This document summarizes the process of gene expression in three main steps: transcription, post-transcriptional modification, and translation. It first defines a gene as a stretch of DNA that encodes information. During transcription, RNA polymerase produces messenger RNA from DNA. The mRNA then undergoes post-transcriptional modification like capping, splicing, and polyadenylation. The mature mRNA is transported to the cytoplasm for translation by ribosomes into proteins. Additional post-translational modifications can occur to proteins after translation. Gene expression is regulated at multiple levels including transcription, RNA processing, translation and protein degradation.

1. GENE EXPRESSION
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2. OVERVIEW
 Gene expression
 Transcription
 Post transcriptional modification
 Transportation
 Translation
 Post translational modification

3. WHAT IS GENE & GENE EXPRESSION ?
 Gene : is a stretch of DNA
that encodes information.
 Gene expression is the process by which information
from a gene is used in the synthesis of a
functional gene product. These products are often
proteins, but in non-protein coding genes such as
transfer RNA (tRNA) or small nuclear RNA
(snRNA) genes, the product is a functional RNA.
RNA PROTEINDNA
TRANSCRIPTION TRANSLATION
The “Central Dogma”

4. Eukaryote gene expression is
regulated at six levels:
1. Transcription
2. RNA processing
3. mRNA degradation
4. mRNA transport
5. mRNA translation
6 . Protein degradation

5. A . TRANSCRIPTION

6. A . TRANSCRIPTION
 “The production of messenger RNA (mRNA) from the DNA by
the enzyme RNA polymerase “
 Uses an enzyme RNA polymerase
 Proceeds in the same direction as replication (5’ to 3’)
 Forms a complementary strand of mRNA
 It involves three steps :
 Initiation.
The DNA molecule unwinds and separates
. RNA polymerase binds to the promoter of the template
strand (also known as the 'sense strand' or 'coding strand').
The synthesis of RNA proceeds in a 5' to 3' direction, so the
template strand must be 3' to 5'.
 Elongation.
RNA polymerase moves along the template strand,
synthesising an mRNA molecule .In eukaryotes there are
three RNA polymerases: I, II and III. The process includes a
proofreading mechanism.
 Termination.
Stop codons UAA UAG UGA come
termination occur

7. 1.CONTROL REGIONS
 A promoter.
A region a few hundred nucleotides 'upstream' TSS
.It is not transcribed into mRNA,
plays a role in controlling the transcription of the
gene. Transcription factors bind to specific
nucleotide sequences in the promoter region and
assist in the binding of RNA polymerases.
 Enhancers:
Some transcription factors (called activators) bind
to regions called 'enhancers'
increase the rate of transcription. These sites may
be thousands of nucleotides from the coding
sequences or within an intron.
 Silencers:
Some transcription factors (called repressors) bind
to regions called 'silencers' that depress the rate of
transcription.

8. B.POST TRANSCRIPTIONAL
MODIFICATION

9. B.POST TRANSCRIPTIONAL MODIFICATION:
 Capping changes the five prime end of the mRNA to a
three prime end by 5'-5' linkage, which protects the
mRNA from 5' exonuclease, which degrades foreign
RNA. The cap also helps in ribosomal binding.
 RNA editing is a process which results in sequence
variation in the RNA molecule, and is catalyzed by
enzymes.
 Splicing removes the introns, noncoding regions that
are transcribed into RNA, in order to make the
mRNA able to create proteins. The two ends of the
exons are then joined together.
 Addition of poly(A) tail otherwise known
as polyadenylation. That is, a stretch of RNA that is
made solely of adenine bases is added to the 3' end,
and protects from 3' exonuclease. In addition, a long
poly(A) tail can increase translation.

