Cell Size and Division Quiz

Cell Size and Division

• Cell size is limited by the surface area-to-volume ratio. A smaller ratio limits the cell's ability to exchange materials efficiently.
• Cell volume determines the cell's needs and waste production.
• Surface area is the contact point for exchange of materials like oxygen, nutrients, and waste. More surface area allows for quicker exchange.
• Cell division solves the problem of size limitations creating two smaller cells.
• Cell division allows for growth, repair, and reproduction (in single-celled organisms).
• Daughter cells are created after cell division, genetically identical to the parent cell.

Asexual Reproduction

• Asexual reproduction creates genetically identical offspring from a single parent. It's a faster method for producing a large number of offspring.
• Prokaryotes use binary fission to reproduce asexually (one cell splits into two).

Interphase

• Interphase is the longest stage in the cell cycle, encompassing when the cell is not actively dividing. Interphase includes three phases:
  • G1 phase: Cell growth and preparation for DNA replication occurs.
  • S phase: DNA replication happens.
  • G2 phase: Additional cell growth and preparation for mitosis occurs.
• During interphase, the cell synthesizes proteins and grows, and the nucleus is visible.
• DNA amount & interphase: Initially, DNA amount is determined in G1, replication doubles it in S, and stays constant in G2; mitosis decreases the amount of DNA in the nucleus to original. (initial amount)

Chromatin and Chromosomes

• Chromatin: DNA and associated proteins in an unpacked state, important for gene expression and DNA replication.
• Chromosomes: Condensed chromatin, essential for movement during cell division.
• Histones are proteins that organize chromatin.
• Nucleosomes: DNA wrapped around histone proteins.

Mitosis

• Mitosis is the process of nuclear division (dividing of the nucleus). Parts of mitosis include:
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

Prophase

• Chromatin coils tightly into chromosomes.
• Chromosome consists of two sister chromatids.
• Sister chromatids contain identical DNA copies.
• Centrioles move to opposite poles of the cell.
• Spindle fibers form and connect to chromosomes at their centromeres.
• Nuclear envelope breaks down.
• Centrioles: Protein structures that organize the spindle apparatus.
• Spindle fibers: Proteins forming the spindle apparatus to organize and separate chromosomes.
• Nuclear Envelope: The membrane surrounding the nucleus; it breaks down during prophase.

Metaphase

• Chromosomes align at the cell’s equator.
• Metaphase plate: Equatorial location of chromosomes during Metaphase.

Anaphase

• Chromosomes separate at the centromeres.
• Chromatids separate becoming individual chromosomes.
• Chromosomes move to opposite poles.

Telophase

• Chromosomes reach opposite poles.
• Nuclear envelope reforms around each cluster.
• Chromosomes begin to uncoil.
• Spindle apparatus breaks down.

Cytokinesis

• Cytokinesis completes cell division by splitting the cytoplasm.
• Cleavage furrow: The indentation in the animal cell membrane that leads to its separation.
• Cell plate: The structure that forms in plant cells and develops into the cell wall during cytokinesis.

Cell Cycle Regulation and Cancer

• Regulator proteins control cell growth and division.
• Cancer is uncontrolled cell division due to lack of cell regulation.
• Unregulated cell division causes uncontrolled growth in cancer cells

Chromosomes

• Chromosomes vary in size, centromere position, staining patterns, and types of genes.
• Ploidy describes the number of chromosome sets in a cell.
  • Haploid, (1N) cells have one chromosome set.
  • Diploid, (2N) cells have two chromosome sets.

Humans

• Humans have 23 pairs of chromosomes (46 total) in somatic cells.
• Somatic cells are body cells, while gametes are sex cells with (23 chromosomes) (haploid).
• Autosomes are chromosomes other than the sex chromosomes.
• Sex chromosomes determine sex (XX = female; XY = male).
• Humans have 23 pairs of Chromosomes, all but one pair determine characteristics, not sex.

Meiosis

• Meiosis creates haploid gametes for sexual reproduction. This is a two-part cell division process.
• Meiosis is a Special type of cell division producing genetically different cells. Homologous chromosomes: Chromosomes that are alike in size and shape, but may carry different alleles.

Meiosis Stages

• Meiosis I: Separates homologous chromosomes.

  • Prophase I: Homologous chromosomes pair up (synapse) and exchange segments of DNA (crossing over).
  • Metaphase I: Tetrads align at the cell’s equator.
  • Anaphase I: Homologous chromosomes separate.
  • Telophase I and Cytokinesis: Two haploid daughter cells are formed.

• Meiosis II: Separates chromatids, similar to mitosis.

  • Prophase II: Chromosomes condense and spindle forms.
  • Metaphase II: Chromosomes align at the equator.
  • Anaphase II: Sister chromatids separate.
  • Telophase II and Cytokinesis: Four haploid daughter cells are produced.

Gamete Formation

• Males produce four equal-sized haploid sperm cells.
• Females make one large ovum (egg) and three smaller polar bodies (cells).

Fertilization

• Fertilization: Fusion of male and female gametes to produce a zygote.
• Zygote: A fertilized egg (diploid).
• Embryonic development: Zygote undergoes mitosis to form embryos.

Genetic Variation in Meiosis

• Meiosis generates genetic variation through:
  • Crossing over
  • Independent assortment (random alignment of chromosomes)
  • Random segregation of homologous chromosomes during anaphase I

Mitosis vs Meiosis

• Mitosis produces two diploid, genetically identical cells for growth and repair. (somatic)
• Meiosis produces four haploid, genetically distinct cells for sexual reproduction. (gametes/sex cells)