The “Central Dogma" of Biology

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

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!1. Consider the following DNA strand:

Complete it!3’-A T G C G C T -5’

2. How can you tell the 5’ end from the 3’ end?

3. If the DNA in an onion is found contain 30% adenine, what percentage of the onion DNA bases would be cytosine?

4. Explain how DNA, chromatin, and chromosomes are related.

Let’s Discuss

HandoutAnimations from CampbellBioflix

DNA Replication Animation (2nd half)

DNA ReplicationSome 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 ReplicationThe star enzymes:

◦helicase◦topisomerase◦SSBP (single-stranded binding

proteins)◦primase◦DNA polymerase III◦DNA polymerase I◦DNA ligase

DNA ReplicationPractice 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 ReplicationPractice 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 ReplicationPractice 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 ReplicationPractice 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 ReplicationPractice 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 ReplicationPractice 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 ReplicationPractice telling the story!

◦Overall:

DNA ReplicationPractice 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:

A. DNA synthesis can take place only in the 53 direction.

B. DNA polymerases can bind to only one strand at a time.

C. Two different DNA polymerases are involved in replication (DNA polymerase I and III).

D. 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:

A. DNA synthesis can take place only in the 53 direction.

B. DNA polymerases can bind to only one strand at a time.

C. Two different DNA polymerases are involved in replication (DNA polymerase I and III).

D. 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 ReplicationPractice 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.”

DNA ReplicationPractice 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