Cell cycle

Principles of Genetics & Population Genetics-AGB 121 2012-13

Cell cycle Dept. Of Animal Genetics and Breeding Veterinary College Hebbal, Bangalore -24

Cell Cycle • Activities of a cell from one cell division to the next – Cell grows, adding more cytoplasmic constituents – DNA is replicated

– cell divides into two identical daughter cells

What do all cells require to survive?

• A complete set of genetic instructions – produce required molecules – direct life processes • Genetic instructions are coded in the DNA of cells

Why do cells divide?

• Growth • Development • Repair

Essential Features of Cell Division 1. Transmit a complete copy of genetic information (DNA)

2. Transmit materials necessary for cell to survive and use genetic information

During non-division phase of cell cycle • DNA molecules in extended, uncondensed form called chromatin – cell can only use DNA to produce molecules when in extended state

During division phase of cell cycle • DNA molecules condense to form chromosomes prior to division

– each chromosome is a single molecule of DNA – easier to sort and organize DNA into daughter cells

Prokaryotic Cell Cycle • Prokaryotic chromosome a circular loop • Chromosome attaches to one point on plasma membrane

• Chromosome is replicated – replicated chromosome attached to plasma membrane at a different nearby point

• Cell elongates – new plasma membrane is added between between chromosomes, pushing them towards opposite ends of cell • Plasma membrane grows inward at middle of cell • Parent cell is divided into two identical daughter cells

Chromosome attaches to one point on plasma membrane Cell wall

Chromosome

Plasma membrane

Chromosome is replicated– replicated chromosome attached to plasma membrane at a different nearby point

Cell elongates – new plasma membrane is added between between chromosomes, pushing them towards opposite ends of cell plasma membrane grows inward at middle of cell

Parent cell is divided into two identical daughter cells

Eukaryotic Cell Cycle 2 major phases: •Interphase (3 stages) – DNA uncondensed (= chromatin) • Mitotic cell division (4 stages) – DNA condensed (= chromosomes)

Interphase • non-dividing state 3 stages: G1 – cell grows in size organelles replicated S – replication of DNA synthesis of proteins associatedwith DNA

G2 – synthesis of proteins associated with mitosis

Interphase

G1 S

Mitotic Cell Division

G2

Mitotic Cell Division

2 major processes: • mitosis – nuclear division => preserves diploid number of chromosomes • cytokinesis – cytoplasmic division => cell divides into two daughter cells