Inquiry into Life Twelfth Edition Lecture PowerPoint to accompany Inquiry into Life Twelfth Edition Sylvia S. Mader Chapter 25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

25.1 Control of Gene Expression Gene Expression in Bacteria Operon: A cluster of structural and regulatory genes that acts as a unit. Sequences consists of: Promoter: A sequence of DNA where transcription begins Operator: A sequence of DNA where a repressor protein binds

25.1 Control of Gene Expression Gene Expression in Bacteria Example: The lac Operon in E. coli When lactose is absent: The regulator gene codes for a repressor that is normally active A repressor protein binds to the operator RNA polymerase cannot transcribe the three structural genes of the operon (the structural genes are not expressed)

25.1 Control of Gene Expression Gene Expression in Bacteria Example: The lac Operon in E. coli When lactose is present: Lactose binds with the lac repressor Repressor is unable to bind to the operator Structural genes are transcribed Enzymes are produced

The lac Operon

25.1 Control of Gene Expression Gene Expression in Eukaryotes “Housekeeping Genes” Not finely regulated Products are always needed to some degree

25.1 Control of Gene Expression Gene Expression in Eukaryotes Levels of Gene Control Chromatin Structure Transcriptional Control Posttranscriptional control Translational control Posttranslational control

25.1 Control of Gene Expression Levels of Gene Control Chromatin Structure Chromatin packing is used to keep genes turned off Heterochromatin: inactive genes located within darkly staining portions of chromatin ex: Barr body Euchromatin: loosely packed areas of active genes Euchromatin still needs processing before transcription occurs Chromatin remodeling complex pushes aside nucleosomes

X-inactivation

25.1 Control of Gene Expression Levels of Gene Control Transcriptional Control Most important level of control Enhancers and promoters on DNA are involved Transcription factors and activators are proteins which regulate these sites Posttranscriptional Control Removal of introns and splicing of exons Different patterns of splicing can occur

25.1 Control of Gene Expression Levels of Gene Control Translational Control Differences in the poly-A tails and/or guanine caps may determine how long a mRNA is available for translation Specific hormones may also effect longevity of mRNA Posttranslational Control Some proteins must be activated after synthesis Many proteins function only for a short time before they are degraded or destroyed by the cell

Levels of Gene Control in Eukaryotes

25.1 Control of Gene Expression Transcription Factors and Activators Transcription Factors- proteins which help RNA polymerase bind to a promoter Several transcription factors per gene form a transcription initiation complex Help in pulling DNA apart and in the release of RNA polymerase for transcription Transcription Activators- proteins which speed up transcription Bind to an enhancer region on DNA Enhancer and promoter may be far apart DNA forms a loop to bring them close together

Transcription Factors and Activators

25.1 Control of Gene Expression Signaling Between Cells Cells are in constant communication Cell produces a signaling molecule that binds to a receptor on a target cell Initiates a signal transduction pathway- series of reactions that change the receiving cell’s behavior May result in stimulation of a transcription activator Transcription activator will then turn on a gene

Signal Transduction Pathway

25.2 Cancer: A Failure of Genetic Control Contact Inhibition: When cells come into contact with neighboring cells, they stop dividing. Cancer cells lose contact inhibition and form tumors. The tumor is deemed noncancerous or benign if it stays as a single mass. Cells are called cancerous when they invade surrounding tissues. Cancer cells can travel through the bloodstream and the lymph and develop into secondary tumors. Metastasis refers to cancer cells that have spread to other parts of the body.

Development of Cancer

25.2 Cancer: A Failure of Genetic Control Characteristics of Cancer Cells Cancer cells are genetically unstable. Cancer cells do not correctly regulate the cell cycle Cancer cells escape the signals for cell death. Cancer cells can survive and proliferate elsewhere in the body.

25.2 Cancer: A Failure of Genetic Control Characteristics of Cancer Cells Cancer cells are genetically unstable. Multiple mutations, chromosome aberrations and may be present.

25.2 Cancer: A Failure of Genetic Control Characteristics of Cancer Cells Cancer cells do not correctly regulate the cell cycle. Normal controls of the cell cycle do not work. The rate of cell division and the number of cells increase.

25.2 Cancer: A Failure of Genetic Control Characteristics of Cancer Cells Cancer cells escape the signals for cell death. Cancer cells do not respond to signals for apoptosis Telomeres of cancer cells do not shorten.

25.2 Cancer: A Failure of Genetic Control Characteristics of Cancer Cells Cancer cells can survive and proliferate elsewhere in the body. As a tumor grows, it stimulates the formation of new blood vessels to supply oxygen and nutrients to the cancerous cells. This is called angiogenesis.

25.2 Cancer: A Failure of Genetic Control Proto-oncogenes and Tumor Suppressor Genes Proto-oncogenes promote the cell cycle and prevent apoptosis. Tumor suppressor genes inhibit the cell cycle and promote apoptosis.

25.2 Cancer: A Failure of Genetic Control Proto-oncogenes Mutate into cancer causing genes called oncogenes. An altered RAS protein is found in approximately 25% of all tumors.

Activity of Ras Protein

25.2 Cancer: A Failure of Genetic Control Tumor Suppressor Genes When these mutate, they no longer inhibit the cell cycle. A gene called p53 normally prevents cell division if there is damage to the DNA. If p53 mutates, the cells may continue to divide indefinitely. About 1/2 of all human cancers have a mutation in this gene.

Activity of p53 Tumor Suppressor

25.2 Cancer: A Failure of Genetic Control Causes of Cancer Heredity Some types of cancer run in families Carcinogens Environmental agents that are mutagenic Radiation, some viruses, organic chemicals

25.2 Cancer: A Failure of Genetic Control Diagnosis of Cancer Screening tests Pap smear, mammogram, colonoscopy Tumor marker tests Genetic tests Confirming diagnosis Biopsy, ultrasound, radioactive scans

Needle Biopsy of the Breast

25.2 Cancer: A Failure of Genetic Control Treatment of Cancer Chemotherapy Radiation therapy Bone marrow transplant Future Treatments Vaccines, Antiangiogenic drugs