Control of Gene Expression

promoter

site where RNA polymerase can bind to DNA and begin transcription

operator

controls access of RNA polymerase to genes

operon

promoter, operator, genes

repressor

binds to operator, prevents RNA polymerase from transcribing genes

regulatory genes

genes that encode the repressor

corepressor

cooperates with a repressor to switch an operon off

activators

Bind to DNA and stimulate transcription of a gene

histone acetylation

acetyl group attaches to histone tail, promotes transcription by opening chromatin structure

histone methylation

methyl group attaches to histone tal, reduces transcription by condensing chromatin

DNA methylation

methylation of cytosine bases, inactive genes are more methylated

epigenetic inheritance

inheritance of traits by mechanisms that don’t involve nucleotide sequences, due to DNA methylation

control elements

segments of non coding DNA that are binding sites for transcription factors which regulate transcription

general transcription factors

essential for transcription of all protein-coding genes, bind to DNA sequences, RNA polymerase and other transcription factors

specific control factors

only bind to specific genes with matching control elements, controls volume of activators and repressors

two types of control elements

proximal and distant control elements

proximal control elements

close to the promoter, help specific transcription factors bind to the promoter

distant control elements/ enhancers

far from the promoter, associated with one gene only, bind to activator proteins

location of unexpressed genes/ heterochromatin

outer part of the nucleus

location of expressed genes/ euchromatin

inner part of the nucleus

3 types of non-coding RNAs (ncRNAs)

micro RNA, small interfering RNA, long non coding RNA

micro RNA/ miRNA

forms an miRNA-protein complex and degrades mRNA or blocks its translation

small interfering RNA/ siRNA

similar function to miRNA

long non coding RNA/lncRNA

shut down chromosomes inside the nucleus, X chromosome inactivation

homeotic genes

regulatory genes that dictate pattern formation during late embryonic or larval development

maternal effect gene

mother's genotype dictates the offspring's phenotype regardless of its genotype

oncogenes

cancer causing genes

3 mechanisms that form oncogenes

gene amplification, translocation, point mutations

gene amplification

replication error produces excess copies of a gene

translocation

DNA segment breaks off and is transported to a hyperactive promoter

point mutation

a single letter change results in an excess amount of proteins