Name: _____________________
Date: _________________
Unit 4B: Asexual Reproduction and Mitotic Cell Division
NOTES
The Cell Theory states:
1) cells are the basic unit of life
2) all living things are made up of at least 1 cell, and
3) all cells come from pre-existing cells (cell reproduction/division)
What is the purpose of cell reproduction?
In Unicellular Organisms: to form a new organism-asexual reproduction
In Multicellular Organisms:
a. _____________________- addition of new cells
b. _____________________- replacement of lost or injured cells
c. _____________________- formation of reproductive cells (egg + sperm) in sexual
reproduction
As you grow from a baby to a teenager, do your cells get bigger or do you gain more cells?
____________________________________________________________________________
Why do cells divide into more cells rather than continue to grow?
2 Reasons:
1. Larger size puts larger demands on the _________________ (information shortage)
2. Larger cells are ______________________________ at moving materials in and out of
the cell (exchanging materials)
Summary/Questions:
1
1. Information Shortage
- DNA contains instructions for making proteins for the cell
- As the cell gets bigger, the DNA stays the same
- If a cell continues to get larger, eventually the DNA would not be able to make
____________________________ quickly enough for the cell
2. Exchanging Materials
Cells pass material in and out through the cell membrane
- Surface area (SA) of the membrane determines the rate of
____________________________________________
Cells use and break down materials within the cell
- Volume (V) of the cell determines ________________________
is needed (larger cells need more nutrients, O2, etc.)
Ratio of Surface Area to Volume
- A ratio is a comparison
Ex. Surface Area: Volume (Surface Area/Volume)
- The amount of surface area for each unit of volume
Volume = l x w x h
Surface Area = l x w (x 6 sides)
Summary/Questions:
2
Determine the SA/V Ratio for cubes 1, 2, & 3 and fill in the table
Cube 1
Cube 2
Cube 3
SA
V
SA/V
a. Which cell has the greatest SA / V ratio? ____________
b. So, which cell has the easiest time moving material in and out of the membrane and
getting nutrients, O2, etc. to all places in the cell? ___________
c. From one cube to the next, the SA increased by a factor of ______.
d. The V increased by a factor of _______.
e. Which is increasing faster as the cell gets bigger? (circle) SA or V
- As a cell grows, its volume increases _________________________ than its surface area
- If a cell becomes too large, ___________________________________________ can
come through the membrane to feed the whole cell.
- Similarly, wastes from the huge cell would not be released fast enough.
- Therefore, _____________________ size allows for ____________________ movement
of materials in, out, and throughout the cell.
Summary/Questions:
3
Thus, instead of growing too large, cells divide in half!
- This ______________________ the SA / V ratio
- 1 cell divides into 2 “______________________” cells.
- This process is called cell division
Before a Cell Divides…
1. The cell gets the _______________ to divide
2. It _______________________ (copies) all of its DNA
3. Then, the cell divides and each daughter cell gets a complete copy of the DNA
Cell Division Solves the Growth Problems
1. Each daughter cell gets its own DNA so there is no information shortage.
2. Volume is reduced in division, so efficient exchange of material can occur through the cell
membrane.
Practice
Two factors important in the transport of materials into or out of cells:
- The surface area of the cell membrane should be
large / small
- The volume of cell matter that materials have to travel through to get to all parts of the
cell should be as
small / large
as possible.
The best combination of surface area and volume factors is one in which:
-
the surface area is
small / large
and the volume is
small / large
the surface area to volume ratio: SA /V is small / large
Cells that conduct transport most efficiently will be
larger / smaller
Summary/Questions:
cells.
4
Structure Leads to Function
- Different cell types in the body have different
functions
Ex: muscles cells and nerve cells have different
functions
Muscle Cells
- All cell types are structured to __________________ their
surface area to volume ratio!
- This allows for efficient movement of materials.
How do the structures of these cells maximize SA/V ratio?
