Ch. 9 Introduction to Microbial Genetics pt. 3
In the presence of lactose, what would happen to the lac operon?
Upon entering cell, lactose (the substrate) becomes a genetic inducer by attaching to the repressor, which is rendered inactive and falls away. The DNA becomes easily accessible to RNA polymerase, which then transcribes structural genes and the mRNA is translated into enzymes that can act on lactose
In the absence of lactose, what would happen to the lac operon?
a repressor protein attaches to the operator of the operon, effectively blocking transcription of structural genes. This prevents the unnecessary synthesis of enzymes for processing lactose
what is the function of lactose permease in lac operons?
acts as a transport protein in a cell membrane to allow lactose to enter a cell
An important point about the lac operon is that it functions ONLY IN THE ABSENCE OF......
glucose or if the cell's energy needs are not being met by the available glucose
Because lactose is ultimately responsible for stimulating the chain of events leading to protein synthesis in a lac operon, it is considered an...
inducer
Many catabolic operons are
inducible
The lactose operon (Lac operon) is a __________ operon
inducible
____________ means that the operon is turned on by the substrate of the enzyme for which its structural genes code
inducible
Operons are described as either __________ or _________
inducible or repressible
Which steps of transcription and translation use the most ATP?
initiation
Genes that are organized in an operon all code for
proteins that have a role in a common process
A feature of a lac operon, __________, is composed of the gene that codes for a protein capable of repressing the operon
regulator (a repressor)
____________ are proteins that influence the regions of a DNA molecule that are transcribed by RNA polymerase during the process of transcription
regulatory proteins
In the case of ____________ operons, several genes in series are turned off by the product synthesized by the enzyme
repressible
A ______________ is coded for by the lac I gene and is NOT a part of the lac operon, but is instead important for regulation of the lac operon
repressor protein
In the absence of lactose, the _________ interacts with the operator and causes the operator to distort into a temporary loop configuration (thus blocking RNA polymerase)
repressor protein
In the absence of lactose, the_____________ binds to the lac operator and prevents transcription
repressor protein
How is coordinate control beneficial for a bacterial cell?
saves energy for the bacteria by turning on all genes in an operon at the same time, instead of having to turn on each gene individually which would take a ton of energy
The enzymes needed to metabolize a nutrient are produced ONLY when.......
that nutrient is present (no need for the enzyme if there are no nutrients to be broken down)
Inducible operons are usually turned on when...
the bacteria need to use a nutrient found in the environment
t or f operons are extremely rare to find in eukaryotes
true
t or f the lac I gene has a promoter, coding region, and a terminator
true
t or f the lac operon, like other inducible systems, is usually in an off mode when the appropriate substrate is absent
true
t or f when a supply of glucose is present, a second regulatory system ensures that the lac operon is inactive, regardless of lactose levels in the environment
true
If the operon is inducible, it is usually _______ but can be turned ____
usually off but can be turned on
If the operon is repressible, it is usually _____ but can be turned _____
usually on but can be turned off
What are the functions of beta-galactosidase?
1. breaks the covalent bond in lactose so that it may be used for energy 2. cleaves the lactose to release glucose and galactose 3. catalyzes the conversion of lactose into allolactose
What are the 3 structural genes in the lac operon?
1. lac Z 2. lac Y 3. lac A
What are the components of a lac operon?
1. one promoter 2. three genes coding for proteins involved in catabolism of lactose 3. an operator
Why have an inducible operon?
Enzymes that catabolize a nutrient only need to be produced when that nutrient is present in the environment
Why do microbial prokaryotes have operons?
It organizes genes that function in a common process together, and allows them to be repressed or induced in unison by the same regulatory element
Most repressible operons contain genes coding for __________ enzymes, such as those used in protein synthesis
anabolic
_________ are metabolic reactions that build things by joining smaller molecules and making large molecules (ex, protein synthesis)
anabolism
operons are found primarily in
bacteria and archaea
Before energy can be derived from lactose, it must be broken in half. ___________ breaks the covalent bond in lactose
beta-galactosidase
__________ is responsible for catalyzing the conversion of lactose into allolcatose (which is still a disaccharide, but moves some atoms around in the lactose)
beta-galactosidase
___________ is responsible for cleaving lactose to release glucose and galactose
beta-galactosidase
__________ are metabolic reactions that break down large molecules into smaller molecules
catabolism
most inducible operons contain genes that code for enzymes that act in...
catabolism
______________ is turning on all genes in an operon at the same time
coordinate control
The repressor protein, which is important for the regulation of the lac operon, is coded for by the.....
lac I gene
The ___________ contains three genes that all code for proteins involved in catabolism of lactose
lac operon
_______ has 2 sugars bound by a covalent bond
lactose
Lactose is too large to enter a cell by itself. Therefore, ____________ acts as a transport protein in a cell membrane, allowing the lactose to enter the cell
lactose permease
_____________ brings lactose across the cell membrane
lactose permease
When transcribed, the lac operon makes.......
mRNA and 3 different proteins
____________ are all biochemical reactions taking place in a cell
metabolism
The ____________ is a feature of the lac operon that is a sequence acting as an off/on switch for transcription
operator
A __________ is a section of DNA that contains one or more structural genes along with a corresponding operator gene that controls transcription
operon
a set of genes coordinately regulated as a single unit
operon
most prokaryotic genes are organized into
operon
two or more structural genes under the control of a single promoter
operon
A __________ is the specific molecule upon which an enzyme acts
substrate
The repressor protein (coded for by the lac I gene) is important for...
the regulation of the lac operon
T or F an operon is ONLY turned on when a substrate is around
true