The Living World - Chapter 5 PDF

What is a Cell? Cell: the basic unit of life in a living organism Examples: bacterial cells, fungal cells, plant cells, animal cells, etc. Bacterial cell 3 Living Organism Energy...

What is a Cell? Cell: the basic unit of life in a living organism Examples: bacterial cells, fungal cells, plant cells, animal cells, etc. Bacterial cell 3 Living Organism Energy intake (Food) à waste disposal Reproduction (DNA) Respiration (breathing) Liquid water intake Life cycle (growth) Movement Reaction to stimuli such as heat, pressure, light, etc. Adapt to environment 4 Structure of a Human Cell 5 Cells Viewed Under Optical Microscope 6 Main Structures of a Cell Under a regular optical microscope, we can easily distinguish three cell components: 1. Cell membrane: a flexible barrier that surrounds and protects the cell content, allowing the cell to interact with its environment. Facilitates absorption of nutrients and other useful substances. Facilitates evacuation of waste and other substances produced by the cell. 7 Main Structures of a Cell 2. Cytoplasm: the gelatinous fluid inside the cell membrane and outside the nucleus. Provides a hospitable environment for most cell activities 8 Main Structures of a Cell 3. Nucleus: AKA control centre (easily recognised by its darker colour), where individual genetic information is protected and stored in DNA strands. DNA controls all cell activity 9 What is DNA? DNA: deoxyribonucleic acid A very long molecule, shaped like a double helix, located inside a cell nucleus Usually appears as long threads Contains genetic information needed to make specialized proteins that build and repair individual organisms 10 DNA Discovery Rosalind Franklin Video: https://youtu.be/fH5hY6Tp5O8?si=ajErOsbF7j5CV2PG 11  Structure of DNA DNA is made up of molecules called nucleotides. Each nucleotide contains a sugar phosphate backbone and a nitrogenous base. Often described as: DNA ladder Double helix (twisted spiral ladder) Chromosome (coiled up DNA) 12  Nitrogenous Bases There are 4 types of nitrogenous bases: Thymine (T) Adenine (A) Cytosine (C) Guanine (G) Binding of these 4 nitrogenous bases is very specific: Thymine (T) always binds with adenine (A) Cytosine (C) always bind with Guanine (G) 13  Genome The nitrogenous base pairs are arranged in a sequence along the double-helix DNA, just like letters are arranged in a sequence to create words and sentences in language. Genome: AKA genetic blueprint, is the complete set of genetic information of an individual or species (dependent on the entire base-pair sequencing). Contains all information needed for development and growth Human genome is made up of approximately 3 billion base pairs. 14  Gene A human genome is made up of about 25,000 genes. Gene: a segment of DNA that contains the genetic information to manufacture specialized proteins with specific job to carry out. 15  Unique DNA We are all unique individuals because our DNA is unique. Every gene can exist in different variations and forms. Virtually impossible for two individuals to possess the same genetic information except identical twins (shown below) 16 Gel electrophoresis of DNA from two pairs of identical twins  Genetic Diversity Genetic diversity: achieved by all the possible genetic variations of a particular species. Sexual reproduction increases the genetic diversity of a species The greater the number of individuals in a population, the greater the gentic diversity, resulting in reduced expression of a defective gene. 17 Diseases of Less Genetically Diverse Gene Pools A small or isolated population is more likely to be less genetically diverse, as are populations in which related individuals breed with one another. Inbreeding results in higher expression of a defective gene, evident in many European royal families in the 19 th and early 20th centuries. Video: https://youtu.be/w9bncp8Sdwo?si=V95HgNFmGFUwTLJU In Quebec, we have the Andermann syndrome, found almost exclusively in children born in Saguenay-Lac-St-Jean and Charlevoix regions. Charles II, the last of the Spanish Habsburg kings with his ”Habsburg Jaw”. 18 Objectives 5.2 1. To learn about cell division: mitosis and meiosis 2. To differentiate between mitosis and meiosis 3. Assignment: Pages 60 to 62 19 Cell Division Cell Division: a process that is essential to the production of new cells for the purpose of growth, tissue repair and sexual reproduction. Cells are not constantly dividing and this period is known as interphase. 20  Types of Cell Division 1. Mitosis: a process of cell division in which cells multiply in order to ensure growth and tissue repair. Occurs in almost all body cells AKA somatic cells 2. Meiosis: the process of cell division in which male and female gametes are produced in order for sexual reproduction to take place Gamete: a reproductive sex cell 21 Mitosis During mitosis, the original cell (AKA the parent cell) divides and produces two identical cells (AKA daughter cells). Each daughter cell is considered as a diploid cell because it possesses two sets of chromosomes, that is two copies of each gene (one from the father and one from the mother) All cells in the human body are diploid, except for sex cells (gametes). 22 Phases of Mitosis Mitosis consists of five phases (excluding interphase): 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase 5. Cytokinesis* 23 Interphase Towards the end of interphase, as a cell prepares to divide, it duplicates the DNA in its nucleus. At the end of interphase, the parent cell will have grown in size and also completely replicated its DNA. 24 DNA Replication (during interphase) During the replication, the double helix of DNA unwinds, splitting into two strands. Each strand serves as a template for building a new complimentary strand. As a result, two helixes, each identical to the original DNA helix, are formed. Video: DNA Replication 25 Phase 1: Prophase As cell division begins, the DNA strands coil and condense to form rod-like structures called chromosomes. The nuclear membrane (nuclear envelope) disappears. 26 Chromosome Vs. Chromatid Chromosomes are shaped like an X because they are made up of two identical rods joined together by the centromere at the centre. Each rod is called a chromatid. Chromosomes form pairs. Within each pair, one chromosome contains genetic material from the mother, while the other contains genetic material from the father. Cells are said to contain 2n chromosomes, where n represents the number of pairs. Humans have 23 pairs of chromosomes. 27 Phase 2: Metaphase Chromosomes align at the centre of the cell. 28 Phase 3: Anaphase Chromosomes split at their centres into chromatids. Chromatids move away from the centre; half goes to one end of the cell while the other half goes to the opposite end. 29 Phase 4: Telophase A new nuclear membrane forms. DNA uncoils into separate strands. Organelles (components inside a cell) and cytosol are evenly distributed Spindles disappear. 30 Phase 5: Cytokinesis Cytokinesis: the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells. 31  Meiosis Meiosis happens when there is an union of two sex cells during fertilization. Sex cells are haploid cells --- they contain only 1 set of chromosomes, that is, one chromosome from each pair of chromosomes. Male sex cells: spermatozoa Female sex cells: ova or egg cells 32 Meiosis Meiosis and mitosis are somewhat similar but in meiosis, the cell divides TWICE: meiosis I and meiosis II. At the end of meiosis I, chromosome pairs are separated, reducing their numbers by half, resulting with 23 chromosomes in each of the two daughter cells. At the end of meiosis II, each chromosome separates into two strands, resulting in four haploid daughter cells. 33 Objectives 5.3 To learn about cellular specialization: cells à tissues à organs à system Tissue types System types To learn about the various types of systems and their functions Assignment: Pg. 63, 64, 74, 75 & 76 (up to Q14) 34 Cellular Specialization The immediate result of fertilization is the formation of a zygote. Zygote: a single cell with a full set of DNA, i.e. 23 pairs of chromosomes A zygote will continue dividing and multiplying until a full formed organism is formed through mitosis. An adult human being is composed of approximately 60 trillion (6 x 1013) cells. 35