A&P - 3.5 Cell Growth & Division

cell cycle

• life cycle of a single cell, from its birth until its division into two new daughter cells

• the two major phases of the cell cycle include mitosis (cell division), and interphase, when the cell grows and performs all of its normal functions

  • mitosis and interphase are both further subdivided

checkpoint

progress point in the cell cycle during which certain conditions must be met in order for the cell to proceed to a subsequence phase

interphase

• entire life cycle of a cell, excluding mitosis

• phases:

  • G₁

  • G₀

  • S

  • G₂

interphase: G₀

• phase of the cell cycle, usually entered from the G₁ phase; characterized by long or permanent periods where the cell does not move forward into the DNA synthesis plate

• cells not actively dividing

interphase: G₁

• first phase of the cell cycle, after a new cell is born

• the cell grows in volume, performs its normal functions, undergoes protein synthesis, and duplicates its organelles

interphase: S

“DNA synthesis” - DNA replicates itself

DNA replication

• process of duplicating a molecule of DNA

  • single-stranded chromosomes form double-stranded chromosomes

  • helicase unwinds and unzips the DNA

  • DNA polymerase binds to the DNA and attaches complimentary nucleotides (A always binds to T while C always binds to G)

  • the daughter DNA is built continuously on the leading strand but discontinuously on the lagging strand

  • Okazaki fragments produced on the lagging strand are “glued” together by ligase

  • two daughter strands of DNA are produced with each having half of the original strand (semi-conservative replication)

helicase

enzyme that functions to separate the two DNA strands of a double helix during DNA replication

DNA polymerase

enzyme that functions in adding new nucleotides to a growing strand of DNA during DNA replication

homologous chromosome

• the chromosomes in a homologous pair each have the same genes in the same order, but there may be variation between them, resulting in different alleles

• homologous: describes two copies of the same chromosome (not identical), one inherited from each parent

single-stranded vs. double-stranded chromosome

• single-stranded: does not typically exist in living cells, the term refers to a single-stranded DNA, which is a DNA molecule consisting of one chain of nucleotides instead of the usual double helix

  • important for DNA REPLICATION

• double-stranded chromosome: chromosomes composed of two identical sister chromatids joined at the centromere, which occurs after DNA replication in preparation for cell division

sister chromatid

• each strand of the double-stranded chromosomes is called a sister chromatid

• one of a pair of identical chromosomes, formed during DNA replication

centromere

region of attachment for two sister chromatids (holds sister chromatids together)

kinetochore

region of the centromere where microtubules attach to a pair of sister chromatids (forms on the centromere)

interphase: G₂

• third phase of the cell cycle, after the DNA synthesis phase

• the cell prepares itself for division by making necessary protein

mitotic phase

phase of the cell cycle in which a cell undergoes mitosis

cell division

• mitosis followed by cytokinesis

• the stages of cell division oversee the separation of identical genetic material into two new nuclei (mitosis), followed by the division of the cytoplasm (cytokinesis)

mitosis

• division of the genetic material, during which the cell nucleus breaks down and two new, fully functional, nuclei are formed

• occurs in all somatic cells (body cells) for the purpose of repair and replacement

somatic cell

all cells of the body excluding gamete cells (sex cells)

stages of mitosis

• prophase

• metaphase

• anaphase

• telophase

prophase

• first stage of mitosis, characterized by breakdown of the nuclear envelope and condensing of the chromatin to form chromosomes

• three changes characterize this phase:

  • nuclear membrane breaks down

  • double-stranded chromosomes condense and become visible

  • spindle fibers form (mitotic spindle)

mitotic spindle

network of microtubules, originating from centrioles, that arranges and pulls apart chromosomes during mitosis

metaphase

• second stage of mitosis, characterized by the linear alignment of sister chromatids in the center of the cell

• “middle”:

  • spindle fibers attached to the kinetochore begin pulling on the chromosome

  • double-stranded chromosomes line up in the middle of the cell called the metaphase plate

metaphase plate

linear alignment of sister chromatids in the center of the cell, which takes place during metaphase

anaphase

• third stage of mitosis, during which sister chromatids separate into two new nuclear regions of a dividing cell

• “apart”:

  • chromatids get pulled apart

  • single-stranded chromosomes migrate to opposite ends of the cell

telophase

• final stage of mitosis, preceding cytokinesis, characterized by the formation of two new daughter nuclei

• reverse of prophase:

  • nuclear membrane reforms

  • single-stranded chromosomes decondense and disappear

  • spindle fibers break down

cytokinesis

• final stage in cell division, where the cytoplasm divides to form two separate daughter cells

• division of cytoplasm into two cells

  • telophase is the end of nuclear division but overlaps cytokinesis

• creates cleavage furrow around the equator of cell

• cell eventually pinches in two

• completion of cytokinesis marks the end of cell division

cleavage furrow

contractile ring that forms around a cell during cytokinesis that pinches the cell into two halves

daughter cells

two daughter cells are produced and each daughter cell has the same number of chromosomes as the parent cell