Physical Science 8th grade (1).pdf

This is an incredible amount of information

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This is an incredible amount of information considering how many proteins there are and how complex a protein is. Splitting the DNA molecule Fortunately, the DNA molecule is able to make exact replicas of itself. When a cell reproduces, enzymes split the DNA molecule down the center. Each half of the molecule contains a complementary code of nitrogen bases. Since guanine only pairs with cytosine and adenine only pairs with thymine, each half of the molecule contains the complete genetic information for how to make proteins. Rebuilding identical DNA molecules Other enzymes called polymerases move along the unzipped DNA molecule rebuilding the nitrogen bases on each side. Still more enzymes rebuild the sugar and phosphate backbone on top of the completed nitrogen base pairs. At the end of the process, there are two identical DNA molecules. Error checking Another set of enzymes compares the old and new DNA strands for errors and corrects them by replacing nitrogen bases where necessary. We believe DNA replication occurs with less than one error out of every billion base pairs. mutation - change in the sequence of base pairs in DNA that may be passed on to successive generations. Mutations and evolution Even with odds of 1 in a billion, over time, the sequence of bases in a DNA molecule does change through random replication errors. Radiation from the environment and other processes also change DNA. Changes in DNA are called mutations . Changes in DNA lead to new proteins, and changes in living organisms that are passed on in successive generations. This is the chemical basis for evolution.
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234 U NIT 4 M ATTER AND C HANGE Figure 11.12: Ascorbic acid, also known as vitamin C. B vitamins Vitamin B-1 (thiamine) Vitamin B-2, also vitamin G (riboflavin) Vitamin B-3, also vitamin P or vitamin PP (niacin) Vitamin B-5 (pantothenic acid) Vitamin B-6 (pyridoxine and pyridoxamine) Vitamin B-7, also vitamin H (biotin) Vitamin B-9, also vitamin M (folic acid) Vitamin B-12 (cyanocobalamin) Vitamins Vitamins Most of the chemicals required for life can be synthesized by your own body, like proteins. However, there are certain chemicals necessary for the chemistry of life that the human body does not make. Collectively, these are called vitamins and minerals. In addition to carbohydrates, fats, and proteins, your body must get vitamins and minerals from food. Vitamin C Ascorbic acid (Figure 11.12), also known as vitamin C, is required for synthesis of several important chemicals in your brain and nervous system. Vitamin C is also needed to synthesise compounds used in the transfer of energy within cells (ADP/ATP). Vitamin C must be supplied daily through food. Vitamin D Vitamin D includes several fat-soluble compounds known chemically as calciferols . Vitamin D is not a true vitamin since it can be synthesized by your skin when cholesterol reacts with ultraviolet light. However, sunscreens and clothes block UV rays from reaching the skin and can result in vitamin D deficiency. To help prevent this
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