Chapter 18 Flashcards by Anna W

feedback inhibition

relies on sensitivity of enzymes to chemical cues that increase or decrease their catalytic activity
o Typical of anabolic (biosynthetic) pathways (these pathways use raw materials to synthesize essential end products)
o Allows cell to adapt to fluctuations in concen. of substance

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operon model

allows for bacterial cell to adjust the production level of certain enzymes
o Works by regulating expression of genes controlling the enzymes
o Cell translates one large mRNA molecule into 5 separate polypeptides

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operator

segment of DNA which serves as an “on-off switch” which controls the cluster of genes
• Found within promoter and between promoter and enzyme-controlling genes
• Controls access of RNA polymerase to genes

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operon

consists of operator, promoter, the genes they control, the stretch of DNA required for enzyme production

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regulatory gene

expressed continuously at a low rate

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repressor

protein which switches operon on/off
 Binds to operator and blocks attachment of RNA polymerase to promoter (prevents transcription)
 Binding is reversible
 Specific to operator of particular operon

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corepressor

small molecule that cooperates with a repressor protein to switch an operon off
• As amino acid accumulates, amino acid molecules associate with the repressor molecules which bind to operator to shut down production of the amino acid’s pathway enzymes

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repressible operon

operon whose transcription is usually on but can be repressed when a specific molecule binds allosterically (or when protein molecule binds to site other than its active site) to a regulatory protein

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inducible operon

operon which is usually off but can be stimulated when a specific small molecule interacts with a regulatory protein
• Ex: lac operon

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inducer

specific small molecule which inactivates the repressor
• Does this by altering repressor’s shape, making it unable to attach to operator
• ALLOWS for gene expression

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inducible enzyme

enzymes whose production must be induced by a chemical signal
• Function in catabolic pathways (which break down nutrients into simpler molecules)

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repressible enzyme

enzyme which is produced continuously
• ‘suspends’ production of end product when it is already present in excess
• This allows for energy to be used in other ways
• Functions in anabolic pathways (these pathways use raw materials to synthesize essential end products)

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Cyclic AMP (cAMP)

• Cyclic nucleotide

small organic molecule which accumulates when molecule is scarce

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activator

proteins that bind to DNA and stimulates transcription of a gene

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differential gene expression

the expression of different genes by cells with the same genome
• Accounts for differences between cell types

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methylate

replace H atom with methyl group

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histone acetylation

promotes transcription by opening up chromatin structure

o Methyl groups are added which condenses chromosomes

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DNA methylation

methylate certain bases in the DNA itself, usually cytosine
o Occurs in plants, animals, fungi
o DNA methylation patterns are reversible

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genomic imprinting

when methylation permanently regulates expression of either maternal or paternal allele of particular genes during start of development
o ‘chemical record’ of methylation patterns

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epigenetic inheritance

inheritance of traits transmitted by mechanisms not involving the nucleotide sequence itself

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control elements

segments of noncoding DNA that serve as binding sites for transcription factors
o regulate transcription

proximal control elements

control elements located close to the promoter

Enhancers (distal control elements)

control elements that are thousands of nucleotides upstream/downstream of a gene or within an intron
o Distal- control elements here are grouped together as ‘enhancers’

activation domains

bind to enhancer DNA sequences, then regulatory proteins
o Eventually binds to RNA polymerase II
o Resulting protein-protein interactions enhances transcription of a gene

mediator domains

interact with proteins at the promoter | o This helps with assembly and positioning of initiation complex on promoter

silencing

when repressors recruit proteins that remove acetyl groups from histones= reduced transcription

transcription factories

when loops of chromatin extend from individual chromosomes to specific sites in the nucleus o These sites are rich in RNA polymerase

ncRNA’s (noncoding RNA’s)

o Regulate mRNA’s o Remodel chromatin structure o Responsible for X chromosome inactivation- prevents expression of genes here

piRNA’s (piwi-interacting RNA’s)

induce formation of heterochromatin

micro RNA's (miRNA’s)

single stranded RNA of about 22 nucleotides | • capable of binding to complementary sequences in mRNA molecules

small interfering RNA’s (siRNA’s)

has the ability to turn off expression of genes with related sequences o Precursors for miRNA and siRNA are both double-stranded

RNA interference (RNAi)

the blocking of gene expression by siRNAs

differentiation

cells specialize in structure and function

morphogenesis

development of form of organism and its structures

cytoplasmic determinants

maternal substances in the egg that influence the course of early development

induction

Signals in embryonic stem cells that come into contact with growth factors and cell-surface molecules and cause changes in target cells

determination

the point at which an embryonic cell is irreversible committed to being a particular cell type

tissue-specific proteins

found in a specific cell type, giving it its particular characteristic structure and function

myoblasts

muscle tissue in which cell determination has occurred

pattern formation

how cytoplasmic determinants and inductive signals contribute to development of spatial organization of tissues and organs

positional information

the molecules that control pattern formation o Tell cell its relative location o Determines how cell and its progeny will respond to future molecular signals

homeotic genes

control pattern formation in late embryo, larva and adult of drosophila • Mutations in these genes can cause abnormal placed legs, eyes, etc.

embryonic lethals

mutations with phenotypes causing death at embryonic or larval stage

maternal effect gene

a gene that, when mutant in mother, results in mutant phenotype in offspring, regardless of offspring’s own genotype • Mutations in these genes often are often embryonic lethals

egg-polarity genes

control orientation of egg and consequently that of the fly

bicoid

‘two-tailed’ | • Offspring whose mother has 2 mutant bicoid alleles lacks front half of body and both of back ends

Morphogen gradient hypothesis

states that a gradient of substances called morphogens establish an embryo’s axis and other features of its form

oncogenes

cancer-causing genes

proto-oncogenes

normal version of cellular genes | o Code for proteins that stimulate normal cell growth and division

tumor-suppressor genes

genes whose products inhibit cell division o Prevent cancer o Repair damaged DNA o Control adhesion of cell to extracellular matrix

Ras gene

gene with mutations- responsible for connective tissue cancer o Ras protein- G protein that relays a signal from growth factor place to protein kinases, resulting in increased cell division o Excessive amounts can cause excessive cell division

P53 gene

tumor-suppressor gene o Has transcription factor that promotes production of cell cycle-inhibiting proteins o Mutation can lead to hyperactive Ras protein and uncontrolled cell growth (cancer) o Can activate cell apoptosis