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End of Ch. 17: Mutations
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When do mutations affect the next generation?
Point mutations single base change base-pair substitution silent mutation no amino acid change redundancy in code missense change amino acid nonsense change to stop codon When do mutations affect the next generation?
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Point mutation leads to Sickle cell anemia
What kind of mutation? Missense!
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hydrophilic amino acid hydrophobic amino acid
Sickle cell anemia Primarily Africans recessive inheritance pattern strikes 1 out of 400 African Americans hydrophilic amino acid hydrophobic amino acid
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Mutations Frameshift shift in the reading frame insertions deletions
changes everything “downstream” insertions adding base(s) deletions losing base(s) Where would this mutation cause the most change: beginning or end of gene?
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Cystic fibrosis Primarily whites of European descent
strikes 1 in 2500 births 1 in 25 whites is a carrier (Aa) normal allele codes for a membrane protein that transports Cl- across cell membrane defective or absent channels limit transport of Cl- (& H2O) across cell membrane thicker & stickier mucus coats around cells mucus build-up in the pancreas, lungs, digestive tract & causes bacterial infections without treatment children die before 5; with treatment can live past their late 20s Cystic fibrosis is an inherited disease that is relatively common in the U.S. Cystic fibrosis affects multiple parts of the body including the pancreas, the sweat glands, and the lungs. When someone has cystic fibrosis, they often have lots of lung problems. The cause of their lung problems is directly related to basic problems with diffusion and osmosis in the large airways of the lungs. People without cystic fibrosis have a small layer of salt water in the large airways of their lungs. This layer of salt water is under the mucus layer which lines the airways. The mucus layer in the airways helps to clear dust and other inhaled particles from the lungs.
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bacteria & mucus build up mucus secreting glands
Chloride channel transports chloride through protein channel out of cell Osmotic effects: H2O follows Cl- Effect on Lungs normal lungs airway Cl- Cl- channel H2O cells lining lungs cystic fibrosis Cl- In people without cystic fibrosis, working cystic fibrosis proteins allow salt (chloride) to enter the air space and water follows by osmosis. The mucus layer is dilute and not very sticky. In people with cystic fibrosis, non-working cystic fibrosis proteins mean no salt (chloride) enters the air space and water doesn't either. The mucus layer is concentrated and very sticky. People with cystic fibrosis have lung problems because: Proteins for diffusion of salt into the airways don't work. (less diffusion) Less salt in the airways means less water in the airways. (less osmosis) Less water in the airways means mucus layer is very sticky (viscous). Sticky mucus cannot be easily moved to clear particles from the lungs. Sticky mucus traps bacteria and causes more lung infections. Therefore, because of less diffusion of salt and less osmosis of water, people with cystic fibrosis have too much sticky mucus in the airways of their lungs and get lots of lung infections. Thus, they are sick a lot. H2O bacteria & mucus build up thickened mucus hard to secrete mucus secreting glands
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Deletion leads to Cystic fibrosis
delta F508 loss of one amino acid
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Ch. 18 Control of Prokaryotic (Bacterial) Genes
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Bacterial metabolism 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
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Remember Regulating Metabolism?
Feedback inhibition product acts as an allosteric inhibitor of 1st enzyme in tryptophan pathway but this is wasteful production of enzymes = inhibition - - Oh, I remember this from our Metabolism Unit!
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Different way to Regulate Metabolism
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 - - - Now, that’s a good idea from a lowly bacterium!
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Gene regulation in bacteria
Cells vary amount of specific enzymes by regulating gene transcription turn genes on or turn genes off turn genes OFF example if 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 Remember: rapid growth generation every ~20 minutes 108 (100 million) colony overnight! Anybody that can put more energy to growth & reproduction takes over the toilet. An individual bacterium, locked into the genome that it has inherited, can cope with environmental fluctuations by exerting metabolic control. First, cells vary the number of specific enzyme molecules by regulating gene expression. Second, cells adjust the activity of enzymes already present (for example, by feedback inhibition). GO
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Bacteria group genes together
Operon genes grouped together with related functions example: all enzymes in a metabolic pathway promoter = RNA polymerase binding site single promoter controls transcription of all genes in operon transcribed as one unit & a single mRNA is made operator = DNA binding site of repressor protein
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So how can these genes be turned off?
Repressor protein binds to DNA at operator site blocking RNA polymerase blocks transcription
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Operon model promoter operator
Operon: operator, promoter & genes they control serve as a model for gene regulation RNA polymerase RNA polymerase repressor TATA gene1 gene2 gene3 gene4 DNA promoter operator 1 2 3 4 mRNA enzyme1 enzyme2 enzyme3 enzyme4 Repressor protein turns off gene by blocking RNA polymerase binding site. repressor = repressor protein
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Repressible operon: tryptophan
Synthesis pathway model When excess tryptophan is present, it binds to tryp repressor protein & triggers repressor to bind to DNA blocks (represses) transcription RNA polymerase RNA polymerase repressor trp TATA gene1 gene2 gene3 gene4 DNA promoter operator 1 2 3 4 mRNA trp trp enzyme1 enzyme2 enzyme3 enzyme4 trp trp trp trp repressor repressor protein trp trp trp tryptophan trp conformational change in repressor protein! repressor tryptophan – repressor protein complex trp
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Tryptophan operon What happens when tryptophan is present?
Don’t need to make tryptophan-building enzymes Tryptophan is allosteric regulator of repressor protein
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Inducible operon: lactose
Digestive pathway model When lactose is present, binds to lac repressor protein & triggers repressor to release DNA induces transcription RNA polymerase RNA polymerase repressor TATA lac gene1 gene2 gene3 gene4 DNA promoter operator 1 2 3 4 mRNA enzyme1 enzyme2 enzyme3 enzyme4 repressor repressor protein lactose lac conformational change in repressor protein! repressor lactose – repressor protein complex lac
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Lactose operon What happens when lactose is present?
Need to make lactose-digesting enzymes Lactose is allosteric regulator of repressor protein
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Jacob & Monod: lac Operon
1961 | 1965 Jacob & Monod: lac Operon Francois Jacob & Jacques Monod first to describe operon system coined the phrase “operon” Jacques Monod Francois Jacob
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Operon summary Repressible operon Inducible 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
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