Question

1. In top-down hormone signaling, after sensory input from the environment, the neuroendocrine signals are released by the ................ of the brain which then travel to the anterior or posterior ................ glands.

2. Housekeeping genes are often under ............ expression whereas regulated genes often are controlled by either ............ or ........... expression.

3. The conversion of preproinsulin to mature insulin requires first the removal of the ................ sequence followed by removal of the .............. peptide.

4. .................. of histone proteins often leads to transcriptional activation of genes by recruiting ...................... to the nucleosome, which eventually leads to decreased affinity of the DNA for the histone protein.

Answer 1

1. In top-down hormone signaling, after sensory inputs from the environment, the neuroendocrine signals are released by the HYPOTHALAMUS of the brain which then travels to the anterior or posterior PITUITARY glands.

(EXPLANATION) The hypothalamus and pituitary gland are the command center of the endocrine system. Hypothalamus is a part of the diencephalon and is located anterior and inferior to the thalamus. Its function is to maintain a stable internal environment inside the body, secrete releasing and inhibiting hormones.  The pituitary gland is a been-shaped organ located adjacent to the hypothalamus. Its function is to store the hormones secret by the hypothalamus and release it into the bloodstream. It has two lobes - anterior or adenohypophysis and posterior or neurohypophysis. Each lobe has distinct functions.  

2. Housekeeping genes are often under CONSTITUTIVE expression whereas regulated genes often are controlled by either INDUCIBLE or REPRESSIBLE expression.

(EXPLANATION) Housekeeping genes are genes that are required for the normal functioning of a cell. These genes are under constitutive expression meaning, they are transcribed continuously.

Example - ACtin, GAPDH, Ubiquitin.

Regulatory genes - are genes that control the expression of one or more genes. The inducible expression could be positive or negative. The repressible expression could also be positive or negative.

3. The conversion of preproinsulin to mature insulin requires first the removal of the SIGNAL PEPTIDE OR LEADER SEQUENCE followed by the removal of the C-PEPTIDE.

(EXPLANATION) Synthesis of insulin takes place on the ribosomes attached to the membrane of the rough endoplasmic reticulum. Insulin is synthesized from a precursor molecule called preproinsulin which after the cleavage of signal peptide generates proinsulin.  Proinsulin consists of three domains -

I. A chain - carboxy-terminal

ii. B chain - amino-terminal

iii. C chain - linking peptide. Joins the A AND B chain

By the action of endopeptidases found in the endoplasmic reticulum, the c- peptide (chain) is cleaved off. In this way, proinsulin is converted to mature insulin.