GENE EXPRESSION

CONSTITUTIVE GENE PRODUCTS ARE NEEDED BY THE BODY AT ALL TIMES

TUMOR SUPRESSOR PROTEINS

ATP

ENZYMES THAT CONTROL CELLULAR RESPIRATION

ADAPTIVE GENE PRODUCTS ARE ONLY REQUIRED UNDER CERTAIN CONDITIONS

GENES FOR PROTEIN DIGESTION ARE TURNED OFF WHEN THERE IS NO PROTEIN AVAILABLE.

THE LAC OPERON

Transcription in bacteria is an easy process. Transcription is initiated when RNA polymerase binds to the promoter. This occurs when there is an inducer present in the bacteria (activation). If there is no inducer, the process is physically unable to occur (repression).

EX: Bacteria use the sugar lactose for energy. They break down lactose with the aide of the enzyme lactase. Lactase will only be made if necessary. This will save the bacteria energy. If lactose, the inducer, is not present, than transcription of the mRNA that is translated into lactase is not made.

Once enough mRNA is produced, it is immediately translated, even if the entire mRNA strand is not completed.

3 parts to an operon Promoter – site where RNA polymerase binds to start transcription Operator – on/off switch Structural gene(s) – codes for the protein

Repression – no inducer is present. Bacteria have regulatory genes that control their expression. This gene produces

the repressor protein. If there is no inducer, the repressor protein latches onto the operator and turns

the operon “off” by physically blocking RNA polymerase from performing transcription.

No mRNA is made. Therefore, no protein.

Activation – inducer is present The repressor protein is latched on to the operator. The inducer comes and

attaches to the repressor protein, causing it to change it shape and let go of the operator.

The operon is now “on” and RNA polymerase can move through and transcribe the gene.

mRNA is made. The protein is made.

Activation will lead to repression once all of the inducer is broken down by the protein, as there will be none left to grab onto the repressor protein.

EUKARYOTIC GENE EXPRESSION

• ONLY EUCHROMATIN CAN BE TRANSCRIBED

• TRANSCRIPTION IS SPATIALLY AND TEMPORALLY SEPARATED FROM TRANSLATION

• DNA IS MORE COMPLEX BECAUSE A GREATER NUMBER OF GENE PRODUCTS ARE NEEDED FOR SPECIALIZED FUNCTIONS.

EUKARYOTIC PROMOTERS (1)

Promoters are the binding site of RNA polymerase

TATA box: an 8-base pair repeating sequence of TATATATA in the promoter that helps RNA polymerase bind

CCAAT box: another sequence in the promoter DNA that helps RNA polymerase bind.

Both are located in front of the genes that will be transcribed.

ENHANCERS: Non-coding control sequences in Eukaryotic DNA located in front of the promoter. Enhancers must be

activated for a gene to be expressed.

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THE STEROID TESTOSTERONE IS ALSO A TRANSCRIPTION FACTOR. MANY STEROIDS AND HORMONES ARE TRANSCRIPTION FACTORS AND HELP TO REGULATE GENE EXPRESSION.

Transcription Factors:.Transcription factors are substances that activate enhancers and cause protein production

ANABOLIC STEROIDS:known commonly for their illegal use by

athletes, anabolic steroids are used medically to treat growth abnormalities, anemia, leukemia, kidney failure, and

other medical problems.

Transcription produces a molecule called pre-mRNA, which is made in the nucleus. Then it is edited and spliced together to form mRNA. The

mRNA goes to the cytoplasm. (2)

Pre-mRNA is very similar for all vertebrates. Splicing is done per organism to make us unique.

From a gene on a chromosome to a sequence of amino acids to a protein.

THINK ABOUT IT . . .

Our structural genes contain information to make products from all organisms, amoeba to zebra. We transcribe it all. We translate only selected exons.

IN MOST MAMMAL CELLS, ONLY 1% OF DNA IS COPIED INTO FUNCTIONAL

RNA

Over our existence on the planet, “junk” DNA has been added to our DNA. Junk DNA is DNA that seems to have no purpose. One theory is that junk DNA is made of viral sequences inserted into our genome.

Control of gene expression (3, 4, &5):