Chapter 8 Cellular Reproduction Flashcards

Basics of Cellular Reproduction

• Multicellular organisms originate from a single cell and grow through cellular reproduction.
• Cellular reproduction replaces worn-out or damaged tissues.

Important Processes

• Growth: Cell duplicates its contents, including DNA and organelles.
• Cell division: Parent cell divides into two daughter cells.
• Both processes are heavily regulated.

Asexual Reproduction

• All cells come from pre-existing cells.
• Reproduction occurs without sperm and egg.
• Examples:
  • Bacteria reproduce via binary fission.
  • California blackworm reproduces by fragmentation.

Binary Fission in Bacteria

• Prokaryotes (bacteria and archaea) reproduce through binary fission.
• Chromosome/DNA replicates, and daughter chromosomes move apart.
• Plasma membrane pinches inward, dividing the cell into two.

Cell Reproduction in Eukaryotes

• More complex than in prokaryotes.
• Eukaryotes have more DNA.
• DNA is wrapped around proteins, forming chromosomes.
• DNA replication copies DNA, passing a full set to each daughter cell.

Chromosomes

• DNA packaged into a thickened complex of DNA and protein.
• Allows easier distribution to daughter cells.
• Chromatin: DNA and associated proteins in thin threads.
• Sister chromatids: Identical DNA copies joined at the centromere.

Chromosome Compaction

• DNA winds around histones to form nucleosomes.
• Chromatin condenses into chromosomes before cell division.
• Humans have 46 chromosomes.
• Duplicated chromosomes consist of sister chromatids joined at the centromere; each has identical DNA.

Cell Cycle: Interphase, Mitosis, and Cytokinesis

• Cell cycle: Orderly sequence of stages from a new cell to its division into two daughter cells.
• Consists of interphase and M (mitotic) phase.

Cell Cycle Stages

• Mitotic (M) phase: Mitosis and cytokinesis.
• Interphase: Cell growth and chromosome copying for cell division.

Interphase

• Majority of the cell cycle; cell performs usual functions.
• Length varies widely.
• Stages: G1, S (DNA synthesis), G2.

Interphase Stages

• G1: Cell doubles organelles, accumulates materials for DNA synthesis, decides whether to divide (G0 is arrested).
• S: DNA synthesis results in chromosomes with two sister chromatids.
• G2: Proteins are synthesized for cell division.

M (Mitotic) Phase

• Division of nucleus (mitosis) into two genetically identical daughter nuclei.
• Followed by division of cytoplasm (cytokinesis).

Mitosis

• Division of one nucleus into two genetically identical nuclei.
• Conventionally divided into prophase, metaphase, anaphase, telophase.
• Cytokinesis overlaps latter stages of mitosis.

M (Mitotic) Phase Details

• Distributes duplicated nuclear contents equally to daughter cells.
• Daughter chromosomes are separated sister chromatids.

Mitosis Outcomes

• Daughter nuclei are genetically identical to each other and to the parent nucleus.

Spindle

• Eukaryotic cells use this structure to pull chromatids apart.
• Part of the cytoskeleton; spindle fibers are microtubules.
• Centrosome: primary microtubule organizing center.

Mitosis Phases

• Traditionally divided into four phases based on chromosome changes and movement:
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Followed by cytokinesis (division of cytoplasm).

Cytokinesis in Animal Cells

• Cleavage furrow forms as anaphase ends.
• Contractile ring (actin filaments) creates a constriction.

Cytokinesis Process

• Occurs via cleavage, forming a cleavage furrow.
• Contractile ring of actin microfilaments and myosin contracts.
• Cleavage furrow deepens until parent cell is pinched in two.

Mitosis Differences

• Plant cells: Spindle fibers but no clearly visible centrosome.
• Animal cells: Each centrosome has 2 centrioles and an aster.

Cytokinesis in Plant Cells

• Rigid cell wall prevents furrowing.
• New plasma membrane and cell walls are built between daughter cells.
• Golgi apparatus produces vesicles.
• Cell plate forms; new membrane releases molecules for new cell walls.

Plant Cell Cytokinesis Details

• Cell plate forms during cytokinesis.
• Vesicles from Golgi move along microtubules to the middle of the cell.
• They coalesce, forming a cell plate.
• Cell wall material is carried in vesicles and collects at the plate.
• The cell plate enlarges until its membrane fuses with the plasma membrane.

Cytokinesis Overview

• Accompanies mitosis in most cells.
• Mitosis without cytokinesis results in multinucleated cells.

Mitosis Summary

• Occurs in somatic cells.
• Used for growth, repair, and embryonic development.
• Produces two genetically identical daughter cells.
• Maintains the chromosomal number of the cell (diploid number).

Mitosis vs. Meiosis Differences

• Mitosis: One round of nuclear division, no synapsis or crossover events, duplicated chromosomes separate, maintains chromosome number.
• Meiosis: Two rounds of nuclear division, synapsis and crossover occur, reduces chromosome number.