warm-up 12/2: why do cells replicate their dna? when do cells replicate their dna? what is the...
TRANSCRIPT
Warm-up 12/2:
• Why do cells replicate their DNA?• When do cells replicate their DNA?• What is the primary purpose of DNA?
Chromosomes: coiled and compact DNA in nucleus
• DNA wrapped tightly around proteins called histones • chromatids: two halves of a dividing chromosome • Chromatids joined by a centromere
Chromosome number: each organism has a specific number of chromosomes
• Sex chromosomes: determine sex of the organism (X or Y)
female: XX male: XY• Autosomes: all other chromosomes• All organisms have two copies that are
homologous
Cell Cycle
• 3 major phases• Interphase: time
between cell divisions - G phases: growth - S phase: copying of DNA• M phase (mitosis):
division of the nucleus• Cytokinesis: division of
the cytoplasm
Mitosis (M phase)
• 2n 4n 2 (2n)• Continuous process starts with interphase• Need to separate the doubled chromosomes• Four phases
prophase metaphase anaphase telophase• PMAT
Prophase• Can see chromosomes• Chromatids stay connected by centromeres• Nucleolus and nuclear membrane break down• Centrosomes and centrioles appear• Early mitotic spindle forms
Metaphase
• Two types of fibers (mitotic spindle) kinetechore fibers: attach to centromere of
chromosome polar fibers: extend centrosome to centrosome, push
cell apart• Fibers line up the chromosomes in middle
Anaphase
• Chromatids of each chromosomes are pulled apart by fibers
• Move towards opposite poles of dividing cells
Telophase
• Chromosomes in opposite ends• Spindle fibers break down• Nuclear envelope reforms• Nucleolus in each cell• Cytokinesis