Invertebrates generally have fairly high production efficiencies  (about 10–50%) than vertebrate. Ectotherms, typically have production efficiencies of around 10%, and birds and mammals, which are endotherms, have production efficiencies in the range of 1–2%.

TLS Online TPP Program

#Id: 4051

#Unit 2. Cellular Organization

The centromeres of all four chromosomes of D. melanogaster aggregate to form a chromocenter that consists largely of heterochromatin.

TLS Online TPP Program

#Id: 4052

#Unit 2. Cellular Organization

Each is produced by the successive replications of a synapsed diploid pair of chromosomes. The replicas do not separate, but instead remain attached to each other in their extended state, a process known as endoreduplication.

At the start of the process, each synapsed pair has a DNA content of 2C (where C represents the DNA content of the individual chromosome). This amount then doubles up to nine times, at its maximum giving a content of 1024C. The number of doublings is different in the various tissues of the D. melanogaster larva.

TLS Online TPP Program

#Id: 6359

#Unit 2. Cellular Organization

Operon consist

Physiology/Mechanism

Molecular biology/Biochemistry of component

Effect of mutations

TLS Online TPP Program

#Id: 6360

#Unit 2. Cellular Organization

Repressors impede access of RNA polymerase to the promoter and Activators enhance the RNA polymerase–promoter interaction.

TLS Online TPP Program

#Id: 6361

#Unit 2. Cellular Organization

Repressors bind to specific sites on the DNA. In bacterial cells, such binding sites, called operators

Regulation by means of a repressor protein that blocks transcription is referred to as negative regulation. Activators provide a molecular counterpoint to repressors; they bind to DNA and enhance the activity of RNA polymerase at a promoter; this is positive regulation.Repressor binding to DNA is regulated by a molecular signal called effector

TLS Online TPP Program

#Id: 6362

#Unit 2. Cellular Organization

Activators that stimulate this kind of promoter work by triggering a conformational change in either RNA polymerase or DNA; that is, they interact with the stable closed complex and induce a conformational change that causes transition to the open complex. This mechanism is an example of allostery.