2.5 CELL CYCLE · CHROMOSOMES Structures found in the nucleus Made up of DNA (deoxyribonucleic acid) and protein DNA contains the genes (instructions for the traits of an organism)

2.5 CELL CYCLECell Division and Mitosis

WHY DO CELLS DIVIDE?

WHY DO CELLS DIVIDE?○ When organisms grow, their cells don’t get bigger ○ Instead, the cells divide (more cells) ○ Why? ● So each cell stays small, and manageable

● To replace old or damaged cells

● For reproduction

THE IMPORTANCE OF CELL DIVISION

Reproduction • Asexual • Sexual

CHROMOSOMES○ Structures found in the nucleus ○ Made up of DNA (deoxyribonucleic acid) and

protein ○ DNA contains the genes (instructions for the traits

of an organism) ○ Before division, a copy of all the DNA is made so

each 2 new cell has its own copy (REPLICATION) ○ Humans have 46 chromosomes

23 + 23 = 46Eye Colour

Hair Colour

Eye Colour

Hair Colour

You have one copy of each chromosome from each parent!

CELL CYCLE

CELL CYCLE○ Interphase

● Cell’s normal life ● DNA is replicated

○ Mitosis (CELL DIVISION) ● Prophase

● Metaphase

● Anaphase

● Telophase

○ Cytokinesis ● Division of cytoplasm and organelles

● Results in formation of 2 identical daughter cells

MITOSIS OVERVIEW

INTERPHASE○ Period between cell divisions ○ normal cell life/growth ○ DNA replication

MITOSIS ! PROPHASE○ Just before mitosis begins, the

DNA coils ○ The long strands form short

and thick chromosomes ○ They appear as a pair of

identical, copied strands attached at a single point (centromere)

○ The nucleus membrane seems to disappear

MITOSIS ! METAPHASE○ Chromosomes line up at equator (middle of cell)

such that the chromosomes copies will be able to split into

MITOSIS ! ANAPHASE○ Sister chromatids are pulled to opposite poles ○ Centromeres divide in half

MITOSIS ! TELOPHASE○ Sister chromatids are at opposite poles ○ DNA starts unravelling again ○ A nucleus starts to reappear.

CYTOKINESIS○ Division of cytoplasm ○ Animals

● Cell membrane pinches in and forms a cleavage furrow

● Plants ● Cell plate forms between

the two daughter cells and will eventually become a cell wall

RECAP-- MITOSIS UNDER THE MICROSCOPE

Prophase Metaphase Anaphase Telophase