Control of gene expression
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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

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Control of Gene Expression

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Control of gene expression

Control of Gene Expression

Pieces of Chapter 16

Pieces of Chapter 17

Pieces of Chapter 18

Pieces of Chapter 19


Objectives

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 genetic 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

  • 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 replication1

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 replication2

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

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 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

Protein Summary

  • Additional to Primase, DNA Polymerase and ligase proteins are 2 others

    • Helicase: responsible for unwinding the DNA

    • Single-strand binding proteins: keep original complimentary strands separated


Other things to consider

Other things to consider

  • Placement of mismatched nucleotides during synthesis is not rare and is repaired by DNA Polymerase through a mechanism called mismatch repair

  • Excision repair takes place in DNA to repair damaged DNA (not related to replication) that could eventually lead to problems


Other things to consider1

Other things to consider

  • RNA polymerase cannot synthesize the extreme ends of a DNA molecule

  • Gradual shortening with each replication could lead to deletion of important information

  • Telomerase adds many copies of TTAGGG nucleotide sequence (Telomere) to ends of DNA

  • Telomerase is usually only found in germ cells and sex cells

  • Presence in cancerous cells may lead to proliferation of tumors


Mutations

Mutations

  • Changes in the genetic material of a cell

  • Point mutations:chemical changes in just a single or a few base pairs in a gene

    • Base-pair substitutions: replacement of one nucleotide with another

      • Silent

      • Missense

      • Nonsense

    • Insertion/Deletion: change in the number of nucleotide pairs

      • Frame shift


Controlled expression operons

Controlled Expression: Operons

  • Genes that are used together are often found associated (linked) on the same chromosome and may require a single promoter for transcription

  • An Operator may regulate transcription by interaction with a repressor protein controlled through allosteric regulation

  • An Operon is the entire stretch of DNA required for the synthesis of enzymes in a specific enzymatic pathway (Operator, promotor, and genes)


Control of gene expression

We have only scratched the surface of gene

expression. Regulatory mechanisms may occur

at many different stages from DNA to Protein

-methylation: leads to inactivation of a gene

-histone acetylation: ease of transcription

-Transcription factors: enable transcription to occur

-intron/exon regulation

-modification of mRNA

-degradation of mRNA: elimination is eminent

-inhibition/activation of ribosome binding

-processing of protein/assembly of subunits

-ubiquitin enhances degradation


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