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179 Cards in this Set
- Front
- Back
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What is needed for the transfer of one carbon groups?
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SAM (s-adenosylmethionine) and folate
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Which form of folate is ingested by the body?
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monoglutamate (Folic acid in supplements is in this form)
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Whats the storage form of folate?
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FH4 (tetrahydrofolate)
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T/F: folate can be synthesized in the body
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FALSE; it has to be gotten from diet
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What three major products rely on folate for synthesis?
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1. Purine and dTMP synthesis
2. Serine Synth. 3. Methylcobalamin synth |
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What cellular processes require folate?
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DNA synthesis and cell division
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What are the two metabolites of vitamin B12 (i.e., what is B12 turned into upon ingestion?)
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Methyl Cobalamin
Deoxyadenosyl Cobalamin |
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What binds B12 to ensure stomach acid doesn't damage it?
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R-binders (ex. = haptocorrin), however these R-binders get broken down
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What binds B12 after the R-binders are broken down?
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Intrinsic factor (secreted by parietal cells)
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Where does the intrinsic factor-B12 complex go?
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It enters ilial cells (enterocytes)
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Whats the role of pancreatic enzymes in B12 digestion?
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They break down the R-binders and allow the B12 to bind to the Intrinsic Factors (IF)
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What is the tole of TCII in B12 absorption?
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B12-IF complex enters cells
B12 is released from IF and binds TCII B12-TCII is secreted as a complex Cells that need B12 have TCII receptors |
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What two enzymes require B12 as a cofactor? Which form of B12 is required?
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Homocysteine --> Methionine (requires methylcobalamin)
Methylmalonyl CoA --> Succinyl CoA (requires adenosylcobalamin) |
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What synthesizes SAM (sadenosylmethionone)?
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methionine
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What is SAM (s-adenosylmethionine) used for?
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methyl donor in synthesis of creatine, some neurotransmitters, and methylation of DNA and histones
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What role does SAM play in our body?
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It donates methyl groups in several important reactions.
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Hyperhomocysteinemia (a build up of homocysteine) is associated with increased risk for what?
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cardiovascular disease
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Would homocysteine levels go up or down in the following cases?
Folate deficiency B6 def. Cystathionine Synthase def. Excess SAM MTHFR def. B12 def. |
UP in all cases
NOTE* the only one that would increase homocysteine in EXCESS is SAM |
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How could you reduce homocysteine levels?
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B6, B12, folate, Betaine and Choline supplementation
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Define Macrocytic Anemia
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RBCs larger than normal but fewer in number
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How can a B12 deficiency cause macrocytic anemia?
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Low B12 = N5-methyl-FH4 build up = folate in its FUNCTIONAL form is deficient = not enough cysteine AA produced = DNA replication(?) translation of RNA to Protein (?) affected
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How can a folate deficiency cause macrocytic anemia?
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Low Folate = N5-methyl-FH4 build up = folate in its FUNCTIONAL form is deficient = not enough cysteine AA produced = DNA replication(?) translation of RNA to Protein (?) affected
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T/F: B12 deficiency can cause neurological symptoms
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TRUE
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A deficiency in folate during pregnancy increases the fetus' chances of what?
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neural tube defects (through effects on DNA replication)
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What is pernicious anemia?
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macrocytic anemia caused by deficient expression of intrinsic factor
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What tests can be done to determine a dietary folate or B12 deficiency?
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1. Measure serum B12 and folate
2. Elevated MCV (mean corpuscular volume = packed cell volume/RBC count) suggests macrocytic anemia 3. Homcysteine and methylmalonic acid levels in serum 4. Schilling test (crystalline B12 given instead of dietary B12) |
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What are some causes of B12 malabsorption due to decreased acid or protease secretion?
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1. gastic atrophy
2. long-term use of certain drugs 3. H. pylori infection (dec. acid = less B12 freed from haptocorrin R-binder OR dec. IF production) 5. neurological symptoms may be seen in absence of anemia 4. |
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Why is B12 deficiency more common in elderly?
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1. gastic atrophy
2. long-term use of certian drugs 3. H. pylori infection 4. inadequate diet 5. neurological symptoms may be seen in absence of anemia |
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Whats the difference between maintenance and de novo DNA methylation
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"de novo" = new...de novo DNA methylation = addition of new methyl groups where previously there were none
maintenance methylation = addition of methyl groups to the daughter strand of hemimethylated DNA |
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What is the role of S-adenosylmethionine in DNA and histone methylation?
