Unit 6: Cell Growth and Division Mrs. Howland Biology 10 Rev. Jan 2016

Living Things GROW How does growth occur in living things? By cells increasing their size? By number of cells increasing? WHY? What happens when cells INCREASE in size?

Larger Cells are Inefficient Cells that are too large have less surface area for transport ~ They cannot keep up with their demand! Cells function using a set amount of DNA and transport of materials across the membrane Many, smaller cells allow for greater efficiency!

Cells DIVIDE Cells DIVIDE into 2 “daughter” cells by way of CELL DIVISION BEFORE cell division, DNA is replicated Each daughter cell gets a complete copy of DNA TWO TYPES of cell division Asexual reproduction Sexual reproduction

ASEXUAL REPRODUCTION Some living things such as bacteria (single cell organisms) do not reproduce the way animals do—they must divide in order to reproduce! Asexual reproduction is when one cell divides to create two cells that are identical to the original Occurs quickly Efficient Bacteria (single celled organisms) Multicellular organisms such as hydra

ASEXUAL REPRODUCTION HYDRA

SEXUAL REPRODUCTION Another way to form new cells is by the fusion of two separate ‘parent’ cells (what does fusion mean?) Sexual reproduction is when offspring (new cells) are produced from two separate parent cells Parent cells are special reproductive cells Offspring inherit some DNA from each parent Occurs for most plants and animals, some single- celled organisms

What we know…location of DNA

VOCAB: Chrom-WHAT??? Chromosome ~ organized package of DNA, located in cell’s nucleus Chromatin ~ fiber within a chromosome, consists of protein and DNA, major proteins are histones DNA coils around the histone proteins to form beadlike structures

VOCAB: Chrom-WHAT??? Chromatid ~ one of TWO (2) identical halves of a replicated chromosome (during cell division)

Why CHROMOSOMES? DNA is specially packaged into CHROMOSOMES Allows for easy and correct separation during cell division Which makes more sense? OR

CELL CYCLE ~ How a cell divides CELL CYCLE: Grow Prepare for division Divide, forming TWO (2) daughter cells REPEAT: Daughter cells enter their own, new cell cycles!

PROKARYOTIC Cell Cycle Bacterial cell (binary fission)

EUKARYOTIC CELL CYCLE FOUR PHASES

MITOSIS = division of cell nucleus PMAT Prophase Metaphase Anaphase Telophase Chromatin condenses into chromosomes. Spindle begins to form. Nuclear envelope breaks down. Chromosomes line up along equator (center) of cell. Chromosomes are connected to spindle fibers. Chromosomes break into separate sister chromatids (think “chromosome kids”) and begin to move apart. Chromosomes gather at two opposite ends of the cell. Formation of two new nuclear envelopes.

VOCAB: Centrioles and spindle Centrioles are located in ANIMAL CELLS Structures that will separate and form spindles during cell division Are duplicated during INTERPHASE

BEFORE and AFTER Mitosis BEFORE mitosis occurs, the cell is in INTERPHASE Cell grows DNA replication AFTER mitosis, final step is CYTOKINESIS CYTOKINESIS is when the cytoplasm pinches along the center, forming two new daughter cells Daughter cells have identical set of duplicate chromosomes

CYTOKINESIS Cytokinesis in ANIMAL vs. PLANT cells

Mitosis under MICROSCOPY

MEIOSIS = produces 4 genetically- unique cells An organism inherits a SINGLE COPY of every gene from each parent HOMOLOGOUS CHROMOSOMES ~ pairs of chromosomes that have 1 chromosome from father and 1 from mother DIPLOID ~ Cell has both sets of homologous chromosomes (2 complete sets of genes, called ‘2N’) HAPLOID ~ Cell has single set of chromosomes (1 set of genes, called ‘N’)

MEIOSIS I PROPHASE 1: Cell begins to divide. Chromosomes pair up. EACH CHROMOSOME PAIRS WITH ITS CORRESPONDING HOMOLOGOUS CHROMOSOME CROSSING OVER ~ produces new combinations of alleles

MEIOSIS I METAPHASE 1: Paired homologous chromosomes line up along center of cell ANAPHASE 1: Spindle fibers pull homologous chromosome pairs to ends of celll

MEIOSIS I TELOPHASE I and CYTOKINESIS Nuclear membrane forms around chromosomes 2 new cells are formed UNIQUE set of genetic info

Meiosis II PROPHASE II: Chromosomes become visible but DO NOT pair METAPHASE II: Chromosomes line up in center of cell ANAPHASE II: Paired chromosomes separate TELOPHASE II and CYTOKINESIS: Formation of 4 daughter cells. Genetically unique from one another. Daughter cells contain only 2 chromosomes each, and are HAPLOID (‘N’)

Mitosis vs. Meiosis

Meiosis = Sexual reproduction lqI TWO (2) STAGES OF MEIOSIS: Meiosis I Meiosis II