bio chapter 11

Initiation of translation

The process of translation-in which an mRNA is used to make a protein- offers additional opportunited for control by regulatory molecules.

RNA processing and breakdown

*RNA processing includes: - the addition of a cap and a tail - the removal of interons (the noncoding DNA segments that interrupt the genetic message) - RNA splicing (the splicing togher of exons) - Within a cell, exon splicing can occur in more than one way, generating different mRNA molecules from the same starting RNA molecule. With this sort of-----> alternative RNA splicing---, and organism can produce more than one type of polypeptide from a single gene. *After an mRNA is produced in its final form, its "lifetime" can be highly variable, from hours to weeks to months. Controlling the timeing of mRNA breakdown provides another opportunity for regulation. But all mRNA's are eventually brekn down and their parts recycled.

Initiation of transcription

*is the most improtant stage for regulating gene expression* -In prokaryotes and eukaryotes, regulatory proteins bind to DNA and turn the transcription of genes on and off. -transcriptional regulation in eukaryotes is complex, typically involving many proteins, collectively called ---> transcription factors---- acting together to bind to DNA sequences called ----> enhancers-- and the promoter. - repressor proteins, which may bind to DNA sequences called silencers, inhibit the start of transcription

how and why genes are regulated

- Every cell in your body was produced through successive rounds of mitosis starting from the zygote, the original cell that formed after fusion of sperm and egg. - Therefore, every cell in your body has the same DNA as the zygote and every somatic (body) cell contains ebery gene.

What does it mean that genes are turned on or off?

- Genes determine the nucleotide sequence of specific mRNA molecutles, and mRNA in turn determines the sequence of amino acids in proteins. - A gene that is turned on is being transcribed and translated into specific proteins. The overall process by which genetic information flows from genes to proteins is called ----> gene expression. *the control of gene expression makes it possible for cells to produce specific kinds of proteins when and where they are needed, allowing cells to respond quickley and efficiently to information from the environment.

Cell signaling

- Within a multicellular organism, inofrmation must be communicated between cells -a signal molecule can act by binding to a receptor protein and inititating a ----> signal transduction pathway--, a series of milecular changes that converts a signal received outside a cell to a specific response inside the target cell. 1. signaling cell secretes the signal molecule 2. THis molecule binds to a specific receptor protein embedded in the targe cell's plasma membrane 3. The binding activates a signal transduction pathway consisting of a series of relay proteins withiin the targe cell. Each relay molecules acitivates the next 4. THe last relay molecule in the series activates a transcription facter 5. That triggers the transcriptions of specific gene 6. Translation of the mRNA produces a protein that can then perform the function originally called for by the signal

Adult stem cells

- are further along the raid to differentiation than ES cells - can thereore give rise to only a few related types of specialized cells - can also generate replacements for some of the body's cells *because no embryonic tissue is involved in their harvest, adult stem cells are less ethically problematic than ES cells.

Gene regulation

-Cells with the same genetic information can develop into different types of cells through-gene regulation-, mechanisms that turn on certain genes whule other genes remain turned off - Regulating gene activity allows for specialization of cells within the body.

Steps development of colon cancer

1.) begins when an oncogene arises through mutation, causing unusually requient division of normal-looking cells in the colon lining 2. Later, additional DNA mutations (such as the inactivation of a tumor-supressor gene) cause the growht of a small benign tumor. The cells of the polyp look normal, although they divide unusually frequently. If detected during a colonoscopy, suspicious polyps can usually be removed before the become a serious risk. 3.) Further mutations lead to formation of a malignant tumor-- one that can metastasize (spread). It typically takes at least six mutations (usually creating at least one active oncogene and disabling at least one tumor-suppressor gene) before a cell becomes cancerous.

proto-oncogenes

A normal gene with the potential to become an oncogene

tumor supressor gene

CHanges in genes whos products inhibit cell division are also involved in cancer. - the proteins they encode normally help prevent uncontrolled cell growth - any mutaion that keeps a growth-inhibiting protein from being made or from functioning may contribute to the development of cancer.

Gene regulation in eukaryotic cells

Eukaryoties, especially multicellular ones, have more sophisicated mechanisms than bacteria for regulating the expression of their genes. - the pathways from gene to protein in eukaryotic cells is a long one, providing a number of points where the process can be turned on or off, speeded up or slowed down

accumulation of mutations

Mutations leading to cancer acculmulate in a lineage of cells. Once a cancer-promoting mutation occurs, it passed to all the descendants of the ell carrying it.

protein activation and breakdown

The final opportunities for regulating gen expression occur after translation - other proteins require chemical modification before they become active - Finally, the selective breakdown of proteins allows cells to adjust the kinds and amounts of its proteins

oncogene

a gene that causes cancer - a cell can acquire an oncogene from a virus or the mutation of one of its own proto-cogenes.

Genetic basis of cancer

cancer can occur when cells escape from the control mechanisms that normally limit their growth and division. This escape involves changes in gene expression. - one of the earliest clues to the role of genes in cancer was the discovery in 1911 of a virus that caused cancer in chickens - viruses that cause cancer can become permanent residents in host cells by inserting their nucleic acid into the DNA of his chromosomes

Progression of a cancer

more than one mutation is needed to produce a cancer cell