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SAM (s-adenosylmethionine) is required for DNA methyltransferases and histone methyltransferases...acts as a methyl donor
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How can a B12 deficiency cause macrocytic anemia?
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Low B12 = N5-methyl-FH4 build up = folate in its FUNCTIONAL form is deficient = not enough cysteine AA produced = DNA replication(?) translation of RNA to Protein (?) affected
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How can a folate deficiency cause macrocytic anemia?
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Low Folate = N5-methyl-FH4 build up = folate in its FUNCTIONAL form is deficient = not enough cysteine AA produced = DNA replication(?) translation of RNA to Protein (?) affected
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T/F: B12 deficiency can cause neurological symptoms
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TRUE
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A deficiency in folate during pregnancy increases the fetus' chances of what?
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neural tube defects (through effects on DNA replication)
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What is pernicious anemia?
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macrocytic anemia caused by deficient expression of intrinsic factor
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What tests can be done to determine a dietary folate or B12 deficiency?
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1. Measure serum B12 and folate
2. Elevated MCV (mean corpuscular volume = packed cell volume/RBC count) suggests macrocytic anemia 3. Homcysteine and methylmalonic acid levels in serum 4. Schilling test (crystalline B12 given instead of dietary B12) |
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What are some causes of B12 malabsorption due to decreased acid or protease secretion?
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1. gastic atrophy
2. long-term use of certain drugs 3. H. pylori infection (dec. acid = less B12 freed from haptocorrin R-binder OR dec. IF production) 5. neurological symptoms may be seen in absence of anemia 4. |
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Why is B12 deficiency more common in elderly?
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1. gastic atrophy
2. long-term use of certian drugs 3. H. pylori infection 4. inadequate diet 5. neurological symptoms may be seen in absence of anemia |
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Whats the difference between maintenance and de novo DNA methylation
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"de novo" = new...de novo DNA methylation = addition of new methyl groups where previously there were none
maintenance methylation = addition of methyl groups to the daughter strand of hemimethylated DNA |
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What is the role of S-adenosylmethionine in DNA and histone methylation?
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SAM (s-adenosylmethionine) is required for DNA methyltransferases and histone methyltransferases...acts as a methyl donor
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Describe homosysteine's affect on the DNA and histone metylation
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INC. Homocysteine = DEC. SAM = DEC. DNA methylation
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Whats the difference between active and passive demethylation?
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Active = enzymatic removal of methyl groups (environmental factors can affect methylation)
Passive = replication in the absence of the maintenance methyltransferase that adds methyl groups to hemimethylated DNA |
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What are some of the factors that can affect DNA methylation patterns and histone modifications thereby influencing gene expression?
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diet, exposure to environmental contaminants, hormone level, etc.
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T/F: Cancer is associated with altered DNA methylation patterns
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TRUE
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What are some characteristics of Prokaryotic Gene Structure
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Operator (turns genes on/off)
genes transcribed into polycistronic mRNA No exons and introns operons (ex. of operator = Lac Operon) |
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What are some characteristics of Eukaryotic Gene Structure
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Lots of non-coding sequences
Regulatory sequences don't have to be near gene exons = coding material introns = removed via splicing |
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How do prokaryotes regulate genes?
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1. operons
2. transcription/translation are coupled 3. Operon controlled via operator 4. operator turns genes on/off 5. repressor protein controls regulation |
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What are some methods of regulating gene expression?
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1. chromatin remodeling
2. trascriptional regulation 3. post-transcriptional regulation 4. mRNA turnover 5. Post-translational modification |
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How does HDAC control gene expression?
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controls unwinding of histones. HDAC is recruited by REPRESSOR proteins to WRAP DNA to histones
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How does HAT control gene expression?
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HAT = histone acetylase Lysine. acetylating makes histone less positive = lysine side chain becomes 0 charge = DNA UNWINDS. HAT recruited by ACTIVATOR PROTEINS
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Is HDAC recruited by activator or pressor proteins to affect DNA expression?
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Repressor
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Is HAT recruited by activator or repressor proteins to affect DNA expression?
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activator
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How can post-transcriptional regulation regulate gene expression
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1. Splicing (remove introns)
2. Capping (7-methyl guanisine cap added to 5` end) 3. Poly-A Tail |
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What is unique about splicing?
