Cell Cycle I Cell Cycle The cell cycle

Cell Cycle

I. Cell Cycle • The cell cycle is a series of events in eukaryotic cells that leads up to cell division. • Cells grow, duplicate, and divide.

4 Stages • 1. Gap 1 (G 1) • 2. Synthesis (S) • 3. Gap 2 (G 2) • 4. Mitosis (M)

2 Processes • The Cell Cycle occurs in two processes: • 1. Interphase- G 1, S, G 2 • 2. Mitosis- Mitosis and Cytokinesis

Interphase • G 1 - cell carries out normal functions. Cell has proteins to “check” the cell and make sure it is ready for synthesis. Organelles increase in number. • S- cell copies its DNA. • G 2 - cell carries out normal functions and grows. The cell has checkpoint proteins to check that the DNA is undamaged and the cell is the right size.

Mitosis • M- nuclear membrane dissolves, DNA condenses to form chromosomes, two new nuclei form. • Cytokinesis- process that divides the cell into two new daughter cells. • Parent cells and daughter cells are identical!

Cell Cycle

Cells are Controlled • Surface area to volume ratio in cell means that as a cell increases in size, the volume increases faster than the surface area. • Contact Inhibition- cell growth is ceases when two cells come in contact with one another.

Cells are Controlled (cont. ) • Growth must be controlled and organized. • If cell division becomes uncontrollable, cancer occurs. • Tumor- is an organized clump of uncontrollably dividing cells.

II. Mitosis and Cytokinesis • Chromosome- is a long strand of DNA that forms an “X” shape. • 46 chromosomes are in the human body.

DNA During Interphase • DNA wraps around Histone Proteins. These proteins make DNA condense. • During interphase, DNA forms chromatin. • Chromatin- is the “loose” combination of DNA and protein. “Loose” refers to how DNA folds in on itself.

DNA at the Beginning Mitosis • DNA tightly condenses into the characteristic “X. ” This is very visible under a microscope. • Chromatid refers to one of the sides. • The sides are identical. • Centromere is an area of condensed chromosome that holds the chromatids together. • Gene- segment of a chromosome that codes for a specific protein.

Phases of Mitosis

Prophase • Chromatin condenses into tight chromosomes. • Nuclear membranes disappear. • Centrosomes go to opposite ends of the cell and spindle fibers form.

Metaphase • Spindle fibers attach to the centromere on each chromosomes. • Chromosomes align on the cell’s equator

Anaphase • Spindle fibers shorten and pull the chromatids away from one another. • Sister chromatids separate from each other into daughter chromatids. • Chromatids go to opposite ends (poles) of the cell.

Telophase • Complete set of chromosomes are at each end (poles) of the cell. • Nuclear membrane starts to form.

Cytokinesis • Cell divides into two identical daughter cells. • Cell Cycle is complete. • In animal cells, a furrow or trench is formed. The membrane gradually pinches closed. • In Plant cells, a cell plate is formed between the two nuclei and a cell wall is formed from cellulose.

Animal vs. Plants

III. Reproduction Two Types: • 1. Asexual- the creation of genetically identical offspring from a single parent by mitosis. • Ex. Binary Fission- asexual reproduction by a single celled organism. The cell divides into two identical parts. • 2. Sexual- fusion of two gametes that creates an offspring that is a genetic mixture of both parents by meioses.

Specialized Cells • Somatic Cells- are body cells. They make up most of the body tissues and organs. • Germ Cells- are cells in the reproductive organs. – Gametes- are the sex cells. –Ex: Sperm and ova (eggs)

Chromosomes • Cells have 46 chromosomes or 23 pairs (one from the mother and one from the father). • Homologous Chromosomes- refers to the pairs of chromosomes. • 22 of the chromosomes are autosomeschromosomes that define characteristics. • 1 sex chromosome that controls the development of sexual characteristics.

Sex Chromosomes • Humans have two different sex chromosomes: –X and Y • Females are XX • Males are XY

Meiosis • Meiosis- is when the cells divide and the chromosome number cuts in half. • Sex cells go from Diploid Cells (46 chromosomes) to Haploid Cells (23). • Diploid also known as 2 n and haploid known as 1 n. • N= chromosomes and # = chromosome amount

Meiosis I • 1. Prophase I- nuclear membrane breaks down, the centrosomes move to opposite poles, and the chromosomes condense into pairs. • 2. Metaphase 1 - the pairs of chromosomes line up along the midline of the cell. • 3. Anaphase 1 - pairs of chromosomes move to opposite poles. • 4. Telophase 1 - the nuclear membrane can reforms and the cell starts to divide. • 5. Cytokinesis- two new daughter cells form

Meiosis I

Meiosis II • 6. Prophase II- The nuclear membrane breaks down, centrosomes move to opposite poles, and spindle fibers form. • 7. Metaphase II- 23 chromosomes align along the equator. • 8. Anaphase II- sister chromatids are pulled apart from each other and move to opposite poles. • 9. Telophase II- nuclear membranes form around each set of chromosomes. • 10. Cytokinesis- nuclear membranes form around the chromosomes at the poles.

Meiosis II

Outcomes • Cells went from DIPLOID to HAPLOID. • Diploid (2 n)- cell has two copies of each chromosome. One from mother and one from father. This refers to the 46 Chromosomes. • Haploid (1 n)- cell only has one copy of each chromosome. – Now there are 23 chromosomes in the cell. – 22 are autosomes and 1 is a sex chromosome.

Mature Sex Cells • Gamete- are mature sex cells. Ex: sperm and egg • Gametogenesis- is the production of gametes. • Sperm- male gamete • Egg- female gamete

Difference Between Sperm and Egg

Sperm and Egg • Sperm production = 4 sperm • Egg Production = 1 Egg + 3 Polar Bodies • Polar Bodies- are cells that are mainly DNA. The polar bodies cannot survive and are broken down. • Once fertilized, the sperm and egg form a diploid cell (2 n).

Crossing Over During Meiosis • Crossing over recombines genes and causes genetic variation. • Crossing Over- is the exchange of chromosome segments between homologous chromosomes during prophase I of Meiosis I. • Chromosomes are very close together. A segment of chromatin breaks off and reattaches to another chromosome.

Crossing Over

QR Mitosis Activity Pictures • Use the following slides to make up the QR Mitosis Activity.

Station 3

Station 5

Station 1

Station 2

Station 4

Station 6 • http: //www. youtube. com/watch? v=Ie. UANx. FV XKc