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 James WatsonFigure 6.2http://www.stern.de/_content/50/44/504453/watson_crick_500.jpg

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

Nucleotide base pairing

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?

DNA RNA Protein

Transcription

The Central Dogma

Figure 6.5

Eukaryotic gene structure

Transcription of DNA into mRNA

TF

TF

AAAAARNA

polymerase II

TFTF

TF

mRNA = messenger RNA

Eukaryotic genes contain introns which are spliced to form mature mRNA

Polycistronic prokaryotic message

Monocistronic eukaryotic message

mRNA structure differs between prokaryotes and eukaryotes

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 histone-modifying 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 Tissue-Specific 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

RNA Polymerase

RNA Polymerase

Promoter LacZ LacY LacA

mRNA

VIDEO

Transcription of DNA into mRNA

TF

TF

AAAAARNA

polymerase II

TFTF

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?

Translation

DNA RNA Protein

The Central Dogma of Molecular Biology

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)AminoAcid

AminoAcid

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=GkdRdik73kU