Nerve Cell
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
The Process of Cell Division
Chromosome Recap:
- Packages of DNA and ____________________ highly condensed.
Prokaryotic Chromosomes
- Prokaryotes have no nucleus
- Usually prokaryotes have 1 ___________________ chromosome
in the cytoplasm.
- Not all prokaryotes have ____________________.
Eukaryotic Chromosomes
- DNA binds to proteins called histones
- DNA and histones condense to form
chromatin
- Chromatin is condensed completely to form
chromosomes after the DNA has replicated
and the cell is ready for division.
- Chromosomes make it possible to separate DNA precisely during cell division.
Summary/Questions:
5
Chromosomes can be seen in two forms:
1. Single-Arm: are composed of a single _________________
2. Double- Arm (Replicated Form, Duplicated form): are made
up of paired, genetically ____________________ chromatids,
called __________________________________.
- Sister chromatids are joined at the ______________________.
- Because the sister chromatids are formed during replication of
DNA, they are identical right down to the nucleotide
sequences!
The Cell Cycle
- The cell cycle is the series of events that cells go through as they grow and divide
The events in the cell cycle are:
- Growth
- Preparation for division
- Division into two daughter cells
Prokaryotic Cell Cycle
- Also called ______________________________ (a form
of asexual reproduction)
- Cell grows, doubles its DNA, and splits in two, dividing
the DNA and cytoplasm between the daughters.
Summary/Questions:
6
Eukaryotic Cell Cycle- Cell division in body
(_____________________) cells
Consists of 4 phases:
-
G1 (Growth)
S (DNA Replication)
G2 (Preparation for Cell Division)
M (Cell Division)
Only during _____________________ does division
actually occur.
The other 3 phases are part of __________________
- the “in-between” period of growth
G1 Phase: Cell Growth
- Cells ____________________ in size
- Synthesize new proteins
- Make new ______________________.
S Phase: DNA Replication
This cell is in _________________________.
- New DNA is synthesized (chromatin replicated)
- At the end of S Phase the cell will have twice the amount of DNA
G2 Phase: Preparing for Cell Division
- Shortest of the phases in Interphase
- Cell produces organelles and ____________________________________ for division
- Now the cell is finally ready to divide
M Phase: Cell Division
- The making of 2 _______________________ cells
- Very quick compared to the lengthy interphase.
- Consists of ___________________ (division of the nucleus) and ____________________
(division of the cytoplasm).
Summary/Questions:
7
Mitosis
Consists of 4 phases:
-
Prophase
Metaphase
Anaphase
Telophase
Remember PMAT
Prophase
- Longest phase of mitosis
- Duplicated chromatin ___________________ to form the double armed chromosomes
seen in the picture.
- Both copies attach to each other at the ________________
- The spindle begins to form
o System of microtubules that will help _____________
the duplicated chromosomes.
o Spindle fibers extend from the __________________
regions where centrioles are located (no centrioles in
plant cells)
o Centrioles move to opposite ends (poles) of the cell
- At the end of prophase…
o Chromosomes coil more tightly
o The nucleolus __________________________
o The nuclear envelope breaks down
Metaphase
- Shortest part of Mitosis
- Centromeres (and thus chromosomes) line up across the
_________________________ of the cell
- Spindle fibers _____________________ each centromere
to both poles of the spindle
Summary/Questions:
8
Anaphase
- Sister chromatids ____________________ into single
armed chromosomes and begin to move apart
- Separated chromosomes ________________________
spindle fibers to either pole of the cell
- When the movement stops, anaphase is over
Telophase
- The condensed chromosomes begin to
_________________________ (back into chromatin)
- A nuclear envelope ________________ around both
clusters of chromosomes
- Spindle breaks apart
- Nucleolus _________________ in each daughter nucleus
Mitosis is now complete
Cytokinesis
- The second portion of M phase
- Splits the _______________ in half, and splits the
cell in two
- Usually occurs at the same time as telophase
Cytokinesis Differs in Animal and Plant Cells
Animal Cells- the cell membrane is drawn inward by
microfilaments creating a __________________________________
- The cytoplasm is pinched into 2 parts until the daughter cells separate
Plant Cells- a ___________________________ forms in between the daughter cells.
