Chromosomes and Cell Reproduction

Chromosome Structure Chromosomes are the coiled up version of DNA. They consist of DNA and proteins: histones and nonhistones Chromosome Packing Animation

Point of Confusion: Chromatin vs. Chromatid vs. Chromosome What is the Difference??? centromere sister chromatids single-stranded chromosomes double-stranded chromosomes

Chromatids are attached at the center called a centromere. Sister Chromatids

What is a Kinetochore? Kinetochore Animation

Centrosome & Centrioles oh the definitions… Centrioles: ANIMAL CELLS ONLY Nonmembrane-bound organelles that occur in pairs just outside the nucleus of animal cells. Each centriole is composed of a cylinder or ring of 9 sets of microtubule triplets with none in the middle (9 + 0 pattern). During cell division a pair of centrioles moves to each end of the cell, forming the poles of the mitotic spindle. Centrioles also give rise to basal bodies that control the origin of cilia and flagella in motile cells of protists. In cross section, flagella and cilia have 9 sets of microtubule doublets surrounding a pair of single microtubules in the center (9 + 2 pattern). This characteristic pattern also occurs in motile cells of higher organisms, such as human sperm. Centrosome: In animal cells the centrosome includes a pair of centrioles surrounded by radiating strands of microtubules called the aster. The microtubule organizing centre that forms the mitotic spindle in dividing cells.

In Plants there is no Centriole They use MTOCs: Microtuble Organizing Centers Plant cells create mitotic spindle fibers and have a centrosome they lack centrioles.

What are spindle fibers made of? Microtubles Microtubles grow from the centrosomes Polar Microtubles: Attach to other polar microtubles spaning the cell. Polar Microtubles: Attach to other polar microtubles spaning the cell. Kinetochore microtubles: attach to the kinetochore. Breakdown From Here. Kinetochore microtubles: attach to the kinetochore. Breakdown From Here. Microtubule formation and disassembly

A gene is a segment of DNA that codes for a protein or RNA molecule which guide the development of traits.

Cell Types Somatic Cells Gametes

Chromosome Numbers Types: Autosomes and Sex Chromosomes (XX or XY). Humans: 22 pair of homologous chromosomes and 1 pair of sex chromosomes.

Chromosome Numbers All of the cells in the body, other than gametes are Diploid (2n=46 in humans). Gametes contain only one set of chromosomes: Haploid (n=23 in humans).

Different species have different numbers of chromosomes.

Change in chromosome number Humans who are missing even one of the 46 chromosomes usually do not survive. Humans with more than two copies of a chromosome, result in a condition called trisomy.

Abnormalities in chromosome number can be detected by analyzing a karyotype. Nondisjunction during the production of gametes results in gametes having more or less chromosomes than normal. Pictures called karyotypes can detect problems after conception.

How do Prokaryotes divide? They divide by binary fission. Their DNA is circular and usually only has one strand. No Mitosis!!!

Bacterial cells divide to reproduce Binary fission is a form of asexual reproduction that produces identical offspring: Mitosis

The Cell Cycle: for Eukaryotes Fig 12.5,12.4, The cell cycle is a repeating sequence of cellular growth and division during the life of an organism. A cell spends 90 percent of its time in the first three phases of the cycle.

Time to divide & multiply! I’m working here!

Key checkpoints at which feedback signals from the cell can trigger the next phase of the cell cycle (green light). Cell Cycle Movie/ Game Overview of the cell cycle

Checkpoint control system 3 major checkpoints: G 1 /S: Called “Restriction Point” can DNA synthesis begin? G 2 /M has DNA synthesis been completed correctly? commitment to mitosis spindle checkpoint are all chromosomes attached to spindle? can sister chromatids separate correctly?

G 1 /DNA Synthesis checkpoint G 1 /S checkpoint is most critical primary decision point primary decision point “ “restriction point” if cell receives it divides if cell receives “GO” signal, it divides internal signals: cell growth (size), cell nutrition external signals: “growth factors” if cell does receive signal, it exits cycle & switches to if cell does not receive signal, it exits cycle & switches to G 0 phase non-dividing, working state

G 0 phase non-dividing, differentiated state non-dividing, differentiated state most human cells in G 0 phase most human cells in G 0 phase  liver cells  in G 0, but can be “called back” to cell cycle by external cues  nerve & muscle cells  highly specialized  arrested in G 0 & can never divide

What molecules control cell division? 2 types of molecules control Cyclins oscillating levels during cell division. Cyclins oscillating levels during cell division. Cycline dependent kinasis or CDKs Cycline dependent kinasis or CDKs First CDK discovered was MPF/ p-phase promotor factor.

