CONTROL OF GENE EXPRESSION

ROLE OF GENE EXPRESSION: Activation of a gene that results in

a protein Cells DO NOT need to produce

proteins for every code.

GENOME: Complete genetic material of an

individual Cells can regulate what genes get

expressed.

GENE EXPRESSION IN PROKARYOTESLac Operon: Control system that regulates the production of

enzymes to break down lactose.

3 Regulatory Elements Control the Expression

1. Structural Genes:

Genes that code for proteins

2. Promoter:

Recognizes RNA Polymerase and promotes transcription

3. Operator:

Binding site for inhibitory protein that blocks transcription.

LAC OPERONCollection of 3 types of genes working

together

Genes for lactose utilization were expressed only when lactose is present

2 Forms of Control:1. REPRESSION2. ACTIVATION

Repression: Repressor attaches to the

operator when lactose is absent

Blocks RNA Polymerase from binding to structural genes

Activation: Lactose binds to the repressor

and removes it RNA Polymerase transcribes

the gene Lactose acts as an INDUCER

A molecule that initiates gene expression

LAC OPERON

GENE EXPRESSION IN EUKARYOTES

Much larger and more complex than in prokaryotes

DNA is located on several chromosomes Control is at the individual chromosome

level Related to coiling and uncoiling of DNA

EUCHROMATIN: Relaxed state of DNA when transcription

is possible

TWO TYPES OF GENES IN EUKARYOTES

Introns:Non-coding for proteins

Exons:Genes that when expressed code for PROTEIN

RNA SPLICING

CONTROL AFTER TRANSCRIPTION

Transcription produces Pre-mRNAContains introns and exons

mRNA is formed when INTRONS are removed and EXONS are spliced together.

ENHANCER CONTROLNon-coding control sequences

that facilitate transcription

Transcription Factors:Bind to Enhancers and RNA

Polymerase and regulate transcription

Activation Enhancers:Have been studied in the

expression of the gene controlling the production of estrogen.

GENE EXPRESSION AND DEVELOPMENT

Cell Differentiation: Development of cells with specific functions.

Morphogenesis: Development of form

HOMEOTIC GENES: Regulatory genes that determine

where anatomical structures will develop during MORPHOGENESIS

HOMEOTIC GENES: Master genes of

development Determine the overall

body organization

HOMEOBOX: Specific DNA sequence

that regulates patterns of development

Mutations of these genes may have devastating impacts

CANCER Tumor:

Abnormal proliferation of cells that result from uncontrolled, abnormal cell division.

Benign:Cells remain within a mass. Generally pose no

threat to life.

Exception: If the mass grows large enough that is compresses against vital organs.

Examples: Fibroid Cysts, warts

Most benign tumors can be surgically removed.

MALIGNANT TUMORSKNOWN AS CANCER Uncontrolled dividing cells invade and

destroy healthy tissues elsewhere in the body

METASTASIS: The spreading of cancer cells beyond their original site

Cancer cells break away from the malignant tumor and spread to other body parts where they begin to form new tumors.

METASTASIS

BENIGN VS. MALIGNANT TUMORS

METASTASIS

KINDS OF CANCER: Tumors are classified

by the types of tissues they affect

Link to national cancer institute

CARCINOMAS: Grow in the skin

and the cells that line the organs of the body.

Examples: Lung cancer and breast cancer breast cancer

TYPES OF CANCER:Sarcoma: Cancer that grows in the bone and

muscle tissues

Lymphomas: Solid tumors that grow in the tissues that

form blood cells May cause LEUKEMIA –

The uncontrolled production of white blood cells

It usually takes several years for cancer to develop, but it may be accelerated in vital organs like the pancreas or liver

CANCER AND THE CELL CYCLEIn normal cells, the frequency of cell division is controlled by

several factors:

1. Adequate nutrition2. Must be attached to another cell, membrane or fibers

3. NOT ALL CELLS ARE DESTINED TO DIVIDE (Neurons)

4. Normal cells stop dividing when it becomes too crowded

5. Normal cells will only divide 20-50 times before they die:

Apoptosis – programmed cell death

WHAT DO CANCER CELLS NEED TO SURVIVE?

HOW CANCER CELLS DIFFER FROM NORMAL CELLS:

1. Loss of DENSITY DEPENDENT INHIBITION: Cells continue to grow even when they are

densely packed together

2. Continue to grow when they become unattached to other cells

3. Block apoptosis: don’t allow natural cell suicide

4. Angiogenesis: Cancer cells can stimulate the formation of

new blood vessels to supply the growing tumor

CAUSES OF CANCER

Normal cells use genes that code for GROWTH FACTORS that control the process of cell division.

Mutations of the genes that code for the growth factors lead to cancer

1. May occur due to a SPONTANEOUS MUTATION

2. Most likely they occur due to an exposure to CARCINOGENS.

CARCINOGENS: Any substance that increases the risk of

cancer with exposure.

EXAMPLES: Tobacco (90% of all lung cancers), Asbestos Ionizing Radiation (X-rays or UV light)

MUTAGEN: (most carcinogens are also mutagens)

Agents that cause mutations to occur

WHAT DETERMINES WHO DEVELOPS CANCER?Depends on many factors:1. Family history (some families have higher than

normal rates of cancer)

2. The number of exposures to the carcinogen

3. The amount of carcinogen in each exposure

4. Usually more than one mutation is needed to cause cancer.

5. Risk of cancer increases with age due to more exposures throughout a lifetime.

ONCOGENESGene that causes cancer or other

uncontrolled cell proliferation Begin as normal PROTO-ONCOGENES –

Controls a cells growth and differentiation. Code for proteins that regulate the rate of

the cell lifecycle An error causes the rate of cell division to

increase

TUMOR-SUPPRESSOR GENES

Code for proteins that prevent uncontrolled cell division.

When they mutate they do not get expressed properly and lead to a predisposition to cancer

VIRUSES AND CANCER May cause cancer to develop in

plants or animals Many viral genes are actually

oncogenes May cause mutations in the Proto-

oncogenes and tumor suppressing genes

Viruses have been found to cause various types of Leukemia.