unit 6 test (6.5-6.8) Flashcards
operons
group of genes that can be turned on or off
have three parts
-promotor
-operator
-gener
promotor of an operon
where RNA p. can attach
operator of an operon
on/off switch
genes of an operon
code for related enzymes in pathway
operons can be — or —
repressible; inducible
repressible operons
(on to off)
transcription is usually on, but can be repressed (stopped)
ex: trp operon
inducible operons
(off to on)
transcription is usually off, but can be induced (started)
ex: lac operon
regulatory gene
produces a repressor protein that binds to the operator to block RNA p. from transcribing the gene
-always expressed, but at low levels
-binding of a repressor to a operator is reversible
allosteric activator
substrate binds to the allosteric site and stabilizes the shape of the enzyme so that the active sites remain open
allosteric inhibitor
substrate binds to allosteric sire and stabilizes the enzyme shape so that the active sites are closed (inactive form)
trp operon
-in bacteria, controls the synthesis of tryptophan
-since its repressible, transcription is active
–it can be switched off by a trp repressor
—allosteric enzyme that is only active when tryptophan binds to it
when too much tryptophan builds up in the bacteria, tryptophan is — likely to bind to the — turning it —, which will then temporarily — — transcription for tryptophan.
more; repressor; active; shut off
the lac operon
-controls the synthesis of lactase, an enzyme that digests lactose (milk sugar)
-since it is inducible, transcription is usually off
–a lac repressor is bound to the operator (allosterically active)
-the inducer for the lac repressor is allolactose
–when present it will bind to the lac repressor and turn it off (allosterically inactive)
—genes can now be transcribed
eukaryotic gene expression is regulated at 5 different stages
chromatin structure, epigenic inheritance, transcription initiation, rna processing, translation initiation
chromatin structure:
if dna is tightly wound, it is — accessible for transcription. how can it be modified?
less;
histone acetylation & dna methylation
histone acetylation
adds acetyl groups to histones, which loosens the DNA
DNA methylation
adds methyl groups to dna, which cause chromatin to condense
epigenic inheritance
chromatin modifs dont alter the — sequence of the dna, but they can be — to future generations. modifs can be — unlike mutations. explains why one — twin may inherit a disease while the other doesnt
nucleotide; heritable; reversed; identical
transcription initiation
once chromatin modifs allow the dna to be more accessible, specific transcription factors bind to — —. sections of non-coding dna that serve as binding sites. — — can be increased/decreased by binding of activators or — to control elements
control elements; gene expression; repressors
rna processing
alternative splicing of a pre-mrna
translation initiation
-translation can be activate/repressed by initiation factors
-micro rna’s and small interfering rna’s can bind to mrna and degrade it or block translation
during embryonic development, cell — and cell — occurs
division; differentiation
-cells become specialized in their structure and function
-morphogenesis: physical process that gives an organism its shape
how do cells differentiate during early development?
cytoplasmic determinants and induction
cytoplasmic determinants
substances in the maternal egg that influence cells
induction
cell to cell signals that can cause a change in gene expression
both cytoplasmic determinants and induction influence
pattern formation
-a “body plan” for the organism
–homeostatic genes: map out the body structures
as cells differentiate, — plays a critical role
apoptosis
ex: if this didnt happen during devel, humans would have webbed feet and hands.
mutation
change in genetic material of a cell, which can alter phenotypes
mutations are the primary source of
genetic variation
-normal function and production of cellular products is essential
–any disruption can cause new phenotypes
mutations or changes can be — — or — —
large scale; small scale
large scale mutations
chromosomal changes
small scale mutations
nucleotide substitutions, insertions, or deletions
ex: point mutations, frameshift mutations
point mutations (small scale mutation)
change a single nucleotide pair of a gene
-substitution: replacement of one nucleotide and its partner with another pair of nucleotides
-types:
–silent
–missense
–nonsense
silent point mutation (small scale mutation)
change still codes for same AA (redundancy)
missense point mutation (small scale mutation)
change results in a diff AA
-conservative: keeps same grouping of AA
nonsense point mutation (small scale mutation)
change results in a stop codon
frameshift mutation (small scale mutation)
when the reading frame of genetic info is altered
-disastrous effects to resulting proteins
–insertion: nucleotide is inserted
–deletion: nucleotide is deleted
large scale mutations
mutations that affect chromosomes
-types:
–nondisjunction
–translocation
–inversions
–duplications
–deletions
nondisjunction (large scale mutation)
when chromosomes dont separate properly in meiosis
-results in the incorrect number of chromosomes
–trisomy 21
translocation (large scale mutation)
segment of one chromosome moves to another
inversions (large scale mutation)
segment is reversed
duplications (large scale mutation)
segment is repeated
deletions (large scale mutation)
segment is lost
any time mutations occur, they are subject to — —
natural selection
genetic changes can sometimes — the survival and reproduction (fitness) of an organism
enhance
prokaryotes can exchange genetic material through
horizontal gene transfer
if there is a mutation that is beneficial to the survival and reproduction of that prokaryote, then it can be
transferred from one prokaryote to another
-types:
–transformations
–transductions
–conjugations
–transpositions
transformations
up taking of dna from a nearby cell
transduction
viral transmission of genetic material
conjugation
cell to cell transfer of dna
transposition
movement of dna segments within and between dna molecules
pcr
polymerase chain reaction: method used in molecular bio to make several copies of a specific dna segment
-segments of dna are amplified
-results can be analyzed using gel electrophoresis
