Chapter 9 Cellular Reproduction. Main Idea – Cells grow until they reach their size limit, then...
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Transcript of Chapter 9 Cellular Reproduction. Main Idea – Cells grow until they reach their size limit, then...
Chapter 9 Cellular
Reproduction
Main Idea – Cells grow until they reach their size limit, then they either stop growing or divide.
Most cells are smaller than the . at the end of a sentence in your textbook.
Why are cells so small?What are the primary stages of the cell cycle?What is interphase?What are the stages of interphase?
Section 9.1 Cellular GrowthCell Size LimitationsThe key factor that limits cell size is the ratio
of its surface area to its volume.
The surface area of a cell is the area covered by the plasma membrane.
Remember the plasma membrane is the structure that all nutrients and wastes must pass through.
The volume is the space made up of the inner contents of the cell, including all organelles and cytoplasm.
Which cell would be able to distribute nutrients and wastes to all parts of the cell more efficiently?
Calculating Cell SizeTo calculate surface area use the formula:Length x Width x Number of Sides = surface areaSmall cube = 1µm x 1µm x 6 sides = 6µm2
To calculate volume use the formula:Length x Width x Height = volumeSmall cube = 1µm x 1µm x 1µm = 1µm3
The ratio of surface area to volume is 6:1
Medium cubeSurface area = 2µm x 2µm x 6 = 24µm2
Volume = 2µm x 2µm x 2µm = 8µm3
Medium cube ratio = 3:1
This is a smaller ratio of surface area to volume.
This means the cell might have a harder time supplying nutrients and expelling wastes products.
What is your prediction for the largest cube?Large cubeYour turn
Surface area = ?Volume = ?Ratio = ?
Large cube calculationsSurface area = 4µm x 4µm x 6 = 96µm2
Volume = 4µm x 4µm x 4µm = 64µm3
Ratio = 1.5:1
Does the nucleusseem to change size?
Would the otherorganelles change size?
Which cell above would be the most efficient?
Another reason cells stay small is to transport substances more efficiently.-Substances move bydiffusion or by motor proteins.
-Diffusion over largedistances is slow andinefficient.
-Small cells maintain more
efficient transport systems.
Another reason cells stay small is to communicate more efficiently. Cell size affects the cell’s ability to communicate
instructions for cellular functions.
If a cell becomes too large, it becomes almost impossible for cellular communications.
Example: The signal to trigger protein synthesis might not reach the ribosome fast enough in large cells to make protein to keep the cell alive.
The Cell Cycle - Once a cell reaches its size limit it will stop growing or divide.Cells reproduce by a cycle of growing and dividing
called the cell cycle.
Most cells will divide.
Cell division prevents the cell from becoming too large.
It also is the way the cell reproduces so that you grow and heal certain injuries.
3 Main stages of the cell cycle
Stage 1 – InterphaseInterphase is divided upinto 3 substages.G1, S, G2
- cell grows (G1)
- carries out cell functions (S)- replicates (G2)
(makes copies of its DNA)
The 3 Stages of interphase
G1 (stage 1)
- the cell is growing, - carrying out normal cell functions- preparing to duplicate
DNA
S (stage 2)
- Cell copies its DNA- Prepares for cell division
The 3 Stages of interphase
Genetic material is replicated (S)
Chromatin is the relaxed
form of DNA in a cell’snucleus.
Chomosomes arestructures that containthe genetic material thatis passed from
generationto generation.
Sister chromatids Chromosomes
Shape:- Chromatin coil around histones- 2 identical halves = sister chromatids- Held together with a centromere.
The 3 Stages of interphase
G2 (stage 3)
- Cell prepares for the division of its nucleus.
- The cell checks to make sure everything is ready to go on to mitosis.
Stage 2 - MitosisDuring mitosis the cell’snucleus and nuclear materialdivide.
Mitosis is divided up into 4 substages.
Stage 3 - Cytokinesis
During cytokinesis a cell’scytoplasm divides,creating a new cell.
Some cells complete thecycle as fast as 8 minutes.
Some cells take a year tocomplete the cycle.
Most animal cells take 24hours to complete the cellcycle.
Section 9.2 Mitosis and Cytokinesis
Main Idea: Eukaryotic cellsreproduce by mitosis,the process of nucleardivision, and cytokinesisof cytoplasm division.
Mitosis – Why is it important?The key activity of mitosis is to accuratelyseparate the cell’s duplicated DNA.Why?1. Genetic information is passed into new cells.2. genetically identical daughter cells are made. (same
DNA, cytoplasm and organelles as parent cell)3. Increases the number of cells so young organisms can
grow to its adult size.-4. Organisms can replace damaged cells.
