Erythrocytes have no nucleus, are made in the red marrow of bones, and live about 120 days. As red blood cells wear out in the bloodstream, they are taken in by the spleen, an organ on the left side of the abdomen below the stomach, and destroyed. Parts of the old cells are salvaged to make new red blood cells. Skin cells are dividing every day (about once every 20 hours). Embryonic human cells divide about once a day (in the early stages of development). Some nerve cells never divide after being formed in an embryo, which means they live as long as you do!
Who has heard of Mitosis – Meiosis?
Toddler/childhood phase of rapid growth and activity
Puberty phase - getting ready for reproduction
Tubulin proteins are formed which will make up the spindle, organelles are replicated, energy is stored up, and cytosol increases in volume
Balloon vs. shoe box demo
The Cell Cycle
The Cell Cycle How Cells Divide and Grow
Humble Beginnings Every living thing on earth starts as a single cell
All Cells Have a “Life Cycle”• Includes periods of growth, rest & replication• Can be short (minutes) or long (years)• Different cell types have very different cycles
Cells Divide for Different Reasons• To replace old/worn out cells (red blood cells)• To repair injured tissues or combat illness• To reproduce (create another entire organism)
Three Types of Cell Division Binary Fission • Used by prokaryotes (unicellular: bacteria) • Fast & simple: every 20 – 30 min. Mitosis • Used by eukaryotic, somatic cells (body) • Much more complex • Highly regulated Meiosis • Even more complicated (cells divide twice) • Used by eukaryotic germ cells (reproductive)
Binary Fission in Prokaryotes Bacteria only have 1 chromosome • A single strand of DNA • Circular in shape
Binary Fission in Prokaryotes DNA duplicates • Two circular DNA strands move apart • Cell doubles in size
Binary Fission in Prokaryotes DNA moves to opposite ends of cell Cell membrane grows inward Cell wall grows from membrane materials & pinches cell in two
Binary Fission in Prokaryotes Two new cells are formed • Identical genetically (same DNA) • Cytoplasm contents vary
Types of Cell Division Binary Fission • Used by prokaryotes (unicellular: bacteria) • Fast & simple: every 20 – 30 min. Mitosis • Used by eukaryotic, somatic cells (body) • Much more complex • Highly regulated Meiosis • Even more complicated • Used by eukaryotic germ cells (reproductive)
Cell Cycle in Eukaryotes Interphase • Longest stage • 90% of cell’s life • G - no division 0 • 3 checkpoints: • G – gap 1 1 • S - synthesis • G – gap 2 2 Mitosis • 4 stages • Cytokinesis completes the cycle
Interphase – G1 (1st Gap or Growth phase) Cell Growth • Organelles replicate • Cell volume doubles Cell does its job • Normal metabolic processes Longest phase Some cells stay here permanently G1 checkpoint • Is cell big enough? • Environment good?
Interphase – S (Synthesis phase) Chromosome Replication • Loose bundles of chromatin • All DNA in nucleus copied resulting in… • Two identical strands of each chromosome • Sister chromatids joined by centromere
Interphase – G2 (2nd Gap or Growth phase) More growth • Cell volume increases G2 Checkpoint • DNA mistakes? • Cell volume OK? • Environment good? Shortest phase
Mitosis - Prophase DNA coils & condenses (like thread on a spool) to form distinct chromosomes Nuclear membrane disappears Spindle fibers form out of centrosomes (2 centrioles ea.)
Metaphase Spindle fibers attach to kinetochores on the centromeres Chromosomes line up at the equatorial plane (middle) of the cell Mitotic spindle checkpoint • Are all chromosomes lined up? • Are they all attached to spindle fibers?
Anaphase Spindle fibers shorten, pulling sister chromatids apart Chromatids are drawn to opposite ends (poles) of the cell Centromere connections are cut
Mitotic Spindle Microtubules of the spindle attach to kinetochores on ? chromosomes Sister chromatids are pulled apart by ? spindle fibers Other unattached spindle fibers push against one another to elongate (stretch out) the cell
Telophase Chromosomes reach the poles New nuclear membranes form around chromatids Chromosomes unwind to become thread-like chromatin again Nucleolus forms
Cytokinesis The cytoplasm is evenly divided New cell membrane forms in animal cells New cell wall is built across for plant cells
Cytokinesis in Animal Cells Microfilaments assemble around cell middle Actin& myosin microfilaments form a ring around cell ATP (energy) used to squeeze cell in half
Cytokinesis in Plant Cells Rigid cell wall can’t just be squeezed in half Golgi apparatus sends vesicles filled with cell wall building materials to center Cell plate forms at equatorial plane Cell wall fills in gaps, cleaves cell in two
Interphase – G0 (pre-growth or resting phase) Mitosiscreates two identical daughter cells that go on to enter Interphase • Some enter G 1 and divide again • Some enter G0 - a rest phase where they do their job
Week 11 Lab ReviewMicroscope Lab: onion root tip mitosis
Cell Cycles vary by Type of Cell Nerve, liver & muscle cells • Most stay in G0 (never divide) • Some divide only after years, if there are injuries • Brain & spinal chord injuries are often permanent because of this Skin, hair, eye, cheek & intestinal lining cells • Exposed to more wear & tear than other cells • Replaced every 1 - 35 Red blood cells (hemoglobin) days • Most rapidly dividing • Formed from bone marrow stem cells cells in humans • Never divide once formed • Die & replaced after ~ 4 months
Cancer - Cell Cycle out of Control Cancer cells • Tumors result from rapid, out of control cells dividing • Bypass normal G1, G2 and/or mitotic spindle checkpoints • Sloppy cell division = big trouble Lack of quality controls • More mutations • Disorganized/deformed cells • Signal proteins lost/changed • Contact inhibition lost
Your Turn… What is binary fission? What type of cells use this process? Draw and label the cell cycle…include G1, S, G2, M and cytokinesis…what happens at each stage? What are the stages of Mitosis? What disease is associated with unregulated mitosis?