chromatin structure: tightly bound dna less accessible for transcription dna methylation: methyl...
TRANSCRIPT
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Chromatin Structure: Tightly bound DNA less
accessible for transcription
DNA methylation: methyl groups added to DNA; tightly packed; transcription
Histone acetylation: acetyl groups added to histones; loosened; transcription
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Modifications on chromatin can be passed on to future generations
Unlike DNA mutations, these changes to chromatin can be reversed (de-methylation of DNA)
Explains differences between identical twins
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Transcription Initiation: Control elements bind
transcription factors Enhances gene expression
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EnhancerEnhancer regions bound to promoterpromoter region by activatorsactivators
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Regulation of mRNA:• micro RNAs micro RNAs
(miRNAs) (miRNAs) and small small interfering RNAs interfering RNAs (siRNAs) (siRNAs) can bind to mRNA and degrade it or block translation
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Section 18.4
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1. Cell Division: large # identical cells through mitosis
2. Cell Differentiation: cells become specialized in structure & function
3. Morphogenesis: “creation of form” – organism’s shape
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Cytoplasmic determinants: maternal substances in egg distributed unevenly in early cells of embryo
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Induction: cells triggered to differentiate
Cell-Cell Signals: molecules produced by one cell influences neighboring cells◦ Eg. Growth factors
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Section 18.5
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1. Proto-oncogene = stimulates cell division2. Tumor-suppressor gene = inhibits cell
division
Mutations in these genes can lead to cancer
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Proto-Oncogene Oncogene
Gene that stimulates normal cell growth & division
Mutation in proto-oncogene
Cancer-causing gene
Effects: Increase product of
proto-oncogene Increase activity of
each protein molecule produced by gene
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Ras gene: stimulates cell cycle (proto-oncogene)◦Mutations of ras occurs in 30% of
cancers p53 gene: tumor-suppresor gene
◦Functions: halt cell cycle for DNA repair, turn on DNA repair, activate apoptosis (cell death)
◦Mutations of p53 in 50+% of cancers
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Cancer results when mutations accumulate (5-7 changes in DNA)
Active oncogenes + loss of tumor-suppressor genes
The longer we live, the more likely that cancer might develop
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Embryonic development occurs when gene regulation proceeds correctly
Cancer occurs when gene regulation goes awry