Unit 3 Cell Division Genetics and Molecular Biology
Unit 3 – Cell Division, Genetics and Molecular Biology TODAY: CELL DIVISION - MITOSIS Outcomes Be able to define: Chromosome, chromatid, chromatin, centromere Somatic vs germ cells Autosome vs sex xsomes Chromosome number (haploid, diploid, polyploid) Be able to explain the cell cycle Be able to explain stages of Mitosis MEIOSIS – TOMORROW ***Bring 4 coloured pens tomorrow***
DNA and Chromosomes are composed of DNA and proteins Chromatin – uncondensed strands of DNA Duplicated xsomes are called sister chromatids Sister chromatids are joined at the centromere (condensed strands of
Chromosome Number The number of individual xsomes varies from one species to another Human somatic (body) cells have 46 xsomes 22 pairs of homologous xsomes (autosomes) 1 pair of sex xsomes (X, Y) Cells that contain pairs of homologous xsomes are called DIPLOID (2 n) Cells that contain unpaired xsomes are called HAPLOID (n) Some organisms are POLYPLOID
Chromosome Number Haploid number is designated as n For Humans n = 23 (gametes) Therefore our diploid number (somatic cells) is: 2 n = 46 For fruit flies (Drosophila) n =4 What is the diploid number?
Heredity and Genes The passing of genes from one generation to another is called heredity Your biological traits are controlled by genes, located on every chromosome, in every cell in your body Your characteristics are a result of interactions of genes from both parents
Principles of Cell Division Somatic cells (body cells) undergo mitosis Germ cells (sex cells) undergo MEIOSIS
Principles of Mitosis All cells are formed from pre-existing cells Initial cell is referred to as the mother/parent cell, subsequent cells are called daughter cells Mitosis: Division of a mother/parent cell to produce two identical daughter cells 2 phases of Mitosis: Division of the nucleus Division of the cytoplasm and organelles
The Cell Cycle - continuous Division Phase: MITOSIS Interphase: Uncondensed xsomes G 1 (gap 1) Rapid growth S (Synthesis) Duplication of xsomes G 2 (gap 2) More cell growth, prepares for cell division http: //www. nelson. co m/ABbio 2030/student/protect/me dia/cell_cycle. html
Stages of Cell Division Cell division occurs in phases It is continuous processes (cells do not pause between phases) (1) Interphase – no cell division occurs (2) Mitosis – cell division Prophase Metaphase Anaphase Telophase
Interphase (G 1, S, G 2) When the cell is not dividing Cells spend the majority of their time in interphase During interphase cells undergo normal cell activity: Grow Absorb and transport nutrients, as well as eliminate waste Metabolize substances During interphase, cells get ready to divide again by duplicating their chromosomes
Mitosis (PMAT) Prophase Metaphase Xsomes line up at equatorial plate (individually) Anaphase Chromatin condenses (chromosomes are visible) Nuclear membrane dissolves Centrioles to poles (spindle forms) Centromeres split – sister chromatids are pulled apart Telophase Nuclear membrane re-forms Xsomes uncondense CYTOKINESIS occurs
Cell Clock – Regulation of the cell cycle • Not completely understood • What we do know • Specialized cells have a lifespan controlled by some biological clock • Age (telomere size) • Specialized cells undergo mitosis less frequently (if at all) compared to unspecialized cells • Ex. Nerve cell vs skin cell • Regulatory signals within the body serve as START and STOP signals for cell division • Interruption of the regulatory signals can cause uncontrolled growth (cancer)
Karyotyping The particular set of xsomes that an individual posesses Image of the condensed xsomes
STOP SLOTH!!!
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