All cells share four common components: (1) a plasma membrane, an outer covering that separates the cell’s interior from its surrounding environment; (2) cytoplasm, consisting of a jelly-like region within the cell in which other cellular components are found; (3) DNA, the genetic material of the cell; and (4) …

How does a bacterial chromosome differ from a eukaryotic chromosome? A bacterial chromosome is a circular, double-stranded DNA molecule with associated proteins. A eukaryotic chromosome is a linear, double-stranded DNA molecule with many associated proteins, including histones.

What is the difference between prokaryotic chromosomes and eukaryotic chromosomes? Prokaryotic cells have a single circular chromosomes attached to the cell membrane, while eukaryotic cells contain free-floating linear chromosomes within a nucleus. Every time a cell divides the telomere gets shorter.

Ø The chromosome of both prokaryotes and eukaryotes contains the genetic material DNA. Ø The chemical composition and structural organization of DNA is similar in both prokaryotes and eukaryotes. Ø In both prokaryotes and eukaryotes, the expression of genetic material is facilitated by transcription and translation.

Prokaryotic DNA can be found in the cytoplasm whereas eukaryotic DNA is found in the nucleus, enclosed by the nuclear membrane. Prokaryotic DNA is organized into a single circular chromosome and eukaryotic DNA is organized into several linear chromosomes. The amount of eukaryotic DNA is higher than prokaryotic DNA.

Operon: A set of genes transcribed under the control of an operator gene. More specifically, an operon is a segment of DNA containing adjacent genes including structural genes, an operator gene, and a regulatory gene. An operon is thus a functional unit of transcription and genetic regulation.

The best-studied examples of operons are from the bacterium Escherichia coli (E. coli), and they involve the enzymes of lactose metabolism and tryptophan biosynthesis. Because the lactose (lac) operon shares many features with other operons, its organization and regulation are described in detail below.

Operons are of two types, inducible and repressible.

An operon is made up of 3 basic DNA components:

• Promoter – a nucleotide sequence that enables a gene to be transcribed.
• Operator – a segment of DNA to which a repressor binds.
• Structural genes – the genes that are co-regulated by the operon.

From left to right, the operon contains a promoter (where RNA polymerase binds), and within the right end of the promoter, an operator (where a repressor binds). There are some additional regulatory sequences, not labeled in this diagram, and then five coding sequences: trpE, _trp_D, trpC, trpB, and trpA.

Operon, genetic regulatory system found in bacteria and their viruses in which genes coding for functionally related proteins are clustered along the DNA. This feature allows protein synthesis to be controlled coordinately in response to the needs of the cell.

A repressible operon is one that is usually on but which can be repressed in the presence of a repressor molecule. The repressor binds to the operator in such a way that the movement or binding of RNA polymerase is blocked and transcription cannot proceed.

The two type of operons that express negative gene regulation are a repressible operon (such as trp operon) and inducible operon (such as lac operon). Repressible operon is normally active and producing the protein that they are meant to make unless the protein is present to activate the repressor.

a. To put down or subdue by force: repress a rebellion. b. To end, limit, or restrain, as by intimidation or other action: repress a heresy; repress inflation.

When tryptophan accumulates, a few molecules (of tryptophan) act as co-repressor and bind to inactive repressor activating it. On activation this attaches to the operator, switching off the operon in turn.

With repressible systems, the binding of the effector molecule to the repressor greatly increases the affinity of repressor for the operator and the repressor binds and stops transcription. Thus, for the trp operon , the addition of tryptophan (the effector molecule) to the E.

Repressible operon is an operon that is usually on, but can be inhibited when a molecule, like tryptophan binds to a regulatory protein. Inducible operon is an operon that is usually off, but can be induced to turn on by interaction between molecules and regulatory proteins. An example would be the Lac operon.

inducible operon

The lac operon consists of three structural genes: lacZ, which codes for β-galactosidase, which acts to cleave lactose into galactose and glucose; lacY, which codes for lac permease, which is a transmembrane protein necessary for lactose uptake; and lacA, which codes for a transacetylase that transfers an acetyl group …

An operon consists of an operator, promoter, regulator, and structural genes. The regulator gene codes for a repressor protein that binds to the operator, obstructing the promoter (thus, transcription) of the structural genes.

In bacteria, genes are often found in operons Such a cluster of genes under control of a single promoter is known as an operon. Operons are common in bacteria, but they are rare in eukaryotes such as humans.

The lac, or lactose, operon is found in E. coli and some other enteric bacteria. This operon contains genes coding for proteins in charge of transporting lactose into the cytosol and digesting it into glucose. This glucose is then used to make energy.

The lac operon is under both negative and positive control. The mechanisms for these will be considered separately. 1. In negative control, the lacZYAgenes are switched off by repressor when the inducer is absent (signalling an absence of lactose).

Single mutants of the lac operon Such mutant are called constitutive mutants. Another type of mutant of lacI called Is prevents the repressor polypeptide from binding lactose, and thus will bind to the operator and be non-inducible.. This mutant constitutively represses the lac operon whether lactose is present or not.

a) Most mutations in the operator, the binding site for repressor, lead to lower affinity for the repressor and hence less binding. Thus these mutations allow continued transcription (and thus expression) of the lac operon even in the absence of inducer; this is referred to constitutive expression.

What happens if there is a mutation observed in the operator gene in the lac operon? if the repressor binds more strongly, there would be less transcription. if the repressor has difficulty binding then it is possible that the operon would be turned on when not needed.

A rob- phenotype occurs if lacI is mutated such that the lac repressor can no longer bind to the operator OR when there is a mutation in lacO so that it no longer can bind to the lacI protein.