CONTROLLING GENE EXPRESSION CHAPTER 11

GENE EXPRESSION - occurs in the DNA- prior to TRANSCRIPTION the activation of a gene that results in the formation of a protein. The gene is said to be “turned on” INDUCERS--- “turn on” a gene- could be a hormone or other substances (i.e. - lactose) REPRESSORS– protein that keeps a gene from being expressed by blocking transcription

Typical gene has 3 parts STRUCTURAL GENE- part of the gene that codes for specific proteins PROMOTER- the beginning part of the gene where RNA polymerase first attaches OPERATOR- located right after the promoter and prevents transcription from occurring ( has a repressor attached)

ACTIVATION The removal of the repressor protein by inducer so that transcription can occur

Promoter elements

Some enhancers increase the rate of transcription initiation Polymerase density and amount of transcription increases in all cells in a population

Transcription Factors bind to Enhancers to speed up Transcription Pol IIa PolII Enhancer Promoter Transcription Factor

Operons An operon is a group of genes that are transcribed at the same time. They usually control an important biochemical process. They are only found in prokaryotes. © NobelPrize.org Jacob, Monod & Lwoff © 2007 Paul Billiet ODWSODWS

The lac Operon  The lac operon consists of three genes each involved in processing the sugar lactose  One of them is the gene for the enzyme β -galactosidase  This enzyme hydrolyses lactose into glucose and galactose © 2007 Paul Billiet ODWSODWS

1. When lactose is absent A repressor protein is continuously synthesised. It sits on a sequence of DNA just in front of the lac operon, the Operator site The repressor protein blocks the Promoter site where the RNA polymerase settles before it starts transcribing promoter lac operon Operator site zya DNA I O Repressor protein RNA polymerase Blocked © 2007 Paul Billiet ODWSODWS

2. When lactose is present A small amount of a sugar lactose is formed within the bacterial cell. This fits onto the repressor protein and causes it to change shape and be removed--- INDUCER Transcription can go on zya DNA IO © 2007 Paul Billiet ODWSODWS promoter

Some DNA is not important (eukaryotes) EXONS- sections of DNA that code for proteins INTRONS- sections of DNA that do not code for amino acids. These are usually removed (spliced) when making mRNA

DEVELOPMENT CELL DIFFERENTIATION- cells becoming specialized to do a specific job. Once cells differentiation they can no longer go back. The last cells to differentiate are “brain stem cells”

TUMOR- abnormal growth of cells that results from uncontrolled cell division. BENIGN TUMOR- tumor in which all the cells in the mass remain in the mass MALIGNANT TUMOR- tumor in which the cells from the mass can leave and invade healthy cells elsewhere in the body. Only MALIGNANT TUMORS are typically referred to as CANCER METASTASIS- the spread of cancer cells from its original site

Types of cancers CARCINOMA- cancer of the skin cells SARCOMA- cancer of the blood vessels LYMPHOMA- cancer of the lymph nodes LEUKEMIA- cancer of the blood forming cells (bone marrow)

Causes of cancer CARCINOGENS- substance that increases the risk of cancer (Give 3 examples ) MUTAGENS- agents that cause a mutation to occur in a cell (most carcinogens are mutagens) ONCOGENE- genes that causes cancer or other uncontrolled cell production-- this gene usually begins as a normal gene then changes and grows out of control