Khaled El Masry, is an assistant Lecturer of Human Anatomy & Embryology, Mansoura University, Egypt. Great thanks to Prof. Dr Salwa Gawish, professor of Cytology & Histology, Mansoura University, for her great effort in explaining Genetics course.

3. By:
Khaled El Masry
Assistant Lecturer of Human Anatomy & Embryology
Mansoura Faculty of Medicine

4. A gene is the sequence of nucleotides in DNA
encoding one polypeptide chain or one mRNA
molecule.
Gene expression is carried out in 2 steps:
1. transcription.
2. translation.

5. 1. Environmental factors as heat and light.
2. Signaling molecules as hormones and growth
factors.

6. HEAT:
Exposure to high temperature
Transcription of heat shock genes
Synthesis of heat shock proteins
Stabilize the internal cellular environment

7. LIGHT:
In plants exposure to light
Activate transcription of the gene for
Ribulose Carboxylase
The enzyme that plays a critical role in
PHOTOSYNTHESIS

8. HORMONES
”STEROID HORMONES”
Hormone receptor complex
Act as a transcription factor
“PEPTIDE HORMONES”
Activate a signaling system

10. 1. Regulatory elements:
Promoters & Enhancers
2. Transcription factors:
Basal & Special

11. Promoters
The region necessary to initiate transcription.
Consists of short nucleotide sequence that serve
as the recognition point for binding of RNA
polymerase.
Located immediately adjacent to the genes they
regulate, upstream from the transcription
startpoint.

12. There are significant differences in number
, orientation and distance between promoters
in different genes.
Promoters for RNA polymerase II include:
TATA box,
CAAT box,
GC box,
& Octamer box.
Promoters for RNA polymerase & I III have a
different sequence and bind different
transcription factors.

13. Site Structure Importance
TATA box 25-30 bp upstream 8 bp sequences Mutations in this
(from the initial composed only of sequence greatly
point of T=A pairs. reduce
transcription transcription
(Loosing the ability
to bind to
transcription
factors)
CAAT box 70-80 bp upstream CAAT or CCAAT Mutations in this
(from the initial sequence. sequence greatly
point of reduce
transcription transcription
GC box 110 bp upstream GGGCGG Documented by
(from the initial sequence, often mutational analysis
point of present in multiple
transcription copies.
Octamer box 120-130 bp ATTTGCAT Affects the
upstream sequence. efficiency of
(from the initial promoter in
point of initiating
transcription transcription.

14. DNA sequences interact with regulatory proteins
increase the efficiency of initiation
of transcription
increase its rate.

15. Enhancers:
Large >>>> up to several hundred bp long).
Tissue- specific >>>> ( stimulate transcription
only in certain tissues).

16. 1. The proteins that bind to enhancers affect the
activity of proteins that bind to promoters.???
2. Enhancers may allow RNA polymerase to bind to
DNA and move along the chromosome till it
reaches a promoter site.
3. May respond to molecules outside the cell ( e.g :
steroid hormones).
4. May respond to molecules inside the cell ( e.g :
during development thus the gene participates in
cell differentiation).

17. Enhancers bind to transcription factors by at
Least 20 different proteins
Form a complex
change the configuration of the chromatin
folding, bending or looping of DNA.

19. DNA looping will bring the distal enhancers
close to the promoter site to form activated
transcription complexes, then the transcription
is activated, increasing the overall rate of RNA
synthesis.

21. 1. The enhancers affect the gene expression
independent of their position or orientation.
2. The enhancers operate from a distance away
from their target genes.

22. Def. :
“ they are proteins essential for initiation of the
transcription, but they are not part of RNA
polymerase molecule that carry out the
transcription process”.

23. Function:
Each RNA polymerase requires a number of
transcription factors which help in:
1. Binding of the enzyme to DNA template.
2. Initiation and maintenance of transcription.
3. Control the rate of gene expression.

24. These proteins contain 2 functional domains (a.as
that perform specific function).
1. DNA binding domain: binds to DNA sequences
present in regulatory regions (e.g : TATA
binding protein).
2. Transcriptional activating domain: activate
transcription via protein-protein interaction

26. 1. Basal transcription factors:
The initiation of transcription by RNA
polymerase II requires the assistance of several
basal transcription factors.
Each of these proteins binds to a sequence
within the promoter to facilitate the proper
alignment of RNA polymerase on the template
strand of DNA.

27. The basal TFs must interact with the promoters in
the correct sequence to initiate transcription
effectively.
TFIID is the 1st basal TF that interact with the
promoter ; it contains TATA- Binding Protein.
Followed by TFII B, F, E, H & J.

29. 2. Special TFs:
Involved in regulation of heat, light, and hormone
inducible genes.
They bind to:
a. enhancers.
b. Basal TFs.
c. RNA polymerase that bind to the gene
promoter.
Thus, special TFs can regulate the
transcriptional activity of the gene.

30. The normal structure of the chromatin suppresses
the gene activity, making the DNA relatively
inaccessible to transcription factors, and thus
active transcription complex can’t occur.
Thus chromatin remodeling is needed
( it is a change in chromatin conformation in
which proteins of nucleosomes are released
from DNA , allowing DNA to be accessible for
TFs and RNA polymerase).

31. Inactive chromatin remodeled into active
chromatin by 2 biochemical modifications:
1. Acetylation of histone proteins by histone acetyl
transferases which loosen the association between
DNA and histone.
2. Specialised protein complexes disrupt the
nucleosome structure near the gene’s promoter
site.
( this protein complex slides histone along DNA
transfer the histone to
other location on DNA molecule.

32. Active chromatin can be deactivated by 3
biochemical reactions:
1. Histone deacetylation ( catalysed by histone
deacetylase).
2. Histone methylation ( catalysed by histone methyl
transferases).
3. Methylation of some DNA nucleotides by DNA
methyl transferases.
(Chromatin subjected to these modifications tends to be
transcriptionaly silent)

34. siRNA & miRNA
These molecules 21-28 bp long.
Able to interact with specific mRNA molecules.
This interaction occurs by base pairing ( ) a
single strand of iRNA and a complementary
sequence in the mRNA molecule.

35. siRNA miRNA
Base pair perfectly with Base pair imperfectly
the target sequence in with the target
mRNA sequence in mRNA
mRNA cleavage and mRNA inhibition of
degradation translation