Enzyme Kinetics

CELL CYCLE:

CELL CYCLE Presented By :– Vatsala Raina

CELL CYCLE :

CELL CYCLE In cells without a nucleus, is that prokaryotes, the cell cycle occurs via a process termed as binary fission. In cells with a nucleus that is eukaryotes, the cell cycle can be divided into two phases- Interphase M phase(mitosis phase)

CELL CYCLE:

CELL CYCLE Interphase -During this phase the cell grows. Before a cell can enter cell division, it needs to prepare itself by replicating its genetic information and all of the organelles. It proceeds in three stages G 1 phase S phase (synthesis) G 2 phase This accounts for approximately 90-95%of the cell cycle. M phase (mitotic phase) The division of the mother cell into two daughter cells, genetically identical t each other and to their parent cell. This accounts for approximately 5-10% of the cell cycle.

INTERPHASE:

INTERPHASE G1phase- The cell is metabolically active and grows continuously DNA is not replicated in this phase S phase – DNA synthesis takes place G2 Phase – Proteins are synthesized in preparation for mitosis.

Slide 5:

Eukaryotic chromosome replicating

The cell cycle.:

The cell cycle.

TWO FORMS OF CELL DIVISION :

TWO FORMS OF CELL DIVISION MITOSIS “The division of a single nucleus into two genetically identical “daughter cells” (clones). MEIOSIS “In a sexually reproducing organism, the division of a single diploid nucleus into four haploid daughter cells (gametes or sex cells).”

MITOSIS:

MITOSIS The division of somatic cells follows a “ 2-D ” process: D uplicate & D ivide 46 Chromosomes 46 Chromosomes 46 Chromosomes 92 Chromosomes ( Duplicate ) ( Divide ) Parent Cell Daughter Cell Daughter Cell

MEIOSIS:

MEIOSIS The division of sex cells follows a “ 3-D ” process: D uplicate, D ivide & D ivide 23 Chromosomes 23 Chromosomes 23 Chromosomes 23 Chromosomes 46 Chromosomes 46 Chromosomes 46 Chromosomes 92 Chromosomes (Duplicate) (Divide) (Divide)

MITOSIS:

MITOSIS The short process of Mitosis takes place in five steps: Prophase Metaphase Anaphase Telophase Cytokinesis (“Cell-splitting”)

Slide 11:

Prophase Metaphase Anaphase Telophase The Stages of M itosis Interphase

THE SPINDLE:

THE SPINDLE A spindle is a web type structure made up of microtubule fibres. It is essential for mitosis because it arranges the chromosomes into their correct positions in preparation for cell division. Mitotic centre Microtubule SPINDLE

CHROMOSOMES ATTACHED TO SPINDLE DURING NUCLEAR DIVISION:

CHROMOSOMES ATTACHED TO SPINDLE DURING NUCLEAR DIVISION

PROPHASE:

PROPHASE The chromatin (unravelled DNA) in the nucleus, condenses to form pairs of chromosomes. The centrioles move to opposite ends of the nucleus. As this is happening the nucleolus begins to break down Nuclear membrane begins to break down

PROPHASE:

PROPHASE Chromatin condenses the nuclear envelope dissolves, centrioles divide and migrate, the spindle forms.

METAPHASE:

METAPHASE The spindle becomes fully developed The nuclear membrane has completely gone. The chromatid pairs place themselves onto individual fibres and are aligned along the centre of the spindle

ANAPHASE:

ANAPHASE The chromatid pairs are split into two (This is done by movement of the spindle fibres) The pairs then travel to opposite ends of the spindle The halved chromatids are now called chromosomes

TELOPHASE:

TELOPHASE Two new nuclei are formed when the chromosomes reach the opposite poles of the cell The nuclear membrane is formed- the nucleolus reappears The chromosomes disperse in the nucleus

CYTOKINESIS:

CYTOKINESIS ANIMAL CELL Literally means division of the cytoplasm. Cytokinesis is the splitting of the cytoplasm. Cytoplasm of a single eukaryotic cell divides to form two daughter cells. This stage ensures that the chromosome number is maintained from one generation to the next.

Cytokinesis:

Cytokinesis Plant Cells: Rigid cell wall surrounding plant cells does not permit cytokinesis by furrowing. Begins with formation of a cell plate which eventually becomes new plasma membrane between the daughter cells.

MITOSIS IN ANIMAL CELLS.:

MITOSIS IN ANIMAL CELLS. © 2003 John Wiley and Sons Publishers

AN OVERVIEW :

AN OVERVIEW Two irreversible points in cell cycle replication of genetic material separation of sister chromatids centromere sister chromatids single-stranded chromosomes double-stranded chromosomes

CHECKPOINTS:

CHECKPOINTS cell cycle controlled by STOP & GO chemical signals at critical points signals indicate if key cellular processes have been completed correctly

CHECKPOINT CONTROL SYSTEM:

CHECKPOINT CONTROL SYSTEM 3 major checkpoints: G 1 /S This checkpoint checks whether DNA synthesis can begin G 2 /M Whether DNA synthesis has been completed correctly spindle checkpoint Whether are all chromosomes are attached to spindle or not Whether sister chromatids separate correctly

MEIOSIS:

MEIOSIS Meiosis involves two sequential cycles of nuclear and cell division called meiosis I and meiosis II but there is only a single cycle of DNA replications. Four haploid cells are formed at the end of meiosis II.

MEIOSIS I:

MEIOSIS I Prophase I Metaphase I Anaphase I Telophase I

MEIOSIS II:

MEIOSIS II Prophase II Metaphase II Anaphase II Telophase II

Interphase I:

Interphase I Similar to mitosis interphase. Chromosomes replicate (S phase). Each duplicated chromosome consist of two identical sister chromatids attached at their centromeres . Centriole pairs also replicate.

Interphase I:

Interphase I Nucleus and nucleolus visible. chromatin nuclear membrane cell membrane nucleolus

Prophase I:

Prophase I Longest and most complex phase (90%). Chromosomes condense. Synapsis occurs: homologous chromosomes come together to form a tetrad . Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids).

Cancer & Cell Growth:

Cancer & Cell Growth Cancer is essentially a failure of cell division control unrestrained, uncontrolled cell growth

FREQUENCY OF CELL DIVISION:

G 2 S G 1 M metaphase prophase anaphase telophase interphase (G 1 , S, G 2 phases) mitosis (M) cytokinesis (C) C Frequency of cell division varies by cell type embryo cell cycle < 20 minute skin cells divide frequently throughout life 12-24 hours cycle liver cells retain ability to divide, but keep it in reserve divide once every year or two mature nerve cells & muscle cells do not divide at all after maturity permanently in G 0 FREQUENCY OF CELL DIVISION