Lesson 1: Cell Theory and Cell Division
What is the cell theory?
http://biology.about.com/od/biologydictionary/g/celltheory.htm
So, we know that all cells come from pre-existing cells. Which leads to the question, why do Cells
Divide?
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Growth
Reproduction (in single celled organisms)
Repair
Some Cells never divide, others divide frequently. The division cells can be represented by the cell cycle.
The Cell Cycle
Control of the Cell Cycle
G1 Checkpoint - Check to see if DNA is damaged
G2 Checkpoint - Check to see if DNA is replicated properly
M Checkpoint - spindle assembly checkpoint, check for alignment of chromosomes
Apoptosis - programmed cell death, if any of the checks fail
Chromosome Structure
Chromosomes also have banding patterns unique to each one. These bands are caused by certain
dyes.
Each chromosome has mane alleles, or alternate forms of genes
Homologous Chromosomes - each chromosome has a match, called a homolog. This is why
normal organisms always have an even number of chromosomes. One homolog you received from
your mother, the other you received from your father. They are not exactly alike, but they are the
same size, shape, and have the same banding pattern.
Diploid Chromosomes (pairs)
Haploid Chromosomes (not paired)
**Sex Chromosomes
In humans, there are two chromosomes that determine sex: the X and the Y
chromosome.
If you have an XX - you are female
If you have an XY - you are male
Diploid vs Haploid
Body cells have the full set of chromosomes – they are DIPLOID (In humans, 46)
Sex cells (sperm and eggs) have half a set – they are HAPLOID (In humans, 23)
A karyotype shows all the chromosomes of an individual, in humans we see 22 pairs of autosomes,
plus 1 pair of sex chromosomes. (total # of chromosomes = 46)
One of the important things that happens in cell division is related to the number of chromosomes that
are found within the nucleus of a cell. Most normal cells, during their cycle, have what is termed a
diploid number of chromosomes because they are a matching pair of chromosome. In humans, the
diploid number is 46 because we have a set of 23 chromosomes and then a matching set of 23
chromosomes. In the process of cell division, the chromosomes are actually copied and doubled, so that
each of the cells after division will have the diploid number of 46. Look at the top of the cell cycle at the
interphase step.
Some cells get created to have only a single set of chromosomes and are known as haploid. For
humans, these cells have 23 chromosomes, or half the number of most cells in the body. These cells are
the sexual reproduction cells known as sperm and egg cells. The reason why they only have 23
chromosomes is that when they come together in fertilization, the chromosomes line up to give the
matching set of two chromosomes, one set from each parent.
Lesson 2: The Nucleus and Genetic Material
What is the brain of the cell?
We know the answer to this question is the nucleus and it controls the cell’s activities while also holding
all genetic material. This material, known as genetic material, can be different depending on the type
of cell. Chromosomes are a threadlike structure of DNA that make up the genes. Genes are on specific
sites of chromosomes and carry specific traits (like eye colour). Genes are always found in a distinctive
position and on specific chromosomes. DNA stands for Deoxyribonucleic Acid and essentially makes up
the genes and the chromosomes. So, chromosomes and genes are DNA, but DNA can also be much
more.
http://www.google.ca/imgres?imgurl=http://www.merckmanuals.com/media/home/figures/MMHE_01
_002_01_eps.gif&imgrefurl=http://www.merckmanuals.com/home/fundamentals/genetics/chromosom
es_and_genes.html&usg=__f7k_QgH1aBXDGdmidphgfpbuhZ8=&h=424&w=429&sz=50&hl=en&start=8
&zoom=1&tbnid=1XiocJ3EDqnvZM:&tbnh=125&tbnw=126&ei=L2wgTq1INK10AHB9d0H&prev=/search%3Fq%3Dgenetic%2Bmaterial%26um%3D1%26hl%3Den%26safe%3Dac
tive%26sa%3DN%26rls%3Dcom.microsoft:en-us%26tbm%3Disch&um=1&itbs=1
The link above shows pictures of all DNA and the chromosomes. So, if we know the genetic material is
all kept in the nucleus, how does it get to the next cell when the cell divides?
Lesson 3: Cellular Reproduction (Mitosis, Meiosis, and Binary Fission)
We will try to begin and end this section by using microscopes to try and see the stages of cell
development.
We are going to study three basic ways in which cells reproduce.
1. Binary Fission
This process occurs in Prokaryote Cells (cells with no nucleus), like bacteria or protists. The DNA is
duplicated, and then the cell splits apart. This is cell division in which the chromosome number remains
the same, diploid to diploid.
http://www.youtube.com/watch?v=3cD3U2pgb5w
2. Mitosis
http://www.bozemanscience.com/science-videos/2012/5/6/mitosis.html
In this process the cell will copy all of its’ DNA (remember two matching strands) to make two complete
sets so that one set can be sent to each of the daughter cells. This is cell division in which the
chromosome number remains the same, diploid to diploid. Mitosis is used for most of the cell division
that occurs within your body and for most development and growth of living things.
Interphase - cell growth, preparation for division, DNA synthesis. Cells spend most of their
lives in interphase, it is the longest part of the cell cycle. (Some cells never leave
interphase)
Mitosis - The division of the nucleus that results in identical complete copies of chromosmes
packaged into two new nuclei.
Occurs in 4 phases: Prophase, Metaphase, Anaphase, Telophase
Cytokinesis - The division of the cytoplasm that results in two daughter cells, occurs at the
end of telophase.
**In plant cells, cytokinesis begins when a new cell wall forms between the two new cells.
**In animal cells, the two new cells pinch and pull apart
Prophase
Metaphase
Anaphase
Telophase
Mitosis produces 2 daughter cells that contain the exact same number of chromosomes as
the original parent cell
Daughter cells are DIPLOID
Mitosis Animations at stolaf.edu, cellsalive,wormclassroom, mcgraw-hill, sumanasinc, johnkryk
3. Meiosis
http://www.bozemanscience.com/science-videos/2012/5/6/meiosis.html
In this process the cell will copy all of its’ DNA and make two complete sets, and then it will split into two
cells so that there is one complete set of DNA in each of the two daughter cells. These two daughter
cells will then split again, making four cells each with a single strand of DNA. This is cell division in which
the chromosome number is halved, or from diploid to haploid. Meiosis is used to create the cells used
for sexual reproduction.
Setting the Stage for Meiosis
Crossing-Over - during prophase I, homologous pairs join together (synapsis) and exchange
genetic information
Exchange of DNA during prophase I increases genetic variability. Chromatids are no longer exact
duplicates.
During metaphase, chromosomes line up in PAIRS, but they line up randomly. This picture shows
all the different possible arrangements for an organism with 6 chromosomes. – a phenomenon
known as INDEPENDENT ASSORTMENT
Fertilization = combining the genes of two different parents. Offspring show variation.
Overview of Meiosis --- occurs in two stages - Meiosis I and Meiosis II
The Phases of Meiosis
Step By Step
See Labels
Meiosis Compared to Mitosis
Mitosis
Meiosis
Number of Chromosomes
Number of Daughter Cells
Where does it Occur?
Reproduction type
Reproduction Time
Meiosis Animations at stolaf.edu, mcgraw-hill, johnkyrk,cellsalive
Please complete the mitosismieosis worksheets.