Molecular genetics of gene
expression
Mat Halter and Neal Stewart
2014
Discussion questions
• What are the differences between DNA
and RNA?
• Describe the main parts of a gene and its
functions.
• What role do cis-regulatory elements and
trans-acting factors play in gene
regulation?
• What is responsible for the wide diversity
of protein structure found in nature?
• In what different ways can gene
expression be regulated?
http://www.yellowtang.org/cells.php
A Chromosome is composed of nucleosome-bound DNA called chromatin
The nucleosome
Fig F09-30A. Nucleosome structure. (Lodish et al., 2000).
Molecular Structure of Nucleic Acids:
A Structure for Deoxyribose Nucleic Acid
April 25, 1953
Francis Crick
http://www.stern.de/_content/50/44/504453/watson_crick_500.jpg
James Watson
Figure 6.2
Nucleotide base pairing
A’s pair with T’s
G’s pair with C’s
Nucleotide base pairing occurs
through “hydrogen bonding”
Strands have directionality from
5’ to 3’ and when paired strands
are in “antiparallel” orientation
DNA and RNA are structurally
similar
Some differences of RNA and DNA
Difference between thymine and uracil
Discussion questions
• What are the differences between DNA
and RNA?
• Describe the main parts of a gene and
their functions.
• What role do cis-regulatory elements and
trans-acting factors play in gene
regulation?
• What is responsible for the wide diversity
of protein structure found in nature?
• In what different ways can gene
expression be regulated?
The Central Dogma
Transcription
DNA
RNA
Protein
Eukaryotic gene structure
Figure 6.5
Transcription of DNA into mRNA
TF
TF
RNA
TF
polymerase II
TF
AAAAA
TF
mRNA = messenger RNA
Eukaryotic genes contain introns which are
spliced to form mature mRNA
mRNA structure differs between prokaryotes
and eukaryotes
Polycistronic prokaryotic message
Monocistronic eukaryotic message
Discussion questions
• What are the differences between DNA
and RNA?
• Describe the main parts of a gene and
their functions.
• What role do cis-regulatory elements and
trans-acting factors play in gene
regulation?
• What is responsible for the wide diversity
of protein structure found in nature?
• In what different ways can gene
expression be regulated?
Cis- acting regulatory elements
• Promoter region- Located immediately upstream of the transcription
start site and serves as a binding site for the RNA -polymerase II
complex.
• Enhancer region- Promotes transcription by recruiting histonemodifying enzymes that open the chromatin structure, making the
sequence more accessible—sometimes acts in trans.
• Insulators- Sequences that have the ability to protect genes from
inappropriate signals emanating from their surrounding genome.
Vascular TissueSpecific Promoter
GUS gene
Terminator
http://www.forschenistkunst.at/bildbewertung/objekt35.php?id=35
Transcription factors: proteins that bind to
promoters to affect transcription
• Transcriptional activators- Recruits the RNA polymerase complex to
the transcription start site by binding to either sequences in the promoter or
distant cis-acting elements to increase transcription.
• Transcriptional repressor- Prevents transcription of a gene by interfering
with RNA polymerase activity on a promoter
Promoter
LacZ
LacY
LacA
RNA
Polymerase
mRNA
VIDEO
Transcription of DNA into mRNA
TF
TF
RNA
TF
polymerase II
TF
AAAAA
TF
mRNA = messenger RNA
The TFs in this case are transcriptional activators
Discussion questions
• What are the differences between DNA
and RNA?
• Describe the main parts of a gene and
their functions.
• What role do cis-regulatory elements
and trans-acting factors play in gene
regulation?
• What is responsible for the wide diversity
of protein structure found in nature?
• In what different ways can gene
expression be regulated?
The Central Dogma of
Molecular Biology
Translation
DNA
RNA
Protein
http://www.yellowtang.org/cells.php
The central dogma revisited
•The order of the DNA template
or coding strand is 3’ to 5’
•This determines the order of the
mRNA strand (5’ to 3’) because
DNA template is complementary
to the mRNA strand.
Transfer RNA (tRNA)
Amino
Acid
AUG
UCG
ACA
GGC
UGA
Initiation of translation
Assembly of the small ribosomal subunit and
initiator tRNA onto the mRNA
The start codon is found by scanning downstream
from the 5’ end of the mRNA
VIDEO
Amino acid backbone
20 amino acids
Discussion questions
• What are the differences between DNA
and RNA?
• Describe the main parts of a gene and
their functions.
• What role do cis-regulatory elements and
trans-acting factors play in gene
regulation?
• What is responsible for the wide
diversity of protein structure found in
nature?
• In what different ways can gene
expression be regulated?
Gene expression regulation
• Transcriptional level:
– Transcription factors (environmental,
physiological)
– Alternate splicing
• Translational level:
– Elongation factors
– RNA interference
Discussion questions
• What are the differences between DNA
and RNA?
• Describe the main parts of a gene and
their functions.
• What role do cis-regulatory elements and
trans-acting factors play in gene
regulation?
• What is responsible for the wide diversity
of protein structure found in nature?
• In what different ways can gene
expression be regulated?
http://www.youtube.com/watch?v=
GkdRdik73kU
• http://www.youtube.com/watch?v=GkdRdi
k73kU