THE CELL CYCLE

THE CYCLE OF LIFE Multicellular You Mitosis Meiosis Unicellular You Unicellular Offspring

 Cells must be small  As cells grow bigger, problems develop  DNA Overload  Same amount of DNA must serve larger and larger areas  Surface Area/Volume Ratio  Cytoplasm increases faster than cell membrane  Cell can’t exchange enough material  Material can’t reach center fast enough WHY MUST CELLS DIVIDE?

SURFACE AREA/ VOLUME RATIOS  Surface Area (cube) = 6 x width 2  Volume (cube) = width 3  Surface Area/ Volume

COMPARING ORGANISMS  Unicellular  Single cell will go through cycle  When cell gets too large, it will divide  Produces two new cell, each one is its own organism  Form of asexual reproduction called binary fission  Each “offspring” is identical to the parent cell  Multicellular  Beginning Cell- Zygote  Cell(s) go through cell cycle to form parts of organism  Cell division continues through development, growth, repair, and wear and tear  Each division creates 2 new cells identical to the parent cell  In some species, can be used for asexual reproduction such as budding and fragmentation

DNA REVIEW  Chromatin-  Form of DNA during interphase  Chromosome  Form of DNA during cell division  Centromere  center point holding two sister chromatids together  Sister chromatids  two copies of a chromosome held together by a centromere

 Diploid (2n)  Cells have 2 sets of chromosomes  one inherited from mom and one from dad  Found in somatic cells (all cells except sex cells)  Different number in different organisms  Humans diploid # is 46  Homologous chromosomes- name of the 2 alike chromosomes from each set DIPLOID

 Haploid (n)  Cells have 1 set of chromosomes  Found in gametes (sex cells)  Diploid # / 2  Human # is 23 (46 / 2)  When fertilization occurs, the organisms will have the diploid number again HAPLOID

 All cells in a multicellular organism except sex cells  Beginning cell- zygote (fertilized egg)  Totipotent- able to divide and create all the cell types needed in the body  Starts dividing to form early embryo (at 5 days is called a blastocyst)  Pluripotent- able to divide and create many of the cell types needed in the body  Continues to divide to form the all the structures  Adult stem cells- found in various parts of the body  Multipotent- able to divide and create some of the cell types needed in the body SOMATIC CELLS

 Also called cell differentiation  Many different cell types  Each has identical copies of DNA  Each type has a unique shape and function CELL SPECIALIZATION

THE CELL CYCLE

INTERPHASE

 Gap phase  Cell grows and carries out normal functions G1G1

S PHASE

 Gap phase  Cell grows and carries out normal functions  Other organelles replicate G2G2

 Some cells will never leave interphase or will stay in interphase for a very long time  Phase looks like G1  These cells will not divide G0G0

CELL DIVISION

 Division of the nucleus of somatic cells  One division with 4 phases  Cell divides into two identical daughter cells  Cells start diploid and end diploid MITOSIS

PROPHASE

PROMETAPHASE

METAPHASE

ANAPHASE

TELOPHASE

CYTOKINESIS

ANIMAL VS PLANT CYTOKINESIS  Animal  Cell membrane pinches together to form two cells  Plant  Cell plate forms  Will become cell wall to form two new cells

 External Controls  Growth Factors and Hormones- stimulate cell division  Crowding- inhibits cell division  Internal Controls  Cyclins- proteins whose levels rise and fall during the cell cycle; must reach a certain amount and interact with kinases to create cell division  Checkpoints- check that cell cycle is proceeding correctly  S phase- checks if all DNA has been copied correctly  Metaphase- checks if all chromosomes are on spindle fiber CONTROLLING CELL DIVISION

 Uncontrolled cell division  Usually results from mutations to  Oncogenes- accelerate the cell cycle  Genes that stop the cell cycle  p53 gene- normally stops cell division from occurring until all chromosomes are replicated  Cells are undifferentiated and don’t do their job  Benign tumors- stay clustered together  Malignant spread into other area creating problems (metastisize) CANCER

 Occurs in  Unicellular prokaryotes  Unicellular eukaryotes  Some multicellular eukaryotes  Done by mitosis or processes similar to mitosis  Examples  Binary fission  Budding  Fragmentation ASEXUAL REPRODUCTION

 Combines genetic information from two parents  Creates a unique offspring  Parents create gametes (sex cells) using meiosis  In humans, egg and sperm SEXUAL REPRODUCTION

MEIOSIS

 Meiosis  Occurs in games (sex cells)  2 divisions with 4 phases each (8 phases total) creating 4 unique cells  Cells start out diploid and end haploid CHARACTERISTICS

PROPHASE I

PROMETAPHASE I

METAPHASE I

ANAPHASE I

TELOPHASE I

CYTOKINESIS I

 Similar to mitosis  Two haploid cells created by Meiosis I both divide  Creates four haploid cells MEIOSIS II

 Formation of sperm  Starts at puberty  Forms 4 sperm during each meiosis  Men will make 5 to 200 million sperm/day SPERMATOGENESIS

 Formation of the egg  Meiosis starts inside the womb, continues is some during every cycle after puberty  1 egg and 3 polar bodies created after every meiosis  Egg must contain lots of cytoplasm to support the developing embryo after fertilization OOGENESIS