need for RNA primers in DNA replication.
RNA primers attaches to the template strand allowing the polymerase to attach itself
Outline the function of the enzyme DNA primase.
Attaches small RNA primers to template strand
Compare the number of RNA primers on the leading and lagging strands.
One RNA primer on leading strand
RNA primers placed at intervals on lagging strand
Outline the function of the enzyme DNA polymerase III.
Assemble new strands of DNA by placing free nucleotides in the correct sequence according to the base sequence of the template strand. Only able to build strands in 5’ to 3’ direction.
Outline the function of the enzyme DNA polymerase I.
Removes RNA nucleotides of primers and replaces them with correct DNA nucleotides
Outline the function of the enzyme DNA ligase.
To connect Okazaki fragments
Explain why there are gaps between adjacent Okazaki fragments on the lagging strand.
Because the polymerase III adds nucleotides in the opposite direction of the replication fork meaning it reaches the end of the strand.
State the function of DNA proofreading.
To correct mismatched bases
Outline the process of DNA proofreading by DNA polymerase III.
As the newly formed DNA is being built, if a nucleotide is placed with a mismatched base, an incorrect nucleotide is removed and replaced with a correctly matching one.
