6/10/2015 The Cell Cycle Omnis cellula e cellula The cell cycle is an ordered set of events, culminating in cell growth and division into two daughter cells

6/10/2015 Structure 1.The role of cell division – what is a need to divide? 2.The mitotic cell cycle – how to divide?

6/10/2015 Chromosome duplication and distribution during mitosis

6/10/ The role of cell division In reproduction – main difference between living organism and nonliving matter In growth – for multicellular organism (including cell renewal and cell repair)

6/10/2015 Unicellular organismMulticellular organism Reproduction and growth

6/10/2015 The important definitions Cell division is a finely controlled process that results in the distribution of identical hereditary material – DNA – to two daughter cells. A dividing cell: Precisely replicates its DNA Allocates the two copies of DNA to opposite ends of the cell Separates into two daughter cells containing identical hereditary information

6/10/2015 The important definitions The DNA is distributed among 1 to more then 50 long linear stretches called chromosomes. The number of chromosomes is a characteristic of every eukaryote. For example our somatic cells – all cells except reproductive – contain 46 chromosomes (2n). Our gametes (reproductive cells) have only 23 chromosomes (n).

6/10/2015 The important definitions The total DNA in the chromosomes of an organism is referred as its genome. Chromosome contains thousands of genes – units of DNA that contains the information to specify synthesis of single polypeptide chain.

6/10/2015 The important definitions Characteristics of chromosomes: They are supercoils of a DNA-proteins complex called chromatin. Each chromosome consists of : Genes Proteins They exist in characteristic number (somatic - 2x, gametes – x) They exists in different states: Loosely folded during interphase Highly folded during mitotic phase

6/10/2015 The DNA structure is maintained via association with different protein – formation of the DNA-protein complex – chromatin. centromere Before the cell can divide all DNA must be copied and then separated to daughter cells. After copying each duplicated chromosome consists of two sister chromatids –identical copies of chromosome’s DNA molecule.

6/10/ The mitotic cell cycle The cell cycle is composed from interphase (I) and mitotic (M) phase Interphase consists of several subphases Mitotic phase consists of both mitosis and cytokinesis. The former one is divided to five subphases with special characteristic for each one

6/10/2015 The eukaryotic cell cycle S G1G1 M G2G2 Interphase

6/10/2015 Short summary of interphase Comprised by three (four) subphases: G 1, (G 0 ), S and G 2. Common feature of all (except G 0 ) subphases: growth of the cell by producing proteins and cytoplasmic organelles. G 1 – “first gap” S phase – chromosome duplication G 2 – “second gap”, DNA repair

6/10/2015 Overview of mitosis Daughter cells (2n) Anaphase cell Chromatid Mitotic apparatus Cytokinesis Parental cell (4n) in G 2 Metaphase cell DNA replication Parental cell (2n) in G 1

6/10/2015 Interphase (G 2 ) Duplicated chromatin Centrosomes with centriole pairs Nucleolus Nuclear envelope Plasma membrane The nucleus is well defined It contains one or more nucleoli Two centrosomes are formed Pair of centrioles, aster around Duplicated chromosomes are still not visible

6/10/2015 Prophase Chromatin condenses into discrete chromosome The nucleoli disappear Mitotic spindle begins to form Centrosomes move apart

6/10/2015 Prometaphase Fragmentation of nuclear envelope Formation of kinetochore Extension of spindle fibers Invasion of microtubules into the nucleus and attachment to kinetochores

6/10/2015 Metaphase Centrosomes are at opposite poles of the cell Chromosomes move to the metaphase plate Formation of imaginary metaphase plate: alignment of all chromosome at the centre Spindle formation

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The mitotic spindle at metaphase

6/10/2015 Anaphase Centromeres separate and sister chromatids move toward opposite poles of the cell as their kinetochore microtubules shorten Nonkinetochore microtubules elongate moving the poles further apart

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Telophase Forming of nuclear envelope Chromatin is less condensed Mitosis is complete Cytokinesis: formation of cleavage furrow and separation of two daughter cells

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Cytokinesis in animal and plant cells

6/10/2015 Cleavage of an animal cell

6/10/2015 Cell plate formation in a plant cell

6/10/2015 Mitosis in a plant cell

6/10/2015 Mitosis in an onion root

6/10/2015 Bacterial cell division (binary fission).

6/10/2015 Evolution of mitosis

6/10/2015 Evolution of mitosis

6/10/2015 Summary

6/10/2015 Summary

6/10/2015 Summary 1. The role of cell division – reproduction and growth (cell renewal and repair). 2.The mitotic cell cycle – consists of: - interphase (I=G 1 +S+G 2 ) – important steps for DNA duplication and initiation of mitosis; - mitosis (P+PM+M+A+T) – separation of two daughter cells with equal amount of genetic material (chromosomes).

6/10/2015 Reading 1. Ch. 12 pp

6/10/2015 Evolution of mitosis (hypothesis) Chromosome Chromosomes Kinetochore microtubulesCentrosome Fragments of nuclear envelope Microtubules A. Bacteria B,C. Unicellular algae D. Animal cell

6/10/2015 Cytokinesis in animal and plant cells contractile ring formation of a new cell wall formation of phragmoplast