Cell Division

4 day old mouse cells

Section 1 Vocabulary

• 1. Cell cycle

• 2. Interphase

• 3. Mitosis

• 4. Cytokinesis

• 5. Chromosome

• 6. Chromatin

Cells are small!But why?

• As cells get bigger, the surface area to volume ratio changes and makes it harder for certain things to occur in the cell!

• -causes problems with the transport of materials            -larger cells need more "stuff" but only so much can cross the cell membrane at a time  

Surface area to volume lab demo

• http://www.youtube.com/watch?v=xuG4ZZ1GbzI&feature=youtube_gdata_player

• Why are cells so small???

• http://www.youtube.com/watch?v=wuXSEOKNxN8&feature=youtube_gdata_player

Lab groups of 6• 2 will measure/time the 1cm cube• 2 will measure/time the 2 cm cube• 2 will measure/time the 3 cm cube• On your own notebook paper• Write: • Title, data chart, calculations for your cube,

observations as it happens. Add the group data to your data chart. Put your paper in your notebook.

• The group will compile one report from this to turn in together for a grade! Answer all questions

Cell communication

• Cell communication can not take place if the cell is too large because it involves signaling proteins that would be too far away from the molecules.

• -cell division solves a cell's size problem

• a cell needs a large surface area relative to its volume         

• (a high surface-to-volume ratio) to survive

When the cell reaches its size limit it will stop growing or it will divide!

Why do we need cell division?to grow, replace worn-out or damaged cells, orreproduce asexually.

Cell cycle

Stages of Interphase Normal cell day to day life of a cell!!

-interphase = when the cell grows, carries out cellular functions and replicates its DNA to prepare for the division phase! Or the period between cell divisions. It is the longest of the phases!

1. -Gap 1 (G1)

     -cell growth & development2. -DNA Synthesis (S)

     -replication of DNA3. -Gap 2 (G2)

     -creation of materials needed for division

• Doubling the nuclear material in the S-phase provides enough DNA to generate 2 complete nuclei at the end of mitosis.  This ensures that each daughter cell has the same number of chromosomes as the original parent cell. 

Mitosis and Cell Division • All cells go through a cell cycle composed

of cell division portion (mitosis) and "resting period" (interphase).

How do some cells know to become lung cells and others to become heart or muscle?

• Genes on the chromosomes (made up of DNA) contain the instructions for building the proteins required for each cell type.

• Cell to cell communication helps cells differentiate into the specialized cells.

Nucleus• Usually large enough to be seen with light

microscope. Double membrane (nuclear envelope) bound organelle with pores. The nucleus is the "control center" for the cell since it contains the hereditary material

DNA

• within chromatin. • Condensed chromatin (during cell

division) is visible with the microscope as chromosomes.

• Inside the nucleus is a dark staining region called the nucleolus which is involved in making ribosomal RNA (rRNA).

• Think of this as city hall • (archives genealogical data)!

How does a Eukaryotic cell reproduce?

• DNA is organized into chromosomes and segments called genes that code for proteins.

How DNA is packaged!6 feet in a cell, WOW!

• http://www.youtube.com/watch?v=gbSIBhFwQ4s&feature=youtube_gdata_player

• Chromosomes are DNA and protein that become visible when the cell is ready to divide.

Making a chromosome

• 1. DNA is 1st copied 2 identical strands make up chromatids

• 2nd the DNA wraps around proteins called histones the chromatids connect at the center called the centromere.

How chromosome # and structure affect development

• Each body cell (somatic cell ) has 23 different chromosome pairs for a total of 46

• Each chromosome has thousands of genes on them that are essential to life!

What are sets of chromosomes called?

• Homologous pairs

• Homologous chromosomes are ones that are similar in size, shape and information that they contain.

• One comes from each parent

• 2 sets of 23 make up the 46 in a human.

• 1 set from mother 23

• 1 set from father 23

• 46

Chromosomes

• Are present in the nucleus. Occur as chromatin (uncondensed) and chromosomes (condensed during cell division). Composed of a strand of DNA and associated proteins. The DNA stores and transmits genetic information, while the proteins are important for packaging these long strands of DNA.

Details of DNA structure

• DNA is a double helix composed of a backbone of phosphate and sugar groups.

• From the sugars, nucleotide bases protrude. Four nucleotides exist in DNA: A, C, G, and T.

• A pairs with T, • G with C. • The two strands run antiparallel (opposite directions)

and the bases hydrogen bond together. Genes are composed of sections of DNA that encompass hundreds to thousands of base pairs.

•  

Prokaryotic Cells

• Since Prokaryotic cells do not have a nucleus they reproduce my a much simpler method with out the cell cycle that eukaryotes have. It is called binary fission.

Binary Fission

• The chromosome replicates and the cell divides making 2 exact copies of the cell.

Asexual reproduction

• http://www.youtube.com/watch?v=DY9DNWcqxI4&feature=youtube_gdata_player

• There is little room for variation in this process so the cells are almost like clones of each other!

• 1. What factor limits the size of a cell the most? Surface area to volume ratio_

• 2. How do most substances move from one area of the cell to another? Difusion

• 3. Is this movement easier when the cell is small or large? Small

• 4. How does cell size affect cell communication? If it gets too large it will no be able to communicate.

• 5. Draw the cell cycle label the parts of the phases. Include G1, S, G2 Mitosis, and Cytokinesis.

