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 Replication2) 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 DNAhttp://www.youtube.com/watch?v

=4PKjF7OumYo&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 Cyclehttp://www.youtube.com/watch?v

=O3_PNiLWBjY

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=VGV3fv-u

ZYI

Meiosis

Producing genetically different copies of cells…

Video: Meiosis

• Biology – Meiosis Cell Division• http://www.youtube.com/watch?v=kVMb4Js9

9tA&feature=related