Biology Ch. 16 Gene Expression

Gene expression can be regulated at any stage, but the key stage is ________________.

transcription

cell differentiation

the process by which a cell becomes specialized for a specific structure or function.

Genes with highly packed heterochromatin are usually ___ _______________.

not expressed

histone acetylation

loosens chromatin structure, enhancing transcription

DNA methylation

The addition of methyl groups to bases of DNA after DNA synthesis; may serve as a long-term control of gene expression.
-associated with reduced transcription in some species

genomic imprinting

silencing genes through methylation

transcription factors

Collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription.

proximal control elements are located

close to the promoter

distal control elements called _________________ are farther away and can even be in an intron

enhancers

an activator is a protein that binds to an ________________ to stimulate _________________ of a gene

enhancer
transcription

repressor

A protein that suppresses the transcription of a gene.

TATA box

A promoter DNA sequence crucial in forming the transcription initiation complex.

coordinately controlled eukaryotic genes

usually not near each other and on different chromosomes
-each have their own promoter and control elements with similar regulatory sequences

In bacteria, genes are often clustered into operons, composed of:

an operator (on/off switch), promoter, genes for metabolic enzymes, and a regulatory gene encoding a transcription factor protein

an operon is usually turned on because ___ _______________ can bind to the promoter sequence

RNA Polymerase

operons can be switched off by a protein called a ______________________

repressor

there are two types of operons

repressible operons and inducible operons

in a repressible operon

binding of a specific repressor protein (activated by a corepressor) to the operator shuts off transcription

in an inducible operon

binding of an inducer to an innately active repressor inactivates the repressor and turns on transcription

the lac operon

regulated synthesis of inducible enzymes

Some operons are also subject to ___ control through a stimulatory protein, such as catabolite activator protein (CAP), an activator of transcription.

positive

lactose present, glucose scarce

cAMP level high: abundant lac mRNA synthesized, if glucose is scarce, the high level of cAMP activates catabolite activator protein (CAP), and the lac operon produces large amounts of mRNA coding for the enzymes in the lactose pathway

lactose present, glucose present

cAMP level low: little lac mRNA synthesized, when glucose is present, cAMP is scarce, and catabolite activator protein (CAP) is unable to stimulate transcription

the trp operon

An example of a repressible operon.

Morphogenesis

The development of body shape and organization.

tissue-specific proteins

enable differentiated cells to carry out their specific tasks

Oncogenes

cancer causing genes

Proto-oncogenes

normal cellular genes that are important regulators of normal cellular processes, they promote growth. alterations in the expression of these cells result in oncogenes

How can a proto oncogene turn into an oncogene?

-translocation or transposition: gene moved to new lock, under new controls
-Gene amplification: multiple copies of the genes
-point mutation within a control element
-point mutation within the gene

tumor suppressor genes

encode proteins that help prevent uncontrolled cell growth

p53

tumor-suppressor protein that is a specific transcription factor that promotes the synthesis of cell cycle-inhibiting proteins

mutagens are ____________________

carcinogens