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21 Cards in this Set

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how is gene expresion controlled by regulating transcription?
binding protein to regulatory sequence blocks transcription by getting in the way of rna polyermase, or stimulates transcrip. by facilitating binding rna polyermase to the promoter
what is transcriptional control in prokaryotes?
adjusts cell's activities to immmediate, external environment to grow and divide as rapidly as possible
what is transcriptional control in eukaryotes?
-most common
-primary funct. is maintaining gene control
-compensate for physiological cnages or mediate product, decisions
what is posttranscriptional control?
influencing mRNA produced from genes or the activity of proteins encoded by the mRNA
what is a major groove?
-proteins can bind to outside surface of double helix
-nucleotides' hydrophobic methyl groups, hydrogen atoms, and hydrogen bond donors & acceptors protrude from major groove
-employ bends in protein chain that permit interlocking w/major groove (dna-binding motifs)
describe the helix-turn-helix motif.
-one helical segment fits snuggly in major groove, other butts against outside of dna molecule
-two binding sites doubles contact zone and greatly strengthens the bond
describe the homeodomain motif.
-special kind of helix-turn-helix motif surrounded by region initiating key develop. stages
describe the zinc finger motif.
-zinc atoms coordinate dna binding
-the more zinc fingers in cluster, the stronger the protein binds to dna
describe the leucine zipper motif.
-formed when region on one subunit containing several hydrophobic amino acids interacts w/similar region on another subunit
what is a lac operon?
multi. genes are part of a single gene expression unit.
what do basal transcription factors do?
they are necessary to eestablish productive initiation; do not increase the rate
what do specific transcription factors do?
they act in a tissue-or time-dependent manner to stimulate higher levels of transcription than the basal levels
what are enhancers?
binding site of specific transcription factors;accomplished by dna bending to form a loop, positioning the enhancer close to the promoter
why is transcriptional control more complicated in eurkayotes than in prokaryotes?
-dna organized in chromatin
-transcrip. occurs in nuclues & translat. in cytoplasm
-complex developm. programs
-multiple tissue types
what is one effect of chromatin structure on gene expression?
promoter blocking by nucleosomes
what does dna methylation do?
blocks accidental transcription of "turned off" genes
what does posttranscriptional control on eukaryotes involve?
invovles the recognition of specific sequences on primary rna transcript. by regulatory proteins and small rna molecules
how does rna interference work?
gene silencing happens when a change in gene expression is passed from one generation to another; appears to play a major role in epigenetic change
what is alternative splicing?
exons can be spliced together in dif. ways to assemble a variety of polypeptides
describe the transport of the transcript out of the nucleus.
passage out of mRNA transcript across nuclear membrane requires the transcript to be recognized
what do translation repressor proteins do?
shut-down translation by binding to the beginning of the transcript so that it can't attach to the ribosome