CELL CYCLE

The Cell Cycle

• Cells must divide to maintain maximum efficiency.

• Mitosis is the process in which somatic (body) cells divide to form a new cell.

• Mitosis consists of four phases.

• Interphase is the period in between each mitotic cell division.

Reproduction

• Asexual Reproduction: A single cell or group of cells each duplicates its genetic material and then splits into two new genetically identical cells. – The offspring are genetically identical

• Sexual Reproduction: Genetic material from each of two parents combines, producing offspring that differ genetically from either parent. – Involves the union of sex cells (egg and sperm)

Cell division = One cell makes two cells

Parent cell

DNA replicates

Two daughter cells are genetically

identical to each other and to parent

cell = clones

Chromatin = uncondensed DNA Chromosome = condensed DNA

The same DNA can appear in two forms

1 Chromosome 1 chromatid per chromosome

1 DNA double helix

1 Chromosome 2 chromatids per chromosome

2 DNA double helices

DNA replication

Cell division in eukaryotic cells:

Cytokinesis = division of the cytoplasm

Interphase

• Interphase is made of 3 stages.

• The Gap 1 and 2 or G1 and G2 phase is when cells grow and make RNA, proteins, and other macromolecules.

• The S or Synthesis phase is when the cell is making DNA.

DNA Replication

• During the S phase of the cell cycle, DNA replicates.

• A short section of the DNA uncoils.

• New nucleotides bond to the open sections of the DNA.

• The “new” and “old” sections of DNA separate and now there are 2 DNA strands.

Interphase

• ATP is synthesized.• Damaged parts are repaired.• Wastes are excreted.• Proteins are made.• Organelles are formed.• Chromosomes are copied.• Specialized tasks are performed .

DNA = Chromatin

Interphase nucleus

Interphase

Chromatin in nucleus

Mitosis

• Mitosis consists of four phases• Prophase• Metaphase• Anaphase• Telophase

Prophase

• Longest phase.• Chromatin coils.• Nucleus disappears.• Centrioles migrate.• Spindle forms.

Prophase

Nuclear membrane disappears

Nucleolus disappears

Chromatin condenses into chromosomes

Spindle fibers appear

Chromatin

Chromosomes

Metaphase

• Chromatids attach to spindle fibers.

• Chromatids migrate to equator of spindle.

MetaphaseChromosomes line up in center of cell

Chromatids (DNA double helix)

Two chromatids per

chromosome

Centromere = holds chromatids together

Anaphase

• Centromere splits.

• Chromatids are separated.

• Chromatids are now called chromosomes.

Anaphase =

Sister chromatids separate from each other

Telophase

• Cytoplasm divides.

• Nucleus reappears.

• Chromosomes uncoil.

Telophase

Cytokinesis makes 2 new cells

Chromosomes decondense into chromatin

Nucleolus reappears

Nuclear membrane reappears

Early Telophase

Late Telophase

Cytokinesis

• In the process called cytokinesis, the cytoplasm divides and two identical daughter cells are formed.

Animal cell membranes

pinches together

between two new cells

Plant cell wall grows

between two new cells

Cytokinesis

Plant Cytokinesis =

division of cytoplasm

Interphase

Telophase

AnaphaseMetaphase

Telophase

Telophase

ProphaseProphase

http://www.unm.edu/~asmund/mitosis.jpg

Interphase

Animal cytokinesis = pinching of plasma

membrane Late Telophase

Early telophase

Anaphase

Prophase Metaphase

Plant or Animal cell

mitosis?

Plant