Topic 1: Control of Gene Expression

 Jamila  Al-ShishaniMehran HazheerJohn Ligtenberg

Shobana Subramanian

Youtube Video

 Gene Expression Video

• http://www.youtube.com/watch?v=OEWOZS_JTgk&feature=related

 

Basic Concepts

• Promoter- a DNA sequence where RNA polymerase binds (with the help of transcription factors) and starts transcription.

• Transcription factors - a protein which binds to DNA at specific sites so it can regulate transcription. involved in initiation stage of RNA transcription.key to determining where the DNA becomes unzipped. o general transcription factorso upstream transcription factors o inducible transcription factors 

Basic Concepts cont. 

• Enhancer - specific DNA sequences which bind with activators to enhance transcription. 

• Activator - transcription factor which binds to an enhancer and stimulates transcription of gene. help position of the initiation complex on the promoter.

• TATA Box - the DNA sequence which indicates where the DNA can be read and decoded.  

• RNA Polymerase -  enzyme which catalyzes the synthesis of RNA from DNA template

• Distal Control Elements- control elements far from the promoter

• Proximal Control Elements -control elements which are close to the promoter

Basic Concepts cont.  • Differentiation- the divergence in form and function as cells become

specialized during an organism's development. • Cellular differentiation in eukaryotes-

o Highly specialized cells (ex. those in muscle or nerve tissue) only express a small fraction of their genes.

o A typical human cell only expresses 3-5% of its genes at any given time. The transcription enzymes must find the right genes at the right time. 

o Most control of gene expression happens at transcription, where the enzymes copy only the genes needed at the time. 

Basic Concepts cont.  • The 3' end is determined by the RNA sequence encoded by the terminator at

the end of the last exon. • RNA processing enzymes add a 5' cap and a 3' Poly A tail to the primary

transcript. • Exons are nucleotides which are coded for a protein.  • Introns are nucleotides in between the exons which do NOT code for

proteins.

Basic Concepts cont.

• Activators (a transcription factor that binds to a enhancer) binds to an enhancer (distal control element) to start Transcription

• The DNA then bends to bring the enhancers closer to the promoters. Other transcription factors and RNA Polymerase are nearby

• Protein-binding domains on activators attach to certain transcription factors and help them form an initiation complex on the promoter 

• DNA is unzipped by helicase separating the two nucleotide chains• RNA Polymerase reads the DNA from the 3 prime end to the 5 prime end and synthesizes RNA

in the 5 prime end to the 3 prime end• Alternative splicing is an example of regulation in which different mRNA molecules are produced

depending on which RNA segments are treated as introns and which are treated as exons•  The ribonucleotides are then read in a series of nucleotide triplets called codons. Each codon codes

for a separate amino acid•  tRNA then brings an amino acid  for each codon by using a anti-codon to distinguish• After translation, posttranslation modification adds functional groups on the protein to increase it

usefulness

Five Words

• Transcription   • Translation 

 • Gene Expression

 • RNA synthesis

 • Codon 

  

Review Questions

 1. What binds to the activator to start transcription? –enhancer 2. What is differentiation? –the divergence of cells to become specialized 3. What happens to the polypeptide after translation? –functional groups get added and it folds to become a functional protein 4. What are removed from the mRNA? –introns

Review Questions cont. (Mehran)