Gene exppression and hormones

All the levels may be regulated:
Transcription
Processing
Translation
AAAAAAA
Genes of DNA
Primary transcript
m-RNA
Polypeptide chain
Modification
Substrate A
Product B
Function
Active protein
Gm3
Intron
Exon

All the genes of DNA in prokaryotic cell are divided in types:
House keeping genes (constitutive)
Inducible (structural)
Gene-regulators
Gene-operators

Operon is composed from promoter sequence,
gene-operator, structural genes
The Lac-operon model investigated in E.coli
(proposed by F.Jacob and J. Monod, 1961)

Gene-regulator is far from operon sequences, it is keeper of information about sequence of amino acid residues in protein-repressor (P-R) molecule
Gene-operator is placed in operon between promoter and structural genes, it has affinity to protein- repressor

Lactose is inducer of transcription made on Lac-operon because of its ability to block activity of P-R and thus to induce mRNA linkage to the promoter

CRP-cAMP enhancer influence
CRP – Catabolite gene Reactive Protein
cAMP – cyclic AMP

The higher Glucose or Glycerol levels
in the intracellular space
the lower levels of cAMP

Different Genes are found in eukaryotic DNA
House keeping genes
Genes required during cellular differentiation
Genes which get triggered as a response to some external factors
Genes which get triggered during apoptosis

Points for Gene Expression in Eukaryotes
Synthesis of proteins is controlled right from the chromatin stage.
Expression of gene is controlled at many steps during the process of transcription and translation.

Two forms of chromatin :
Euchromatin – A lesser coiled transcriptionally active region which can be easily accessed by the RNA polymerases.
Heterochromatin – A highly condensed transcriptionally inactive region. The genes in this region cannot be accessed by the RNA polymerases for active transcription .

Mechanisms which affect the chromatin structure and hence the expression of gene are:
Acetylation of Histones : ↑ Acetylation ----↓ Condensation of DNA -----
↑ Transcription of genes in that region
Methylation of histone H4 on R4 (arginine residue at the 4th position) ->-> opens the chromatin structure ->-> leading to transcriptional activation

Mechanisms which affect the chromatin structure and hence the expression of gene are:
Methylation of histone H3 on K4 and K79 (lysine residues at the 4th and 79th position) ->-> opens the chromatin structure ->-> leading to transcriptional activation
Methylation of histone H3 on K9 and K27 (lysine residues at the 9th and 27th position) ->-> condenses the chromatin structure ->-> leading to transcriptional inactivation

Ubiquitination
Ubiquitination of H2A – Transcriptional inactivation
Ubiquitination of H2B - Transcriptional activation
Methylation of DNA
Target sites of methylation are - The cytidine residues which exist as a dinucleotide, CG (written as CpG)
↑ methylated cytidine -- ↓Transcriptional activity

3`
5`

TATA-box binding protein (TBP) is found in eukaryotic cells, and it is the component of the complex TFIID containing other several proteins (TBP-associated factors) and bound to the TATA box
TATA-box binding
protein (TBP)

Enhancer-bending protein (EBP) changes the DNA single strand conformation to form special loop which promotes the stimulation and the increase of the rate of initiation phase of transcription.

Except EBP and TF,
there is the group of mediator proteins to stimulate transcription process, too

Proteins-mediators can control the rate of trans-
cription due to their ability to change conformation
of their molecules

Proteins-mediators are in close relations with general
transcription factors placed in the complex TFIID

Interaction of homodimeric leucine-zipper (A)
and basic helix-loop-helix (B) proteins with DNA
(A)
(B)

Classification of hormones
according chemical nature

INTERCELLULAR MECHANISM of COMMUNICATION

Endocrine
Paracrine
Autocrine

The receptor (R)
for
hydrophilic
hormones (H)
is located
in the cellular
membrane of target cell

Lipophilic
hormones
(H) may be
linked to
cytoplasmic (R)
and
nuclear ( R`)
receptors

The feed-forward and feed-back control
of a hormone level in the blood

All of the steps below
are subject to regulation:
biosynthesis of the hormone
storage, secretion of the hormone
transport of the hormone to the target cell
reception of the signal by the hormone receptor
transmission and amplification of the signal, biochemical reaction in the target cell
degradation and excretion of the hormone.

Cerebral cortex
T3↑↑
Cortisol↑↑
Θ
Θ
Cortisol↑↑
Cortisol↑↑
T3↑↑
T3↑↑
Glucose↑↑
pO2↓
Cerebral cortex
Liver
Myocardium
__
__

Types of signal transmission due to G-proteins

Inactive Gs protein is composed from three subunits: α, β, γ . Hormone-receptor complex can stimulate Gs - it means :
dissociation of Gs to dimmer and single α−subunit linked
to GDP that is formed from GTP
Gsα−GDP
is named
active Gs
protein

Some factors influenced
G-proteins
Cholera toxin modifies α-subunit of Gs as the result – the block of hydrolysis of GTP to GDP and superstimulation of Adenylate cyclase
Pertussis toxin (produced at whooping cough) modifies α-subunit of Gi to allow Adenylate cyclase to produce cAMP in excess levels

GAP function:
GTPase-Activating Proteins, or GAPs can bind to activated G-proteins and stimulate their GTPase activity, with the result of terminating the signaling event. GAPs are also known as regulator of G protein signaling proteins, or RGS proteins, and these proteins are crucial in controlling the activity of G proteins. GAP role is to turn the G protein activity off .

cAMP structure
PDE – Phosphodiesterase
Inhibitors: metyl xanthines

cAMP-dependent protein kinase (PK) activation
Inactive PK
Active PK
_

ne

Calmodulin-4Ca 2+
complex
Ca 2+

Examples of different signals, receptors, Gα like-subunits, second messenger changes, and affected intracellular enzymes

X-ray structure by and drawing courtesy of Abraham
de Vos and Anthony Kossiakoff,
Genentech Inc., South San Francisco, California.
Complex of human growth hormone
and its receptor.
Two identical molecules
of the receptor extracellular
domain (blue and green
ribbon models) bind
a single molecule of
growth hormone (red).

Guanylate cyclases
Left: ANF –Atrial
Natriuretic Factor
Mechanism of action

Structure of Insulin Receptor

The Mechanism of action
for Lipophilic Hormones (H);
HRE –Hormone Response Elements

They have affinity to
receptors of
steroidal hormone
containing so named
“zink-fingers”
AF1, AF2 domains that mediate the stimulation of the transcription