DNA, Genes & Chromosomes - National 4 скачать в хорошем качестве

DNA, Genes & Chromosomes - National 4

All new cells produced by cell division contain DNA. The nucleus of the cell controls all cell activity due to the unique sequence of chemicals in DNA. The sequence is different in every person. DNA carries the instructions to make proteins eg. hormones, enzymes, muscle, hair. The DNA chain is therefore very long as it codes for thousands of proteins. To fit in the nucleus, the DNA molecule must be wound up very carefully into structures called chromosomes. The sequence on DNA that instructs a cell to make a protein is called a gene. The nucleus of each human body cell contains 46 chromosomes. Each chromosome contains about 1000 genes. There is enough DNA in all the cells in a human body to stretch to the sun and back again over 60 times! Humans inherit 23 of their chromosomes from their mother and 23 chromosomes from their father. Other mammals also inherit half their chromosomes from each parent. If we know what versions of genes two parents have we can predict the chance that children will inherit certain characteristics. This proves useful, if parents know they are carrying a gene for a certain condition, the chance of the child getting the condition can be worked out. DNA in the nucleus codes for specific proteins to be made in the cell. The DNA transfers instructions to a structure in the cytoplasm called a ribosome. The ribosome allows amino acids to join together to make proteins.