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It doesn't have to be protein mediated - RNA can catalyze reaction by itself (this is an example where RNA is an enzyme)
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What is the length of the poly-A tail correlated with?
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The half-life of the mRNA
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Describe why splicing is imoprtant
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It allows you to put exons together in any combination, creating new proteins.
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What controls the ability to put exons together in different orders to make dif. proteins?
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SR proteins and HNRP proteins
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What is the function of ferritin?
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Iron storage. High Iron - high Ferritin
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What is the function of Tranferin?
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transports Iron. High iron = Low TfR
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Explain how iron levels regulate translation of ferritin
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Low iron = iron doesn't bind IRE = IRE binds 5` mRNA = Ferritin NOT produced
High iron = Iron binds IRE = IRE can't bind 5` mRNA = Ferritin produced |
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Explain how Iron levels regulate translation of transferrin
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High iron = IRE can't bind IRBP = degradation occurs
Low iron = IRE binds IRBP = NO degradation occurs |
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What happens to transferrin levels when iron is high?
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High iron = half life of transferrin DECREASES = Decreasing Transferrin.
High Iron = Transferrin mRNA (TfR) LESS Stable |
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Define Nonsense Mediated Decay
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If there is a mistake, we need a mechanism that prevents that mistake from being translated.
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Define Genetic Imprinting
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Genetic Imprinting is due to DNA methylation. Ex. = in GC-rich promoter region we have guanine and cytosine. When they are methylated it blocksRNA Pol II from binding the promoter = gene expression shut off
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How can methylation affect phenotypes?
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males and females methylate DNA differently, causing dif. genes to be expressed. Methylate promoter region = Turn gene off = Shut down gene expression
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What causes Prader-Willis syndrome?
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missing gene 2 of chromo 15 in PATERNAL
(Prader = Paternal missing) |
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What causes Angelman syndrome?
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missing gene 2 of chromo 15 in MATERNAL
("Man = Maternal missing) |
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Define Mutation
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Any change in a DNA Sequence They may or may NOT produce a birth defect
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Define Point Mutation
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Alteration of one codon, usually due to a single base pair substitution
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Define Silent Mutation
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A sequence change that produces no phenotypic affect
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Define a Transition Point Mutation
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Substitution of a pyrimidine for a pyrimidine, or a purine for a purine (pyrimidine = C, U), (purine = G, A)
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Define Transversion Point Mutation
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Substitution of a pyrimidine for a purine, or a purine for a pyrimidine (more serious than a transition point mutation)
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Define Missense Mutation
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A single base pair substitution altering one AA (ex. - sickle cell anemia)
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Define Nonsense Mutation
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A base pair substitution producing a premature stop codon, resulting in a truncated protein
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Define a Frame Shift Mutation
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Insertion or deletion of a sequence that is not a multiple of three, so that the codon reading frame is altered and a random AA sequence is produced beyond the change.
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Define Teratogenesis
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To produce a defect by interfering with a developmental process, without changing any DNA sequence
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What are the principles of teratology?
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1. Act on specific molecular/cellular processes, producing specific defects
2. Defects include malformations, growth retardation, and death 3. susceptibility influenced by fetal/maternal genetics 4. Extent of malformation depends on dose/duration of exposure 5. susceptibility varies w/ developmental stage (most sensitive period = 3-8 weeks) |
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Why are teratogenic events before 3 weeks seldom observed?
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Because they will most likely kill the fetus, thereby never allowing the teratogenic affect to present itself
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What type of mutation is seen with Chromosome 3 Duplication-Deletion Syndrome?
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Inversion of the center of chromo 3, including the centromere
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What type of mutation is seen with Cri-du-chat syndrome (cry of the cat syndrome)?
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Deletion of part of the short arm of chromo 5
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Name some types of silent (sequence change w/ no phenotypic affect) mutations
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1. 3rd base wobbly codon
2. Intron spliced out of message 3. Spacer region of chromo is outside of expressed gene 4. Similar AA w/ same effect on protein function 5. Region of a protein that is not critical for function, such as a linker protein |
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List the types of point mutations
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1. Transition
2. Transversion 3. Missense 4. Nonsense 5. Frame Shift |
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What type of mutation is seen with Down Syndrome
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trisomy 21
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What type of mutation is seen with Edward Syndrome
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trisomy 18
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What type of mutation is seen with Patau Sundrome
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trisomy 13
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What type of mutation is seen with Turner Syndrome
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monosomy of the X chromo (XO)
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What type of mutation is seen with Klinefelter syndrome?
