Download Intro to Cell Division

Intro to Cell Division
Pre-Assessment
• Asexual vs. Sexual reproduction
• How do skin cells/blood cells/muscle cells
regenerate?
• Where is DNA located in a cell?
• Organize the following from smallest to
largest: chromosome, gene, DNA, nucleus,
organ, tissue, cell, organism
• How many chromosomes do humans have?
Asexual Reproduction
• Offspring are identical to parents
• Does not require fertilization
• Advantages –
• Disadvantages -
Sexual Reproduction
• Male and female (or +/- mating types)
• Exchange genetic information = offspring have
unique combination of traits
Cell Division
• How one cell divides into two
• 2 ways: Mitosis and Meiosis
Cancer Cell Division
Organize the following...
Human Chromosomes
Down’s Syndrome
How many chromosomes are in the
following cells?
Skin Cells
Egg Cell
Nerve Cell
Zygote
Sperm Cell
Blood Cell
DNA:
Deoxyribonucleic
Acid
• Located in nucleus of cell
• Responsible for cell’s
hereditary info
• Found “packaged“ in
chromosomes in a cell
Structure of DNA Molecule
DNA and Cell Division
• DNA needs to
be copied
before cell
division occurs
• Process called
DNA
replication
DNA Replication
• DNA replication: cell
makes an exact copy of its
DNA
• Semiconservative
process (each new strand
has half the original
strand)
Steps of DNA Replication
1) Enzyme called DNA Helicase breaks H-bonds
between nitrogenous bases (allows helix to
“unzip”)
- points where 2 strand separate is called the
replication fork
Steps of DNA Replication
Note: one end of a
DNA strand is called
the 5’ (5 prime) end
and one is called the
3’(3 prime) end. The
5’ end has the
phosphate group and
the 3’ end has the
sugar group
Steps of DNA Replication
2) DNA polymerase (enzyme) adds nucleotides to
the strands.
- nucleotides are added from the 5’ end to the 3’
direction
- Base pairing method (A=T and C=G)
- One strand is continuously formed while the
other forms in short sections (later bonded
together by and enzyme called DNA ligase).
* Leading strand vs. Lagging strand
• Video: Making a chromosome
http://www.youtube.com/watch?v=4PKjF7OumYo&feature=related
To Do:
• Model the process of DNA replication in groups
of 3
• Grab the following Materials:
- Liquorice (3 strands)
- ~20 toothpicks (may need more later)
- 40 marshmallows (10 of each colour)
• Step 1: Create DNA Molecule & show me
• Step 2: Begin DNA replication. Show me when
finished.
• Video: Molecular Visualizations of DNA
http://www.youtube.com/watch?v=4PKjF7Oum
Yo&feature=related
• Assessment:
Create a concept map summarizing
DNA Replication
The Cell Cycle
• Phases occur
continuously
• Explains how cells
continue to divide
• Functions to maintains
our body
– New cells for growth
– Replaces worn out cells
Cell Cycle Phases
• G1 Phase – Rapid cell Growth
– Cells uses nutrients from its surroundings to
increase in size
– Chromosomes remain unduplicated
• S Phase – DNA Replication
– Cells begin to prepare for division
– DNA replicates and chromosomes are duplicated
– Known as the “synthesis” stage
Cell Cycle Phases
• G2 Phase – Growth and Prep for Division
– Period of cell growth
– Preparation for cellular division
• M Phase – Mitosis and Cytokinesis
– Mitosis is the process when one parent cell
divides into two daughter cells that are exact
copies
– Cytokinesis = cytoplasm splitting  cytoplasm
divides and two new cells are produced
Cell Cycle Phases
• The G1, G2 and S phases are usually grouped
together and called interphase
• Interphase is the time between divisions when
a cell increases in mass, doubles its internal
contents, and duplicates chromosomes
• Basically its all the stages except mitosis
(when division occurs)
Can Cells Divide Indefinitely??
• Research indicates a biological clock may
regulate number of cell divisions
– E.g. Frozen heart cell division
• Some cells divide more often than others
– Skin cell vs. Nerve cell
• Some cells seem to divide indefinitely
– Sperm cells (males can produce 1 billion/day),
cancer cells
Applications of the Cell Cycle
• Cloning
– Considered form of asexual reproduction
– Natural Cloning:
• i.e. Hydra budding.....Monozygotic (identical) twins
– Artificial Cloning:
• i.e. Nucleus taken from frog embryo and inserted into cell
without nucleus.
• Why Dolly Died
– Cloned from an 8 year old adult
– Telomeres are reduced in size each time a cell divides
– Dolly began life with shorter telomeres, so she
developed arthritis & died of lung disease (age of 6 –
½ life expectancy)
• Video: Eukaryotic Cell Cycle
http://www.youtube.com/watch?v=O3_PNiL
WBjY
To Do:
1) Research the following terms: chromatin,
chromosome, centromere, sister chromatids,
homologous chromosomes, tetrad, synapsis
and crossing over. Draw a diagram showing
how these terms are related to one another.
MITOSIS
Producing Exact Copies of Cells
Interphase
• Stage prior to
mitosis
• DNA is arranged
in long fibres
called chromatin
• Chromatin is
replicated
• Cell grows in sizes
and prepares to
divide
Prophase
• Chromtin forms
chromosomes
– Each chromosome is
made of 2 chromatids
(identical)
– Chromtids are held
together by
centromeres
• Nuclear membrane
dissolves
• Centrioles appear and
spindle fibres attach to
centromeres of
chromosomes
Metaphase
• Chromosomes line up
at the equatorial
plate
• Chromosomes still
attached by spindle
fibres
• Nuclear membrane
completely dissolves
Anaphase
• Centromeres divide
and sister
chromatids move to
opposite poles of
the cell (pulled by
spindle fibres)
• Identical set of
chromosomes move
to each pole
Telophase
• Chromosome reach
opposite poles and
begin to form thin
threads of chromatin
again
• Spindle fibres
disappear
• Nuclear membrane
reforms around each
mass of chromatin
Cytokinesis
• “cytoplasm
splitting”
• Begins once
chromosomes
move to opposite
sides of cell
• Animal cells:
furrow forms
• Plant cells: Plate
forms
Video: Mitosis
• The stage of mitosis
• http://www.youtube.com/watch?v=VGV3fvuZYI
Meiosis
Producing genetically different copies
of cells…
Video: Meiosis
• Biology – Meiosis Cell Division
• http://www.youtube.com/watch?v=kVMb4Js9
9tA&feature=related