Exam Two from Study Guide

Describe the experiment that led to the discovery of “split genes.”

electron microscopy was used to see that that the mature mRNA did not line up perfectly with the DNA and created loops

What is the chemical nature of the spliceosome?

made up of RNAs and proteins and has catalytic ability.

helicase removes U4 from U6, and U6 binds to the 5’ splice site and to U2, forming an active site that catalyzes a reaction that removes introns and joins exons

What are the three components on a premature mRNA that are recognized by the spliceosome, allow it to locate an intron, and are required for intron removal?

the 5’ splice site (GU)

the branch point adenosine

the 3’ splice site (AG)

What is mutually exclusive exon splicing?

when one exon is spliced out, the other must be retained and vice versa

Would a single neuron that is finding its target cell in the embryo have the same version of DSCAM or a different version of DSCAM?

different version

How are chemorepellents in regions of the limb, along with specific transcription factors and cell surface receptors, used to guide motor neurons to the dorsal or ventral parts of the limb?

create gradients to attract or repel axons, guiding them where they need to go

transcription factors lead to the presence or absence or receptors to external guidance cues

Which class of intracellular proteins are used to link external guidance cues with cytoskeletal changes within the growth cone?

Rho GTPases

What is “concordance” and what does it tell us about genetic contributions to autism risk?

the presence of the same trait in both twins if one twin exhibits the trait

tells us that ASD has a high heritability, and risk for ASD increases both when one identical twin has it or when one sibling has it

What is a copy number variant and how does it arise?

the number of copies of parts of genes, entire genes, or sets of genes that differ in humans and are larger than 50 base pairs

result of duplications or deletions of a region of DNA

What is a de novo mutation and how does it arise?

mutations that are present in the offspring but not present in the parents

arise from mutations in the germ line

What are the functions of some of the few classes of genes that code for proteins that impact the synapse in some way?

brain development

neuron production, organization, and function

synapse formation, strength, and plasticity

high or low neuron number in the frontal and temporal cortices

How did the authors of the autism article construct the genetic mouse model of autism?

knocking down Shank3B, which is known to cause autism

How did the authors of the autism article construct the environmental mouse model of autism?

introducing environmental factors known to cause autism, such valproic acid

How did the authors of the autism article construct the idiopathic mouse model of autism?

using BTBR inbred mice

In the autism article that we discussed, how did they rescue sociability in these autism mouse models?

introducing L. reuteri bacteria

In the model from the autism article, what provided the link between the digestive system and sociability and how did they show this to be the case?

the vagus nerve

they showed this by removing the vagus nerve, and when this was done, the L. reuteri did not rescue sociability in the autism models

Histone modifications are known to affect gene expression. What are two molecular mechanisms by which histone tail modifications have been shown affect chromatin changes?

reducing positive charges on histones

providing signals to recruit transcriptional activators or repressors

can be done through methylation, acetylation, phosphorylation, ubiquitination, and sumoylation

What is the gene expression output best associated with methylation of the promoter?

repression of expression

What is the gene expression output best associated with methylation of the gene body?

activation of expression

 What is the gene expression output best associated with methylation of the 3’ end of a mRNA?

repression of expression

In controlled rodent studies, mice provided a mom that extensively licked and groomed them produced higher levels of glucocorticoid receptor. What was the methylation status for the GR promoter in both groups of this study?

the GR promoters in the mice that were not extensively licked and groomed were methylated

the GR promoters in the mice that were extensively licked and groomed were not methylated

What are two classes of enzymes that act as epigenetic “writers?”

acetyltransferases

methyltransferases