chapter 11 gene expression

QuickTime™ and a decompressor

are needed to see this picture.

Chapter 11Gene Expression

http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related


What is gene expression?

• DNA RNA Proteins• Turning “on” and “off” genes• Don’t need specific proteins

all the time• Make them when you need

them

Gene Expression in Prokaryotes

• E. coli (bacteria that live in intestines of mammals)

• Discovered how genes control the metabolism of the sugar lactose

• Lactose: disaccharide made of glucose and galactose

• Milk sugar QuickTime™ and a decompressor




When there is/is not lactose

LACTOSE PRESENT: It induces E. coli to produce three enzymes which will metabolize lactose

LACTOSE ABSENT: three enzymes will not be made. Lactose will not be broken down.



Operon: series of genes that code for specific products and the regulatory elements that control these genes

Lac operon: segment of DNA that

codes for the enzymes that regulate lactose metabolism



DNA of E.coli

Regulator gene: codes for repressor genePromoter: DNA segment that is recognized by the enzyme

RNA polOperator: DNA segment that serves as a “switch” controlling

the access of RNA pol to the promoterStructural genes: code for 3 enzymes that break down lactose



Operon “turned off”• Repressor protein attaches to the operator

physically blocking RNA pol from attaching

RNA pol

Operon “turned on”

• Lactose present (acts as inducer starts gene expression)

• Binds to the repressor protein

• Repressor changes shapes and detaches from operator

• RNA pol is not blocked anymore

• All three enzymes can be produced

Operator “turned on”



lactose


are needed to see this picture.Why is this good?

• E. coli is able to turn off and on genes when lactose is present/absent

• Bacteria saves resources and produce only those proteins that are needed

Let’s watch it again

• http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related



Eukaryotes• How is DNA different

than Prokaryotes?• “junk DNA”• ~98% Non-coding• Operons not found very

often• Gene expression occurs

at the level of the individual chromosome



• Introns: “non-coding sections”– are transcribed but not translated

~ 98% of genome

• Exons: “coding sections” – are transcribed and translated

~2% of genome (23,688 human genes)



Modification of RNA • Transcription: both introns and exons are transcribed:

pre-mRNA• Introns are removed and exons are spliced (joined) together• Result: mRNA only with exons (coding regions)• What spliced the DNA?



snRNPs

• Small nuclear ribonucleoproteins• Composed of a small protein molecule and RNA

• Pronounced “snurps”• 60-300 nucleotides• Also called “spliceosomes”• responsible for pre-mRNA splicing• Beginning and ends of introns are recognized

and removed• At least 4 different kinds of snRNPs• Main ones (U1, U2, U4&U6, U5)

Alternative splicing

• Shuffle exons

• Produce alternative ribonucleotide arrangements

• Produces different proteins (isoform proteins)

• Synthesis greater variation of proteins



What about the introns?• Perhaps not just “junk”• Regulation functions and Structural purposes• "the cell puts a huge amount of its energy into the creation of

these introns, then discards them ... Nature would not go to all that trouble without a reason." – C.C. Kopezynski and M. A. T. Muskavitch

• "a complex mix of different DNA, much of which are vital to the life of the cell." – Nowak

• At least a dozen studies have found evidence that introns are either directly or indirectly involved in cancer causation.

• “..at least some introns, and possibly other noncoding DNA, may be involved in DNA packaging in eukaryotes”– Marculis and Sagan

Control at Transcription

• Transcription Factors: regulatory proteins– Help in the placement of RNA pol at the

promoter

• Enhancers: (located far away..upstream or downstream) stimulates transcription– Pg 222

Cell differentiation: development of cells that have specialized functions

Homeotic Genes

• Guide the emergence of shape and form

• Drosophilia (fruit fly)

• Homeobox: Specific 180nb DNA sequence within a homeotic gene

Mutation in Homeobox

Cancer

Four changes

1. Immortalization: indefinite growth and replication

2. Transformation: becomes independent of factors needed for cell growth

3. Angiogenesis: recruit vascular supply4. Metastasis: cells dissociate from origin and

begin invading normal tissue

Angiogenesis

Pathways of mutationNeed to accumulate mutations in 6 pathwaysCells die after about 60 division• Telomeres (caps) on end of chromosome

– Get smaller and smaller– Suicide (apoptosis)

• Tumor cells-telomerase-puts caps back on (live forever)

Cytochrome c in mitochondria• Involved in cell suicide (apoptosis)

Oncogenes: mutation of proto-oncogene(regulate cell growth and division)

• Gene that causes uncontrolled cell proliferation

• May lead to over expression of proteins

• Over 100 oncogenes identified

Tumor-suppressor genes

• Act as “brakes”• ~30 identified• Slow cell division, repair DNA mistakes,

tell cells when to die (apoptosis)• Can lead to cancer when don’t function

properly• Abnormalities can be inherited as well

as acquired (oncogenes:mutations)

Carcinogens• Substance that can

induce or promote cancer

• Most are mutagens

• Chemicals in tobacco smoke, asbestos, radiation, UV

Viruses can also cause cancer

HPV

Types of Cancer

Carcinomas: grow in the skin and tissues that line organs

Sarcomas: grow in bone and muscle tissue

Lymphomas: grow in the lymphatic system

Leukemia: uncontrolled production of white blood cells

chapter 11 gene expression

Documents

lactose slide

lactose metabolism slide

u5 slide

related slide

lactose lactose present

sugar lactose lactose

lactose lactose absent

attaching rna pol slide