Cell likes to stay compact so its more efficient. Less odds things get list in the extra space. Waste & nutrients need to to travel fast in and out of the cell.

Surface Area / Volume Ratio Problem

Volume increases faster than the surface area. Not enough membrane to handle the size of the cell if it grows too big.

Reasons Cells Divide

• Growth - adding new cells.
• Repair - replace damaged or dead cells.
• Reproduction - how single celled organisms reproduce.

Meiosis

For sperm/egg cells.

Only used for reproduction.

Produces Gametes.

Mitosis

For growth - any other types of cell.

Cell Cycle

• Interphase = 90% of the cycle
  • Includes the normal function of the cell.
  • The cell exists and performs its functions.
• Mitosis/Cytokinesis
  • Segregate chromosomes/split cells.

Interphase

• The cell does its specialized job.
• Makes proteins
• Copies its dna
• Grows larger
• Prepares to divide.
• DNA is copied before it divides, so each daughter cell gets a full set.

M Phase

• Divided into two parts: Mitosis and Cytokinesis

Mitosis

• Splitting nucleus/dna.

Cytokinesis

-Splitting cytoplasm + everything else (the entire cell).

Cells that divide can recover from injury - cells that don't divide (neurons) result in permanent damage when injured.

DNA Organization

• Genes = area (subset) of dna that is read into proteins.

Chromatin

Level 1 Organization

• DNA wrapped around proteins called histones (like beads).
• Chromatins can be open (loosely packed) or closed (tightly packed).
• Open chromatin is used (to be read by rna and make proteins).
• Closed chromatins are kept tightly packed for storage and safety.

Chromosomes

Level 2 Organization

• Super-condensed organized dna + protein structure.
• DNA can't be read, but it is tightly packed for efficient movement and transport.
• Loose dna could get tangled or break.
• Humans have 23 pairs of chromosomes (46 total).
  • The number of chromosomes does not relate to the complexity.
• Homologous chromosomes:
  • They have the same shape so they match up (1 from mom, 1 from dad).

Homologous Pairs have the same genes in the same locations (though the genes may not be exactly identical).

Genes are always matched up when copied.

Sister Chromatids

Mitosis

• Before mitosis = homologous pairs (one from mom, one from dad) (single chromatids)
• Chromosomes are copied (still are chromosomes) into 2 identical chromatids.
  • In a homologous pair, 2 identical chromatids from mom, 2 identical chromatids from dad in each chromosome pair.

1 Centromere = 1 Chromosome

• Same if a single chromatid before mitosis and is used to pair together sister chromatids after mitosis begins.

Centromeres are build outside of nucleus and spindle fibers have to cross nuclear envelope (why it is broken down) to attach spindle fibers.

Centrosomes

• Exist on opposite poles of the cell, outside the nucleus.
• They extend spindle fibers that grab sister chromatids and pull them apart.

Mitosis

P.M.A.T

• Every cell except for sperm and egg cell uses this process.

Prophase

Pre

• DNA Condenses
• Nuclear envelope breaks down.
• Spindle fibers emerge from centrosomes.

Pro-metaphase

Pre

Continuation of prophase.

Metaphase

Middle

Spindle fibers are attached and they line up the chromosomes in the middle of the cell (along the equator).

Anaphase

Apart

Spindle fibers pull apart chromosomes, now twice as many chromosomes. Centromeres duplicate as well.

Telophase

The End

. Chromosomes start condensing back into chromatin.

• Nuclear envelope re-emerges around each set of chromosomes
  • Still all in the same cell.

Cytokinesis

• Cells officially split
• Cells divide their contents into 2 new cells.

Chromosomes are only used for mitosis. For normal cell function, they de-condense into chromatin.