Download Cell Reproduction - wentworth science

Cell Reproduction
Many Cells from One
 Many living organisms are multi-cellular. This means that
they are made of many cells
 Humans, for instance, are made of approximately 100
trillion cells
 But, we all started out as one cell. Where did the other
99,999,999,999,999 cells come from?
Body Growth and Repair
 Bodies make new cells to grow and repair themselves
 Each cell has the ability to divide into two new cells
 These new cells, called daughter cells, are identical to
the original cell, called a parent cell.
 These daughter cells can then divide into two more, and
so on, and so on.
 This type of cell division is referred to as mitosis.
Mitosis
 Mitosis: Cell reproduction in which two identical cells are
made from one.
 All body cells in you, for instance, are formed by mitosis
 “Body cells” refers to all cells that make up most of the
body, such as skin, blood, bones and your internal
organs.
 Mitosis occurs at different rates for different tissues
 Brain cells may last up to 50 years whereas the cells in
your stomach lining only last 2 days
Introduction to Mitosis
 Mitosis is sort of like photocopying. You get copies
based on the original
 Mitosis involves the chromosomes, centrioles, nucleus
 An important step that happens before mitosis is when
each chromosomes is doubled.
 The DNA strands make copies of themselves
 The two strands are held together at one single point
(called a centromere)
 The stands that are joined are called sister chromatids
 The centrioles double also
Step 1:
Sister chromatids start to shorten and thicken
Nuclear membrane starts to breakdown
Centrioles move away from each other
Fibers form between centrioles
Step 2:
Centrioles move to opposite ends of cell
Sister chromatids attach to the fibers
Chromatids are pulled toward the center of cell
Chromatids are now lined up at center of cell
Step 3:
Sister chromatids are pulled apart by fibers
Sister chromatids are pulled to opposite ends of the cell
Step 4:
Each end of cell now has a complete set of DNA
Fibers disappear
Nuclear envelopes re-form around DNA
Cell membrane pinches in at both sides to form two new
cells
After Mitosis
 The two new daughter cells are genetically identical to
the parent cell
 This means that their chromosomes are identical to the
parent cell’s and they both have the same number of
chromosomes as the parent cell
 The new cells are slightly smaller than the parent cell but
they will grow
Benefits of Mitosis
 Helps organisms grow
 Replaces cells that have died or are damaged
Plant Cells vs. Animal Cells
 Plant cells do not have centrioles
 After mitosis in plant cells, a new cell forms to make the
two new cells
Meiosis
 Meiosis is a different type of cell division
 Meiosis results in the formation of sex cells (sperm and
egg cells)
 The big difference between meiosis and mitosis is that
meiosis involves two cell divisions and results in 4 cells.
Each with half the number of chromosomes as the
original cell
Step 1:
Sister chromatids shorten and thicken
Nuclear membrane breaks down
Centrioles move away from each other
Matching chromosomes come together to form pairs
Step 2:
Centrioles move to opposite ends of cell
Sister chromatids attach to the fibers
Fibers move the two pairs of chromosomes to center of cell
Step 3:
Fibers move matching chromosomes apart (sister chromatids
remain together)
Cell membrane pinches together and forms two new cells