Chaperones. A class of specialized proteins which help in folding of proteins. One major function of chaperones is to prevent both newly synthesized polypeptide chains and assembled subunits from aggregating into nonfunctional structures.
REGULATION OF GENE EXPRESSION
Dr. S.Chakravarty MD
Gene: A DNA segment that contains the all genetic information required to encodes RNA and protein molecules.
Genome: A complete set of genes of a given species.
Gene expression: A process of gene transcription and translation.
Referred to as Housekeeping genes.
Positive regulation- expression of genetic information is quantitatively increased by presence of specific regulatory molecule, called positive regulator or activator.
Negative regulation- expression of genetic information diminished by presence of a specific regulatory molecule called negative regulator or repressor.
- includes structural genes, control elements, regulator/inhibitor genes, promoter or operator areas.
a. Special DNA sequence
For prokaryotic systems:
Operon is composed of structural genes, promoter,operator, and otherregulatory sequences.
Other requlatory sequence
3 structural genes-
lac Z-codes - galactosidase
lac Y- codes permease
lac A- codes thiogalactosidasetransacetylase
Regulatory gene-lac I
Promoter region-attachment of DNA dependent RNA polymerase
Structure of lac operon
Metabolism of lactose
A segment from the DNA moves from one location to another on the genome.
Forms a new combination of genes.
C) Gene Loss:-
D)Modification of DNA:-
maintenance of inactive heterochromatin
Histone acetylation and deacetylation: addition of acetyl groups to histones – disruption of nucleosome and DNA separation
DNA methylation: addition of methyl groups to DNA – gene silencing
Ex: pancreatic cell, hematopoietic cell, neurons etc.
B)Histone covalent modification:
They bind to promoter regions (TATA and CAAT box)
2. Activators – steroid receptors, vitamin A receptors (RXR)
They bind to enhancer regions and increase
transcription 1000 folds
1. Helix-Turn-Helix motif
2. Zinc Finger motif
3. The Leucine zipper motif.
The Zinc Finger Motif
The bacterial lac operon is controlled by both glucose and lactose levels. Which of the following conditions would result in the greatest level of transcription from the lacoperon?
Lactose was added to the culture
cAMP concentration increased in the cells
Glucose was added to the culture
Repressor protein dissociated from the operator
Repressor protein became bound to the operator