Sunday, March 17, 2013
Germs and Traits
This post relates to big idea 3: living systems store, retrieve, transmit and respond to information essential to life processes. In pages 125-153, we learn that a mutation that happens in our germ line can cause an instruction change for our offspring. Genes, traits and proteins can be altered.
Gene expression can also be altered in other ways. Explain the two types of DNA packaging (methylation and acetylation). What do lipid hormones do? How do tandem repeats cause disorders? What does histone acelytation do to express DNA?
-Jayanthi Selvaraj (jselvaraj95@gmail.com)
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i'll take this
ReplyDeleteHistones are proteins that are responsible for packing chromosomes into nucleosomes, which are protein-DNA complexes. The modification of histones affects the rate of transcription. Two of the ways histones can be modified is through acetylation and methylation. During acetylation, acetyl functional groups are attached to the histone tails. This results in structural changes of the nucleosomes, increasing the access of transcription factors to the DNA as the winding histones are loosened. Therefore, histone acetylation increases the rate of transcription. During methylation, methyl functional groups are attached to the histone tails. This results in structural changes of the nucleosomes, however unlike acetylation this decreases the access of transcription factors to the DNA as the histones are more tightly wound. Therefore, histone methylation decreases the rate of transcription.
ReplyDeleteSignals are transferred between nerve cells by chemical messengers called neurotransmitters. Neurotransmitters come in many forms. Some neurotransmitters are lipids, and are known as lipid hormones or steroid hormones. The Campbell text states, “Many hormones, including vertebrate sex hormones, are steroids produced from cholesterol” (77). Lipid hormones change gene expression by turning on or off DNA’s instructions for making proteins. Once a steroid enters a cell through the semi-permeable membrane, it interacts with a specific carrier protein in the cytoplasm. This soluble complex enters the nucleus, where it interacts with DNA to activate or repress transcription. ¹
Tandem repeats are patterns of two or more nucleotides repeated (and the repetitions are adjacent to each other) in a strand of DNA. Dynamic mutations are expansions in tandem repeats, and are known to cause many disorders mainly affecting the nervous system. One of the most common of these disorders is Huntington’s disease. Tandem repeat polymorphisms (TRPs) provide a unique source of genomic variability. Recent evidence suggests they can regulate a range of biological processes. This relates to big idea 3: living systems store, retrieve, transmit and respond to information essential to life processes. Tandem repeats can change length during meiosis and mitosis, providing a dynamic source of genetic variation. Post-mitotic TRPs have high instability, and recent suggests their possible roles in neuronal function and dysfunction. The mutation rate of TRPs is higher and the extent of polymorphism is far more diverse than that of single nucleotide polymorphisms (SNPs).² Since the mutation rate is higher, this makes sense that many more disorders rise from TRPs than SNPs.
1. http://www.britannica.com/EBchecked/topic/342808/lipid/257753/Physical-characteristics-of-membranes
2. http://www.discoverymedicine.com/Anthony-J-Hannan/2010/10/08/trping-up-the-genome-tandem-repeat-polymorphisms-as-dynamic-sources-of-genetic-variability-in-health-and-disease/
(Sarah Terwilliger, sterwil3@students.d125.org)