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An extra A chromosome (XXY)
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What type of mutation is seen with Extra sex chromos
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XYY, XXX
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Define Aneuploidy
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To have the wrong number of chromosomes in a parental set.
Trisomy = 3 copies of a chromo Monosomy = 1 copy of a chromo |
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List the Endogenous Mutagenic Agents
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1. Deamination
2. Depurination 3. DNA Polymerase Infidelity 4. Unequal Crossing Over 5. Nondisjunction 6. Cytochrome P450 7. Phosphodiester bonds formed by ligase between free 5` and 3` 8. Tautomeric Shift "DDDUNCPT" |
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Which Endogenous Mutagenic Events/Agents occur spontaneously and cause problems during DNA replication?
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Depurination, Deamination, Tautomeric Shift
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How do endogenous DNA Ligase errors damage DNA?
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Forms phosphodiester bonds between any free 3` OH and 5` phosphate DNA
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How does (endogenous) Unequal Crossing Over damage DNA?
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A displaced exchange of strands during crossing over, so that a sequence is deleted from one homolog and duplicated in the other.
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How does (endogenous) nondisjunction damage DNA?
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Produces aneuploidies
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How does DNA Polymerase infidelity (endogenous) damage DNA?
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This is just the inherent error rate: 1 mismatch per 10^9-10^10 replicated base pairs
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How does the (endogenous) cytochrome P450 system damage DNA?
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Cytochrome P450 system is a natural function of the liver for the removal of toxins. Oxidizes hydrophobic compounds to make them water soluble so they can be excreted. System can accidentally make innocuous products mutagenic
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How does depurination (endogenous) damage DNA?
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Depurination = remove purine.
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How does Deamination (endogenous) damage DNA?
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Deamination = remove amine
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How does a tautomeric shift (endogenous) damage DNA?
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changes in electron configuration of a base, causing it to resemble another base
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What are the Exogenous Mutation Agents?
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1. Radiation (UV, Ionizing radiation, Gamma rays)
2. Chemical (Alkylating, Strand Cleavers, Base Analogs, Intercalating Agents, Insertion Elements) |
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How does UV Light (exogenous) damage DNA?
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Electrons absorb UV, become chemically reactive, causing point mutations and chromosomal aberrations
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How does ionizing radiation (exogenous) damage DNA?
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collide with molecules causing point mutations
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How do gamma rays (exogenous) damage DNA?
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Break DNA strands, producing chromosomal aberrations
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How do Alkylating agents (exogenous) damage DNA?
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Add one or two carbons to DNA, interfering with DNA replication, causing point mutations and chromosomal aberrations
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How do strand cleavers (exogenous) damage DNA?
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sever phosphodiester bonds directly, inducing chromo aberrations
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How do Base Analogs damage DNA?
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mimic nucleotides, inducing pair substitutions
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How do Intercalating Agents damage DNA?
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multi-ring structures wedge between DNA bases resulting in chromo aberrations
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How do insertion elements (exogenous) damage DNA?
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DNAs integrate into chromo/gene and disrupt function
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What are the four types of DNA repair mechanisms?
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1. DNA polymerase delta
2. Direct Base Repair 3. Excision Repair 4. Ligation of Strand Breaks |
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How does the DNA repair mechanism of excision repair work?
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1. Utilize specific enzymes that recognize base pair mismatches or covalently damaged bases
2. ex. = endonuclease nicks phosphodiester bond at 3` end of dimer, DNA Pol beta fills in gap, DNA ligase seals nick |
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What are the 3 ways to transport things across the membrane?
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Passive Diffusion
Facilitated Diffusion Active Transport |
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What are the properties of passive diffusion?
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1. transport of molecules across membrane w/o the use of energy
2. Down a conc. gradient 3. w/ electric potential |
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What are the properties of Facilitated Diffusion?
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1. Passive diffusion through a specific transmembrane protein
2. Specific 3. Diffusion rates are faster than other forms of membrane transport 4. Diffusion rates are saturable |
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What are the properties of Active Transport?
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1. Forced movement across a membrane
2. Driven by ATP 3. Against conc. gradient or electric potential |
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What are the structural characteristics of the membrane transport proteins?
