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Home , Aster (cell biology), G1 phase, G2 phase, Kinetochore

Human Skin (Epidermis) Replacement Hydra Top layers = dead cells ●Multicellular organisms: Are constantly shed –Growth

–Cell replacement and repair

–Asexual reproduction Middle Layers = Living Cells Replace dead cells ●Unicellular organisms:

–Reproduction (asexual) Bottom Layers = Dividing Cells Replace living cells

Kinetochore Chromosomes = ●All chromosomes have a partner, condensed DNA w/ ●These pairs of chromosomes are called homologous during cell division chromosomes and contain genes for the same traits

●During cell division, a single chromosome consists of 2 identical

sister

Chromosomes Chromosomes = uncondensed DNA with associated proteins ●Humans have 46 = proteins that help maintain shape of chromosomes / 23 pairs chromosome and aid in packing ●Most chromosomes are

called autosomes

●Karyotype = photo- micrograph of

chromosomes Chromosomes Cell Division

●Chromosomes which determine sex are called sex – 2 types: = division of the nucleus,

chromosomes results in 2 identical diploid “daughter” cells

●In humans these are called X and Y = division to produce gametes = sex cells, results in 4 haploid gametes ●Diploid vs. haploid: in humans: normal cells = diploid - have 46 chromosomes (23 pairs) sex cells = haploid - have 23 chromosomes

Cell Division

●Prokaryotes ●Cytokinesis = the division of

the cytoplasm ●all are unicellular so division = reproduction ●Happens at the same time as

mitosis (and meiosis) ●called Binary Fission

●Except in cells with multiple

nuclei

●Animals – cells pinch inward

The Cytokinesis •4 stages for cells

●In – new cell wall forms that divide:

•G1 ●Called a cell plate

•S

•G2

•M •1 for cells that

don't:

•G0 The Cell Cycle The Cell Cycle

●G1 phase – Gap 1 ●G2 phase – Gap 2

– –continued cell growth

–organelles duplicate ●M phase – Mitosis and Cytokinesis

● – Synthesis –cell division

–DNA is replicated

The Cell Cycle The Cell Cycle

●Controlled by checkpoints ●M checkpoint – checks to see if spindle is assembled, checks to see if chromosomes are ●G1 checkpoint – checks to see if DNA is aligned properly damaged

●If the cell fails a checkpoint, either the problem ●G2 checkpoint – checks to see if DNA was (ex. damaged DNA) is fixed (DNA is repaired) replicated properly or the cell undergoes

Mitosis

●I+PMAT+C (not condensed)

●Before Mitosis → Interphase

● → → →

●During/after Mitosis → Cytokinesis

●Mnemonic device: Internet President Milford Ate Tacos Constantly

–Or, Interesting People Make A Terrific Conversation Prophase Chromosome Prophase detailed consisting of Pair of ●During prophase: two sister –the breaks down and chromatin chromatids condense

(Condensed) –Spindle fibers attach to chromosomes at

Centromere

Aster

Prophase

Prophase detailed Metaphase Nonkinetochore ●Two types of spindle fibers microtubules –Kinetochore microtubules = attach to kinetochore proteins at of chromosomes / move chromosomes

–Nonkinetochore microtubules = attach to other Mitotic nonkinetochore microtubules from other side of the cell / lengthen cell to prepare for cytokinesis

Chromosomes line up in the

center

Anaphase Telophase & Cytokinesis Sister Cell pinches inward in chromatids the center, separate 2 nuclei begin and move to reforming opposite ends of the cell Telophase & Cytokinesis detailed Telophase & Cytokinesis detailed

●During telophase & cytokinesis: - In plants, cell plate forms which will become new cell wall - 2 new daughter cells are formed –Nuclear envelope reforms & chromosomes uncoil into

chromatin

–Mitotic spindle breaks up

– furrow forms (pinching inward of plasma

membrane)

Mitosis in actual cells Factors Affecting Cell Division

●Growth factors (hormones) stimulate

growth/division

●Anchorage – cells need to be attached to a surface

●Cell density – if cells touch each other they stop

growing

●Checkpoints in the cell cycle

The Cell Cycle and Checkpoints Density of Cells - Growth factors control whether cells can pass checkpoints and divide G1 checkpoint

