The initial step of synthesizing mRNA is transcription. Once these processes are completed the mature mRNA can then be transported from the nucleus into the cytoplasm for protein translation. See also:. Genes are expressed through the process of protein synthesis. This elaborate tutorial provides an in-depth review of the.. The body is comprised of different elements with hydrogen, oxygen, carbon, and nitrogen as the major four. This tutorial.. Bryophytes nonvascular plants are a plant group characterized by lacking vascular tissues.
They include the mosses, th.. Hormones are chemical messengers produced by specialized glands and they were produced by switching on the genes designe.. This tutorial describes the different types and causes of brain damage. Find out how genetics, physical injury, lack of.. This page has been archived and is no longer updated. Location: India. I Am A: Graduate Student. Location: United States. I Am A: Researcher.
I Am A: Librarian. Displaying - of questions. Prev Next. Latest Reply:. Hello Jill, Mutations, which are changes in a genetic sequence, come in many forms.
It seems you are interested in both the smallest of these changes, which involve single base pair changes i. Point mutations base substitutions are changes in single nucleotide pairs in which one pair of nucleotides is swapped for another during DNA replication.
The effects of these small changes vary widely depending on which nucleotides are swapped and where the change occurs. Sometimes, point mutations have little or no effect. This can be true if they occur in noncoding regions. Even if a point mutation occurs within the coding region of a gene, the altered codon might still encode the same amino acid.
This type of change is known as a silent mutation, and it is not likely to have much of an effect. However, if a point mutation is a missense mutation — in which an altered codon results in a different amino acid getting placed in a protein — the altered protein may or may not be functional. Similarly, if the point mutation is a nonsense mutation — wherein a codon gets changed to a stop codon — then protein synthesis will stop prematurely.
The results of nonsense mutations are truncated proteins, which may not be functional. Chromosomal mutations affect longer stretches of DNA and may encompass anywhere from several genes to entire chromosomes.
One type of chromosomal mutation is a translocation. In translocations, a piece of one chromosome is transferred to a different site on another chromosome.
This sounds like a dramatic change, but some translocations have little if any effect on the phenotype — that is, the outward appearance — of an individual. If a translocation is balanced, this means that all the genetic material is still there, just in different places. If no genetic material has been lost or gained when a balanced translocation occurs, then an individual might be unaffected.
In other cases, translocations can cause big problems. Translocations can cause infertility because they can result in problems during meiosis.
Translocations are not always balanced. In cases that involve a translocation of a portion of human chromosome 21, Down syndrome can occur. If translocations involve the disruption of a gene or the fusion of two different genes, they can also cause diseases. Translocations such as these have been linked to certain types of cancer. Another type of chromosomal mutation is an inversion. An inversion happens when a piece of a chromosome gets reversed.
Some inversions have little affect on individuals. For example, there is a kb inversion on chromosome 17 that is fairly common among Europeans.
However, similar to translocations, if inversions result in genes being disrupted or fused, they can then lead to disease phenotypes. Scientists first began looking at chromosomes with microscopes in the late s. Naturally, the structure of DNA was not known at that time. Consider this fact for a moment: each human cell contains approximately two meters of DNA! Cells must efficiently compact all this material yet still allow the DNA to remain accessible to their replication and transcription machinery.
As it turns out, specialized proteins in eukaryotes, known as histones, bind DNA and play a major role in chromatin packaging. Histones are the most abundant proteins found in eukaryotic cells and are organized into nucleosomes, which associate tightly with the DNA double helix at regular — base pair intervals. High-resolution structural data suggest that nucleosomes bound by DNA are organized further by zigzagging to form a structure resembling a double stack of coins, wherein the nucleosomes are like coins stacked on top of each other.
The DNA-nucleosome complex is further organized into compact fibril-like structures during metaphase.
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