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Transcript
The nucleus Nuclear membrane double membrane Nuclear pores Nucleolus RNA production Chromosomes genetic material Chromosomes and Cell Division Chromosomes What are they ? How they are replicated? Cell Division Why are there two types: mitosis and meiosis? How are they different? How does meiosis produce new combinations of genes? What is a chromosome? It is a linear strand of DNA in combination with nuclear proteins We refer to this complex of DNA and proteins as chromatin It is a linear array of genes As a set - they are our genome Chromosomes exist in different states As visible structures seen during cell division. Most of the time they are not visible because they exist as uncoiled threads of chromatin distributed through out the nucleus. Chromosome basics. The number of chromosomes present within the nucleus is a characteristic of the species. Chromosomes of humans and most other eukaryotic species occurs in pairs. Members of a chromosome pair are known as homologues. The state in which there are two copies of each chromosome present is known as diploid. Haploid – only one copy of a chromosome is present All of the somatic cells in our bodies are diploid cells The only cells in our bodies that are haploid are our gametes – eggs and sperm Human somatic cells have 46 chromosomes diploid number (2n) = 46 23 from mom - 23 from dad 22 pairs are autosomes –true homologous pairs 1 pair is not necessarily homologous - sex chromosomes females are XX males are XY – a non homologous pair. Figure 2.9 Figure 2.8 Cell division mitosis is the process of cell division in which one cell becomes two identical daughter cells development renewal regeneration The cell cycle • S phase: DNA synthesis • G phase: gap for growth • M phase: mitosis (nuclear division) • Cell division or cytokinesis is part of G1 Replication of chromosomes • Replication is the process of duplicating a chromosome • Occurs prior to division • Replicated copies are called sister chromatids • Held together at centromere Figure 2.12 Mitosis Purpose: to make copies of cells and their DNA • Replicated chromosomes align at the metaphase plate. • Sister chromatids separate and move to opposite poles. • Nuclear membranes form around each new nucleus. • Division of cytoplasm or cytokinesis occurs. Prophase • Replicated chromosomes condense. • Microtubules organize into a spindle Metaphase • Chromosomes line up on the metaphase plate. • Spindle microtubules are attached to centromeres of chromosomes. Anaphase • Centromeres of sister chromatids separate • Chromosomes move to opposite ends of the cell Telophase • Nuclear membranes form • Spindle disappears • Division of cytoplasm occurs (cytokinesis) Cytokinesis Cytoplasmic division occurs after nuclear division is complete. Two cells are formed. Figure 2.15 Cell cycle control Proteins called checkpoint proteins monitor progression through the cell cycle. Cell division mitosis is the process of cell division in which one cell becomes two identical daughter cells Cell death apoptosis is the process of cell death in which cells signal their own demise in a programmed way development response to abnormality Apoptosis Programmed cell death is part of normal development chicken embryo Death receptor binds signal molecule. Capase enzymes destroy proteins. Cells fragment. Phagocytes engulf cell remanants. Different amounts of apoptosis create feet with digits versus webbing.