M checkpoint G2 checkpoint Tumors Tumors ●Form when mutations in DNA cause ●may be benign = non-cancerous, remain in place

checkpoint system to malfunction –cysts, warts and moles are all benign tumors

●Cells grow without growth factors and despite ●tumors can also be malignant = uncontrolled dividing

a high density cells that invade and destroy healthy tissues

●When cells grow out of control they form a –called cancerous tumors or just tumor = abnormal growth of cells caused by

uncontrolled cell division

Types of Cancer Causes of Cancer

●Carcinoma = in the skin or cells that line organs ●Mutations in DNA that mess up how the cell regulates

division ●Sarcoma = grow in bone and muscle tissue –can be spontaneous mutations

– ●Lymphoma = solid tumors in tissues that form blood cells mostly caused by Carcinogens = any substance that increases the risk of cancer –can cause Leukemia = uncontrolled production of white blood cells

Causes of Cancer Meiosis ●many carcinogens are mutagens = cause ●Meiosis = cell division which reduces the number of

mutations to occur in cells chromosomes

–examples: tobacco, asbestos, X-Rays, UV ●Divides twice: Meiosis I and Meiosis II

radiation ●Produces 4 daughter cells ●cancer risk and incidence increases with

exposure to carcinogens and age Meiosis Meiosis

●4 daughter cells: Are haploid ●Essential for sexual ●Have unpaired chromosomes reproduction – gametes ●Are not identical to each other combine in the process of ●Most are gametes = sex cells (sperm and egg) fertilization to form a diploid

zygote Diploid parent cell

●The reduction in chromosomes allows the zygote and thus the offspring

to be diploid Haploid daughter cells

Sexual Reproduction The Phases of Meiosis

23 Before Meiosis → still have Interphase chromosomes ●Meiosis I ●Meiosis II in humans –Prophase I –Prophase II 46 chromosomes –Metaphase I –Metaphase II in humans –Anaphase I –Anaphase II

–Telophase I & –Telophase II & ●Zygote is the first cell in the new organism Cytokinesis I Cytokinesis II

●Offspring = new organism (aka child)

Interphase (Before Meiosis) Chromosomes review Kinetochore ●During cell division, a single proteins chromosome consists of 2 identical

●All chromosomes have a partner,

●These pairs of chromosomes are called homologous chromosomes ●Ordinary cell processes (G1 and G2) and contain genes for the same ● DNA is replicated (S) traits ●Pretty much the same as interphase before mitosis Prophase I of Meiosis I Metaphase I of Meiosis I Spindle fibers Nonkinetochore centrioles

microtubules Kinetochore microtubules

●Tetrads line up in the middle of the cell

●Synapsis occurs = homologous chromosomes ●Chromosomes are lined up 2 by 2

pair up to form a tetrad ●Homologous chromosomes next to each other

●Crossing over occurs at chiasma

Anaphase I of Meiosis I Telophase I & Cytokinesis I of Meiosis I

Cleavage furrow

●Cytokinesis divides the cytoplasm to form 2 cells ●Homologous chromosomes separate and ●Most cells undergoing meiosis I proceed directly into move to opposite ends of the cell meiosis II

●Nuclei don't really fully reform

Homologous chromosomes Crossing Over Crossing over = the exchange of genes Chiasma between homologous chromosomes These genes are for the same trait but may Crossing over occurs during be a different version Ex. - gene for the trait prophase I of meiosis I hair color may be for New recombined chromosomes brown or black hair The 4 chromosomes that end up in the 4 daughter cells after meiosis Prophase II of Meiosis II Metaphase II of Meiosis II

●Essentially the same as prophase in mitosis, except: ●Chromosomes line up in the center of the cells ●2 cells

●cells don't have a full set of chromosomes ●Essentially the same as metaphase in mitosis

Anaphase II of Meiosis II Telophase II and Cytokinesis II of Meiosis II

●Chromosomes separate and the sister chromatids

move to opposite ends of the cell ●4 unique haploid daughter cells produced

●Essentially the same as anaphase in mitosis

Independent Assortment Importance of Genetic Variation

●Homologous chromosomes line up randomly during ●Allows for variations in traits amongst individuals in a metaphase I of meiosis I and separate randomly population during anaphase I of meiosis I

●Helps ensure survivability of a population and species ●Results in increased genetic variation

●ex. A factor (disease, predator, etc.) that effects an individual with a particular trait will only effect those

that have the trait

●Necessary for evolution Sources of Genetic Variation

●Independent assortment

●Crossing over

●Meiosis producing non identical cells w/ unpaired chromosomes

●Sexual reproduction