The “Central Dogma" of Biology (DNA Replication and Protein Synthesis) Concept 2: Analyzing the processes of DNA replication Holtzclaw: p. 117-122 Campbell: Ch 16

The Main Point… What IS DNA? Why does DNA have to replicate? Cell Division Discussion

The Main Point…

Concept 2: Analyzing the processes of DNA replication You must know: The structure of DNA. The major steps to replication. The differences between replication, transcription, and translation. How DNA is packaged into a chromosomes.

Concept 2: Analyzing the processes of DNA replication You must know: The structure of DNA. The major steps to replication. The differences between replication, transcription, and translation. How DNA is packaged into a chromosomes. Already learned.

Try These! Consider the following DNA strand: Complete it! 3’-A T G C G C T -5’ How can you tell the 5’ end from the 3’ end? If the DNA in an onion is found contain 30% adenine, what percentage of the onion DNA bases would be cytosine? Explain how DNA, chromatin, and chromosomes are related.

Let’s Discuss  Handout Animations from Campbell Bioflix DNA Replication Animation (2nd half)

DNA Replication Some vocab: parent strand daughter strand leading strand lagging strand Okazaki fragments origins of replication replication bubble replication fork 5’ to 3’ continuous synthesis discontinuous synthesis semi-conservative

DNA Replication The star enzymes: helicase topisomerase SSBP (single-stranded binding proteins) primase DNA polymerase III DNA polymerase I DNA ligase

DNA Replication Practice telling the story! When it is time to replicate DNA (during S phase), proteins bind to the origins of replication and separate the DNA strands, forming the replication bubble, with two replication forks (one at each end)

DNA Replication Practice telling the story! At the replication fork. the enzyme HELICASE unwinds and unzips the two DNA strands by breaking the hydrogen bonds between nitrogen bases. Helicase needs help! Single stranded binding proteins (SSBP) stabilize the DNA by “holding” the two separated parental strands from each other Topoisomerase helps relieve the twisting strain of the parent strands in front of the replication fork

DNA Replication

DNA Replication Practice telling the story! At each replication fork, there are two daughter strands that need to be synthesized: the leading strand and the lagging strand Both strands can only be synthesized in the 5’ to 3’ direction The leading strand is synthesized in the 5’ to 3’ direction continuously towards the replication fork The lagging strand is synthesized discontinuously away from the replication fork Process is semi-conservative because each of the new DNA strands will contain one original parent strand and one new daughter strand

DNA Replication

DNA Replication Practice telling the story! Leading Strand: PRIMASE reads the DNA code and synthesizes an RNA primer: a short RNA chain (~10 nucleotides long). DNA POLYMERASE III adds DNA nucleotides to the primer in the 5’ to 3’ direction (towards the fork) Forms hydrogen bonds between the nitrogen base on the parent strand and the complementary nitrogen base of the new daughter nucleotide Forms covalent bonds between the 3’ end of the previous daughter nucleotide and the 5’ end of the new daughter nucleotide (hence 5’ to 3’ direction)

DNA Replication Practice telling the story! Lagging Strand: PRIMASE reads the DNA code and synthesizes an RNA primer: a short RNA chain (~10 nucleotides long). DNA POLYMERASE III adds DNA nucleotides to the primer in the 5’ to 3’ direction (away from the fork) Forms hydrogen bonds between the nitrogen base on the parent strand and the complementary nitrogen base of the new daughter nucleotide Forms covalent bonds between the 3’ end of the previous daughter nucleotide and the 5’ end of the new daughter nucleotide (hence 5’ to 3’ direction)

DNA Replication Practice telling the story! Lagging Strand: DNA POLYMERASE III keeps adding DNA nucleotides until it reaches the primer of the next Okazaki fragment. DNA Polymerase I takes over and keeps adding complimentary DNA nucleotides to the daughter strand in the 5’ to 3’ direction while replacing the RNA nucleotides of the primer on the next Okazaki fragment DNA LIGASE joins the two Okazaki fragments together

DNA Replication Practice telling the story! Overall:

DNA Replication Practice telling the story! Overall:

Try This! In the elongation of the leading daughter strand, synthesis occurs ___________ the replication fork In the elongation of the lagging daughter stand, synthesis occurs ____________the replication fork.

Try This! In the elongation of the leading daughter strand, synthesis occurs TOWARDS the replication fork In the elongation of the lagging daughter stand, synthesis occurs AWAY FROM the replication fork.

Try This! During DNA replication, the leading strand is synthesized continuously, while the lagging strand is synthesized as Okazaki fragments. This is because: DNA synthesis can take place only in the 53 direction. DNA polymerases can bind to only one strand at a time. Two different DNA polymerases are involved in replication (DNA polymerase I and III). There are thousands of origins of replication on the lagging strand.

Try This! During DNA replication, the leading strand is synthesized continuously, while the lagging strand is synthesized as Okazaki fragments. This is because: DNA synthesis can take place only in the 53 direction. DNA polymerases can bind to only one strand at a time. Two different DNA polymerases are involved in replication (DNA polymerase I and III). There are thousands of origins of replication on the lagging strand.

Don’t forget about the themes of AP Biology... For example: Structure/Function Brainstorm the relationship of structure to function the enzymes of DNA Replication

Checkpoint in two Classes… Concept 1 (Cell Cycle, Ch 12) Concept 2 (DNA Replication, Ch 16) Project due Apr 30th

DNA Replication Practice telling the story! This process is very efficient! DNA polymerases are good proofreaders… a mistake is made only in 1 of every 10 000 nucleotide parings… DNA polymerases need help… mismatch repair! Ex: nucleotide excision repair in which the enzyme nuclease cuts the damaged segment so that DNA replication “tries again.” You have 30 000 to 40 000 genes with about 3 billion nucleotides base pairs.

DNA Replication Practice telling the story! At the ends of chromosomal DNA are special sequences called telomeres. Telomers get shorter with every round of RNA replication In some embryonic tissue, TELOMERASE lengthens the telomers, restoring their original length