2.7/7.1 (DNA Unit) Flashcards
Describe the meaning of “semi-conservative” in relation to DNA replication.
Semi-conservative means the products of DNA replication each contain one of the original DNA strands and one new strand.
Explain the role of complementary base pairing in DNA replication.
Complementary base pairing (A-T, C-G) ensures that the DNA sequence remains consistent after DNA replication. This ensures that the genetic code remains intact between generations.
State why DNA strands must be separated prior to replication.
The two strands of the parent DNA molecule must separate so that each can serve as a template for the new DNA strands that are being built.
Outline two functions of helicase.
Helicase is an enzyme that attaches to the DNA and moves along the molecule separating unwinding the helix and separating the two strands by breaking hydrogen bonds.
State the role of the origin of replication in DNA replication.
The origin of replication is the sequence of DNA nucleotides at which replication is initiated.
Contrast the number of origins in prokaryotic cells to the number in eukaryotic cells.
- Prokaryotic cells have 1 origin of replication (therefor one replication bubble with two replication forks)
- Eukaryotic cells have many origins of replication (therefor multiple replication bubbles that eventually fuse)
Describe the movement of DNA polymerase along the DNA template strand.
- DNA polymerase moves along the parent DNA strand from the 3’ end to the 5’ end of the parent strand. The parent/template is read from 3’ to 5’.
- DNA polymerase builds a complementary strand of DNA from the parent/template strand. The daughter strand is built from 5’ to 3’.
Describe the action of DNA polymerase III in pairing nucleotides during DNA replication.
- DNA polymerase “reads” a parent/template DNA strand and adds complementary nucleotides to build a new strand of DNA.
- DNA polymerase can only add new nucleotides to the 3’ end of the growing daughter strand.
Outline the features of DNA structure that suggested a mechanism for DNA replication.
- Complementary base pairing
- A to T, C to G ensure that genetic message conserved when each strand replicate
- Covalently bonded sugar-phosphate backbone
- relatively strong bonds keep nucleotides in backbone connected in correct sequence
- Hydrogen bonds between complementary strands
- allow complementary strands separate easily for replication
Compare replication on the leading strand and the lagging strand of DNA.
- On leading strand, DNA polymerase III move in same direction as helicase, adding complimentary nucleotides to growing daughter strand
- On lagging strand, DNA polymerase III move opposite as helicase
Explain why replication is different on the leading and lagging strands of DNA.
Because DNA polymerase III only add new nucleotides to 3’ of growing strand, replication run opposite on leading & lagging strands
Outline the formation of Okazaki fragments on the lagging strand.
Because DNA polymerase III moving away from replication fork on lagging strand, must build DNA in short sections called Okazaki fragments
Outline the role of the following proteins in DNA replications: helicase, topoisomerase (AKA gyrase), single stranded binding proteins, primase, DNA polymerase III, DNA polymerase I, and DNA ligase.
- Helicase open DNA helix by breaking hydrogen bonds between nitrogenous bases
- Topoisomerase (gyrase): hep relieve tension stress on DNA when unwinding
- Single stranded binding proteins: bind to single stranded DNA, preventing parent strands from reconnecting
- Primase: synthesize RNA primers needed to start replication
- DNA polymerase III: main enzyme that build complementary DNA strand by adding nucleotides in 5’ to 3’ direction
- DNA polymerase I remove RNA primer & replace with DNA nucleotides
- Ligase covalently bond sugar-phosphate backbone between adjacent okazaki fragments on lagging strand
Explain the need for RNA primers in DNA replication.
- Primer is short strand of RNA (=10 bases) tht act as starting point for DNA replication
- Needed because DNA polymerase III can only add nucleotides to existing strand
Explain what is meant by DNA replication occurring in a 5’ to 3’ direction.
- 5’ to 3’ has 2 meanings
- new DNA strand built from its 5’ end towards 3’ end
- new incoming nucleotide triphosphate added from its 5’ end to 3’ end of previously placed nucleotide