06 cell growth and reproduction
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TRANSCRIPT
• CELL SIZE LIMITATION (8 .2)•THE CELL CYCLE (8 .2)
• CONTROL OF THE CELL CYCLE (8 .3)
Cell Growth and Reproduction
• WH Y C AN’ T OR GANI SMS BE JUST ONE GI ANT C E L L?
• I F A C E L L WANT S T O MAKE A C OPY OF I T SE L F, WH AT DO YOU T H I NK I S T H E F I R ST ST E P?
• WH AT OR GANE L L E S AR E I NVOLVE D I N C E LLUL AR R E PR ODUC T I ON?
Answer these questions:
Cell Size Limitation
Cell size is limited by… Diffusion rate DNA Surface area-to-volume ratio
Diffusion Rate Fast and efficient over short distances Becomes slow and inefficient as distances become
larger
Cell Size Limitation
DNA To build proteins, the blueprints for those proteins
(DNA) must be copied The cell cannot survive unless there is enough DNA to
support the protein needs of the cell
Answer these questions: What does DNA code for? Where is DNA stored? How can we increase cell size and still have enough
DNA to support the protein needs of the cell?
Surface area-to-volume ratio As size increases, volume increases much faster than
surface area
Answer this question: How does the surface area-to-volume ratio affect cell
function?
Cell Size Limitation
Cell Size Limitation
Surface area-to-volume ratio The demand for oxygen, nutrients and waste removal
grows faster than the surface area of the plasma membrane allows
• WHAT 3 FACTORS LIMIT CELL SIZE?
• WHY DO WE (AND OTHER ORGANISMS) MAKE NEW CELLS?
• WHAT ARE CHROMOSOMES?
Answer these questions:
Cell Reproduction
Cell division results in two cells that are identical to the original, parent cell
Cells are constantly growing, dividing and dying
New cells are used for growth, repair/replacement
Cell Reproduction
In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes.
Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing.
However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope.
Cell Reproduction
For most of a cell’s lifetime, chromosomes exist as chromatin
Chromatin is long strands of DNA wrapped around proteins called histones
Cell Reproduction
Before a cell can divide, it must pack up and untangle the chromatin so it can be moved easily
We see chromosomes when the chromatin is tightly packed
https://www.youtube.com/watch?v=gbSIBhFwQ4s
The Cell Cycle
The cell cycle is the sequence of growth and division of a cell
The growth period is called interphase
The division period is called mitosis
The Cell Cycle - Interphase
Divided into 3 parts G1 – cell growth, high
protein production S – DNA synthesis G2 – Organelles and
other cell parts for cell division are assembled
The Cell Cycle - Mitosis
The 4 phases of mitosis Prophase Metaphase Anaphase Telophase
The Cell Cycle – Mitosis: Prophase
Prophase
The long stringy chromatin coils up into visible chromosomes
Each duplicated chromosome is made up of two halves called sister chromatids held together by a centromere
The Cell Cycle – Mitosis: Prophase
As prophase continues, the nuclear membrane and nucleolus disintegrate
In animals, two pairs of centrioles begin to migrate to opposite ends of the cell
The spindle (made of microtubules) begins to form
The Cell Cycle – Mitosis: Metaphase
Metaphase
The chromosomes line up across the middle of the cell
Each sister chromatid is attached to its own spindle fiber at the centromere.
The other end of the spindle fiber attaches to the centriole (in animals) or the cell wall (in plants)
The Cell Cycle – Mitosis: Anaphase
Anaphase
Anaphase is marked by the separation of sister chromatids
Centromeres split apart and each chromatid of a pair is pulled to opposite ends of the cell
The Cell Cycle – Mitosis: Telophase
Telophase
Chromatids reach the opposite poles of the cellChromosomes unwind The spindle breaks downThe nucleolus reappearsA new nuclear membrane forms around each
set of chromosomesA new plasma membrane begins to form
between the two new nuclei
Cytokinesis
Following telophase, the cells cytoplasm divides in a process called cytokinesis
In animal cells, the plasma membrane folds in at the equator
In plant cells, a cell plate is constructed between the two new cells, allowing new cell membranes and cell walls to form
Results of Mitosis
Mitosis results in 2 new cells with identical chromosome sets
The two daughter cells will carry out the same cellular processes and functions as those of the parent cell
Each daughter cell will grow and divide
Videos
Computer animated mitosis: https://www.youtube.com/watch?v=VGV3fv-uZYI
Black and White: https://www.youtube.com/watch?v=ZeW8HaCUtOQ
Colored: https://www.youtube.com/watch?v=P7m3WfzgZdI
Hank Green: https://www.youtube.com/watch?v=L0k-enzoeOM
Control of the Cell Cycle
Control of the Cell Cycle
At each checkpoint, if conditions are met, cyclin tells cyclin-dependant kinase to move to the next step of the cell cycle
Control of the Cell Cycle
DNA holds the code for the construction of cyclin, cyclin-dependant kinase and all of the other proteins and enzymes involved in control of the cell cycle
If the genes that code for any of these are mutated, dysregulation of the cell cycle occurs Checkpoints may not work The signal for cell division may be given when more
cells are not needed This is cancer