Expression Control

Regulation of an entire chromosome

*important for mammals and how sex chromosomes are handled

Histone tail modifications

- loosen chromatin - give greater access to transcription factors and other proteins. *groups that you can add >> Lysine >> monomethyl >>Trimethyl >> Acetyl

What are the characteristics of Heterochromatin?

>>Highly condensed in interphase • Transcriptionally inactive • Replicates late in S phase

What does histone code hypothesis state?

>>Modifications of the Histone tails act as marks that can be read by other proteins to control the expression or replication of chromosomal regions >>The coding in the histones may be heritable >>Generally, histone acetylation is associated with transcriptionally active genes. (in a less condensed state) >>Deactylation is associated with inactive genes (= gene silencing)

Methylation inhibits transcription by: • A) Adding a methyl group to cytosine • B) Adding a methyl group to the phosphate backbone • C) Adding a methyl group to the ribose sugar • D) None of these

A

Epigentic effects

Changes in gene expression without DNA mutation **reversible **can be passed down to the next generation.

Which of the following statements is true? A. Only human viruses use the lysogenic pathway B. Lytic bacteriophages must undergo lysogeny first C. The lytic pathway is mediated by the Cl protein D. The Cro protein mediates the lytic pathway and the Cl protein the lysogenic pathway

D

• Posttranscriptional regulation includes: • A) Alternative splicing • B) RNA editing • C) Methylation • D) A and B • E) All of the above

D

Tissue Specific RNA editing

EX: in the liver the unedited mRNA encodes a protein of 2152 amino acids that absorbs lipids from foods.

RNA editing Post translational

Process in which the protein-coding sequence of an mRNA is altered after transcription. The amino acids specified by the altered mRNA are different from those predicted from the nucleotide sequence of the gene encoding the protein. >> chemical modification that causes a change in the bases.

regulatory transcription factors

bind to enhancers, silencers, and promoter-proximal elements, and are responsible for the expression of particular genes in particular cell types and at particular stages of development

small regulatory RNA

binds mRNA and either promotes translation or stops it (mechanism for regulating protein levels)

chromatin remodeling

changes in nucleosome position along DNA *places a role in condensed DNA regulating and how it get's expressed

Outcome of infection

disease

Small regulatory RNA miRNA

encoded for in the host genome expressed and act on other genes that are expressed and regulate them. >>inhibits translation folds back into a hairpin structure (double stranded) >>less of a match= less degraded

Why is the modification state of the histone tail important?

for recruiting heterochromatin assembly factors. (additional proteins) • In human cells, HP1 protein binds to the lysine 9 methylated tail of H3

Transcriptional regulation

increases or decreases the synthesis of mRNA encoding a specific enzyme *regulate transcription factors

lytic pathway vs. lysogenic pathway

lysogenic- resource poor environments >>Cl protein higher in abundance in host Lytic- resource rich environments >>Cro protein higher in abundance in host

X inactivation

one of two X chromosomes is randomly inactivated and remains coiled as a Barr body >>Xist RNA- important because the presence of it triggers DNA methylation and other changes associated with reduced transcriptional activity. EX. Calico Cats (black and orange furr)

small regulatory RNA (siRNA)

small antisense RNA fragments that silence mRNA transcripts >>produced from double stranded RNAs or single stranded RNA that forms a hairpin >>usually come from viruses >>has to match perfectly and all the transcript is degraded

Eukaryotic Gene Regulation

the control of gene expression in the cells of eukaryotes *when, where, how much

histone code hypothesis

the hypothesis that the pattern of histone modification acts much like a language or code in specifying alterations in chromatin structure. *Histone tails are subject to a variety of covalent modifications *how they fold and interact with other tails

Methylation of DNA

the process by which the methyl groups are added to certain nucleotides in genomic DNA CpG islands inhibits transcription factors to be able to bind correctly

alternate splicing Post translational

the process that results in more than one protein per gene >>one way to control and have different proteins produced >>not all the Exons and present in the final mRNA- causes differences in the amino acids. Exon present- low affinity Exon Missing- High affinity **Important in eukaryotes

What are the characteristics of Euchromatin?

• Organized in 30 nm fiber during interphase • Transcriptionally active • Replicates early in the S phase