Chapter 8 Cellular Reproduction Bio 103

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Binary fission

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is a type of cell division in bacteria produces two bacteria cells

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Asexual reproduction

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is new cells from an original and are identical to the original

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Sexual reproduction

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involves a sperm and egg introduces variation to the offspring

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Cellular reproduction involves two important processes

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growth and cell division during growth a cell duplicates its contents including the organelles and its DNA--The in cell division the DNA and other cellular contents of the parent cell are distributed to the daughter cells

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DNA replication

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is an import step of cellular reproduction a full copy of DNA is passed to the daughter cell

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To pass all of this DNA and associated proteins they are packaged into

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a set of choromesomes

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DNA and associated proteins have the apperance of thin threads called

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chomatin

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Chromatin is wound around a core of eight protein molecules so that it looks like beads on a string

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these are called Histones which are protein molecules each bead is called a nuleosome

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The chormatin before cell division condenses multiple times into large loops which produce

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highly compacted Chromosomes each species has a characteristic number of chromosomes a human cell had 46

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By the time we can clearly see the chromosome, they are duplicated

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a duplicated chromosome is composed of two halves, called sister chromatids held together by at a constricted reagion called a centromere--each sister holds an identical DNA double helix

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To pass all of this DNA and associated proteins they are packaged into

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a set of choromesomes

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DNA and associated proteins have the appearance of thin threads called

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chomatin

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Chromatin is wound around a core of eight protein molecules so that it looks like beads on a string

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these are called Histones which are protein molecules each bead is called a nuleosome

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The chormatin before cell division condenses multiple times into large loops which produce

Back 14

highly compacted Chromosomes each species has a characteristic number of chromosomes a human cell had 46

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By the time we can clearly see the chromosome, they are duplicated

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a duplicated chromosome is composed of two halves, called sister chromatids held together by at a constricted reagion called a centromere--each sister holds an identical DNA double helix

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The Cell cycle

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is an orderly sequence of stages that take place between the time a new cell has arisen from the division of the parent cell to the point when it has given rise to two daughter cells

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interphase

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this is the time when a cell performs its usual functions depending on its location within the body this amount of time varies widely

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Embryonic cell complete the entire cell cycle in a few hours

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a rapidly dividing mammalian cell such as adult stem cell typically takes typically about 24 hours to complete the cell cycle 22hour interphase

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DNA replication occurs in the middle of interphase and serve as a way to divide interphase into 3 stages

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G1, S and G2
G1 is the phase before DNA replication-organelles begin to double
G2 is the phase following DNA replication--cell prepares to divide
S DNA replication occurs as chromosome duplicate

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Some cells after reaching typically remain in interphase and cell division is arrested

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they are said to have entered G0 phase---muscle and nerve cell

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At the beginning of S phase each chromosome has one chromatid consisting of a single one double helix

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at the end of this stage each chromosome is composed of two sister chromatids they remain attached at the centromere

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G2 phase extends from the completion

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of DNA replication to the onset of mitosis

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Mitotic Phase or (M) phase

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cell division occurs in this phase which encompasses both division of the nucleus and division of the cytoplasm

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The type of nuclear division associated with the cell cycle is called`

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mitosis as a result of mitosis the daughter nuclei are identified to the parent cell and each other they have the same type and number of chromosomes

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Division of the cytoplasm which starts before mitosis is finished is called

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cytokinesis

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Most eukaryotic cells have a even number of

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Chromosomes because each parent has contributed half of the chromosomes to the new individual

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Most eukaryotic cell rely on a

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spindle, a cytoskeletal structure to pull the chromatids apart

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A spindle has spindle fibers made of microtubules that are able to assemble and disassemble

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First the microtublesw assemble to form the spindle that takes over the center of the cell and seperate the chromatids later they diasemble

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A centrosome is the

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primary microtubule organizing center of a cell

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In an animal cell each centrosome has two barrel-like structures

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called centrioles vand an arry of microtubles called an aster

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Plant cells cells have centrosomes

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but they are not as clearly marked because they lack centrioles

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During M phase the Centrosomes which started to double in s phase and completed in G2

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now seperate and move to opposite sides of the nucleus. where they form poles of the spindle

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As the nuclear envelope breaks down spindle fibers

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take over the center of the cell Some overlap at the spindle equator which is midway between the poles

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Others attach to duplicated chromosomes in a way that ensures the

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separation of the sister chromatids and their proper distribution to the daughter cells

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Mitosis is divided into a sequence of events even though it is a continuous process

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The stages are: Prophase, metaphase, anaphase, telophase.

