THE CELL CYCLE THE CYCLE OF LIFE Unicellular

THE CELL CYCLE

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

WHY MUST CELLS DIVIDE? 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

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 Diploid (2 n) § 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

HAPLOID 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

SOMATIC CELLS 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

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

THE CELL CYCLE

INTERPHASE

INTERPHASE

G 1 Gap phase Cell grows and carries out normal functions

S PHASE

G 2 Gap phase Cell grows and carries out normal functions Other organelles replicate

G 0 Some cells will never leave interphase or will stay in interphase for a very long time Phase looks like G 1 These cells will not divide

CELL DIVISION

MITOSIS 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

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

CONTROLLING CELL DIVISION 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

CANCER Uncontrolled cell division § Usually results from mutations to § Oncogenes- accelerate the cell cycle § Genes that stop the cell cycle § p 53 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)

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

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

MEIOSIS

CHARACTERISTICS 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

PROPHASE I

PROMETAPHASE I

METAPHASE I

ANAPHASE I

TELOPHASE I

CYTOKINESIS I

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

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

OOGENESIS 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