- Cell membrane and cell wall form at the cell plate from vesicles containing membrane
and cell wall materials
Summary/Questions:
9
After cytokinesis is complete…
- The cell may enter G1 again and continue the cycle
- OR the cell may enter a phase called G0 or resting phase.
- During this time a cell is not preparing for division but rather
is making protein and doing normal cell functions.
- Different cells stay in G0 for different amounts of time.
(Nerve? ________ Skin? _______)
Compare plant and animal cell division:
Differences:
1. ___________________________________________________________________
2. ___________________________________________________________________
Similarities:
_____________________________________
Summary/Questions:
10
Regulating the Cell Cycle
Cell Growth and Cell Division are Controlled Carefully in Multicellular Organisms
- These controls can be turned on and off
Example: if you get a cut, new cells fill in the space only until the cut is healed
How do cells know when to divide?
Cyclins and Regulatory Proteins
 Cyclins- A family of _________________ that
regulate the timing of the cell cycle in eukaryotes.
- Act like _______________________ at
different points in the cycle to prevent it from
going forward if mistakes have occurred.
- Work with a family of proteins called _______
 Other regulatory proteins: Proteins inside and
outside the cell that help regulate the cell cycle
- Internal Regulatory Proteins- Proteins that respond to events ______________ the
cell, letting the cell know whether or not to proceed with the cell cycle.
Examples:
1. An internal regularity protein keeps the cell from entering mitosis until the
chromosomes have replicated.
2. A different protein prevents the cell from entering anaphase until the spindle fibers
have attached to all chromosomes.
- External Regulatory Proteins- Proteins that respond to events ____________ the cell
o Direct the cell to speed up or slow down the cell cycle
Examples:
1. Growth Factors- tell the cell to grow and divide
2. Inhibitory signals- proteins on the surface of other cells; tell the cell to slow down or
stop the cell cycle
o This prevents excessive replication
Summary/Questions:
11
Cells die and are replaced all the time
Two ways that cells end their life cycle
1. Accidental death by damage or injury
2. Programmed cell death called apoptosis.
- helps shape structures during development
- kills infected cells
- kills cells with DNA damage or cancer
- etc.
Cancer: Uncontrolled ___________________________
Cancer- a disorder in which body cells lose the ability to control
division
- Cancer cells _______________ respond to signals that
regulate cell growth and thus, divide uncontrollably.
Tumors
- A mass of cells
- Cancerous tumors are called ________________invade and destroy surrounding tissue
- Not all tumors are cancerous
- Some are ________________ – do not spread to
surrounding healthy tissue or around the body
Summary/Questions:
12
What Causes Cancer?
- ____________________ in genes that regulate the cell cycle
Example: the protein from the gene p53 normally halts the cell cycle until all
chromosomes have replicated (an ________________________ regulatory protein).
- If this gene is defective, the cell cycle will proceed _____________________
The defective gene is not the same for all cancers
- Some cancer cells do not respond to internal regulation, others do not respond to
external regulation, etc.
Possible Reasons for Defective Cell Cycle Genes
-
Innate ________________________ (born with it)
Smoking or chewing tobacco
Radiation exposure
Other defective genes
Viral infections
Etc.
Treatments for Cancer
- Some tumors can be removed by surgery
- Radiation is used to kill cancerous tumors
- Chemotherapy- using _______________________ (drugs) to kill cancer cells
o These drugs target _______________ dividing cells
o Will also kill normal, healthy cells that are dividing
Like? _____________________________________________________________
o Scientists seek to find a drug that kills cancer cells but not healthy cells
Summary/Questions:
13