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1. Selective
2. Span from one side to another 3. Have a hydrophilic (water-loving) polar head region on each side of the membrane 4. Transmembrane domain = internal hydrophilic passageway, external hydrophobic AAs face lipid bilayer. |
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What are the different types of transport proteins?
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1. Channels
2. Transporters 3. ATPase Pumps |
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Describe how channel transport proteins operate
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Mediate facilitated diffusion by single file flow of specific factors through the protein. They are selective, gated, close in response to stimuli
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Describe how Transporter transport proteins operate
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Pass one factor (or set) at a time by conformational change of protein. Diffusion rates slower than with channels
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Describe how ATPase pumps transport proteins mediate active transport
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By directly hydrolyzing ATP
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What are the basic mechanisms used by Transporter transport membrane proteins?
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Uniporters (one at a time), Symporters (two at a time), Antiporters (two at a time in opposite directions).
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What type of diffusion do Transporter transport proteins facilitate?
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passive diffusion
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How do P Class ATPase Pumps work?
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1. Two transmembrane proteins beta and alpha, often tetrameric
2. Energy provided by ATP hydrolysis 3. Two conformational states exist, E1 (resting, high affinity) and E2 (bound = low affinity) |
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What is the function of Na+/K+ ATPase pumps?
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To establish electric potentials across all membranes, and to withhold Na+/K+ gradients
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How many molecules of Na+ and K+ are exported for every one ATP hydrolyzed?
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3 Na+, 2 K+
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How does an electrical potential build up due to the activity of Na+/K+ ATPases?
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3 Na+ leaves cell for every 2 K+ that enters, meaning exoplasmic is positive, endoplasmic is negative
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What is the name for the charge generated across the membrane and what is it used for?
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Capacitor (= electrical potential across the membrane) By establishing conc. gradients and electrical potential, separate transport proteins utilize this energy to drive factors against their conc. gradients.
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Define Action Potential
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Transient reversal of electric polarity across a neuronal membrane, propagated down an axon
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What produces Action Potentials?
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Transient changes in the permeability of Na+ and K+ across the membrane. Peak Na+ permeability coincides with the peak of the action potential
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What is the MDR-1 Pump?
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An ATPase pump that excretes hydrophobic compounds from numerous tissues (liver, kidney, intestine, brain, capillary endothelia)
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Wha tis the function of the MDR-1 pump?
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detoxify cells. Also excretes hydrophobic drugs
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How does the CTFR pump differ from other ABC family member proteins?
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1. functions as channel, not an ATPase pump (ATP hydrolysis required to OPEN channel, but once open ATP not needed)
2. CFTR has a regulatory domain - Must be phosphorylated to open domain |
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Define Intercellular Signaling Molecule
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A ligand secreted by one cell to induce a response in another cell
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Define Hormone
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An intercellular signaling molecule that controls cell cycle progression, cellular differentiation, or morphogenesis during development
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Define Cytokine
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A growth factor involved with hematopoiesis
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Define Isoreceptors
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different receptors bound and activated by the same ligand, often inducing distinct responses in dif. cells
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Define Paracrine
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For an intercellular signaling molecule to diffuse over a short distance, usually through interstitial spaces, to induce a response
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Define Endocrine
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For an intercellular signaling molecule to diffuse through the blood
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What are the general characteristics of receptors?
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1. Specificity
2. High binding affinity for ligand 3. Saturable binding 4. Reversible Binding 5. Tissue specific distribution 6. Biological Response |
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What are the classifications of nuclear receptors based on ligand binding?
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1. Glucocorticoid family (glucocorticoid and testosterone receptors)
2. Estrogen Receptor family (only estrogen) 3. Non-steroid family (thyroid hormones and retinoic acid receptors) |
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T/F: Nuclear Receptors constitute a gene family
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TRUE. They all have similar sequences, structures, and act by the same basic mechanism
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T/F: Nuclear Receptors can also function as zinc finger transcription factors.
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TRUE...oddly enough, nuclear receptors can also function as zinc finger transcription factors because they can leave the membrane and float free.
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How do nuclear receptors work as zinc finger transcription factors?
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Ligand binding activates steroid receptors by causing them to form dimers and translocate into the nucleus. They bind their recognition sequence, thereby activating (or repressing) transcription of specific genes.
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What are the three domains that allow transmembrane receptors to propagate signals across membranes?
