Breaking Down The Definitions—Regular Bio 1.Cancer 2.Mutation 3.Operon 4.Operator 5.Differentiation 6.Hox gene 7.Genome
Control of Gene Expression GENE EXPRESSION is the activation or ‘turning on’ of a gene for transcription and mRNA. Not all proteins are required by cells at all times so the cell as the ability to control when each protein is made.
Gene Expression in Prokaryotes E. Coli (bacteria in mammal intestines) were studied in great detail Structural Genes—are genes that code for polypeptide chains, a final product such as a protein A Promoter– is an enzyme that helps RNA begin transcription An Operator is a DNA segment that controls the ability of RNA polymerase to move along the structural gene.
Structural Gene PromoterOperator Operon
An Operon is a series of genes that code for specific products. Lac Operon is a series of genes that code for lactose metabolism in E. Coli.
Turning it On/Off A REPRESSOR PROTEIN is a protein that inhibits genes from being expressed…it blocks the advancement of RNA polymerase and stops transcription. So if the Repressor Protein is present, the operon is turned OFF. An INDUCER is a molecule that starts gene expression. Inducers can be many things…in E.Coli, lactose acts as the inducer. When lactose is present, the operon is turned ON and can produce proteins.
Operon Video Clip
Gene Expression in Eukaryotes Eukaryotic cells are more complex, larger, and contain more genes than prokaryotes When the DNA is NOT coiled in X-shaped chromosomes (during cell division), it is called EUCHROMATIC and is where transcription occurs. DNA in Eukaryotes has a promoter and also INTRONS and EXONS.
Gene Expression in Eukaryotes cont. INTRONS are sections of the structural gene that are transcribed but not translated. EXONS are the sections of a structural gene that when expressed are transcribed and translated. There is currently a lot of research being done with Introns and Exons…
Gene Expression in Eukaryotes cont. After transcription in the nucleus both Introns and Exons have been transcribed resulting in a large molecule knows as pre-mRNA. Pre-mRNA is a form of mRNA that has both Introns and Exons. mRNA is formed after the Introns are removed (now the mRNA has only Exons)
Pre-mRNA to mRNA DNA is transcribed into pre-mRNA Introns are removed Exons are spliced together forming mRNA. mRNA travels to Ribosome for translation
RNA Splicing Video
Quick Lab (p.221) 1.Write a sentences that contains only 3 letter words. (at least 5 words) a.“The cat ate the bat.” 2.Hide the words in a long sequence of letters, both random, and with other words. a.ATRCTHEGBPXAPELOCATFRATENMPHATTTHEDQWBATFESTOO 3.Trade papers with another group and cut/tear out the “introns” a.THE CAT ATE THE BAT b.The remaining letters and words “Exons”, are spliced or put together and move on to the ribosome.
Gene Control in Eukaryotes Like prokaryotes, gene control takes place in transcription, but instead of repressors, they use TRANSCRIPTION FACTORS (same type of thing; more complex)
Gene Expression in Development As eukaryotic creatures grow, control of gene expression allows certain traits to be developed and others to be ‘turned off’ until needed. HOMEOTIC GENES are regulatory genes that determine where certain anatomical structures (such as appendages) will develop and when. HOMEOTIC GENES are the ‘master genes’ and know how to organize the organisms overall body.
Cell Division PROTO-ONCOGENES are genes that regulate cell division; ensuring that cell division occurs in the proper sequence and at the correct rate. A mutation of a proto-oncogene can change the gene into a ONCOGENE, which causes uncontrolled cell growth. A TUMOR is an abnormal growth of cells that is uncontrolled. A BENIGN TUMOR causes no threat to life (the uncontrolled cells stay in the mass) unless it presses on vital organs in which case is can be surgically removed. A MALIGNENT TUMOR cell’s invade and destroy healthy tissue as it grows uncontrollably. This is called CANCER.
Cell Division Cont. Some genes act as ‘brakes’ to suppress tumor formation= TUMOR-SUPPRESOR GENES code for proteins to prevent cell division from occurring too quickly or too often. In cancer these ‘brakes’ are often damaged.
Causes of Cancer Mutations may occur in the genetic code that result in cancer. More likely, the organism is exposed to a CARCINOGEN or a substance the induces cancer CARCINOGENs are also called MUTAGENS, an agent that causes mutations to occur in the cells. Well Known carcinogens—tobacco smoke, asbestos, radiation, some viruses