Cell Cycle and Mitosis Video 1

Asexual Reproduction Asexual reproduction is reproduction that involves a single parent producing an offspring. The offspring produced are, in most cases, genetically identical to the single cell that produced them.

Asexual Reproduction In single-celled organisms, cell division is a way to create new individuals. Asexual reproduction is a simple, quick, and effective way for an organism to produce a large number of offspring.

Asexual Reproduction Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually.

Asexual Bacteria reproduce using binary fission.

Asexual Kalanchoe plants form plantlets.

Asexual Hydra reproduce by budding.

Sexual Reproduction In sexual reproduction, offspring are produced by the fusion of two sex cells – one from each of two parents. These fuse into a single cell before the offspring can grow.

Sexual Reproduction The offspring produced inherit some genetic information from both parents. Most animals and plants, and many single-celled organisms, reproduce sexually.

Sexual Reproduction Main advantage: creating genetic diversity in a population -gives the population a better chance of surviving in a changing environment.

Sexual vs. Asexual

An advantage of sexual reproduction over asexual reproduction is that sexual reproduction A) takes less time B) requires more time C) provides genetic diversity D) produces identical offspring

Cell Division The process by which a cell divides into two new “daughter” cells. Daughter cells are the NEW cells  the product of cell division.

Cell Division Before cell division occurs, the cell replicates (copies) all of its DNA. Each cell gets one complete copy of genetic information

Chromosomes and the Cell Cycle Threadlike structure within the nucleus that contains genetic information

Chromosomes and the Cell Cycle Bundle of DNA Replicated at the beginning of the cell cycle Passed on from parent cell to daughter cell

Chromosomes Organisms contain various numbers of chromosomes. Humans have 46 chromosomes per cell. Fruit flies have 8 chromosomes per cell. Adders-tongue fern =1,440 chromosomes!

Chromosomes Chromosomes coil up to make it possible to separate DNA precisely during cell division. Chromosomes form a close association with histones (type of protein).

Chromatin Video 2 This complex of unwound DNA and proteins is known as chromatin.

What is the product of cell division? Two genetically identical “son” cells Two genetically different “son” cells Two genetically identical “daughter” cells Two genetically different “daughter” cells

Chromosomes contain: Wisdom Genetic information The nucleus RNA and proteins

Cell Cycle During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells.

Cell Cycle Consists of 4 phases G1 phase S phase G2 phase M phase

Interphase Period of cell cycle between cell divisions. Divided into 3 phases: G1 phase S phase G2 phase In interphase, most of the chromatin is decondensed in the nucleus so that individual chromosomes cannot be seen, and the microtubules are organized in a radial array from the centrosome.

G1 Phase G1= Growth; increase in size Cells synthesize some proteins and organelles during this phase.

S Phase S stands for synthesis (to make). During this phase, new DNA is synthesized when the chromosomes are replicated (doubled). DNA makes a new copy of itself- each chromosome is doubled They immediately attach themselves to their new copy

S Phase The cell at the end of this phase contains twice as much DNA as it did at the beginning.

G2 Phase organelles and molecules required for cell division are produced. The replicated DNA is checked for errors, and repaired if needed.

Curse of the ‘C’ words! Chromatid Chromatid – one of two identical “sister” parts of a duplicated chromosome

Curse of the ‘C’ words! Centromere Centromere – region of a chromosome where the two sister chromatids attach

Curse of the ‘C’ words! Centriole Centriole – structure in an animal cell that helps to organize cell division Curse of the ‘C’ words! …chromosome, chromatin, cytokinesis…

Which pair includes a phase of the cell cycle and a cellular process that occurs during that phase? a. G1 phase, DNA replication b. G2 phase, preparation for mitosis c. S phase, cell division d. M phase, cell growth

When during the cell cycle is a cell’s DNA replicated? a. G1 phase b. G2 phase c. S phase d. M phase

The structures labeled B in Figure 10–5 are called A) centromeres. B) centrioles. C) sister chromatids. D) spindles.

M Phase Two new daughter cells are produced during this phase. M comes from the word mitosis.

M Phase This phase has two stages – Mitosis Cytokinesis In many cells, this process may overlap.

Mitosis Video 3 Consists of 4 stages Prophase Metaphase Anaphase Telophase

Prophase Chromatin inside the nucleus condenses and the duplicated chromosomes become visible.

Prophase Outside the nucleus, the centrioles begin to move to opposite sides of the cell Centriole starts to form a spindle. Spindles –system of microtubules that will help to separate the duplicated chromosomes. During prophase, the chromosomes become highly condensed, and the centrosomes begin to separate. Nuclear envelope breakdown manifests the transition between prophase and prometaphase so that the individual chromosomes are no longer constrained in the nucleus

Prophase Nucleolus disappears Nuclear envelope (membrane) breaks down

Prophase During prometaphase, kinetochore (k)-fibres (bundles of stabilized microtubules) connect the spindle microtubules and the kinetochores on the chromosomes, such that the chromosome can align at the spindle equator, which defines metaphase.

Metaphase Sister chromatids line up in middle of cell Spindle fibers connect the centromere of each chromatid to opposite poles The microtubules are uniformly oriented with their minus ends at the centrosome and their plus ends extending towards the spindle equator, where they often overlap. The astral microtubules emanate from the centrosomes and extend their plus ends towards the cell cortex

Anaphase During anaphase, the chromosomes separate by contracting spindle fibers Once anaphase begins, each sister chromatid is now considered an individual chromosome. .. The movement of the chromosomes towards the poles occurs during anaphase A, and the two spindle poles separate during anaphase B. The nuclear envelope begins to reform and the DNA begins to decondense during telophase. An organized central spindle bundle of microtubules is also present. Cytokinesis divides the cytoplasm of the cell so that the two daughter nuclei are segregated into individual cells, which enter interphase and begin the process again.1

Anaphase Anaphase comes to an end when this movement stops and the chromosomes are completely separated into two groups.

Telophase Chromosomes begin to unwind into chromatin A nuclear envelope reforms around each cluster of chromosomes Spindle breaks down

Telophase

Cytokinesis Cytokinesis is the division of the cytoplasm This process is different in animal cells and in plant cells.

Cytokinesis in animal cells The cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts.

Cytokinesis in plant cells The cell membrane is not flexible enough to pinch because of the rigid cell wall. A structure known as the cell plate forms halfway between the divided nuclei. The cell plate gradually develops into cell membranes and a cell wall

B) prophase, metaphase, and anaphase C) metaphase only During which phase(s) of mitosis are structures like the one shown visible? A) anaphase only B) prophase, metaphase, and anaphase C) metaphase only D) anaphase and interphase

Which of the following represents the phases of mitosis in their proper sequence? A) prophase, metaphase, anaphase, telophase B) interphase, prophase, metaphase, anaphase, telophase C) interphase, prophase, metaphase, telophase D) prophase, anaphase, metaphase, telophase

During normal mitotic cell division, a parent cell that has four chromosomes will produce two daughter cells, each containing A) two chromosomes. B) four chromosomes. C) eight chromosomes. D) sixteen chromosomes.

1. Nature Reviews Molecular Cell Biology 11, 91-102 (February 2010) | doi:10.1038/nrm2832