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1. Extracellular ligand binding domain
2. Transmembrane domain 3. Signal Transduction Domain |
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Define Transport Protein Receptors
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Receptors that transport molecules. Ligand binding opens passageway, allowing specific factors to pass through membrane. (ex. = ligand-gated channels of neurons)
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What are the three main types of transmembrane receptors?
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1. Tyrosine Kinase
2. G Protein Coupled 3. G protein coupled more often than tyrosine kinase |
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What Pathway does the Tyrosine Kinase transmembrane receptor activate?
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Ras-MAPK more often than phosphoinositide
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What pathway does G Protein Coupled transmembrane receptor activate?
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cAMP as often as Phosphoinositide
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What pathway does G Protein Coupled More than Tyrosine Kinase activate?
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Phosphoinositide
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Define Differentiation
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The process of transforming into a different cell type
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Define Commitment
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When the developmental fate of a cell becomes restricted, so that it will differentiate in a specific manner
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Define Specification
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The first phase of commitment, when the fate is still reversible. For instance
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Define Determination
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The final phase, when commitment becomes irreversible. May occur becasue of the onset of differentiation
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Define Autonomous Specification
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Intracellular signals (within a cell) controlling cellular differentiation
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Define Intercellular Inductions
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Signals between cells controlling cellular differentiation
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Define Growth Factors
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Hormones that control cell cycle progression, cellular differentiation or morphogenesis during development
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Define Specialized cell types
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cells with distinctive morphological characteristics and/or molecular processes
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What are Generalized cell types
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cells lacking specialized characteristics
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Define Totipotency
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To have the potential to differentiate into any cell type and produce an entire organism (germ line, gametes, zygotes, and early blastomeres)
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Define Pluripotency, Multipotency
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To have the potential to differentiate into multiple cell types
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Define Stem Cells
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Cells that differentiate into other cell types (i.e.spermatogonia, mesenchymal stem cells etc.) They either divide into more stem cells to propagate their own population, or they differentiate when they divide.
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Define Progenitor, or Precursor Cell
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Cells that must differentiate into other cell types and so cannot propagate their own population
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Define Blastomeres
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Cells from cleavage stage embryos or blastocysts
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Define Blast Cells
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Stem cells from any embryonic stage. Blast cells are usually named after the cell types they produce (ex = neuroblast --> neurons)
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Define Mesenchyme
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Loosely organized blast cells
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Define Metaplasia
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Transformation of one differentiated cell type to another
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Define De-Differentiation
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To reverse the process of differentiation. For a specialized cell to transform into less specialized cell type
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Define Anaplasia
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De-Differentiation to an embryonic cell type
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Define Neoplasia
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Abnormal, new growth (i.e. tumor formation). Most Neoplasias are Anaplasias
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How does differentiation relate to development and regeneration?
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1. Number of differentiated cells increases throughout development
2. As cells differentiate, their ability to divide diminishes and they lose the ability to proliferate (undifferentiated tissues regenerate more readily) |
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What do Wnt and Shh (sonic hedge hog) do?
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Interncellular induction by Wnt and Shh initiates intracellular or autonmous myogenic pathway.
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What role does the helix-loop-helix transcription factor play in differentiation?
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It induces skeletal myogenesis
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What causes Lesch-Nyhan Syndrome?
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Definciency in HGPRT
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Define Lesch-Nyhan Syndrome
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A deficiency in HGPRT which causes the affected individual to bit his or her nails. Cause is thought to be high levels of uric acid in brain
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What are the sings and symptoms of Lesch-Nylan Syndrome?
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Hyperuricemia (Build Up of uric acid)
Uric Aciduria |
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What are the regulatory enzymes in the Purine nucleotide pathway?
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GMP, GDP, GTP, AMP, ADP, ATP (via negative feedback)
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What is the relationship between a defect in the purine breakdown pathway and gout?
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Gout is caused by purine buildup, so if we can't break down purine, uric acid crystals will lodge into capillaries etc. (=Gout)
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Why do we need a salvage pathway for nucleotide purine synthesis?
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Because it costs so much energy to make them
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What is SCIDs?
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A deficiency in ADA (Adenosine DeAminase). Results in lymphocyte depletion, and lack of both cellular and humoral immune function (i.e. "bubble boy")
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What is the cause of SCIDs?
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SCIDs = ADA (Adenosine DeAminase) deficiency = build up of Adenosine.
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