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Transcript
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 5/24/2017 Structure 1. The role of cell division – what is a need to divide? 2. The mitotic cell cycle – how to divide? 5/24/2017 Chromosome duplication and distribution during mitosis 5/24/2017 1. 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) 5/24/2017 Reproduction and growth Unicellular organism 5/24/2017 Multicellular organism 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 5/24/2017 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). 5/24/2017 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. 5/24/2017 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 5/24/2017 • The DNA structure is maintained via association with different protein – formation of the DNA-protein complex – chromatin. •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. 5/24/2017 centromere 2. 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 5/24/2017 The eukaryotic cell cycle M G1 G2 G0 S 5/24/2017 Short summary of interphase • Comprised by three (four) subphases: G1, (G0), S and G2 . • Common feature of all (except G0) subphases: growth of the cell by producing proteins and cytoplasmic organelles. • G1 – “first gap” • S phase – chromosome duplication • G2 – “second gap”, DNA repair 5/24/2017 Overview of mitosis Parental cell (2n) in G1 Chromatid Parental cell (4n) in G2 DNA replication Mitotic apparatus Metaphase cell Anaphase cell Daughter cells (2n) Cytokinesis 5/24/2017 Interphase (G2) Duplicated chromatin Centrosomes with centriole pairs • • • • • 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 Nucleolus Nuclear envelope Plasma membrane 5/24/2017 Prophase Early mitotic spindle Chromosome, consisting of two sister chromatids • Chromatin condenses into discrete chromosome • The nucleoli disappear • Mitotic spindle begins to form •Centrosomes move apart Centromere 5/24/2017 Prometaphase • Fragmentation of nuclear envelope • Formation of kinetochore •Extension of spindle fibers • Invasion of microtubules into the nucleus and attachment to kinetochores Fragments of nuclear envelope Spindle pole 5/24/2017 Kinetochore Nonkinetochore microtubules Kinetochore microtubules 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 Spindle 5/24/2017 Metaphase plate 5/24/2017 The mitotic spindle at metaphase 5/24/2017 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 Daughter chromosomes 5/24/2017 5/24/2017 Telophase Cleavage furrow •Forming of nuclear envelope •Chromatin is less condensed •Mitosis is complete Nucleolus forming •Cytokinesis: formation of cleavage furrow and separation of two daughter cells Nuclear envelope 5/24/2017 5/24/2017 Cytokinesis in animal and plant cells 5/24/2017 Cleavage of an animal cell 5/24/2017 Cell plate formation in a plant cell 5/24/2017 Mitosis in a plant cell 5/24/2017 Mitosis in an onion root 5/24/2017 Bacterial cell division (binary fission). 5/24/2017 Evolution of mitosis 5/24/2017 Evolution of mitosis 5/24/2017 Summary 5/24/2017 Summary 5/24/2017 Summary 1. The role of cell division – reproduction and growth (cell renewal and repair). 2. The mitotic cell cycle – consists of: - interphase (I=G1+S+G2) – 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). 5/24/2017 Reading 1. Ch. 12 pp. 228-237 5/24/2017 Evolution of mitosis (hypothesis) A. Bacteria Chromosome Microtubules D. Animal cell Chromosomes Fragments of nuclear envelope 5/24/2017 Centrosome B,C. Unicellular algae Kinetochore microtubules Cytokinesis in animal and plant cells contractile ring 5/24/2017 formation of phragmoplast formation of a new cell wall