chpt 7.4-7.5 test Flashcards
human insulin is required when??
glucose level in blood is high
Evolution enzyme that facilitated the breakdown of lactose is transcribed and translated when…
the bacteria are exposed to lactose
optimal functioning of an organism requires…
genes to be turned on and off as they are needed (cells know which genes to express and when)
proteins that are always needed in a cell, their genes are continuously transcribed and translated
housekeeping genes
liver cells require repair enzymes to manage…
the toxins in the body
genes that produce hemoglobin molecules are transcribed and translated only in cells that…
give rise to red blood cells
Prokaryotic gene control mechanism:
gene expression in prokaryotes is regulated in response to concentrations of two molecules (lactose and tryptophan) via negative feedback control
lac operon:
is a cluster of three genes that contains the DNA sequences to code for the proteins and regulate the metabolism of lactose
the site where DNA transcription begins
the promoter
what contains the sequence of bases that control transcription and is the region in the operon that regulatory factors bind to. it contains the coding regions for the various enzymes that actually metabolize the lactose
the operator
protein that binds to the operator to repress gene transcription (is dependant on concentration of lactose in the cell, is always present in the cell, in lac operon is called lacI protein or lac repressor, takes cues from environment and regulates the production of lactose metabolizing proteins)
repressor protein
absence of lactose
- lac repressor is active and binds to operator
- RNA polymerase prevented from binding to promoter region, stops lactose metabolizing enzymes from being synthesized
- active lac repressor binds to operator of lac operon and blocks transcription
presence of lactose
- some lactose binds to a site on the lac repressor and renders it inactive
-inactive lac repressor is unable to bind to operator and block transcription - RNA polymerase can bind to promoter region, transcription of lac genes begins. translation of mRNA = 3 lactose metabolizing enzymes (metabolism + break down lactose)
lactose acts as a signal molecule and the cell responds by synthesizing the lactose metabolizing enzymes. The signal molecule is called an inducer and triggers…
the expression of an operons genes and serves to initiate the production of enzymes
lac operon is known as an inducible operon because…
the inducer inactivates the repressor and allows the genes to be transcribed
as concentration of lactose increases, transcription of the lac genes increases or decreases
increases also. there is a direct correlation between the two
tryptophan is
important amino acid used to build proteins
operon that regulates the production of tryptophan in a cell is the…
trp operon (contains an operator and promoter that precede the genes coding for tryptophan synthesizing enzymes)
trp operon and lac operon same structure?
yes
trp repressor protein acts to what, and is activated by what?
- acts to regulate the expression of tryptophan enzymes
- is activated in presence of tryptophan
absence of tryptophan
-The repressor protein is in inactive state, does not bind to the operator.
-RNA polymerase is able to bind to the promoter region.
-transcription of genes responsible for the biosynthesis of tryptophan can proceed
Presence of Tryptophan
+ what is a corepressors function
-Tryptophan acts as a signal molecule+activates the repressor protein which then is able to bind to the operator and stop transcription of the tryptophan-synthesizing genes.
b) A corepressor is a signal molecule that binds to a regulatory protein to reduce the expression of an operon’s genes. It serves to repress instead of inducing the expression of a set of genes.
example of negative feedback mechanism
negative correlation between the amount of tryptophan in the environment and the rate of tryptophan synthesis
the methods for regulating eukaryotic gene expression are more or less complex than the methods for regulating prokaryotic gene expression
more complex, more steps.
Eukaryotes do not use the operon system. The control mechanisms in eukaryotes fall into four categories:
-Transcriptional in which mRNA is being synthesized
-Post-transcriptional in which mRNA is being processed
-Translational in which the protein is being synthesized
-Post-translational occurs after the protein has been synthesized
Transcriptional Regulation regulates what
genes are transcribed (DNA to mRNA) or controls the rate at which transcription occurs.
**short answer
Promoter access is provided by…
loosening a DNA molecule from histones.
In eukaryotic chromatin…
the DNA is wrapped around histone proteins and the gene promoters are not accessible to the proteins that initiate transcription
For a gene to be transcribed, the chromatin must…
be partially unwound to expose the promoter.
Activator and repressor proteins do what
bind to the promoter and enhance or decrease the rate of transcription
3 methods
expose promoter
1) promoter exposed: the activator molecule binds upstream the genes promoter + signals protein remodelling complex, histone core proteins displaced)
2) activator molecule bound upstream of gene being transcribed to regulatory sequence and this signals enzyme that can add acetyl group to histones= loosens histones= promoter accessible
3)methylation: methyl group added to cytosine bases in promoter of a gene, inhibiting transcription, called “silencing”
Methylation is another way to…
put genes or entire regions of chromosomes “on hold” until they are required.
Post Transcriptional Regulation controls…
the availability of mRNA molecules to ribosomes; pre-mRNA molecules undergo changes in the nucleus, resulting in final mRNA before translation occurs.
alternative splicing (occurs in post transcriptional regulation) does what?
produces different mRNAs from pre-mRNA by removing different combinations of introns, remaining exons are spliced together.
an intron in one pre-mRNA may be considered an exon in another pre-mRNA and may therefore
not be spliced out of the second pre- mRNA transcript
About what % of human genes are alternatively spliced at the pre-mRNA level
75%
Masking proteins: bind to what, common form of control in what, bunch of info
The masking proteins bind to mRNA and inhibit further processing. Involves binding masking proteins to mRNA and thus does not undergo protein synthesis. Masking proteins are a common form of control in many animal eggs, keeping mRNAs in an inactive form until an egg has been fertilized and embryonic development is underway. When it is time for the mRNA to be translated, other proteins remove the masking proteins.
