Biology 10-2
Nucleus: Consist of DNA bound to protein-chromatin, chromosome
Prokaryotic Chromosome
- In cytoplasm
- A single circular DNA molecule
Eukaryotic Chromosome
- In nucleus
- More DNA than prokaryote
- Linear chromosome
DNA + histones (protein) = nucleosome→ coils → supercoils → chromatin/chromosome
Nucleosome: DNA wrapped twice around histones to form beadlike structure
Chromosomes make it possible to separate DNA precisely during cell division
- Chromosome=DNA + histone protein, Chromatin = uncoiled chromosome
Eukaryote Structure
a. Before Division
– invisible
–Less condense, Spread throughout nucleus
b. After Division
–Visible
–More condense
–Duplicated, each chromosome has 2 identical sister chromatids
Division due to reproduction, Growth and development, tissue renewals
- Bacteria-Binary Fission, Eukaryote-mitosis
Cell Cycle
Cell Cycle: A series of events as cell grow and divide
Phases of cell cycles in eukaryotes include:
1. Interphase – none dividing period
2. Cell Division – M phase
Interphase
G1 phase-primary growth phase
S phase- DNA replication
G2 phase-Preparing for cell division
Cell Division (M phase)
Mitosis- Nucleus division
Cytokinesis – cytoplasm division
Interphase
G1 Phase – Cell grows, increase in size
- Synthesize new organelles and proteins (centriole)
S Phase – chromosome is replicated, DNA amount doubled
G2 Phase– Shortest phase of interphase
- Many cell organelles and molecules for cell division are made
Cell Division
Mitosis: Division of Nucleus
1. Prophase–first and longest phase of mitosis
Chromatin condenses into chromosome
2 centrioles of centrosome
_ separate from another 2 centrioles (plants only have centrosome)
Spindle is formed to connect centrioles
Nucleolus disappears
Nuclear envelops break down
Spindle
Fanlike structure made of microtubules
Centrosome organize spindle
Includes: Aster, Spindle Fiber
Helps separate chromosome
2. Metaphase – Shortest phase of mitosis
Individual chromosomes line up across center of cell – metaphase plate
Centrioles pull the spindle fibers that connect the centrosome of each chromosome to the 2 poles of
the spindle
Tetrads line up randomly
-Independent Assortment
Spindle fibers attach on pairs of
sister chromatid
3. Anaphase
Spindles shortening spindle, pulling sister chromatids to poles of cell
Sister chromatids separate and becomes individual chromosome
Chromosome number doubled
4. Telophase
Chromosomes disperse (spread out into tangle of chromatin) and become invisible
Nuclear envelope reforms
Nucleolus forms
Spindle disappears
Cytokinesis
- Division of Cytoplasm
- Occurs at the same time as telophase
- Divide into 2 identical daughter cells and gather into nuclei
Animal Cell: cell membrane is drawn inward and forms a cleavage furrow
Plant Cell: Cell plate forms at the equator to divide cell
- Cell plate divides into cell membrane, cell wall forms in between 2 membranes
Cells make complete copy of genetic information before cell division.
Genetic information is bundled into packages of DNA called chromosome
Prokaryotes
Lack nuclei
DNA molecules are found in to cytoplasm
Single, circular DNA chromosome
Cell Division-Binary Fission (Bacterium)
Eukaryotes
DNA and histone molecules for beadlike structure nucleosome, which makes a thick fiber
HW B
Prokaryotic cell division is called Cell division
1. DNA forms one circle
2. DNA duplicates
3. Membrane indents
4. Two new cells are formed
Biology 10-3
Signals regulate the cell cycle – protein family cyclin
Cell cycle is controlled by regulatory protein both inside and outside the cell
Internal Regulators
Control the phase of mitosis and anaphase
External Regulators
Direct cells to speed up or slow down
Growth Factor stimulate the growth and division of cell.
- Important on embryonic development and wound healing
- On surface on the cell
Apoptosis
Programmed cell death
1. Chromatin shrink
2. Parts of cell membrane breaks down
3. Neighboring cells clean up
Important on developing the structure and shaping
Cancer
Uncontrolled cell growth in a multicellular organism
Cancer cell do not respond to the signals that regulates the growth of most cell
Tumor: a mass of cells caused from cancer
Benign tumor– do not spread to other parts
Cancerous (Malignant) tumor – invade and destroy surrounding cancer
Cancer cell spread – absorb nutrients, block nerve connection, prevent proper functioning
Cause
Smoking, radiative exposure, defective genes, viral infection
Defect on gene p53, halts proper replication of chromosome
- Cause cell to lose the information needed to respond on control signals
Treatments
Localized cancer- surgery (skin cancer-melanomas)
Carefully targeted beams of radiation
Chemotherapy – use of chemical compound to slow the growth of cells
- May interfere on healthy cell division