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Metaphase

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during this phase the chromosomes are aligned at the spindle poles. the spindle fibers on either side of a chromosome extend to opposite poles of the spindle. Unattached spindle fibers reach beyond the equator and overlap

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Prophase

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the chromosomes are condensing. the two sister chromatids held together at a centromere Outside the nucleus the spindle begins to assemble between the separating centrosomes

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Anaphase

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This phase the sister chromatids separate and become daughter chromosomes. the spindle fibers attached to the chromosomes disassemble each pole receives a set of daughter chromosomes

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Telophase and Cytokinesis

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the spindle disappears as a new nuclear envelopes form around the daughter chromosome Spindle fibers are still visible between the two nuclei division of the cytoplasm begins

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In most cells, cytokinesis follows mitosis when mitosis occurs but cytokinesis doesn't result

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we have a multinucleated cell for example skeletal muscle cells in vertebrate animals and the embryo sac in flowering plants are multinucleated

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Cytokinesis

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a cleavage or furrow appears as early as anaphase and a contractile ring, composed of actin filaments gradually gets smaller until there are two cells

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Cell plate or Cytokinesis in plant cells

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is simply newly formed plasma membrane until it reaches the old plasma membrane and fuses with it.

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Cell Cycle Checkpoints

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checkpoints can delay the cell cycle until certain conditions are met

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G1 checkpoint

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if the cell cycle passes this checkpoint, the cell is committed to divide--if the cell does not pass this point it can enter G0 where it performs its normal functions

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If the DNA protein is damageed

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the cell can try to repair it or under go programmed cell death or apoptosis

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Cytokinesis

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a cleavage or furrow appears as early as anaphase and a contractile ring, composed of actin filaments gradually gets smaller until there are two cells

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Cell plate or Cytokinesis in plant cells

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is simply newly formed plasma membrane until it reaches the old plasma membrane and fuses with it.

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Cell Cycle Checkpoints

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checkpoints can delay the cell cycle until certain conditions are met

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G1 checkpoint

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if the cell cycle passes this checkpoint, the cell is committed to divide--if the cell does not pass this point it can enter G0 where it performs its normal functions

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If the DNA protein is damaged

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the cell can try to repair it or under go programmed cell death or apoptosis

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G2 Checkpoint

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the cell cycle halts briefly until the cell verifies that the DNA has been replicated

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Another checkpoint takes place during the metaphase and anaphase

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to make sure the chromosomes are properly attached to the spindles

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The checkpoints are controlled by internal and external signals

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A signal is a molecule that stimulates or inhibits an event

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cyclins

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are internal signals

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kinases

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remove phosphates from ATP and add it to another molecule this acts as an on/off switch

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Some external signals

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such as hormones stimulate cells to go through the cell cycle

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the cell cycle can be

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inhibited by cells cells coming into close contact with other cells this is called contact inhibition

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A Telemere

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is a repeating DNA base sequence they are like the protective caps at the end of shoelaces Telomores are lost with each cell division when they become to short the cell is old and dies

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Apoptosis is how an old cell dies

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is often called programmed cell death because the cell through a typical series of events that bring about its destruction

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Cell division and apoptosis

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are two opposing processes that keep the number of cells in the body at an appropriate level

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Cancer

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cancer is a disease of the cell cycle in which cellular reproduction occurs repeatedly without end

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Carcinogenesis

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the developement of cancer is gradual it may take decades before a tumor is visible

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Cancer cells lack differentiation

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cancer cells lose their specialization and do not contribute to the function of a body part

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Cancer cells have abnormal nuclei

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the nuclei of the cancer cell are enlarged and may contain abnormal number of chromosomes

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cancer cells do not undergo apoptosis

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ordinarily cells with damage DNA undergo apoptosis

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Cancer Cells form tumors

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they do not stop reproducing as in contact inhibition forming multiple layers that are tumors

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Cancer cells undergo metastasis and promote angiogenesis

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a benign tumor is usually contained in a capsule and does not affect other tissue---Additional enezymes may cause the capsule to allow the tumor cells to escape the tumor is now malignant

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Malignant means the tumor may now enter other parts of the body and start new tumors this is called

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metastasis

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An actively growing tumor can grow only so large before it become unable to obtain sufficient nutrients to support further growth

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additional mutations in the cancer cells allow them to secrete factors that promote angiogenesis the formation of new blood cells to gain addition nutrients and oxgen

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Cancer prevention

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Preventive behaviors aviod smoking sunbathing and excessive alcohol consumption
Protective diet eat Vitamins A and C Avoid salt cured or pickled foods also Nitrates