Chapter 18 Flashcards
how can a cell regulate the production of enzymes?
by feedback inhibition or by gene regulation
operons
the entire stretch of DNA that includes the operator, the promoter, and the genes they control
operator
the regulatory “switch” is a segment of DNA called an operator
-positioned within the promoter
repressor
a protein that switches off the operon
-the repressor prevents gene transcription by binding to the operator and blocking RNA polymerase
regulatory gene
the repressor is the product of a separate regulatory gene
corepressor
a molecule that cooperates with a repressor protein to switch an operon off
how can a repressor be in an active or inactive form?
depends on the presence of other molecules
by default the trp operon is __ and the genes for tryptophan synthesis are (not transcribed/transcribed)
- on
- transcribed
what happens when tryptophan is present?
binds to the trp repressor protein and turns the operon off
when tryptophan levels are high what does this mean?
operon is turned off if tryptophan levels are high
what is a repressable operon?
one that is usually on, binding of a repressor to the operator shuts off transcription
trp operon is a ____ _____
repressible operon
inducible operon
one that is usually off; a molecule called an inducer actives the repressor and turns on transcription
lac operon is an ____ operon and contains genes that code for enzymes used in the hydrolysis and metabolism of lactose
inducible
when the lac repressor is active what does this do to the lac operon
when the lac repressor is active, it switches the lac operon off
inducer
inactivates the repressor to turn the lac operon on
CAP (catabolite activator protein)
postive control through a stimulatory protein
- when CAP is activated it attaches itself to the promoter of the lac operon and increases the affinity of RNA polymerase, thus accelerating transcription
- when glucose levels increase CAP detaches its self from the lac operon and transcription returns to normal rate
in multicellular organisms, regulation of gene expression is ______
-essential for cell specialization
differential gene expression
the expression of different genes by cells with the same genome
-abnormalities can lead to diseases like cancer
what can be done to influence both chromatin structure and gene expression
chemical modifications to histones and DNA of chromatin
histone acetylation
acetyl groups are attached to positively charged lysines in histone tails
-this loosens chromatin structure and thus promoting the initiation of transcription
methylation
- addition of methyl groups
- this condenses chromatin
phosphorylation
-addition of phosphate groups next to methylated amino acid to loosen chromatin as well
histone code hypothesis
proposes that specific combinations of modifications, as well as the order in which they occur, help determine chromatin configuration and influence transcription
DNA methylation
the addition of methyl groups to certain bases in DNA
- associated with reduced transcription in some species
- can cause long term inactivation of genes in cellular differentiation
genomic imprinting
methylation regulates expression of either the maternal or paternal alleles of certain genes at the start of development
epigenetic inheritance
The inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence
-so smoking before the age of 12 can cause your children to be obese (example)
how do chromatin-modfying enzymes provide initial control of gene expression?
by making a region of DNA either more or less able to bind the transcription machinery
control elements
segments of noncoding DNA that serve as binding sites for transcription factors that help regulate transcription
transcription factors
- essential for the transcription of all protein-coding genes
- to initiate transcription; gives assistance
- high levels of transcription of particular genes depend on control elements interacting with specific transcription factors
enhancers
distal (situated away from the body) control elements
proximal control elements
-located close to the promoter
activator
a protein that binds to an enhancer and stimulates transcription of a gene
- have two domains
(1) binds to DNA
(2) activates transcription
what do bound activators facilitate?
a sequence of protein-protein interactions that result in transcription of a given gene
true or false:
some transcription factors can function as repressors, inhibiting expression a gene
true
does each eukaryotic gene have its own promoter and control elements?
yes, a prokaryotic operon doesn’t
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
which is more long lived in the cytoplasm? eukaryotic mRNA or porkaryotic mRNA
eukaryotic mRNA
the nucleotide sequences that influence the lifespan of mRNA in eukaryotes reside in….
the untranslated region (UTR) at the 3’ end of the molecule
what do the regulatory proteins that bind to sequences or structures of the mRNA do?
block the initiation of translation of selected mRNAs
proteasomes
giant protein complexes that bind to protein molecules and degrade them
where does noncoding RNAs regulate gene expression (2)
- mRNA translation
2. chromatin confiugaration
true or false:
A significant amount of the genome may be transcribed into noncoding RNAs (ncRNAs
true
MicroRNAs
small single stranded RNA molecules that can bind to mRNA
-these can degrade mRNA or block its translation
RNA interference
inhibition of gene expression by RNA molecules
what causes RNA interference?
small interfering RNAs
- similar to microRNAs
- induce heterochromatin (making DNA tighter) thus can block large regions of the chromosome (in some yeasts)
cell differentiation
the process by which cells become specialized in structure and function
morphogenesis
the physical processes that give an organism its shape
cytoplasmic determinants
maternal substances in the egg that influence early development
induction
signal molecules from embryonic cells cause transcriptional changes in nearby target cells
-thus, interactions between cells induce differentiation of specialized cell types
determination
commits a cell to its final fate
- determination precedes differentiation
- cell differentiation is marked by the production of tissue-specific proteins
myoblasts
produce muscle specific proteins and form skeletal muscle cells
MyoD
one of several “master regulatory genes” that produce proteins that commit the cell to becoming a skeletal muscle
-a transcription factor that binds to enhancers of various target genes
pattern formation
the development of a spatial organization of tissues and organs
-pattern formation begins with the establishment of the major axes
positional information
the molecular cues that control pattern formation, tells a cell its location relative to the body axes and to neighboring cells
homeotic genes
control pattern formation in late embryo, larva, and adult stages
maternal effect genes
cytoplasmic determinants that initially establish the axes of the body of Drosophila
egg polarity genes
maternal effect genes can also be called this…control orientation of the egg and the consequently of the fly
bicoid
maternal effect gene
–affects the front half of the body
morphogens
establish an embryo’s axes and other features
what are the three reasons bicoid research is important?
- identified a specific protein required for some early steps in pattern formation
- increased understanding of the mother’s role in embryo development
- demonstrated a key developmental principle that a gradient of a molecule can determine polarity and position in the embryo
oncogenes
cancer causing genes
proto-oncogenes
corresponding normal cellular genes that are responsible for normal cell growth and division
how can oncogenes be converted to oncogenes
- movement of DNA within the genome; if it ends up near an active promoter, transcription may increase
- amplification of a proto-oncogene; increases the number of copies of the genes
- point mutations in the proto-oncogene or its control elements; cause an increase in gene expression
tumor suppressor genes
help prevent uncontrolled cell growth
-mutations that decrease protein products of tumor suppressor genes may contribute to cancer onset
what are three things tumor suppressor genes can do?
- repair damaged DNA
- control cell adhesion
- inhibit cell cylce in the cell cignaling pathway
what is common in human cancers?
*mutations in the ras proto-oncogene and p53 tumor suppressor gene
what happens if there is a mutation in the ras gene
can lead to production of a hyperactive Ras protein and increased cell division