When control is lost: cancer Fig 12.19, Cancer is the uncontrolled growth of cells due to loss of contact inhibition / density-dependent inhibition. Overcrowding and tumors Mutations in genes that control cell division may result in cancer. If Telomerase ends are left on DNA, cells don’t die after 50 or so divisions. (Built in destruction control) HeLa Cells: Most widely used cancer cell line. Named after a woman 40 years ago with cervical cancer Immortal. Each cell has chromosomes instead of 46. Hit the Cancer Biology Documentary Link

Why do cells have to divide? They outgrow their nuclear capacity. Surface area to volume ratio Surface area to volume ratio Metabolism Metabolism Some cells are large. How do they overcome the problem? Multinucleated Multinucleated Human skeletal muscle cells Paramecium (2 nuclei) Slime Mold Fungus (1000’s of nuclei)

The Phases of Mitosis pg (How to make a clone) InterphaseProphaseMetaphaseAnaphaseTelophaseCytokinesis I Prefer My Awesome Teacher…Cool! MITOSIS The Jazzy Version of Mitosis

Prophase 1.Chromosomes coil and become visible. 2.Nuclear envelope & nucleolus breaks down. 3. Mitotic Spindle fibers begin to form. MITOTIC SPINDLE CENTRIOLES CENTROMERE NUCLEAR ENVELOPE HOMOLOGUES

Metaphase 1.Chromosomes line up along the equator of the cell. 2.Spindle fibers attach to kinetochore. 3.Centrioles migrate to the poles of the cell.

Anaphase 1.Spindle fibers begin to shorten. 2.Chromatids separate. 3.Chromatids begin moving toward the poles of the cell.

Telophase 1.Nuclear envelope reforms. 2.Cleavage furrow forms pinching the cytoplasm. 3.Chromosomes uncoil. 4.Cytokinesis begins.

Cytokinesis Fig 12.9 During telophase, cytokinesis occurs. During cytokinesis, the cytoplasm of the cell is divided in half, and the cell membrane grows to enclose each cell.

Cleavage In Action Actin and Myosin in a ring formation contract causing cleavage.

How does a cell plate form in plants? In Telophase: Golgi apparatus filled with cell wall materials move by microtubles to the middle of the cell and fuse.

Plants do not separate. Middle Lamella holds cells together. Sticky Sticky

Meiosis Fig.13.7 & 13.8 USA 300,000,000 strong and growing Meiosis produces gametes and reduces the number in chromosomes in half. Meiosis produces gametes and reduces the number in chromosomes in half. The following presents mitosis on the left and the corresponding meiosis phase on the right….notice the differences. The Theory of Inheritance of Genes First Link First

A forest from the trees moment Meiosis 1 Reduction Division: Process by which homologous chromosomes separate. Reduction Division: Process by which homologous chromosomes separate. Each Chromosome pairs up precisely with its homologue. Each Chromosome pairs up precisely with its homologue. Meiosis 2 Separation of sister chromatids. Separation of sister chromatids. Similar to Mitosis. Similar to Mitosis.

Prophase Prophase I Prophase Prophase I Genetic Recombination: Cross- over Synaptomeal Complex: Pairing of homologues (Synapsis) The Longest Phase

Chiasmata (pl) Chiasma (s) Genetics The point of contact between paired chromatids during meiosis, resulting in a cross-shaped configuration and representing the cytological manifestation of crossing over.

Metaphase Metaphase I Metaphase Metaphase I Chromosomes line up on metaphase plate. (double file) Spindle fibers attach at kinetochore.

Anaphase Anaphase I Homologous chromosomes separate

Telophase Telophase I & Cytokinesis & Cytokinesis I & Cytokinesis & Cytokinesis I Each pole has the monoploid number of chromosomes May or may not go into interphase.

None Prophase II

None Metaphase II

None Anaphase II

None Telophase II & Cytokinesis II & Cytokinesis II

Formation of Gametes Spermatogenesis spermatids

Oogenesis OVUM Third Link Comparison of OOGENESIS & SPERMATOGENISIS

So How Do Mitosis and Meiosis Compare?. Comparison of Mitosis and Meiosis

Types of Reproduction Sexual and Asexual Sexual: Meiosis Sexual: Meiosis Asexual: Binary fission Asexual: Binary fission

What are the three ways genetic variation is produced? Independent Assortment Meiosis 1: random separation of homologous chromosomes. 50% maternal or paternal C (2^23) Meiosis 1: random separation of homologous chromosomes. 50% maternal or paternal C (2^23)Crossover Recombinant chromosomes are produced Recombinant chromosomes are produced Humans: 2-3 crossovers/chromosome pair Humans: 2-3 crossovers/chromosome pair Random Random Random Fertilization Human Ovum = 8 million chromosomal combos Human Sperm = 8 million chromosomal combos Human Ovum = 8 million chromosomal combos Human Sperm = 8 million chromosomal combos Fertilization = 8 million X 8 million recombinations possible. Fertilization = 8 million X 8 million recombinations possible. Did you know? A man and a woman Can create 64 trillion different offspring?