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Law_Sherrice_B5_MM8 (The mitotic phase alternates with interphase in the…
Law_Sherrice_B5_MM8
The mitotic phase alternates with interphase in the cell cycle
Phases of the Cell Cycle
Mitotic phase (mitosis and cytokinesis)=shortest
interphase=90%
Cell grows and copies chromosomes in preparation for cell division
G1, S (Synthesis/duplicate), G2
Grows by producing proteins and cytoplasmic organelles (like mitochondria and ER)
1 division in 24 hours
M is less than an hour while S is 10-12 hours
The Mitotic Spindle: A Closer Look
Interphase: centrosome replicates
Each two sister chromatids has kinetochore (proteins with specific sections of chromosomal DNA at the centromere)
Non kinetochore microtubules are responsible for elongating the cell during anaphase
Motor proteins fueled by ATP walk on them and push spindle poles apart
Cytokinesis: A Closer Look
Aka cleavage
First sign is cleavage furrow
Actin interact with myosin causing ring to contract
In plant cells, there is no cleavage furrow
Cell walls carry vesicles in the cell plate as it grows
Cell plate enlarges and surrounding membrane fuses with plasma membrane
Binary Fission
Prokaryotes (bacteria and archaea)
Replicate DNA at specific part on chromosome
Evolution of Mitosis
Came from binary fission
The cell cycle is regulated by a molecular control system
Evidence for Cytoplasmic Signals
Can be stimulated by chemicals in cytoplasm
The Cell Cycle Control System
Cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle
3 checkpoints in G1, G2, M
Most cells are in G0 stage
The Cell Cycle Clock: Cyclins and Cyclin Dependent Kinases
Protein kinases are enzymes that activate or inactivate other proteins by phosphorylating them
Gives go ahead signal in G1 and G2
Must attach to cyclin to be active
MPF corresponds to concentration of cyclin
Rises during S and G2, falls during M
Acts like kinase and can activate others
Stop and Go Signs: Interval and External Signals at the Checkpoints
When kinetochores of all chromosomes are attached to spindle, sister chromatids can separate
Growth factor=protein released by certain cells that stimulate other cells to divide
Effect of external physical factor on cell division is in density dependent inhibition
When cell pop reaches certain density, availability of nutrients becomes insufficient to allow continues cell growth and division
Animal cells show anchorage dependence
Loss of Cell Cycle Controls in Cancer Cells
Cancer cells divide excessively and invade other tissues
No density dependent inhibition
Stop dividing at random points, not checkpoints
Begins when cell in tissue goes under transformation (conversion of normal to cancer cell)
Abnormal cells remain in original site=benign tumor
Malignant tumor becomes invasive to impair functions of one or more organs
Spread of cancer cells to locations distant from their original site=metastasis
High energy radiation damages DNA in cancer cells bc lost ability to repair
Cell division results in genetically identical daughter cells
The Key Roles of Cell Division
The continuity of life based on reproductive cells=cell division
Part of the cell cycle (life of a cell from formation from diving parent cell into 2)
Cellular Org of the Genetic Material
Cells establishment of DNA=genome
DNA packaged in chromosomes
Somatic cell (all body cells except reproductive) contain 46 chromosomes (2 sets of 23, one from each parent)
Reproductive cells (gametes) have one set of 23 chromosomes
Eukaryotic chromosomes are made of chromatin (complex of DNA and associated with protein molecules)
Helps maintain structure of chromosomes and gene activity
Distribution of Chromosomes During Cell Division
Once sister chromatids separate, they are considered individual chromosomes
Mitosis (division of nucleus) followed immediately by cytokinesis (division of cytoplasm)
Meiosis yields non identical daughter cells and occurs in gonads (ovaries or testes)
Offspring acquire genes from parents by inheriting chromosomes
Hereditary Similarity and Variation
heredity=transmission of traits from one gen to next
Inheritance of Genes
Genes are segments of DNA
Gametes transmit genes when sperm and egg fertilize
locus=a gene’s specific location along the length of a chromosome
Comparison of Asexual and Sexual Reproduction
Asexual: passes copies of all genes
Mitotic cell division
Budding
Sexual: unique combinations of genes
Fertilization and meiosis alternate in sexual life cycles
Sets of Chromosomes in Human Cells
Life cycle is gen to gen sequence of steps in reproductive history of an organism
Karotype
2 chromosomes have the same length, centromere position, and staining pattern
Homologous chromosomes
Carry genes controlling same inherited characters
XX and XY (sex chromosomes vs autosomes)
Any cell with 2 sets of chromosomes=diploid cell (2N)
Haploid cells (N)=23 chromosomes (22 autosomes and 1 sex chromosome)
Behavior of Chromosome Sets in the Human Life Cycle
Fertilized egg=zygote is diploid bc 2 haploid sets of chromosomes
The Variety of Sexual Life Cycles
Plants and some algae have alternation of gens
Both diploid and haploid stages
diploid =sporophyte (meiosis produces spores)
haploid=gametophyte
Either haploid or diploid can undergo mitosis, but only diploid can undergo meiosis
Meiosis reduces the number of chromosome sets from diploid to haploid
A Comparison of Mitosis and Meiosis
Synapsis and crossing over
In prophase I
Tetrads on metaphase plate
Metaphase I
Separation of homologues
Anaphase
Meiosis I is reductional division bc halves the number of chromosomes per cell
Genetic variation produced in sexual life cycles contributes to evolution
Origins of Genetic Variation Among Offspring
Independent Assortment of chromosomes
Random orientation of homologous pairs of chromosomes at metaphase I
50% chance to get paternal or maternal chromosome
8 million possible combinations of chromosomes inherited from parents
Crossing Over
Produces recombinant chromosomes (individual chromosomes that carry genes from 2 different parents)
Random Fertilization
Over 70 trillion combinations in a zygote
Evolutionary Significance of Genetic Variation Within Pops