The rate of degradation of mRNA is dependent on…
the need of the cell for the gene product
Changes in the rate of degradation of mRNAs in which a regulatory molecule, such as a hormone, will directly or indirectly affect…
the rate of mRNA breakdown.
Translational Regulation controls…
how often and how rapidly mRNA transcripts will be translated into proteins.
Translational Regulation occurs during…
protein synthesis by a ribosome
The variation of the length of the poly(A) tail is related to…
the rate of translation.
-specific enzymes can add or delete repeating sequences of adenine at the ends of the mRNA molecules.
Post-Translational Regulation controls…
when proteins become fully functional, how long they are functional, and when they are degraded.
The three methods used in Post-Translational Regulation:
processing, chemical modification, and degradation.
Processing occurs and the polypeptide is…
chemically modified to render it an active protein.
When proteins are initially synthesized, they are in an inactive form and must be activated by …
various processing mechanisms such as removing specific sections of the protein to activate it. Processing mechanisms can be used to control the availability of activated proteins and thus regulate the end product of certain genes.
In chemical modification the presence of hormones may…
lengthen or shorten the length of time that a protein is functional
Ubiquitin-tagged proteins are degraded during…
post translational regulation
Proteins are subject to constant degradation where?
both inside and outside the cell
The degraded proteins are broken down into…
their constituent amino acids and recycled to synthesize new proteins
A cell responds to changes in its environment by…
regulating the rate at which its genes are expressed
Prokaryotes use —— to regulate gene expression.
operons
An operon is…
a section of DNA that includes a promoter, an operator, a regulatory protein, and the sequence of genes that code for one or more specific proteins
The lac operon uses a signal molecule (lactose) that ——the expression of the operon’s genes, whereas the trp operon uses a signal molecule (tryptophan) that ——– the expression of the operon’s genes.
induces, represses
Gene regulation in eukaryotes can occur during…
transcription, post-transcription, translation, or post-translation
Transcriptional control regulates…
which genes are transcribed and/or the rate at which transcription occurs
Forms of post-transcriptional control include:
alternative splicing of exons and introns, masking proteins binding to mRNA, and the rate of degradation of mRNA
Translational control involves
how often and how rapidly an mRNA is translated
Post-translational control regulates
when proteins become fully functional, how long they are functional, and when they are degraded
Cancerous cells lack…
the regulatory mechanisms that allow healthy cells to grow and express their genes properly
Genetic mutations are…
changes in the DNA sequence, caused by various mechanisms
A susceptibility locus is a…
region on a given chromosome where mutations that affect one or more genes are more likely to be present, based on statistical evidence
types of point mutations (4)
-substitution (replacement of one base pair)
-insertion (addition of a base pair or larger coding region)
-deletion (the removal of a base pair or larger coding region)
inversion- two adjacent bases trading places or the reversal of a sequence of DNA
The differences in the DNA of individuals caused by point mutations are referred to as
single nucleotide polymorphisms
small-scale mutations can be categorized into four groups:
a) missense mutations = changes a single amino acid in the coding sequence, may function differently.
b) nonsense mutations = change of a single base pair or group of base pairs results in a premature stop code in the gene.
c) silent mutations = mutated DNA sequence codes for the same amino acid as the non-mutated sequence, and the resulting protein is not altered.
d) frameshift mutations = a shift in the reading frame resulting in multiple missense and/or nonsense effect. nucleotides are inserted into or deleted from a DNA sequence.
Any deletion or insertion of base pairs in multiples of three…
does not cause frameshift
Tay- Sachs disease is a result of…
insertion of four base pairs
LS- Gene duplication (amplification) occurs when
a gene or group of genes is copied to multiple regions of chromosomes and can lead to a larger number of copies of the gene or group of genes
LS: Chromosomal translocation occurs when
entire genes or sequences of DNA (groups of genes) are moved from one chromosome to another.
Translocation between two non- homologous chromosomes usually occurs when…
portions of each chromosome break off and exchange places
If transposable elements (move freely ab the genome) are inserted near an existing gene sequence…
can enhance, disrupt, or otherwise modify the expression of the gene
Inversion (is LS) occurs when…
a portion of a DNA molecule, often containing one or many genes, reverses its direction in the genome
trinucleotide repeat expansion
increases in the number of repeats from one generation to the next
A spontaneous mutation is a mutation that is caused by…
n error in DNA replication
An induced mutation is a mutation that is caused by…
an environmental agent.
A mutagen is… + 2 most common forms
an environmental agent that directly alters the DNA within a cell. -chemicals and radiation.
Chemical mutagen is… + examples
any chemical agent that can enter the cell nucleus and chemically alter the structure of the DNA . ex: carbon monoxide and nitrous acid
Benzene and ethidium bromide are mutagens that cause mutations by …
mimicking a DNA nucleotide
Radiation can cause mutations such as…
ultraviolet B radiation, X-rays and gamma rays
Mutations have given rise to
diversity of life
