Biology Proteins Express DNA Notes

Proteins Express DNA Genes are expressed when DNA is transcribed into RNA and translated into proteins. Gene Expression is a general term that refers to the processes that make proteins, those processes are transcription of RNA from a DNA molecule, then the translation of that RNA into a protein When activated, genes make proteins. When repressed, genes don't make proteins. The segment of DNA that codes for a protein (or part of a protein) is called a gene, Organisms develop, differentiate, and grow by regulating their gene activity. Cells turn genes on so that they make proteins, or they turn genes off by repressing transcription and translation. Some proteins are made all the time, while others are made only in response to the body's needs. All of an organism’s cells contain identical DNA molecules and identical genes. However, different genes are active in different cells. All body cells also contain the exact same genes—that is, skin cells and muscle cells have very different functions, but they all contain the same genes. Cells differentiate and specialize by controlling which genes are turned on. Some genes are active in skin cells and inactive in muscle cells. At any given time, only a portion of any cell's genes are active and producing proteins. The other genes are turned off. Cells differentiate when different genes are expressed. Different types of cells often have unique appearances and functions. If you could look deeper into cells, to the level of the protein, you would see different sets of proteins in different cells. Your hair, for example, is made of the protein keratin. Cells in your hair follicles produce this protein, while other types of cells in your body do not. Scientists would say that the gene for keratin is expressed in hair follicle cells, but the gene for keratin is not expressed in many other cells. Recall that gene expression means that an mRNA transcript is made from the gene's DNA sequence. Then, the mRNA transcript is translated into a protein—in this case, keratin. The activation of specific genes is the most important step in cell differentiation. As an organism grows and develops, different genes are either turned on or off in various cells. That regulation is a key part of cell development. Cells differentiate because different genes turn on and turn off. Genes do not disappear, and they aren't removed from cells during differentiation. They are just expressed differently. Different genes are also active during different stages of development. From fungi to plants to people, development depends on the expression of different genes at different times and in different parts of an organism. When a human embryo is developing, it produces a unique form of hemoglobin called fetal hemoglobin. Hemoglobin is the molecule found in red blood cells that carries oxygen throughout the body. Fetal hemoglobin attracts oxygen more strongly than adult hemoglobin, and that stronger attraction helps the growing fetus take in the oxygen provided from its mother's bloodstream. While the embryo is growing, cells in its liver transcribe genes that produce the proteins making up fetal hemoglobin. Just before birth, several changes take place. The liver stops transcribing those genes, and bone marrow begins transcribing a different set of genes to produce adult hemoglobin. Gene expression is controlled by transcription factors, which are proteins Genes make proteins, and proteins do much of the work of the cell. Controlled gene expression allows for cell specialization and an organism's growth and development. But what regulates gene expression? It's a topic of intense scientific research today. Scientists still don't have all the answers, but one thing they have figured out is that a class of proteins called transcription factors has the ability to turn genes on and off. These proteins either can allow transcription to proceed or can block it.