effect of chromatin structure on gene expression - DNA organized around histones into nucleosomes
- DNA methylation - blocks accidental transcription of genes that are turned off
- vertebrates have protein that binds to methylated base pairs, prevents transcription from starting
- ensures that genes stay turned off when turned off
- coactivators add acetyl groups to amino acids in chromatin >> makes DNA accessible to transcription factors
- remove high order chromatin structure >> faster transcription
eukaryotic posttranscriptional control - uses regulatory proteins, small RNA
- small RNAs - interacts directly w/ main gene transcripts to regulate gene expression
- 21-28 nucleotides long
- RNA interface - inhibition of genes by RNA
- double-stranded RNA forms when 2 ends complementary to each other loop
- dicer - enzyme that makes small RNAs
- microRNAs (miRNA) - binds directly to mRNA, prevents translation
- small interfering RNAs (siRNA) - degrades mRNA before they get translated
- epigenetic change - change in gene expression passed down in generations
- not caused by changes in DNA sequence
- due to changes in DNA packaging
- changing how strands twist >> changes which genes are more easily accessible for expression
- primary transcript - initial mRNA molecule copied by RNA polymerase
- includes introns/exons
- spliceosomes (made of snRNPs) cut out the introns
- alternative splicing >> creates different proteins from same gene
- RNA editing - produces altered mRNA not coded for the genome, usually through deamination
- nuclear membrane makes sure that only completely processed transcripts reach the cytoplasm
- translation factors - controls how mRNA gets translated by ribosomes
- translation repressor protein - binds to beginning of transcript >> mRNA can’t attach to ribosomes
- transcripts for regulatory proteins, growth factors less stable than other mRNA, more easily degraded by other enzymes
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