Campbell Biology Chapter 18

operator

region of DNA within the promoter that controls RNA polymerase's access to a set of genes with related functions

operon

a unit of gene regulation and transcription in bacterial DNA that consists of a promoter, an operator, and one or more structural genes

repressor

a protein that binds to an operator and physically blocks RNA polymerase from binding to a promoter site. is specific to the operator it binds.

regulatory gene

a gene that produces a repressor substance that inhibits an operator

trpR

regulatory gene or trp operon; codes for trp repressor that is active when effector is bound and attaches to DNA

corepressor

a small molecule that cooperates with a repressor protein to switch an operon off

repressible operon

transcription is usually on, but can be inhibited (repressed) when a specific small molecule binds allosterically to a regulatory protein (example tryptophan)

inducible operon

usually off, but can be stimulated (induced) when a specific small molecule interacts with a regulatory protein (example lac operon)

inducer

A specific small molecule that inactivates the repressor in an operon.

allolactose

inducer in LAC operon

cAMP

Catabolite repression occurs when its high concentrations accumulate in the cell and interact with catabolite repressor protein.

CAP

stimulatory protein, activator of transcription

activator

A protein that binds to DNA and stimulates transcription of a specific gene.

differential gene expression

The expression of different sets of genes by cells with the same genome.

histone acetylation

the attachment of acetyl groups (-COCH3) to certain amino acids of histone proteins, the chromatin becomes less compact, and the DNA is accessible for transcription

histone code hypothesis

specific combinations of modifications, rather than the overall level of histone acetylation, help determine the chromatin configuration, influencing transcription.

DNA methylation

addition of methyl group to DNA (usually to Cytosine), associated with decreased transcription (permanent deactivation)

genomic imprinting

A phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent.

epigenetic inheritance

Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence.

control elements

Segments of noncoding DNA that help regulate transcription of a gene by binding proteins called transcription factors.

specific transcription factors

Increase the level of transcription in certain cell types or in response to signals

proximal control elements

Control elements located close to the promoter

Still do the same job of binding proteins to DNA so that transcription can take place

Increase rate of transcription

Distal control elements

Also called enhancers. They are segments of eukaryotic DNA that contain multiple control elements, usually located far from the gene whose transcription is regulated.

enhancers

A DNA sequence that recognizes certain transcription factors that can stimulate transcription of nearby genes

alternative RNA splicing

different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns

proteasome

A giant protein complex that recognizes and destroys proteins tagged for elimination by the small protein ubiquitin.

protein-coding DNA

~1.5% of human genome

noncoding RNA

ncRNA - forms an extensive and sophisticated genome regulatory network

microRNAs

small single stranded RNA molecules that bind to mRNA and can degrade mRNA or block its translation - miRNAs

RNA interference

Blocking gene expression by means of an miRNA silencing complex

small interfering RNAs

length of 21-23 nucleotides

double-stranded

inhibit gene expression by degrading homologous mRNA

piwi-associated RNAs

Small noncoding RNAs that induce heterochromatin blocking expression of parasitic DNA elements in the genome

differentiation

process in which cells become specialized in structure and function

morphogenesis

The cellular and tissue-based processes by which an animal body takes shape.

cytoplasmic determinants

The maternal substances in the egg that influence the course of early development by regulating the expression of genes that affect the developmental fate of cells.

induction

The process in which one group of embryonic cells influences the development of another, usually by causing changes in gene expression.

determination

The progressive restriction of developmental potential, causing the possible fate of each cell to become more limited as the embryo develops.

pattern formation

The ordering of cells into specific three-dimensional structures, an essential part of shaping an organism and its individual parts during development.

positional information

the molecular cues that control pattern formation

homeotic genes

Regulatory genes that determine where certain anatomical structures will develop in an organism during morphogenesis

embryonic lethal

A mutation with a phenotype leading to death of an embryo or larva.

maternal effect gene

A gene that, when mutant in the mother, results in a mutant phenotype in the offspring, regardless of the offspring's genotype. first identified in Drosophila.

egg polarity genes

Another name for maternal effect genes, these genes control the orientation (polarity) of the egg

bicoid

A maternal effect gene that codes for a protein responsible for specifying the anterior end in Drosophila - two tailed

morphogens

A substance that provides positional information in the form of a concentration gradient along an embryonic axis.

oncogenes

cancer causing genes

proto-oncogenes

code for proteins that stimulate normal cell growth and division

tumor-surpressor genes

code for proteins that prevent the uncontrolled rate of cell division, a gene that normally functions to inhibit cell division; prevents development of mutated cells and tumors.

ras gene

gene that codes for a G protein that relays a growth signal from a growth factor receptor on the plasma membrane to a cascade of protein kinases that ultimately results in the stimulation of the cell cycle

p53 gene

a tumor-suppressor gene that codes for a specific transcription factor that promotes the synthesis of cell cycle-inhibiting proteins

BRCA

Either of two tumor suppressor genes (BRCA1 and BRCA2) that in mutated form tend to be associated with an increased risk of certain cancers and especially breast and ovarian cancers