Chapter 17 Flashcards
why are complex traits difficult to see
because there are a lot of genes involved
what is epistasis
genes interact with one another
what does genotype by environment imply
that the interplay between gens and the environment is difficult to predict
where can gene regulation take place
- in the chromosome
- during transcription
- during RNA processing
- RNA stability
- during translation
- during post transcriptional modification
what are the different levels gene regulation can occur at
- chemical modification
- chromosome inactivation
- trasncriptional regualtion
- translational regulation
what are the types of chemical modification
methylation of cytosine and chromatin remodeling
what happens in methylation
- occurs to cytosine bases that are adjacent to guanosine bases on a DNA strand
- transcription factors bind to promotor region and recruiters RNA polymerase 2 to start transcription
- the methylated cytosines inhibit transcription factors from binding to the promotor, so transcription does not occur
what is gene expression
genes have been translated
what are epigenetic effects
regulation of gene expression caused by mechanisms other retain changes in the DNA sequence
what are examples of epigenetic effects
chemical modification of histones and alterations in chromatin structure
what happens in chromatin remodeling
- histone tails are modified through methylation
- when chromatin is coiled proteins that carry out transcription cannot access the DNA
- methylation of histone tails allow chromatin to unravel enough for transcriptional enzymes and proteins to access the DNA
how are histone tails modified in chromatin remodeling
- lysine amino acids in the histone tails are methylated
- methyl and acetyl groups can either be added or removed
what is dosage compensation
explains the regulation mechanism that differs between males and females in the x-chromosome
what is X-inactivation
where only one X chromosome is used in females
what is the mechanism in X-inactivation
- the Xist gene is transcribed and Xist noncoding RNA binds with the X chromosome inactivation center (XIC)
- transcription of Xist continues and the X chromosome becomes coated with Xist RNA
- eventually the entire chromosome becomes coated with Xist RNA
- presence of Xist RNA triggers DNA methylation and other changes associated with transcription activity
what do small regulatory RNA do
regulate gene expression by either binding to transcripts and blocking translation or causing degradation
what do micro RNAs do
- they are transcribed just like protein coding genes
- RNA folds back up on itself to form 1 or more hairpin structures
- enzymes recognize the folded miRNAs and cleave the stems from the hairpin leaving small double stranded segments
- one strand of the fragment becomes incorporated into a protein complex called RISC that base pairs with some mismatches with a region of the target mRNA
- translation is inhibited
why do microRNAs buldge
imperfect base pairing
what do small interfering RNAs do
- they are transcribed and incorporated into the RISC complex like miRNAs
- when small interfering RNAs pair with a target mRNA there are no mismatches
- the targeted mRNA is cleaved by RISC which leads to degradation of the RNA transcript
why is gene regulation simpler in prokaryotes
- DNA isn’t packages into chromosomes
- mRNA is not processed
- there’s no nuclear membrane separating transcription and translation
what is positive regulation
a regulatory molecule (Activator protein) binds DNA in order for transcription to take place
what is the mechanism for positive regulation
- RNA polymerase can bind to the promotor only if an activator protein binds to site near the promotor
- if the activator does not bind to the DNA, the RNA polymerase cannot bind and transcription does not occur
what is negative regulation
a regulatory molecule (repressor protein) binds DNA in order for transcription to be prevented
what is the mechanism for negative regulation
- when repressor protein is absent, the DNA can recruit the RNA polymerase complex and transcription takes place at a constant rate
- when repressor protein is present and can bind to DNA, RNA polymerase cannot bind and there is no transcription
