A network of membranes within a cell which has ribosomes attached to it. They are important in the synthesis and transportation of proteins.
Transcription factors are proteins which bind to the nuclear DNA, regulating the transcription of the genetic material and sometimes changing the mRNA which is formed as a result.
The addition or removal of different groups from histones makes the heterochromatin structure more or less open, affecting whether the DNA can be transcribed or not.
Chemicals made in response to first messengers (eg steroid hormones) that cannot pass through the cell membrane.
The removal of a methyl (CH3) group from a cytosine positioned next to a guanine in the DNA chain with a phosphate bond between them, (a CpG site).
The organ system in the body which breaks down large insoluble food molecules into small soluble molecules which can be used by the body
The addition of a methyl (CH3) group to a cytosine positioned next to a guanine in the DNA chain with a phosphate bond between them, (a CpG site) by DNA transferase.
Enzyme involved in the transcription of DNA and the production of mRNA. The enzyme is involved in the breakdown of the hydrogen bonds between the two strands of DNA in the formation of mRNA, and the build up of the mRNA strand from 5-3 end.
About 98% of the transcribed RNA thought to regulate transcription of the DNA directly, or by histone modification, or to modify the products of transcription.
Sequence of bases in a DNA molecule which codes for the sequence of amino acids in a protein. Each group of three bases, codes for an amino acid.
RNA molecule found in the cytoplasm of the cell which transports specific amino acids to the surface of the ribosomes
Enzymes that remove introns from pre mRNA and change the arrangement of exons to give different proteins from the same bit of DNA.
Epigenetics is the study of external factors which affect gene expression and differentiation, often by switching particular genes on or off, so changing the proteins made by a DNA sequence.
A long chain of hundreds or even thousands of amino acids joined by peptide bonds.
Cyclic adenosine monophosphate. The most common second messenger molecule in cells, derived from adenosine triphosphate (ATP)
Non-coding regions of DNA or RNA
A protein-digesting enzyme found in the mammalian stomach.
A protein produced during the clotting of the blood which traps platelets and red blood cells to form the clot
A group of three bases within the DNA molecule which code for a specific amino acid or for the beginning or ending of a transcription sequence.
Coding regions of DNA or RNA.
A short piece of DNA which is responsible for the inheritance of a particular characteristic. It codes for the production of a specific protein. Genes occupy a fixed position, called a locus, on a particular DNA molecule.
Deoxyribonucleic acid. This is the molecule which contains the genetic code. It coils up tightly inside chromosomes. DNA is a double helix made from two strands which are joined together by pairs of bases.
Protein synthesis is the process by which the information in the DNA code is translated into proteins. Some of these proteins form part of the cell structure. Others are enzymes that then control the production of all the other materials that make up the cell or the entire organism.
Protein synthesis is a continuous process but we break it down into stages to help us understand what is taking place and where it happens in the cell.
For many years scientists thought each gene coded for a single protein. Now we know that a variety of different factors act on the DNA itself or on the mRNA that is formed in the nucleus. As a result, a single gene may code for many different proteins depending on both the internal and external environment of the cell.
Factors affecting gene expression
The transcription of the DNA itself may be affected by transcription factors in a number of different ways
The initial mRNA is a transcription of all of the DNA including introns or non-coding regions of DNA. It needs to be modified before it is transported to the ribosomes for translation. The introns are removed by enzymes called spliceosomes. Sometimes spliceosomes join some of the exons, or coding regions, in different sequences so the same region of DNA can result in several different types of mRNA.
Epigenetics is a relatively new way of looking at the effect of the environment on the genome. It describes how different chemicals associated with the DNA or RNA can affect the way the genetic code is read. This external control of the genome may be brought about by
Some proteins are produced in an inactive form. Post-translational changes as a result of second messengers such as cyclic AMP (cAMP) in the cell, or specific enzymes in the body, will modify and activate the proteins, changing the molecule produced. Examples are the production of fibrin from fibrinogen in the clotting cascade and the production of pepsin from pepsinogen in the digestive system.