Ribonucleic acid (RNA) consists of nucleotides made of a sugar, phosphate group and bases, just like DNA, although it differs in 3 ways:
Sugar present Complementary base partner of adenine Number of strands in one molecule
DNA
RNA
Deoxyribose
Ribose
Thymine
Uracil
Two
One
The sequence of bases in a DNA strand represent the genetic code from which enzymes are coded for and, therefore, all information is passed on for the inherited characteristics. DNA has only four bases, however, and there are around 20 types of amino acids. Three bases are required to code for each amino acid (64 possible combinations). Each of the 20 amino acids is coded for by one, or more of these triplets of bases
Each triplet of bases is called a codon.
The information coded for by the triplets of bases of DNA in the nucleus need to reach the structures responsible for protein synthesis In the cytoplasm. This function is performed by messenger RNA (mRNA) which is formed (transcribed) from one of the DNA strands from free RNA nucleotides in the nucleus
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DNA unwinds Weak hydrogen bonds between bases separate, separating the DNA strands Free RNA nucleotides find their complementary DNA base partner Weak hydrogen bonds form between the base pairs Strong chemical bonds formed between the sugars and phosphates of the RNA nucleotides by RNA polymerase Weak hydrogen bonds between the DNA and RNA bases break allowing the RNA strand to separate from the DNA template Weak hydrogen bonds between the DNA bases form and reunite the DNA strands which then wind up, forming a double helix again.
Transcription animation - detail
A second type of RNA exists in the cytoplasm called transfer RNA (tRNA). Only one triplet of bases in RNA is exposed, known as an anticodon. Each anticodon corresponds to a particular amino acid.
Ribosomes are the site of translation of mRNA into protein. Some are found free in the cytoplasm but others are attached to the rough endoplasmic reticulum. Ribosomes contain enzymes essential for protein synthesis and large numbers of ribosomes are found in growing cells.
This is a system of tubules and flattened “sacs” which is continuous with the nucleus membrane.It is encrusted with ribosomes on it’s outer surface.
The function of the Rough ER is to transport proteins
The Golgi Apparatus (or Golgi body) is made up of groups of fluid-filled sacs. Vesicles containing newly made proteins become “pinched-off� from the Rough ER and fuse with the sacs of the Golgi body. Proteins then pass through the Golgi body via vesicles During this time, proteins are processed by the Golgi e.g. by adding a carbohydrate component to make it a glycoprotein
Eventually the processed protein is packaged in a vesicle and excreted from the cell by exocytosis. Golgi bodies are especially numerous in secretory cells e.g. those of gland cells that produce and excrete hormones. The function of the Golgi body is to process and package proteins for release