DNA Replication Flashcards
Meselson and Stahl big idea
DNA undergoes semiconservative replication
What does semiconservative replication mean?
DNA opens gets copied and a new strand bonds with an old strand
Step 1 of DNA Replication
DNA must unwind to expose a single stranded template
What enzymes do step 1 of DNA replication use?
- Helicase
- Topoisomerases (Gyrase)
What does helicase do?
- Unzips and unwinds the double helix
- Breaks hydrogen bonds
What does topoisomerase (gyrase) do?
- Detangler
- Prevents supercoils by nicking and resealing DNA
Step 2 of DNA Replication
DNA must be held open, not to reform a coil
What do Single Stranded Binding Proteins do?
- Bind to the uncoiled DNA and keep it open
Step 3 of DNA Replication
A primer must be created before DNA synthesis can occur
What is primer?
- Short sequence of RNA, complementary to template
- 3’ end where DNA synthesis can begin
What is primase?
Enzyme that synthesizes RNA primer
What is RNA polymerase?
Synthesizes primers on leading strand
Note about primase
Primase is a type of RNA polymerase
Leading strand
- New strand that is synthesized continuously
- Synthesized towards replication fork
Lagging Strand
- Synthesized in short fragments called Okazaki fragments which are later joined together
- Discontinuously
- Synthesized away from replication fork
Step 4 of DNA Replication
DNA synthesis begins
What is DNA polymerase 3
- Enzyme that catalyzes the addition of nucleotides complementary to the template strand
What is a nucleoside triphosphate
- Free floating nucleotides with extra phosphate for energy
- Each nucleotide that is added to a growing DNA strand is a nucleoside triphosphate
What does the phosphate in a nucleoside triphosphate do?
- The phosphate provides energy needed to drive the reaction that makes phosphodiester bonds
What direction does DNA synthesis occur in?
5’ to 3’ direction
DNA polymerase 1, first function
- Edits mistakes
- Proofreads chain
- Exonuclease activity
Step 5 of DNA Replication
Synthesis of DNA occurs on both template strands
Step 6 of DNA Replication
RNA primers are removed
DNA polymerase 1, second function
- chews up RNA primers and replaces them with DNA nucleotides
- All primers are removed
What is Nick Translation?
When primers are replaced by DNA nucleotides
Step 7 of DNA Replication
All nicks are repaired
What is DNA Ligase
- Acts like glue to make phosphodiester linkages
- Seals the nicks between Okazaki fragments
