Chapter 4 - Cell Replication1 Area of Study One Pages 75-92

Chapter 4 - Cell Replication2 Reproduction of Cells New cells are constantly being produced in multicellular organisms. In mammals, red blood cells, skin cells and gut cells are constantly being produced to replace the cells that have died. Replacement cells are produced only by reproduction of existing cells.

Chapter 4 - Cell Replication3 Reproduction of Cells Eukaryote cells have a nucleus, which contains the genetic material deoxyribonucleic acid (DNA). DNA is found in thread like structures called chromosomes. As cells reproduce, it is critical that the genetic material is also reproduced so that any new cells produced have the same amount of genetic material as the parent cell. The process that ensures that the genetic material is transmitted from one generation to the next as cells reproduce is called mitosis.

Chapter 4 - Cell Replication4 Reproduction of Cells

Chapter 4 - Cell Replication5 Mitosis Mitosis is a process of nuclear division in which the replicated genetic material is separated and two new nuclei are formed. There 5 distinct phases of mitosis (IPMAT). These include: 1. Interphase 2. Prophase 3. Metaphase 4. Anaphase 5. Telophase

Chapter 4 - Cell Replication6 Mitosis

Chapter 4 - Cell Replication7 Mitosis

Chapter 4 - Cell Replication8 Cytokinesis Once the nuclei have reproduced and separated from mitosis – the rest of the cell forms during a process know as cytokinesis. As the two new nuclei form at the end of mitosis, the cytosol and organelles such as mitochondria and chloroplasts, surround each nucleus and cytokinesis begins. ‘Cytokinesis brings the curtain down on the cell cycle; it is the final dramatic act in which one cell becomes two.’

Chapter 4 - Cell Replication9 Cytokinesis

Chapter 4 - Cell Replication10 Chromosomes – ‘gene carriers’ Genetic instructions are present in the DNA in the nucleus of each somatic cell. Genes are organised into larger structures known as chromosomes with each chromosome carrying a large number of genes. Each species has a characteristic number of chromosomes in its somatic cells – For humans this number is 46. This number is often denoted as ‘2n’ and is referred to as the diploid number.

Chapter 4 - Cell Replication11 Chromosomes – ‘gene carriers’

Chapter 4 - Cell Replication12 Human Chromosomes Chromosome images are organised according to an international convention to form a karyotype. The 46 human chromosomes in a human male can be arranged into 23 pairs. These have 22 ‘matched’ pairs and one ‘odd’ pair consisting of an X and Y chromosome (XY). In a human female the odd matched sex chromosomes are those of two X’s (XX). A shorthand way of denoting this is: Male – 46 XY Female – 46 XX

Chapter 4 - Cell Replication13 Human Chromosomes

Chapter 4 - Cell Replication14 Human Chromosomes The 22 matched pairs of chromosomes present in both males and females are called ‘autosomes’. These can be distinguished by: Their relative size, The position of the centromere (near the middle of the chromosome), Patterns of light and dark bands that result from special staining techniques. Autosomes are identified by the numbers 1 to 22 in order of decreasing size.

Chapter 4 - Cell Replication15 Human Chromosomes

Chapter 4 - Cell Replication16 Control Mechanisms Can Fail As seen earlier, when a cell reaches the end of its cell cycle, a programmed death instruction known as ‘apoptosis’ is given. Sometimes a breakdown in the processes of apoptosis or mitosis can occur, which causes severe outcomes for the organism. If too much apoptosis occurs – a degenerative disease will develop as too many cells die (ie Alzheimer’s Disease).

Chapter 4 - Cell Replication17 Control Mechanisms Can Fail If too much mitosis occurs – there will be a formation of too many cells and a cancerous tumour will form.

Chapter 4 - Cell Replication18 Chapter Review Bio-Challenge Questions Chapter Review Questions