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