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?

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 CrickJames Watson Figure 6.2

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?

DNARNAProtein Transcription The Central Dogma

Figure 6.5 Eukaryotic gene structure

Transcription of DNA into mRNA TF AAAAA RNA polymerase II 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

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 PromoterLacZLacYLacA mRNA VIDEO

Transcription of DNA into mRNA TF AAAAA RNA polymerase II 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 DNARNAProtein The Central Dogma of Molecular Biology

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 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?

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