10. 2.(RNA PROCESSING CONTROL)
 . : RNA processing regulates mRNA production
from precursor RNAs.
 Two independent regulatory mechanisms occur:
 Alternative polyadenylation = where the polyA
tail is added
 Alternative splicing = which exons are spliced
Alternative polyadenylation and splicing can
occur together.
 Examples: Human calcitonin (CALC) gene in
thyroid and neuronal cells

11. Fig. 18.14, Alternative polyadenylation and splicing of the human
CACL gene in thyroid and neuronal cells.
Calcitonin gene-
related peptide

12. D.TRANSPORTATION :
D.TRANSPORTATION :
Transcription
DNA
messenger
RNA
Gene
Nucleus

13. D.TRANSPORTATION :
 after post transcription the mature mrna is
transported from the nucleas to the cytoplasm
for translation process
 4. mRNA transport control:
 Eukaryote mRNA transport is regulated.
 Some experiments show ~1/2 of primary
transcripts never leave the nucleus and are
degraded.
 Mature mRNAs exit through the nuclear pores.

14. 5. mRNA degradation control:
• All RNAs in the cytoplasm are subject to degradation.
• tRNAs and rRNAs usually are very stable; mRNAs vary considerably
(minutes to months).
• Stability may change in response to regulatory signals and is thought to
be a major regulatory control point.
• Various sequences and processes affect mRNA half-life:
• AU-rich elements
• Secondary structure
• Deadenylation enzymes remove As from poly(A) tail
• 5’ de-capping
• Internal cleavage of mRNA and fragment degradation

15. C. TRANSLATION

16. C. TRANSLATION
 In translation the mature
mRNA molecule is used as a
template to assemble a series
of amino acids to produce a
polypeptide with a specific
amino acid sequence
 RIBOSOME.
The complex in the cytoplasm .
 It is a mixture of ribosomal
proteins and ribosomal RNA
(rRNA), and consist of a large
subunit and a small subunit.
 Amino acids , Transfer RNA
 Mature RNA transcript ,
translation factors

17. MECHANISM OF TRANSLATION
 Transcription involves four steps:
Initiation.
The small subunit of the ribosome binds at the 5' end of the mRNA
molecule and moves in a 3' direction until it meets a start codon (AUG).
It then forms a complex with the large unit of the ribosome complex
and an initiation tRNA molecule.
Elongation
. Subsequent codons on the mRNA molecule determine which tRNA
molecule linked to an amino acid binds to the mRNA.
 An enzyme peptidyl transferase links the amino acids together using
peptide bonds. The process continues, producing a chain of amino acids
as the ribosome moves along the mRNA molecule.
Termination.
Translation in terminated when the ribosomal complex reached one or
more stop codons (UAA(ochre ), UAG(amber), UGA(opal).
 3.mRNA translation control:
 Unfertilized eggs are an example, in which mRNAs (stored in the egg/no
new mRNA synthesis) show increased translation after fertilization).
 Polyadenylation and 5’ caping allows efficianet translation

18. E.POST TRANSLATIONAL
MODIFICATIONS:

19. E.POST TRANSLATIONAL
MODIFICATIONS:
• The chemical modifications that take place at
certain amino acid residues after the protein is
synthesized after translation are known as Post
Translational modifications.
• They are essential for normal functioning of the
proteins.
• They occur mostly in ER and Golgi bodies.
 FUNCTIONS:
• Increase functional diversity of the proteome.
• Generate heterogeneity in proteins.
• Transport

20. PTM’S
• Phosphorylation
• glycosylation
• Acetylation
• Alkylation
• Methylation
• Glycylation
• Lipoylation
• sulphation
 5 .POST-TRANSLATIONAL CONTROL-PROTEIN DEGRADATION:
• Proteins are degraded in subcellular organelles, such as lysosomes or in
macromolecular structures called proteasomes.
• Proteins can be short lived or long lived e.g lens proteins in our eyes.
• Protein degradation in eukaryotes requires a protein co-factor called
ubiquitin. Ubiquitin binds to proteins and identifies them for degradation by
proteolytic enzymes.
• Amino acid at the N-terminus is correlated with proteins stability and
determines rate of ubiquitin binding.

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