Transcription is the process where information stored in DNA is copied into mRNA. This involves RNA polymerase adding nucleotides to the growing mRNA molecule in a 5' to 3' direction. In eukaryotes, nucleosomes help regulate transcription by modifying histone tails, which affects how tightly wound the DNA is. Post-transcriptional modifications of mRNA in eukaryotes include splicing of introns. Gene expression can be regulated by proteins binding to specific DNA sequences and by environmental factors that impact processes like DNA methylation and histone modification.

1. Essential idea: Information stored as a code in DNA is
copied onto mRNA
7.2 Transcription & Gene Expression
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Trait vs Fate

2. Understandings
Statement Guidance
7.2 U.1 Transcription occurs in a 5’ to 3’ direction. [RNA
polymerase adds the 5´ end of the free RNA nucleotide
to the 3´ end of the growing mRNA molecule.]
7.2 U.2 Nucleosomes help to regulate transcription in
eukaryotes.
7.2 U.3 Eukaryotic cells modify mRNA after transcription.
7.2 U.4 Splicing of mRNA increases the number of different
proteins an organism can produce
7.2 U.5 Gene expression is regulated by proteins that bind to
specific base sequences in DNA.
7.2 U.6 The environment of a cell and of an organism has an
impact on gene expression.

3. Applications and Skills
Statement Utilization
7.2 A.1 The promoter as an example of non-coding DNA with a
function.
7.2 A.2 Analysis of changes in the DNA methylation patterns.

4. 7.2 U.1 Transcription occurs in a 5’ to 3’ direction. [RNA polymerase
adds the 5´ end of the free RNA nucleotide to the 3´ end of the growing
mRNA molecule.]
• Transcription occurs in a 5’ to 3’
direction where the 5’ end of the
free RNA nucleotide is added to
the 3’ end of the
RNA molecule that is being
synthesized.
• Transcription consists of 3 stages
called initiation, elongation and
termination
• Transcription begins when
the RNA polymerase binds to the
promoter with the help of specific
binding proteins

5. 7.2 U.2 Nucleosomes help to regulate transcription in eukaryotes.
Epigenetics
• The changes related to gene
expression or cellular
phenotype of without changes
to the nucleotide sequence of
the genome.
• Examples of mechanisms that
produce such changes are DNA
methylation and histone
modification of the
nucleosomes, each of which
alters how genes are expressed
without altering the
underlying DNA sequence.
Trait vs Fate

6. 7.2 U.2 Nucleosomes help to regulate transcription in eukaryotes.
• Supercoiling helps regulate
transcription, one supercoiling
modification is through the
modification of the histone tails.
• Acetyl groups can be added to the
positively charged histone tails, they
become negative and that repels the
negatively charged DNA. This opens
up the nucleosome so the DNA is not
as close to the histone anymore.
• This acetylation of the positive
histone tails and opening up of the
DNA structure allows the gene to be
transcribed more often.
• If this does not occur, the DNA
remains tightly packed and
transcription is inhibited.

7. 7.2 S.1 Analysis of changes in the DNA methylation patterns.
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• Another way gene expression can be controlled is through methylation (adding a methyl CH3
group) to the histone proteins.
• Methylation of the histone proteins decreases transcription of the gene
• The amount of methylation can vary over an organisms lifetime and can be affected by
environmental factors

8. 7.2 A.1 The promoter as an example of non-coding DNA with a function.
• The promoter region is
a DNA sequence that
initiates transcription
and is an example of
non-coding DNA that
plays a role in gene
expression. This
promoter region is
called the TATA box.
• The promoter sequence
is located near the start
site of transcription and
is where the RNA
polymerase binds in
order for transcription
to take place.
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9. 7.2 U.3 Eukaryotic cells modify mRNA after transcription.
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a) The gene has a promotor
region and a terminator
region
b) Transcription requires the
presence of a regulator
protein from another gene
(possible from another
chromosome).
c) The RNA polymerase can
now bind to the promotor
and begin the transcription
of the gene.
d) The mRNA is transcribed
including introns
e) The completed mRNA which
will require post
transcriptional modification
to remove the introns.
click4biology
TATA box

10. 7.2 U.4 Splicing of mRNA increases the number of different proteins an
organism can produce
1. Promotor region
2. Free Nucleotide
Phosphates
3. Addition of Nucleotides
to the new mRNA
4. Early mRNA
5. Early mRNA showing
introns (non-coding)
6.Introns removed allowing
exons to combine
7. Mature mRNA ready for
translation
8. mRNA going to
cytoplasm.click4biology

11. Post Transcriptional Modification

12. 7.2 U.5 Gene expression is regulated by proteins that bind to specific
base sequences in DNA.
• Gene expression can also be regulated by the environment causing it to be expressed or
repressed
• Regulatory proteins are unique to a particular gene they are called enhancers, silencers
and promoter-proximal elements
• Enhancers increase the rate of transcription when proteins bind to them.
• Silencers decrease the rate of transcription when proteins bind to them.
• Promoter-proximal elements have binding sites closer to the promoter and their binding
is necessary to initiate transcription

13. 7.2 U.5 Gene expression is regulated by proteins that bind to specific
base sequences in DNA.
• In prokaryotic cells such as
E.coli repressor proteins block the
production the enzymes needed
to break down lactose in the cell.
• However, when Lactose is
present, it will bind to the
repressor protein, causing it
to fall off, and allowing
transcription to occur.
• As transcription occurs,
these enzymes are made
and lactose is broken down into
glucose and galactose. Since
there is small amounts of lactose
now in the cell, the repressor
binds again to the
operator, blocking
transcription from taking place.
• This is an example of negative
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Remember: PROG

14. Prokaryotic Gene Expression (transcription)
Operons:
• Groups of genes that are expressed together
• Only found in Prokaryotes
e.g. Lac Operon: Lactobacillus bacteria require two
enzymes and a transport protein when metabolizing
lactose sugar.
7.2 U.5 Gene expression is regulated by proteins that bind to specific
base sequences in DNA.

15. 1. Regulator gene produces a repressor protein.
2. Promotor gene is where RNA polymerase binds
3. Operator gene is where the repressor binds
Lac Z, Lac Y, and Lac A are the genes for the three proteins that
are required to metabolize lactose.
Prokaryotic Gene Expression (transcription)
7.2 U.5 Gene expression is regulated by proteins that bind to specific
base sequences in DNA.

16. 7.2 U.6 The environment of a cell and of an organism has an
impact on gene expression.
• The environment, as well as the organism's internal
world, which includes such factors as its hormones
and metabolism can have an impact on gene
expression
• Temperature and light are external conditions which
can affect gene expression in certain organisms.
• As an example, Himalayan rabbits carry the gene,
which is required for the development of pigments in
the fur, skin, and eyes, and whose expression is
regulated by temperature
• Specifically, a gene called the C gene is inactive
above 35°C, and it is maximally active from 15°C to
25°C. This temperature regulation of gene expression
produces rabbits with a distinctive coat coloring.
• In the warm weather no pigments fur is white
• In low temperature the rabbit's extremities (i.e.,
the ears, tip of the nose, and feet), where the,
the C gene actively produces pigment, making
these parts of the animal black.
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