Notes: Life Cycle of a Cell
Chapter 10
10.1 Cell Growth
Cells are the basic unit of life; all living organisms are made up of one or more cells
As organisms grow, they acquire more cells.
Cells are limited in size Why?
DNA overload: as a cell gets larger more DNA is needed to perform its life’s
activities, but there is a limited amount of DNA
Cell Membrane overload: exchange of materials must occur through the cell
membrane, not enough cell membrane for all the exchange that would need to
occur.
Ex: Surface Area (area the cell membrane takes up)
Length x Width x the number of sides
Volume (area inside the cell where the life functions occur)
Length x Width x Height
How much SA is required to supply enough nutrients to the volume inside a cell?
Calculated SA:V ratio.
SA = 1cm x 1cm x 6 = 6cm2
V = 1cm x 1 cm x 1cm = 1 cm3
1 cm cube cell Surface Area to Volume Ratio = 6 : 1
SA = 2cm x 2cm x 6 = 24cm2
V = 2cm x 2 cm x 2cm = 8 cm3
2 cm cube cell Surface Area to Volume Ratio = 3 : 1
SA = 4cm x 4cm x 6 = 96cm2
V = 4cm x 4 cm x 4cm = 64 cm3
4 cm cube cell Surface Area to Volume Ratio = 3 : 2
The surface area to volume ratio decreases, as the cell gets larger.
There is more volume in the cell where the chemical reaction of life occur
than there is area on the cell membrane to take in materials for and let out
wastes from the chemical reactions.
In order to solve the problem of cell size a cell must divide
10.2 Cell Division - Cell divides into 2 daughter cells
In order for each new cell to get a copy of the genetic material it must first be
replicated.
In Eukaryotes the genetic material is made up of Proteins and DNA
( ___________________ are complex. Cell must copy genetic info first so that each daughter cell receive a copy of genetic info)
In Prokaryotes the genetic material is made up only of DNA
(________________________ are simple. Cell division separates contents into 2 parts)
Eukaryotic Structure of the Genetic Material
During most of the life of a cell DNA is in long strands called Chromatin because
the cell must be able to have access to the DNA to read it. Chromatin is not visible
under a microscope.
Cell Membrane
Nuclear Envelope
Chromatin
However, after DNA has been replicated and it is needed to transfer into a new
nucleus it must be condensed so that it is more easily moved. Chromosomes are
visible only during Mitosis or Meiosis (nuclear division).
Chromosome
Sister
Chromatid
Centromere
__________________ carry genetic info from one generation to next.
Chromosomes are made from ____________ & _______________
Chromosomes are not visible except the time of _________________(as
DNA and protein
is spread through nucleus).
At the time of cell division Chromosomes condense into compact structure
& can be seen through light microscope.
Larger view of _________________
Chromosome: Two sister chromatids joined together at the centromere
Chromatid: One, condensed strand of DNA and proteins
Sister Chromatids: Genetically Identical Chromatids
Centromere: location where sister chromatids are joined together
Chromatin: Uncondensed (strands) DNA
Life Cycle of a Cell
Life of cell – one division after another .
Cell cycle – cell grows, prepares for division, divides into 2 daughter cells, each daughter cell begins the cell cycle.
4 phases of cell cycle – G1, G2 (gap- growth & activity), S(copying chromosomes), M (Mitosis + cytokinesis)
1.
2.
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Interphase
Longest phase of the cell cycle
Normal life processes occur (except cellular division)
DNA is uncondensed, not visible, Chromatin
3 Steps
o G1 – Growth; Number of organelles and the amount of cytoplasm
increases
o S – DNA replication
o G2 – Preparation for Division; cell makes organelles (centrioles) and
substances needed
Nuclear Division
Division of the nucleus can occur to form cells that will reproduce either
Sexually or Asexually.
ASEXUAL Nuclear Reproduction = MITOSIS
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter11/animations.html#
Results in 2, genetically identical, diploid nuclei that will produce Somatic Cells
46
Chromosomes
46
Chromosomes
46
Chromosomes
Humans have 46 chromosomes (23 pairs)
Diploid : 2 sets of chromosomes; chromosomes in pairs
All the cells in an organism descended from a single cell (ZYGOTE) created by the
joining of a sperm and an egg.
Although all somatic cells have the exact same DNA in their nucleus, they do not
all perform the same functions (blood cells, nerve cells, bone cells etc.)
WHY?
All the genes on the DNA are not turned on all the time. Only specific genes are
turned on for particular types of cells.
4 Steps to Mitosis
Prophase – sister chromatids condense, nuclear envelope and nucleolus
disappear; centrioles begin to move to opposite ends of the cell, spindle fibers
begin to form
Metaphase – sister chromatids line up in the middle of the cell, spindle fibers
attach to centromeres
Anaphase – sister chromatids pulled apart by spindle fibers contracting, pulled
to opposite poles of cell.
Telophase – nuclear envelope and nucleolus reform, chromosomes
uncondensed (chromatin), centrioles disappear, cytoplasm begins to split.
Check out this website for a great animation http://www.cellsalive.com/mitosis.htm
3. Cytokinesis
Division of the cytoplasm, formation of 2 new cells from a parent cell
Animal Cell(______ ______________ is drawn inwards until cytoplasm is pinched into equal parts)
Cell Membrane forms by pinching in at a cleavage furrow.
Cleavage Furrow
Plant Cell
New Cell Wall forms by creating a Cell plate at the equator
Growth and Division can be turned on and off. Not all cells move through cell cycle at the same rate.
10.3
Regulating the Cell Cycle
The Cell Cycle is regulated by proteins called cyclins
When cytoplasm from a cell in mitosis is injected into another cell, it enters mitosis.
There are 2 types of cell cycle regulators:
1. Internal - Respond to events inside a cell (make sure that cell does not enter mitosis till all the
chromosomes are copied
2. External - Respond to events outside a cell (growth factors, speed up or slow down growth cycle,
embryo development, wound healing)
Cancer results when cells are growing out of control; abnormal cell growth
Benign – not spreading,
all cells are sticking together
Malignant – spreading,
cells are breaking off and traveling throughout organism
http://www.hhmi.org/biointeractive/cancer/animations.html