Microbiology Chapter 8

Question 1

Theory that says one gene one protein

DNA Polymerase makes RNA polymerase in transcription to Mrna to Translation in the ribosome to make protein.

Answer 1

flow of central dogma theory

Question 2

Flow of Genetic Material in Expression?

Answer 2

Genetic information is used within a cell to produce the proteins needed for the cell to function.

Question 3

Flow of Genetic Material in Recombination?

Answer 3

Genetic information can be
transferred between cells
of the same generation.

Question 4

Flow of Genetic Material in Replication?

Answer 4

Genetic information can
be transferred between
generations of cells.

Question 5

Monocystronic vs Polycistronic

Answer 5

An mRNA molecule is said to be monocistronic when it contains the genetic information to translate only a single protein. This is the case for most of the eukaryotic mRNAs. On the other hand, polycistronic mRNA carries the information of several genes, which are translated into several proteins. These proteins usually have a related function and are grouped and regulated together in an operon. Most of the mRNA found in bacteria and archea are polycistronic.

Question 6

Why is it important to regulate the expression of genes?

Answer 6

Prokaryotes: environmental conditions
Adapt and Survive
Growth and Division

Eukaryotes: multicellular organisms = homeostasis
Embryological development
Tissue and organ differentiation

Question 7

Constitutive genes are expressed at a fixed rate
Other genes are expressed only as needed
Inducible genes 
Repressible genes
so whats the difference?

Answer 7

nducible operons are used to produce proteins only under specific conditions. Most bacteria use glucose as their main energy source. Therefore, the unusual arrival of the milk sugar lactose in the cell turns the operator switch to the “on” position, which allows transcription to occur. Repressible operons have operators that are always on (transcription occurring) unless a signal (for example, too much product) turns them off.

Question 8

Cluster of adjacent genes oriented in the same direction
Co-transcribed into a single polycistronic mRNA
Coordinately regulated

Answer 8

operon

Question 9

One type of signal (i.e. lactose) can regulate expression of several genes that are clustered together on a chromosome

Empirical evidence has shown many bacterial genes are clustered and transcribed together as single mRNA (co-transcribed)

The gene clusters are termed operons

The mRNA transcript is called polycistronic

Answer 9

jacob and manod :operon theory

Question 10

Lac operon, trp operon is inducible or repressible

Answer 10

inducible = lac and repressible trp

Question 11

structure of inducible lac operon

Answer 11

Structure of the operon. The operon consists of the promoter (P) and operator (O) sites and structural genes that code for the protein. The operon is regulated by the product of the regulatory gene

The lacI gene coding for the repressor lies nearby the lac operon and is always expressed (constitutive)

Question 12

mechanism of inducible gene

Answer 12

Repressor active, operon off. The repressor protein binds with the operator, preventing transcription from the operon. which means when no lactose is present repressor binds tightly, inhibits transcription

Repressor inactive, operon on. When the inducer allolactose binds to the repressor protein, the inactivated repressor can no longer block transcription. The structural genes are transcribed, ultimately resulting in the production of the enzymes needed for lactose catabolism.

Lactose induces further induction of lacZYA gene cluster expression

Question 13

Induction of Gene Expression

scenarios: no lactose or with lactose

Answer 13

No lactose in medium:
lacI produces repressor which binds to operator => no gene expression

Lactose in medium:
Lactose (inducer) binds to repressor => repressor cannot bind to operator anymore => gene expression can start

Question 14

Repressible operons structure?

Answer 14

Structure of the operon. The operon consists of the promoter (P) and operator (O) sites and structural genes that code for the protein. The operon is regulated by the product of the regulatory gene (I ).

In repressible operons, the structural genes are transcribed until that are turned off.

Question 15

Repressible operon mechanism?

Answer 15

Repressor inactive, operon on. The repressor is inactive, and transcription and translation proceed, leading to the synthesis of tryptophan.

Repressor active, operon off. When the corepressor
tryptophan binds to the repressor protein, the activated
repressor binds with the operator, preventing transcription
from the operon.

Question 16

positive vs negative regulation

Answer 16

(a) Negative Regulation:

Turning off of the structural gene expression by a repressor protein is known as negative regulation. In an inducible system, the repressor protein alone binds to the operator and inhibits transcription in the absence of an inducer.

However, in the presence of an inducer, the repressor protein binds to it and undergoes a conformational change. The resultant repressor-inducer complex can not bind to the operator ancKhereby, initiates transcription. (Example: lac-operon)

(b) POSITIVE REGULATION:

Turning on of the structural gene expression by the active repressor protein is known as positive regulation.

In a repressible system, the repressor protein alone can not bind to the operator and thus, facilitates the binding of the RNA polymerase and transcription. The repressor-co-repressor complex undergoes a conformational change in the structure. This complex can bind to the site and inhibit transcription

Question 17

Mecahnism of epigenetic control
Methylating nucleotides
Methylated (off) genes are passed to offspring cells 
Not permanent
May explain biofilm behavior

Answer 17

1.Transcription of
miRNA occurs.
2.miRNA binds to target
mRNA that has at least six
complementary bases.
3.mRNA is degraded

Question 18

mutations terms?

Answer 18

Mutagen: agent that causes mutations

Spontaneous mutations: occur in the absence of a mutagen

Question 19

X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone
UV radiation causes thymine dimers

Answer 19

ionizing radiation

Question 20

Positive (direct) selection detects mutant cells because they grow or appear different
Negative (indirect) selection detects mutant cells because they do not grow
Replica plating

Answer 20

modes of selection based on mutation

Question 21

Kinds of Horizontal Gene Transfer

Answer 21

the transfer of genes between cells of the same generation
Transformation
Conjugation
Transduction
Generalized
Specialized
Transposons

Question 22

Vertical gene transfer

Answer 22

occurs during reproduction between generations of cell(cell division)

Question 23

Exchange of genes between two DNA molecules

Crossing over occurs when two chromosomes break and rejoin

Answer 23

Genetic recombination

Question 24

modes of conjugation

Answer 24

sex pillus and mating bridge

Question 25

Kinds of Plasmids

Answer 25

Conjugative plasmid: carries genes for sex pili and transfer of the plasmid
Dissimilation plasmids: encode enzymes for catabolism of unusual compounds
R factors: encode antibiotic resistance

Question 26

Transposons

Answer 26

Segments of DNA that can move from one region of DNA to another
Contain insertion sequences for cutting and resealing DNA (transposase)
Complex transposons carry other genes