The Cell Cycle Where a cell exists there

The Cell Cycle “Where a cell exists, there must have been a preexisting cell, just as an animal arises only from an animal and the plant only from a plant. ” - R. Virchow 1855

The role of cell division

Asexual Reproduction n Involves the distribution of identical genetic material (DNA) to two daughter cells. Prokaryotic cells = Binary fission n Eukaryotic cells = Mitosis n

Cellular organization of genetic material Genome: a cell’s endowment of DNA, or it’s genetic information. n When cell is not dividing DNA is tangled mass called chromatin n At cell division, chromatin condenses and are now visible as chromosomes. n Prokaryotic Cells: single long continuous DNA molecule n Eukaryotic Cells: Many linear DNA molecules, each chromosome is one continuous DNA molecule though

Eukaryotic chromosomes determine cell type Every eukaryotic species has a characteristic number of chromosomes in each cells nucleus. Types of cells based on chromosome # n Diploid: (2 n) cells that have two sets of each chromosome (homologous pairs) n n Found in somatic cells (Body cells) of eukaryotes (few exceptions) Humans 2 n=46, crayfish 2 n=200

Cell Type Based on Chromosome # n Haploid: (n) cells that have one of each pair of chromosomes Many eukaryotic organisms these are the gametes (sex cells) n Humans n=23, crayfish n=100 n

In order for cells to asexually divide they must retain their specific chromosome number n Chromosomes cells divide n must be copied before Sister chromatids= each one connected at centromere.

Distribution of Chromosomes During Eukaryotic cell division

QOD Starting with a fertilized egg (zygote), a series of five cell divisions would produce an early embryo with how many cells? 2. How many chromatids are in a duplicated chromosome? 3. A chicken has 78 chromosomes in its somatic cells; how many chromosomes did the chicken inherit from each parent? How many chromosomes are in each of the chicken's gametes? How many chromosomes will be in each somatic cell of the chicken's offspring? How many chromosomes are in a “set”? 1.

Answers 1) 32 cells 2) 2 3) 39; 78; 39

The cell cycle Has 2 over-all stages 1. Interphase: Majority of cells life has 3 phases n G 1 = metabolic activity (photosynthesis, respiration, transcription/translation) n S = DNA replication Chromatin sister chromatids n G 2 = preparation cell division (centrioles) 2. M stage: entire cell division (includes mitosis or meiosis and Cytokinesis) n Mitosis = nuclear division, including contents (DNA) n Cytokinesis = Division of organelles, cytoplasm, and plasma membrane

Phases of Mitosis

Phases of Mitosis

Cytokinesis In Plants and Animals

Plant Mitosis

Prokaryotic Cell Division: Binary Fission

QOD 1. During which stages of a cell cycle would a chromosome consist of two identical chromatids? 2. Compare cytokinesis in animal cells and plant cells. 3. Identify three similarities between bacterial chromosomes and eukaryotic chromosomes, considering both structure and behavior during cell division.

Control of the Cell Cycle Series of checkpoints along the cell cycle that coordinates key events. Like a washers timing device Checkpoint: A critical control point in the cell cycle where stop and go–ahead signals can regulate stages of the cycle. Three Check Points: n G 1, G 2, M n G 0 phase: A nondividing state in which a cell has left the cell cycle.

Enzymes control the signaling at each checkpoint These regulatory molecules are proteins of two main types: Kinases and cyclins. n Kinases: give the go–ahead signals at the G 1 and G 2 checkpoints. n n n present at a constant concentration in the growing cell, but much of the time they are in an inactive form cyclin–dependent kinase (Cdk) A protein kinase that is active only when attached to a particular cyclin. Cyclin: To be active, kinase must be attached to a cyclin; a protein that gets its name from its cyclically fluctuating concentration in the cell.

Enzymes control the signaling at each checkpoint n MPF: Maturation–promoting factor (M– phase– promoting factor) a protein complex required for a cell to progress from late interphase to mitosis. n n. M Consists of a cyclin and a kinase bound into 40 structure. checkpoint

The Lack of Cyclin at G 1 is the go signal for the G 1 checkpoint

Cancer n Mistakes in the control mechanism of cell cycle which result in uncontrolled cell division.