The Cell Cycle 1 Reproduction Asexual Reproduction Involves

The Cell Cycle 1

Reproduction • Asexual Reproduction: – Involves only 1 organism – New individual is genetically identical to parent-clone • Single celled organisms – - binary fission: cell divides in 2 2

Multicelled organisms: • Budding • Plant propagation • Parthenogenesis 3

Reproduction • Sexual Reproduction: – Involves 2 parental organisms – New individual is different from either parent – Leads to greater genetic diversity 4

• Sexual Reproduction: 5

Chromosome Structure • Chromatin: DNA and protein in long, thin thread-like, invisible form 6

Chromosome Structure • Chromosomes: Condensed chromatin that appear right before cell division – Sister chromatids- contain exact copies of DNA– Centromere- protein “button” holds chromatids together 7

Chromosome Structure 8

The Cell Cycle • The time it takes from 1 cell division to the next • Varies in length of time depending on cell type 9

The Cell Cycle • Function -asexual reproduction – Single celled organisms -produce new individuals– Multicelled organisms – • Growth -increase in size by increasing in cell number • Tissue replacement and repair 10

The Cell Cycle Two alternating periods 1. Interphase- growth 2. Mitosis- division Interphase Growth Division Mitosis 11

Phases of the Cell Cycle 12

The Cell Cycle Interphase: • • The growth period. Longest phase of the cell cycle Cell spends 98% of time in interphase 3 stages 13

3 Stages of Interphase G 1 -1 st Gap phase: • The cell grows in size and carries on normal functions S - Synthesis phase: • DNA Replication • Chromosomes copied in preparation for cell division. G 2 - 2 nd Gap phase: • Structures needed for cell division are assembled. • No turning back- cell division will occur 14

Phases of the Cell Cycle How the Cell Cycle Works 15

The Cell Cycle • Mitosis: – The division period – Division of the nucleus – Four distinct phases. • Prophase • Metaphase • Anaphase • Telophase The Cell Cycle 16

Prophase • First phase of mitosis • Chromatin condenses and chromosomes become visible • Nuclear membrane and nucleoli disappear • Structures necessary for cell division appear – Centrioles- barrel shaped, 2 pair, each moves to opposite poles – Spindle fibers- span the two poles 17

Prophase 18

Metaphase • Chromosomes line up along the midline of the cell 19

Anaphase • Centromeres and sister chromatids separate • Spindle fibers shorten and pull chromatids, now called chromosomes, toward opposite poles 20

Telophase • Reverse of Prophase • Begins when chromosomes stop after reaching poles • Chromosomes decondense to less visible chromatin form • Nucleoli reappear • Nuclear membrane appears around each set of chromosomes 21

Telophase 22

Cytokinesis Division of the cytoplasm and organelles Results in 2 daughter cells New cells begin a new cell cycle Different for plants and animals 23

Animal Cell Cytokinesis Cleavage furrow-cell membrane pinches in Animation: Mitosis 24

Plant Cell Cytokinesis Cell plate formation- new cell wall is added to separate 2 daughter cells onion root tip 25

Control of the Cell Cycle • A series of enzymes monitor a cell’s progress from phase to phase. • A disrupted cell cycle can result in excessive cell division, or cancer 26

Skin Cancers Benign Malignant Symmetrical Asymetrical Borders are even Borders are uneven One shade Color: Two or more shades Smaller than 1/4 inch Diameter: Larger than ¼ inch 27 http: //www. skincancer. org/skin-cancer/melanoma_2. html