Four Stages of Mitosis
1. Prophase - 3 phases early-nucleoi break down
middle nuclear membrane break down
late centrioles on opposite sides
2. Metaphase
3. Anaphase
4. Telophase
Prophase – The 1st stage
-Longest stage of mitosis-Chromatin tightens into chromosomes-Chromosome contains genetic material-Each half of the X is a Sister Chromatid -Sister Chromatids are
structures that contain identical copies DNA.
-Centromere is where sister chromatids are attached at the center.
Spindle Apparatus isimportant for moving andorganizing chromsomes beforecell division. 1. Nucleolus seems to disappear2. Spindle fibers form in
cytoplasm (microtubules)3. Centrioles migrate to the
ends or poles of the cell.4. Aster fibers appear at the
centrioles
During middle prophase….
Near the end of prophase…
- Nuclear envelope seems to disappear
- Spindle fibers attach toeach side of sister chromatids- Spindle fibers attach at
each pole of the cell.If the cell were to divide now,
where do you predict it would split?
Metaphase is the 2nd stage of mitosis
One of the shortest stages1. Sister chromatids are pulled bymotor proteins toward the centerof the cell2. Chromatids line up in the middle or equator of the cell.
Anaphase – the 3rd stage of mitosis
Chromatids are pulled apartduring anaphase.1. Microtubules shorten and
pull apart at the centomere2. Sister chromatids separate into 2 identical chromosomes3. Chromosomes move towards
the poles of the cell.
Telophase – 4th stage of mitosis
The stage when chromosomesarrive at the poles of the cell.1. Chromosomes relax back into
chromatin2. Two new nuclear membranes
start to form3. nucleoli reappear4. spindle apparatus disassembles
Cytokinesis…the division of cytoplasm
In animals1. Microfilaments will constrict
to pinch off cytoplasm to form a groove.
2. will result in 2 cells with identical nuclei
In plants1. a cell plate forms between
the 2 daughter nuclei2. cell wall then forms3. two genetically identical
cells are formed
Cells alive www.cellsalive.com
Section 9.3 Cell Cycle RegulationMain Idea: Normal Cell CycleThe timing and rate of cell division is
important to healthy cells.
The rate of cell division depends on the type of cell.
The cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong.
Types of cells
All somatic (body cells) have the same number of chromosomes. (46) 2n
Body cells are called diploid as they have 2 copies of each chromosome. (di = 2)
All gametes (sex cells) have half the number of chromosomes (23) n
Sex Cells are called haploid as they have half the number of chromosomes.
Apoptosis – programmed cell death
Not all cells are destined to survive.
Example: Human development-Hands and Feet of embryo
Cells between fingers and toesundergo apoptosis.When it is time to separatefingers and toes in theorganism.Cells shrivel and shrink to bedisposed of by the cell.
Example of Problem with Apoptosis: Web Fingers
Protecting normal cell growth
Apoptosis also occurs when…-Cells have been damaged beyond repair-DNA has been damaged that could lead to
cancer-In plants apoptosis is what causes leaves to
fall from the trees.
Cancer.. uncontrolled cell growth and division of cells
When the normal controlmechanisms in a cell fails,cancer can result.
Cancer cells can be identifiedbecause they have anabnormal shape compared tothe normal cell.
Left unchecked, a canceroustumor can destroy its hostorganism.
More about CancerCancer occurs due to mutations or changes
in the segments of DNA that controls the production of proteins.
Often the genetic change or damage is repaired by the cell’s repair system.
Environmental Factors can affect cells.Carcinogens are substances that are
known to cause cancer.Avoiding carcinogens can help reduce the
risk of cancer.
Carcinogens are substances that are known to cause cancer.
Avoiding carcinogenscan help reduce the riskof cancer.
Lung cancer can resultfrom 1 and 2 at theright.
Is lung cancer passed onin cells by geneticmaterial?
Known Carcinogens1)Tobacco products:-first hand smoke
(smoking)-second hand smoke-smokeless tobacco2) Asbestos Ultraviolet radiation (sun)X-ray radiationHarmful chemicals
Cancer geneticsMore than one change in DNA is needed in a
normal cell to cause cancer.Over time, there might be many changes in
DNAThis might explain why the risk of cancer
increases with age.An offspring that inherits one or more changes
from a parent may be at a higher risk for developing cancer.
Stem Cells are unspecialized cellsthat can develop intospecialized cells underthe right conditions.
Because stem cells arenot locked intobecoming a certain cell,they might be the key tocuring many medicalconditions and geneticdefects.
Prokaryotic Cells divide by Binary Fission