Control of Gene Expression.ppt

Control of Gene Expression
Pieces of Chapter 16
Pieces of Chapter 17
Pieces of Chapter 18
Pieces of Chapter 19
Objectives
Understand the process of DNA replication
Understand why DNA is synthesized from the 5’ end to the 3’end
Recognize the function of telomeres
Understand how protein structure and function are affected by ic mistakes
Be familiar with the kinds of mutations that may occur during replication of DNA
Understand the role of an operon
Be aware that gene expression can be regulated at many points from DNA to polypeptide synthesis
DNA Replication
DNA replication is semiconservative in that a each new molecule incorporates and old strand that serves as a template
Requires many enzymes for assistance
Few mistakes (~1/billion nucleotides)
DNA Replication
Origins of Replication: regions on the DNA where synthesis begins
synthesis occurs in both directions of the “bubble” along the replication fork (site of DNA elongation)
DNA Replication
Elongation of DNA
Catalyzed by DNA Polymerase and driven by the hydrolysis of phosphate groups from nucleosides (a nucleoside is a nucleotide with three phosphate groups)
DNA Strands are Antiparallel
New DNA grows from 5’3’ as DNA Polymerase only adds nucleotides to the 3’ end of the DNA strand (leading strand)
Okazaki fragments, short pieces of synthesized DNA, are formed and joined together by DNA ligase to form the lagging strand of DNA
DNA must be Primed
DNA Polymerase is unable to replicate DNA directly and requires that the original DNA be primed
Primase makes the initial nucleotide (RNA primer) to which DNA polymerase attaches
RNA primer is replaced with DNA nucleotides later
Protein Summary
Additional to Primase, DNA Polymerase and ligase proteins are 2 others
Helicase: responsible for unwinding the DNA
Single-strand binding proteins: keep plimentary strands separated
Other things to consider
Placement of mismatched nucleotides during synthesis is not rare and is repaired by DNA Polymerase through a m