“Central Dogma” · AP Biology “Central Dogma” replication DNA RNA protein trait
1. What is the Central Dogma? 2. How does prokaryotic DNA compare to eukaryotic DNA? 3. How is DNA...
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Transcript of 1. What is the Central Dogma? 2. How does prokaryotic DNA compare to eukaryotic DNA? 3. How is DNA...
1. What is the Central Dogma?
2. How does prokaryotic DNA compare to eukaryotic DNA?
3. How is DNA organized in eukaryotic cells?
1. Draw and label the 3 parts of an operon.
2. Contrast inducible vs. repressible operons.
3. How does DNA methylation and histone acetylation affect gene expression?
1. List and describe the 3 processes that are involved in transforming a zygote.
2. Compare oncogenes, proto-oncogenes, and tumor suppresor genes.
3. What are the roles of the ras gene and the p53 gene?
Chapter 18
Transcription
Bacteria need to respond quickly to changes in their environment◦ if they have enough of a product,
need to stop production why? waste of energy to produce more how? stop production of enzymes for synthesis
◦ if they find new food/energy source, need to utilize it quickly why? metabolism, growth, reproduction how? start production of enzymes for digestion
STOP
GO
Feedback inhibition◦ product acts
as an allosteric inhibitor of 1st enzyme in tryptophan pathway
◦ but this is wasteful production of enzymes
= inhibition-
-
Gene regulation ◦ instead of blocking
enzyme function, block transcription of genes for all enzymes in tryptophan pathway saves energy by
not wasting it on unnecessary protein synthesis
= inhibition-
--
Cells vary amount of specific enzymes by regulating gene transcription◦ turn genes on or turn genes off
turn genes OFF exampleif bacterium has enough tryptophan then it doesn’t need to make enzymes used to build tryptophan
turn genes ON example if bacterium encounters new sugar (energy source), like lactose, then it needs to start making enzymes used to digest lactose
STOP
GO
OperonOperon: cluster of related genes with on/off switch
Three Parts:1. Promoter – where RNA polymerase attaches2. Operator – “on/off”, controls access of RNA
poly3. Genes – code for related enzymes in a pathway
operatorpromoter
DNATATA
RNApolymerase
repressor
repressor = repressor protein
Operon: Promoter, Operator & Genes they controlserve as a model for gene regulation
gene1 gene2 gene3 gene4RNApolymerase
Repressor protein turns off gene by blocking RNA polymerase binding site.
1 2 3 4mRNA
enzyme1 enzyme2 enzyme3 enzyme4
Repressor protein◦ binds to DNA at operator site ◦ blocking RNA polymerase◦ blocks transcription◦ Produced by regulatory gene
Regulatory geneRegulatory gene: produces repressorrepressor protein that binds to operator to block RNA poly
Normally ON Anabolic (build organic molecules) Organic molecule product acts as
corepressor binds to repressor to activate it
Operon is turned OFF Eg. trptrp (tryptophan) operon (tryptophan) operon
mRNA
enzyme1 enzyme2 enzyme3 enzyme4
operatorpromoter
DNATATA
RNApolymerase
tryptophan
repressor repressor protein
repressortryptophan – repressor proteincomplex
Synthesis pathway modelWhen excess tryptophan is present, it binds to trp repressor protein & triggers repressor to bind to DNA◦ blocks (represses) transcription
gene1 gene2 gene3 gene4
conformational change in repressor protein!
1 2 3 4
repressortrpRNApolymerase
trp
trp
trp trp
trp trp
trptrp
trp
trp
trp
What happens when tryptophan is present?Don’t need to make tryptophan-building enzymes
Tryptophan is allosteric regulator of repressor protein
trptrp operon operon
Normally OFF Catabolic (break down food for energy) Repressor is active inducerinducer binds to and
inactivates repressor Operon is turned ON Eg. laclac operon operon
mRNA
enzyme1 enzyme2 enzyme3 enzyme4
operatorpromoter
DNATATARNApolymerase
repressor repressor protein
repressorlactose – repressor proteincomplex
lactose
lac repressor gene1 gene2 gene3 gene4
Digestive pathway model When lactose is present, binds to lac repressor protein & triggers repressor to release DNA
◦ induces transcription
RNApolymerase
1 2 3 4
lac lac
laclac
lac
lac
lac
conformational change in repressor protein!
lac
lac
What happens when lactose is present?Need to make lactose-digesting enzymes
Lactose is allosteric regulator of repressor protein
laclac operon operon
Repressible operon ◦ usually functions in anabolic pathways
synthesizing end products
◦ when end product is present in excess,cell allocates resources to other uses
Inducible operon ◦ usually functions in catabolic pathways,
digesting nutrients to simpler molecules
◦ produce enzymes only when nutrient is available cell avoids making proteins that have nothing to do,
cell allocates resources to other uses
Many stages
Typical human cell: only 20% of genes expressed at any given time
Different cell types (with identical genomes) turn on different genes to carry out specific functions
Differences between cell types is due to differential gene expressiondifferential gene expression
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
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
Transcription Initiation: Control elements bind
transcription factors Enhances gene expression
EnhancerEnhancer regions bound to promoterpromoter region by activatorsactivators
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
Section 18.4
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
Cytoplasmic determinants: maternal substances in egg distributed unevenly in early cells of embryo
Induction: cells triggered to differentiate
Cell-Cell Signals: molecules produced by one cell influences neighboring cells◦ Eg. Growth factors
Section 18.5
1. Proto-oncogene = stimulates cell division2. Tumor-suppressor gene = inhibits cell
division
Mutations in these genes can lead to cancer
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
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
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
Embryonic development occurs when gene regulation proceeds correctly
Cancer occurs when gene regulation goes awry