9 DNA Replication: 3 Stages: - Figure 10-9 - page 187 replication - it does have primerase and polymerase 1DNA replication animation- v. realistic but hard to follow1. Unwinding DNA helicase unwinds and separates the two strands of the molecule, exposing the bases. This is called the “Replication Fork”
10 2. Formation of the Complementary Strand - the parental DNA strands act as a template- DNA polymerase attaches to the opened strands (one on each side)
11 - it “reads” the parental DNA strand and attaches the appropriate nucleotide to the template; A to T, G to C (and vise versa)DNA polymerase
12 - it also connects the sugars and phosphate sides of the new strand using dehydration synthesis reactions.
13 - DNA polymerase can only travel in one direction - from 3’ to 5’ , therefore, the 2 polymerases will travel in opposite directions in the replication forks
15 The pieces are joined together by DNA ligase As the two DNA polymerases move along the DNA molecule, ONE will be following the DNA helicase, while the other one will be going in the opposite direction.
16 - the DNA polymerase that follows the helicase is on the “LEADING STRAND” - the other polymerase is going to run into the “end” of the replication fork (where the helicase started to open the DNA helix)- it must detach at that point.
17 - a new polymerase will attach further up the “LAGGING STRAND” and synthesis a new daughter strand up to the point were the first polymerase began, and then IT will detach
18 - this process continues in steps until all of the lagging strand is replicated
19 - every time the polymerases detach, they leave a gap in the sugar-phosphate back-bone - DNA ligase will travel along the newly synthesized strands, locate the gaps, and make the necessary connections to fill them.
20 Finally, both the leading strand and the lagging strands are “proof-read” by specific enzymes to ensure that the replication was accurate. ( if it wasn’t corrected, it would be called a MUTATION.)
21 What is the significance of the order of the nitrogenous bases?
22 Protein SynthesisDNA - a ____________ for making proteins.BLUEPRINT
23 A 2 Step Process:1. Transcription: the information is copied form the DNA molecule to a mRNA molecule
25 2. Translation: the information in the mRNA is “read” in the ribosome and “translated” by a tRNA to make a protein.
26 Breaking “THE CODE”:DNA Molecules can be thought of as a type of“sentence”.- the bases, (A,T,G,C) make up the “letters”- these ‘letters” are arranged into “words” of three letters-called “triplets”- the triplets each have a specific “meaning”- they code of a specific amino acidTHE CAT ATE THE RATAUG CCG GCA AAG UAGMet pro ala lys stop
48 Types of Mutations Deletion Addition Substitution Positive Neutral Example: DeletionThe result can be a completely non-functional protein…doesn’t make sense.i.e THE CAT ATE THE RAT---If you delete a base (letter) ‘C’---THE ATA TET HER AT-----DeletionAdditionSubstitutionPositiveNeutralNegativeMutagens
49 Changing the sequence Another example: Original message: THE BIG DOG BIT TED AND RAN OFFADDITION/FRAMESHIFTTHE BIG FDO GBI TTE DAN DRA NOF F--Changing the sequence