MICROBIOLOGY

1. EUKARYOTIC GENE
EXPRESSION
NAME – SAMADRITA BANIK
ST. GEORGE COLLEGE OF MANAGEMENT AND SCIENCE
M.Sc MICROBIOLOGY
2ND SEMESTER

2. INTRODUCTION
Eukaryotic gene expression is regulated during
transcription and RNA processing, which take place in
the nucleus, and during protein translation, which takes
place in the cytoplasm. Further regulation may occur
through post-translational modifications of proteins.

3. EUKARYOTIC GENE EXPRESSION
 Gene regulation is the process of controlling which genes in a cell's DNA
are expressed (used to make a functional product such as a protein).
 Different cells in a multicellular organism may express very different sets
of genes, even though they contain the same DNA.
 The set of genes expressed in a cell determines the set of proteins and
functional RNAs it contains, giving it its unique properties.
 In eukaryotes like humans, gene expression involves many steps, and gene
regulation can occur at any of these steps. However, many genes are
regulated primarily at the level of transcription.

4. Gene regulation makes cells different
Gene regulation is how a cell controls which genes, out of the many genes in its genome, are "turned on"
(expressed). The gene regulation of, each cell type in our body has a different set of active genes – despite the
fact that almost all the cells of your body contain the exact same DNA.
These different patterns of gene expression cause your various cell types to have different sets of proteins,
making each cell type uniquely specialized to do its job.
For example, one of the jobs of the liver is to remove toxic substances like alcohol from the bloodstream. To
do this, liver cells express genes encoding subunits (pieces) of an enzyme called alcohol dehydrogenase. This
enzyme breaks alcohol down into a non-toxic molecule. The neurons in a person's brain don’t remove toxins
from the body, so they keep these genes unexpressed, or “turned off.” Similarly, the cells of the liver don’t
send signals using neurotransmitters, so they keep neurotransmitter genes turned off.

6. How do cells "decide" which genes
to turn on?
• Many factors can affect which genes a cell expresses. Different cell types
express different sets of genes, as we saw above. However, two different
cells of the same type may also have different gene expression patterns
depending on their environment and internal state.
• Broadly speaking, we can say that a cell's gene expression pattern is
determined by information from both inside and outside the cell.
• Examples of information from inside the cell: the proteins it inherited from
its mother cell, whether its DNA is damaged, and how much ATP it has.
• Examples of information from outside the cell: chemical signals from other
cells, mechanical signals from the extracellular matrix, and nutrient levels.

8. CELL DIVISION AND GROWTH
• The cell detects the growth factor through physical binding of the growth
factor to a receptor protein on the cell surface.
• Binding of the growth factor causes the receptor to change shape, triggering
a series of chemical events in the cell that activate proteins called
transcription factors.
• The transcription factors bind to certain sequences of DNA in the nucleus
and cause transcription of cell division-related genes.
• The products of these genes are various types of proteins that make the cell
divide (drive cell growth and/or push the cell forward in the cell cycle).

9. Eukaryotic gene expression can be
regulated at many stages
Eukaryotic gene expression involves many steps, and almost all
of them can be regulated. Different genes are regulated at
different points, and it’s not uncommon for a gene (particularly an
important or powerful one) to be regulated at multiple steps.
• Chromatin accessibility. The structure of chromatin (DNA and
its organizing proteins) can be regulated. More open or
“relaxed” chromatin makes a gene more available for
transcription

10. • Transcription. Transcription is a key regulatory point for
many genes. Sets of transcription factor proteins bind to
specific DNA sequences in or near a gene and promote or
repress its transcription into an RNA.
• RNA processing. Splicing, capping, and addition of a
poly-A tail to an RNA molecule can be regulated, and so
can exit from the nucleus. Different mRNAs may be made
from the same pre-mRNA by alternative splicing.

12. • RNA stability. The lifetime of an mRNA molecule in the cytosol affects how many
proteins can be made from it. Small regulatory RNAs called miRNAs can bind to
target mRNAs and cause them to be chopped up.
• Translation. Translation of an mRNA may be increased or inhibited by regulators.
For instance, miRNAs sometimes block translation of their target mRNAs (rather
than causing them to be chopped up).
• Protein activity. Proteins can undergo a variety of modifications, such as being
chopped up or tagged with chemical groups. These modifications can be regulated
and may affect the activity or behavior of the protein.

13. Gene regulation and differences
between species
• Differences in gene regulation makes the different cell types in a multicellular organism unique in structure
and function. If we zoom out a step, gene regulation can also help us explain some of the differences in
form and function between different species with relatively similar gene sequences.
• For instance, humans and chimpanzees have genomes that are about 98.8%98.8%98, point, 8, percent
identical at the DNA level. The protein-coding sequences of some genes are different between humans and
chimpanzees, contributing to the differences between the species. However, researchers also think that
changes in gene regulation play a major role in making humans and chimps different from one another.
• For instance, some DNA regions that are present in the chimpanzee genome but missing in the human
genome contain known gene-regulatory sequences that control when, where, or how strongly a gene is
expressed

14. CONCLUSION
The human genome encodes over 20,000 genes; each of
the 23 pairs of human chromosomes encodes thousands
of genes. The DNA in the nucleus is precisely wound,
folded, and compacted into chromosomes so that it will
fit into the nucleus. It is also organized so that specific
segments can be accessed as needed by a specific cell
type.