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(1) DIVISION AND DIFFERENTIATION IN HUMAN CELLS (F) Cancer Cells (A) Somatic cells (B) Differentiation in cells Human Cells (C) Stem cells (E) Uses of stem cells (D) Germline cells DIVISION AND DIFFERENTIATION IN HUMAN CELLS (B) Define what is meant by ‘cell differentiation’ Define what is meant by ‘selective gene expression’ Describe the difference in gene expression between an undifferentiated and differentiated cell. You have learnt that there are different types of cells in your body: BUT… we all started off from ONE fertilised egg! How did the variations in cells arise? What is this process called? It’s all to do with your DNA and a process called cell differentiation Every cell contains DNA (genes) DNA (genes) carries the code to make a variety of different proteins e.g. Hair, nails, antibodies, hormones CELL DIFFERENTIATION Differentiation is the process by which an unspecialised cell becomes altered and adapted to perform a specialised function as part of a permanent tissue. Once a cell becomes differentiated it only expresses the genes that code for the proteins characteristic for that type of cell. Fertilised egg cell Repeated mitosis and cell division Early embryo (blastocyst) • Now let’s look at ONE of these cells... • Inside the nucleus of ONE cell, there are ALL the genes… • But this cell is destined to become a blood cell, so it only switches on the genes, it NEEDS to the job of a blood cell • And switches off the genes that are not necessary. Genes switched on in ALL cells Genes switched on in SOME cells •enzymes needed for aerobic respiration •insulin made by pancreas cells •proteins in plasma membrane •antibody production Genes that are only Genes that code for vital switched on in certain metabolites necessary differentiated cells. for basic life processes e.g. e.g. •Proteins needed to make cell organelles •Production of digestive enzymes •Production of keratin SELECTIVE GENE EXPRESSION SELECTIVE GENE EXPRESSION Every cell contains DNA. Short sections of DNA which have a specific job are called genes. Genes carry the code to make a variety of different proteins. Not all proteins are needed at the same time. Therefore, the genes that control the production of proteins can be switched on or off. This prevents resources (energy) being wasted. SELECTIVE GENE EXPRESSION BACK TO DIFFERENTIATION… Fertilised egg cell Early embryo (blastocyst) Repeated mitosis and cell division (see figure 1.1 on page 2 for more details!) Fully grown adult Growth and DIFFERENTIATION BACK TO DIFFERENTIATION & SELECTIVE GENE EXPRESSION (see figure 1.4 on page 4)