Cell Reproduction

Starting at the beginning… Biologically speaking, where did YOU come from?

Cells How many cells make up a human body? Did you have the same number last year? What about when you were 2 years old? 2 months old?

Cells Your body is made up of between 10 and 100 trillion cells. (100,000,000,000,000) One-thousandth of them die every day

Cells Where do all these cells come from?

Cell Reproduction

Cell Specialization Different body cells perform different functions Examples: skin, nerve, red blood cells, liver cells, platelets

Cell Specialization Different cells live for different amounts of time

Cellular Reproduction New cells are made from copies of old cells This process began occurring before you were born and will continue until after you die

Types of Cellular Reproduction MITOSIS – results in two identical cells; used for the majority of cells in the body MEIOSIS – results in four cells that are different from the “parents”; used for sex cells only

Mitosis Results in body growth or body repair Two new cells are called “daughter cells”

A Review of Cell Features Cell Membrane Cytoplasm Nucleus Nuclear Membrane Chromosomes – strands that carry a cell’s DNA Centrioles – strong, barrell-shaped organelle

Mitosis Goals – duplicate chromosomes and move them to two new daughter cells

Before Mitosis Begins (interphase) Chromosomes are duplicated within the cells (exact copies) Held together at center Two strands are called “sister chromatids”

Mitosis Step 1: PROPHASE Sister chromatids thicken Nuclear membrane breaks down Two centrioles move apart Fibers (strands of protein) form between centrioles

Mitosis Step 2: METAPHASE Centrioles to opposite ends of cell Fibers stretch between Sister chromatids attach to fibers Sister chromatids line up at center of the cell

Mitosis Step 3: ANAPHASE Sister chromatids pulled apart from partner Fibers pull chromatids towards centrioles at opposite ends of the cell

Mitosis STEP 4: TELOPHASE Each side now has complete set of chromosomes Fibers disappear Nuclear membrane re-forms Cell membrane pinches inwards to form 2 cells

Cytokinesis Cytokinesis Division of the cytoplasm (cytokinesis) is complete. The two daughter cells are now separate cells in their own right. Cytokinesis

Mitosis in Plant Cells 2 Differences No centrioles Cell wall must re-form between new cells

How to remember order of phases? In Patiki, Men Are Tough. Stages of mitosis/meiosis including interphase as a phase! Interphase, Prophase, Metaphase, Anaphase, Telophase.

Importance of Chromosomes All chromosomes come in pairs Humans have 23 pairs, so a normal cell has 46 chromosomes All cells need a full set to function properly (except sex cells)

Chromosome Number Before mitosis begins, cells have two of each chromosome (2N) After chromosomes duplicate, cells have four of each chromosome (4N) After mitosis, cells have two of each chromosome (2N)

Meiosis

Meiosis Process that creates gametes (eggs and sperm) Cells divide twice

Chromosome Number Cells start with two of each chromosome (2N) Chromosomes double (4N) Pairs divide (2N) Sister chromatids divide (N)

Importance of Meiosis During fertilization, sperm (N) and egg (N) fuse to create one cell (2N) New cell has complete set of chromosomes (half from mother, half from father)

Chromosome Number N represents number of PAIRS of chromosomes 2N = total number of chromosomes in a normal cell N – total number of chromosomes in a gamete (sex cell)

Steps of Meiosis Step 1 PROPHASE I Sister chromatids thicken Nuclear membrane breaks down Two centrioles move apart Fibers (strands of protein) form between centrioles

Steps of Meiosis Step 2: METAPHASE I Centrioles to opposite ends of cell Fibers stretch between Sister chromatids attach to fibers Sister chromatids line up at center of the cell

Steps of Meiosis Step 3: ANAPHASE I TELEPHASE I Sister chromatids DO NOT separate. TELEPHASE I

Steps of Meiosis Step 4: PROPHASE II Cell has been split in two No nuclear membrane forms

Steps of Meiosis Step 5: Occurs in both cells METAPHASE II

Steps of Meiosis Step 6: ANAPHASE II TELEPHASE II

THE MOST IMPORTANT DIFFERENCE In the first cell division, CHROMOSOME PAIRS are pulled apart. In the second cell division, SISTER CHROMATIDS are pulled apart.

Meiosis Meiosis: the division of a diploid nucleus to form four haploid genetically different daughter nuclei. Role of Meiosis • Increases genetic variation in the population – role in evolution • Makes sexual reproduction possible • Gamete formation in animals, fungi, protoctista e.g. Man Site of Meiosis Animals • testis - forming sperm, the haploid male gametes; • ovary - forming egg cells, the haploid female gametes. Flowering plants: • anther of the stamen - forming the haploid male spores (microspores), • ovule of ovary - forming the haploid female spores (megaspores).

Cancer and Aging

Cancer/Aging How are cancer and aging similar?

Cancer/Aging Changes in rates of mitosis

Aging What properties of a person’s body change as they age? Physically? Physiologically?

Cancer Rapid, abnormal, uncontrolled mitosis What causes cancer?

Cancer Causes Viruses Chemicals Radiation