Cell Growth and Division

Cell Division — process by which a cell divides into 2 new cells Why do cells need to divide? Living things GROW by producing more cells, NOT because each cell increases in size; If cell gets too big, it cannot get enough nutrients into the cell and wastes out of the cell REPAIR of damaged tissue REPRODUCTION

Types of Cell Reproduction Asexual reproduction - single cell dividing to make 2 new, identical daughter cells Ex: Mitosis & binary fission Sexual reproduction - egg & sperm joining to make a zygote, NOT identical to the original cells Ex: Meiosis

Cell Division in Prokaryotes (Binary Fission) Parent cell Chromosome (plasmid) doubles Cell splits 2 identical daughter cells

Animation of Binary Fission

Cell Division in Eukaryotes

Parent Cell 2 Daughter Cells Cell Division The original cell is called the parent cell; 2 new cells are called daughter cells Before cell division occurs , the cell replicates (copies) all of its DNA, so each daughter cell gets complete set of genetic information from parent cell Each daughter cell is exactly like the parent cell – same kind and number of chromosomes as the original cell 2 Daughter Cells Parent Cell

DNA DNA is located in the nucleus and controls all cell activities including cell division Long and thread-like DNA in a non-dividing cell is called chromatin Doubled, coiled, short DNA in a dividing cell is called chromosome Consists of 2 parts: chromatid and centromere

2 identical “sister” chromatids attach at an area in the middle called a centromere When cells divide, “sister” chromatids separate and 1 goes to each new cell

Coils up into chromosomes Chromatin to chromosomes illustration: Chromatin Coils up into chromosomes Duplicates itself Why does DNA need to change from chromatin to chromosome? More efficient division

Eukaryotic Chromosomes Eukaryotic cells store genetic information in chromosomes Eukaryotes can have 10 to 50 chromosomes in their body cells (somatic). Human body cells have 46 chromosomes or 23 identical pairs.

Chromosomes Every organism has its own specific number of chromosomes Human = 46 chromosomes or 23 pairs Dog = 78 chromosomes or 39 pairs Goldfish = 94 chromosomes or 47 pairs Lettuce = 18 chromosomes or 9 pairs

All somatic (body) cells in an organism have the same kind and number of chromosomes. Ex: Human = 46 chromosomes Human skin cell = 46 chromosomes Human heart cell = 46 chromosomes Human muscle cell = 46 chromosomes Fruit fly = 8 chromosomes Fruit fly skin cell = 8 chromosomes Fruit fly heart cell = 8 chromosomes Fruit fly muscle cell = 8 chromosomes

Cells prepare for Division Cell Divides into Identical cells The Cell Cycle DNA Copied Cells Mature Cells prepare for Division Daughter Cells Cell Divides into Identical cells

Interphase - G1 Stage 1st growth stage Cells mature by making more cytoplasm & organelles Cell carries on its normal metabolic activities

Two identical copies of DNA Interphase – S Stage Synthesis stage DNA is copied or replicated Two identical copies of DNA Original DNA

Interphase – G2 Stage 2nd Growth Stage Occurs after DNA has been copied Both organelles & proteins are synthesized

Mitosis Division of the nucleus Only occurs in eukaryotes Has four stages Doesn’t occur in some cells such as brain cells

1st Phase (Prophase) Longest Phase DNA and proteins condense (PACK) into chromosomes Nuclear membrane breaks apart (or pops)

1st Phase: DNA PACKS into Chromosomes

2nd Phase (Metaphase) Chromosomes line up across the center (middle) of the cell Spindle fibers attach at centromere

2nd Phase: Chromosomes line up in the MIDDLE of the cell

3rd Phase (Anaphase) Centromeres divide Spindle fibers shorten Sister chromatids separate (move apart) into individual chromatids Spindle fibers pull the chromatids to opposite sides of the cell Chromatids are now called Each ½ of the pair is now called a chromosome

3rd Phase: Chromosomes are pulled APART to opposite ends of the cell

4th Phase: (Telophase) Chromosomes gather at opposite ends of the cell and lose their shape Two new nuclear membranes form

4th Phase: TWO new cells are formed (still attached)

Cytokinesis Division of cell into two, identical halves called daughter cells In plant cells, cell plate forms at the equator to divide cell In animal cells, cleavage furrow forms to split cell

Mitosis Dance Review Discuss the following with your table:  1. What color shirts were the kids wearing who were part of the cell membrane? 2. The students in the white shirts represent what organelle? 3. What color shirts were the kids wearing who were the chromosomes? 4. What did the kids do during metaphase? 5. How many cells were there at the end of mitosis?

Uncontrolled Mitosis DNA controls all cell activities including cell division Some cells lose their ability to control their rate of cell division – the DNA of these cells has become damaged or changed (mutated) These super-dividing cells form masses called tumors

Benign tumors are not cancerous – these cells do not spread to other parts of the body Malignant tumors are cancerous – these cells break loose and can invade and destroy healthy tissue in other parts of the body (called metastasis)

Cancer is not just one disease, but many diseases – over 100 different types of cancers

Meiosis Formation of Gametes (Egg,Sperm,Pollen,Ovule)

Why Do we Need Meiosis? It is the fundamental basis of sexual reproduction Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote

Fertilization

Meiosis Daughter cells contain half the number of chromosomes as the original cell Produces gametes Occurs in the testes in males (Spermatogenesis) Occurs in the ovaries in females (Oogenesis) rossing-over occurs and causes greater genetic variety

Meiosis

Four sperm cells are made from meiosis. They are carrying one of each chromosome. Four eggs cells are made. Three are very small and called polar bodies. They die.

Meiosis Forms Haploid Gametes Meiosis must reduce the chromosome number by half Fertilization then restores the 2n number from mom from dad child meiosis reduces genetic content

This is a Karyotype. It shows the Homologous chromosomes.

Crossing-Over Homologous chromosomes in a tetrad cross over each other Pieces of chromosomes or genes are exchanged Produces Genetic recombination in the offspring

Why would genes on separate chromosomes be inherited differently than genes on the same chromosome? Independent assortment of chromosomes leads to greater genetic variety!

Genetic variation in sexually reproducing organisms 1. Crossing over- during meiosis, homologous chromosomes exchange DNA

Genetic variation in sexually reproducing organisms 2. Gene mutation- when the DNA changes 3. Fertilization- gametes join in sexual reproduction.

Genetic variation in sexually reproducing organisms 4. Nondisjunction - Occurs when the homologous chromosomes do not separate properly during meiosis. Results in a wrong # of chromosomes and conditions such as Down syndrome.

Comparison of Divisions Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 4 Genetically identical? Yes No Chromosome # Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction