Chapter 13 Regulation of Gene Expression Title Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Page 238 Operons – prokaryotes. Regulator gene makes a repressor that binds to operator to shut down structural genes or allows transcription. RNA polymerase will bind if repressor is not in the way!

5 Types of Control 3 In Nucleus: Fig. 13.4 5 Types of Control 3 In Nucleus: 1)chromatin packing tightly or loosely around histones 2) transcriptional control – many proteins needed 3) Post-transcriptional control (mRNA processing – introns, cap, poly A tail) 2 In Cytoplasm: 4) Translational control – how long does the mRNA last 5) Post translational control

Control #1 – chromatin packing Control #1 – chromatin packing. If tightly coiled, RNA polymerase can’t fit on, shuts gene down. Methylation can do this (epigenetics). Barr body – inactivated X chromosome in female mammals.

Fig. 13.7 #2 – Transcriptional Control. All proteins and pieces of the puzzle are needed to initiate transcription.

Fig. 13.8 #3 – Post Transcriptional Control. Alternative processing of pre mRNA. Due to different introns being processed 2 distinctly different proteins can result from the same gene.

Fig. 13.9 #3 Post Transcriptional Control Only 1.5% of DNA codes for proteins, the rest is regulatory. RNAi – can bind and prevent mRNA from transcribing. See NOVA RNAi video.

#4 – Translation Control A mRNA can “live” a long time and hit several ribosomes to make as many proteins as possible. The cap and tail staying on promote this. Half lives can be 15 minutes up to 12 hours.

#5 Post- Translational Control Proteosomes detect tagged proteins and break them down into fragments. Used to control the amount of protein in the cytoplasm. #5 Post- Translational Control Fig. 13.10

So males look like (and develop) as females. If a mutation in enzyme EA is inherited a person can’t convert A to B. Phenylalanine builds up and causes mental retardation (PKU). In this same pathway, if a person inherits a mutated a faulty EB, then B is not converted to C and the individual is an albino. Androgen Insensitivity Syndrome results from a mutation that codes for testosterone receptors. So males look like (and develop) as females. Page 249

Fig. 13.13 A mutated tumor suppressor gene codes for a protein that directly or indirectly stimulates the cell cycle – possible beginnings of CANCER. Remember p53 is a tumor suppressor that promotes apoptosis of bad cells – if it is mutated the chances of cancer occurring are very high!

Sickle Cell Mutation – watch the HHMI video A single point change