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What is the most important part of a cell when it wants to divide? What important “stuff” is inside the nucleus? What role does DNA play in our cells? It tells your cell how to act and what to become What is DNA made up of? Nucleic Acid What does DNA look Like? DNA looks like spaghetti in the cell In this form it is called chromatin • DNA can wind up on itself to form chromosomes – 46 chromosomes in human cells Human Karyotype Human Karyotype • Shows many chromosomes are present • Shows chromosomes with their pair • One from mom and one from dad • Also can identify gender • Y Chromosomes are much smaller • XX = female (two long chromosomes) • XY = male (1 short and 1 long chromosome) • Can use karyotypes to identify chromosomal abnormalities (trisomy 21) Chromosome Parts Single stranded chromosome Double stranded chromosome – It has gone through DNA replication Sister chromatids (identical copies) Why Do Cells Reproduce? • To make new cells in order to grow and repair itself Cell Cycle • A repeating process of cell growth and division CELL CYCLE • Interphase – A cell spends 90% of it’s life in interphase. 3 Phases of Interphase G1- First growth phase S phaseDNA copied G2Second growth phase Mitosis (M) Phase The nucleus and DNA divide Mitosis is divided into phases: Prophase Metaphase Anaphase Telophase What Cell Parts Are Involved? Nuclear Membrane Cytoplasm Nucleus Chromosomes (DNA) Cell Membrane Centrioles Nuclear Membrane Prophase Centriole Chromosomes Spindle Fibers Prophase Chromosomes thicken Nuclear membrane begins to disappear Spindle fibers start to form between the centrioles Metaphase Centriole Chromosomes Spindle Fibers Metaphase Chromosomes line up across middle Spindle fibers are attached to each chromosome (at the centromere) Anaphase Centriole Chromosomes Spindle Fibers Anaphase Centromeres divide Sister chromatids are pulled toward opposite ends of the cell Nuclear Membrane Telophase Centriole Chromosomes Furrowing Telophase Nuclear membrane begins to re-form Chromosomes uncoil (becoming less visible) Furrowing occurs Cytokinesis • Cytoplasm divides and two separate daughter cells are produced Mitosis • Each cell now has 46 chromosomes (same it started with) • Each new cell grows until it is ready to divide Mitosis • All body cells in humans are made through mitosis • Sex cells (egg & sperm) are NOT made through mitosis Put It All Together!!! Animal Cell Mitosis All Cells are Different!! • All cells live for different lengths of time • Cells carry out mitosis at different speeds to replace cells that are worn out Brain cells 30-50 yrs Red Blood Cells 120 days Platelets 10 days Stomach Lining 2 days Cells Liver Cells Intestine Lining 200 days 3 days Cells Skin cells 20 days Mitosis • In which body organs do cells carry out mitosis the most often? Stomach, Intestine, Skin • In which body organs do cells carry out mitosis the least often? Brain Plant vs. Animal Cell Mitosis • Plant cells do not have centrioles • There is no furrowing in telophase. A cell wall forms instead. Put It All Together!!! Plant Cell Mitosis Flaws in Mitosis When cells are dividing out of control, tumors are produced Cancer is one type of tumor that can result from out of control mitosis Mutations • Mutations = random mistakes in DNA copied during Interphase • Can result from UV radiation, genetics, smoking, etc.