CELL GROWTH & REPRODUCTION

Cells cannot grow indefinitely ... they can mature then divide OR die If the cell is going to divide, new cells need both *cytoplasm (cytokinesis =division of cytoplasm) *copies of nuclear material In unicellular organism, reproduction=cell division In multicellular organism, cell reproduction allows growth, replacement of cells that wear out (skin, blood, etc), NOT reproduction of whole organism

Mitosis Mitosis- the process by which the nucleus of a cell divides, while maintaining the chromosome number. Cytokinesis- the division of the cytoplasm of the cell after mitosis or meiosis.

Mitosis Mitosis is essential for growth & repair of an organism It is the process that distributes the genetic material evenly between two daughter cells, so that each daughter cell is genetically identical to the parent cell. It’s simply a way to make more of the same cell

In animals… Somatic cells (cells of the body) are diploid. This means that each cell has two chromosomes of each type. They are in PAIRS. Biologists use “2N” to symbolize diploid. Gamete cells (egg, sperm) are haploid. This means that each cell has only one of each type of chromosome. Biologists use “1N” to symbolize haploid.

MITOSIS When somatic cells reproduce themselves the process is called MITOSIS. Mitosis leads to the production of two “daughter cells”. Each daughter cell has the same number of chromosomes as the parent cell. 2N Parent Cell Daughter Cells

Terminology: DNA= hereditary information, found in nucleus Chromosomes= DNA wrapped around proteins, thick rod-like structures – (cells undergoing division) Chromatin= DNA in form of long, thin, twisted threads “ball of yarn” – (non-dividing cells)

Replicated Chromosomes Sister chromatids Bound at center by centromere Product of DNA replication Chromatids are identical How many chromatids are in a human cell that is going through Prophase & Metaphase??? centromere chromatid

Homologues versus chromatids Homologous chromosomes One from Mom and One from Dad Have different versions of the same genes Sister chromatids Bound at center by centromere Product of DNA replication Chromatids are identical

Chromosomes What’s a homologous pair? Chromosomes that code for the same traits They code for the same traits but each member of the pair has different information (different versions of the same genes)

Chromosomes (n) n refers to the number of pairs (or the number of different types of chromosomes) 2n refers to the total number of chromosomes In humans n = 23 In chimpanzees n = 24 In the king crab n = 104

Phases of Mitosis

Mitosis Interphase Prophase Metaphase Anaphase Telophase REPEAT (This process produces two identical cells. The process then repeats for each of the new cells.)

Mitosis

The Cell Cycle The repeating set of events that make up the life of a cell is known as the Cell cycle The life cycle of a cell consists of interphase and cell division Interphase occurs between cell divisions and includes G1phase- cell grows to mature size S phase- DNA is copied G2 phase- cell prepares for cell division Cell division consists of the M phase and Cytokinesis M phase- (Mitosis) where nucleus divides Cytokinesis- cytoplasm divides Some cells exit the cell cycle after interphase and enter the G0 phase, these cells are fully developed and never divide again

Mitosis Interphase Prophase DNA replication Centrioles replicate & become visible Cell spends most of life carrying on 8 life processes (all but reproduction) Prophase Chromatin condenses become visible as sister chromatids (chromosomes) Centrioles move toward the poles Asters & Spindle form Nuclear membrane disappears

Metaphase Anaphase Centrioles at opposite poles Chromosomes line up at metaphase plate/equator Spindles attach to each replicated chromosome at the centromere Anaphase Each of the sister chromatids separate at the centromere and move toward the opposite poles of the cell

Mitosis Telophase Cell divides  2 identical copies New Interphase begins And the process starts all over in each daughter cell Telophase Chromosomes decondense to chromatin Formation of cleavage furrow (animal cell), or cell plate (plant cell) spindle disappears New nuclear membranes form the cytoplasm divides in two, this is called cytokinesis

INTERPHASE - DNA replicates centrioles The steps of Mitosis: INTERPHASE - DNA replicates centrioles replicate; cell spends most of life (carries on all life processes except reproduction) PROPHASE - chromatin condenses into discrete chromosomes, centrioles move to poles, spindle forms; nuclear membrane disappears METAPHASE – chromosomes (attached to spindles @ centromere) are lined up at the equatorial plane (in the middle) ANAPHASE - Sister chromatids separate at the centromere and migrate to opposite poles. TELOPHASE - chromosomes decondense to chromatin, a cleavage furrow deepens in the middle of the cell, nuclear membranes form, spindle disappears. Finally, the cytoplasm divides in two, this is called cytokinesis. 2 form identical cells, Interphase begins.

Plant Mitosis vs. Animal Mitosis CELL PLATE NO CENTRIOLES NO ASTERS ANIMAL: CLEAVAGE FURROW CENTRIOLES ASTERS Animal & plant cell mitosis QT video clips

Reproduction Asexual reproduction (1 parent gives rise to 1 or more clones) Offspring are identical to the parents (Identical hereditary information) Accomplished by mitosis and cytokinesis Types of Asexual Reproduction Binary fission, budding, spore formation, regeneration, vegetative reproduction/propagation What are some examples of organisms that reproduce asexually? Amoeba, bacteria, sponge

BACTERIA Binary fission

PORIFERA (SPONGE) Budding (additional example= worms, yeast)

PLANARIA (FLATWORMS) Regeneration (additional example= starfish, earthworm)

HYDRA budding

AMOEBA Binary fission

https://youtu.be/4JIytOL-Q18

TULIP vegetative propagation/reproduction Small new buds sprout from old ones (additional example= onion, lily)

STRAWBERRY vegetative propagation/reproduction Uses “runners” (stem that grows sideways along ground and has buds)  new plant develops

POTATOES Vegetative propagation/reproduction Tuber: enlarged underground stem with stored food Eyes: tiny buds – send shoots upward – new plant

Geraniums / Poinsettias “cuttings”  vegetative part of plant (stem, leaf, root) placed in moist sand/water to develop roots Independent plant

Asexual reproduction advantages Genetically identical Cheaper Quicker