• 6. Which phase seems to be the longest? interphase 7. What happens in Mitosis? The genetic material divides

• 8. What happens in cytokinesis? The cytoplasm and organelles divide 9. What happens in the G1 phase of interphase? -cell growth & development

• 10. What happens in the S phase? -replication of DNA

• 11. What happens in the G2 Phase? creation of materials needed for division

• 12. What is the difference between chromosomes and chromatin? Chromosomes are packaged and only show up when the cell is ready to divide, chromatin is the unwound form of DNA when it is in use by the cell.

• 13. Do prokaryotic cells divide with this cell cycle? No What is the method they use called? Binary fission

How does a Eukaryotic cell reproduce?

• DNA is organized into chromosomes and segments called genes that code for proteins.

Section 2 Vocabulary:• 1. Prophase

• 2. Metaphase

• 3. Anaphase

• 4. Telophase

• 5. Sister chromatid

• 6. Centromere

• 7. Spindle apparatus

Stages of mitosis

• The division of the nucleus is considered a separate process from the division of the cytoplasm.

• Mitosis: nucleus division

• Cytokinesis: cytoplasm division

chromosome

• Spindle

apparatus

spindle

Mitosis video!

• http://www.youtube.com/watch?v=VlN7K1-9QB0&feature=youtube_gdata_player

Prophase

• the chromatids continue to condense; the nuclear envelope and nucleolus disintegrate;

• the spindle apparatus forms (fibers composed of microtubules responsible for the movement of the chromosomes);

• kinetochores form (protein containing structures that serve to attach the chromatids to the spindle fibers)

Metaphase

• spindle fibers attach to chromosomes at the kinetochores;

• kinetochore fibers orient the chromosomes so that only one chromatid will move to each pole {8-13R}

• the central region where the chromosomes align is called the equator or metaphase plate

Anaphase

• shortest phase;

• sister chromatids are separated at the centromeres and are pulled to opposite poles

Telophase

• Telophase: chromosomes uncoil,

• spindle disappears,

• nuclear envelope reforms,

• nucleoli form;

• cytokinesis takes place here by the formation of a cell plate

Interphase:

• period between cell divisions which consists of processes associated with cell growth (expansion) and preparation for mitosis

Result of mitosis

• Where there was once one cell, there are now two "daughter cells".

• Each cell is identical genetically since the genetic material was simply duplicated during interphase.

• This is essentially the same as cloning. The chromosome number remains the same.

Animations• Biology Learning Center

• Molecular Expressions

• Mitosis World

• Onion root tips on line

• http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html

Interphase

• Normal, non dividing cell

Make a cell divide!!• 1. Tie a piece of string into a big circle to

represent the cell membrane.

• 2. Cut a piece of string to represent the nuclear membrane; do not tie this one into a circle.

• 3. Cut 6 chromosomes out of string, make sure they each have a “copy” of them selves.

Play with your chromosomes!!!

• First make a cell with 6 chromosomes in interphase

The chromosomes replicate

• Match them with their copy!

• Just twist the two strings together to represent the centromere

The black star represents the centromere that connects the two sister chromatids

Make the cell go through all of the phases

• P

• M

• A

• T

Prophase:

1. nuclear membrane dissolves2. Identical chromosome pairs are attached, into "sisters chromatids", which are attached to each other by a centromere3. In animal cells, centrioles migrate to opposite ends of cell (poles)4. Spindle fibers form between poles to attach to chromatids

Metaphase:

•Sister chromatids line up at the equator of cell

Anaphase:

• 1. Chromatid pairs are separated and each is pulled to an opposite pole2. Two identical groups of chromosomes are now clustered at opposite sides of cell

Telophase:

• 1. "parent" cell begins to separate into two "daughter" cells, each having an identical set of chromosomes

Telophase:

• While the genetic components are dividing up, CYTOKINESIS is also occurring (division of cytoplasm)2. Nuclear membranes re-form3. Spindle fibers break down4. Cells return to interphase

2 Daughter cells in interphase

• And the process starts again…

The major differences in how plant

and animal cells divide are:

• Animal cells have centrioles to mark the poles, plant does not

• Animal cells divide differently than plant during cytokinesis

• In plant cells, a cell plate forms in the middle of the dividing cell and expands outward until a complete wall is formed between the two daughter cells

• In animal cells, a cleavage furrow forms at the outer edges and constricts inward until the two daughter cells are separated

Animal cells

Plant cell

The Importance of Mitosis

• Mitosis ensures that each new body cell has the same genetic makeup as its parent. Mutations can and do occur occasionally but, for the most part, all of your body cells have identical DNA

• Mitosis not only functions to replace cells and make new cells (growth) it also reduces cell size.

• Can you think of three reasons that cell size must remain so small?

Skin replacement

Wound healing

Onion root tip

• Onion root tips on line

• http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html

• Online Onion Root Tips

Plant mitosis

• 1. What divides in mitosis? The DNA

• 2. Draw the phases of mitosis and briefly describe what happens in each phase.

• 3. Why do cells need to undergo mitosis? To reproduce, to replace themselves when they get old or damaged to maintain the chromosome number.

• 4. What are 3 differences in animal and plant cell mitosis? Animal cells have centrioles, a cleavage furrow during cytokinesis and no cell plate. The plant cell forms a cell plate to produce a new cell wall between the new cells.

• 5. What happens in cytokinesis? The cytoplasm and organelles are divided between the two new cells.

• SC.912.L.16.15 Compare and contrast binary fission and mitotic cell division.

• 1. Prokaryotes reproduce by binary fission. How is binary fission different from mitotic cell division? In prokaryotes there is no nucleus and a single chromosome so there are not phases , the cell simply replicates the DNA and then divides in two making exact copies of it self.

reflections

• Do your reflection for section 2 benchmarks

Section 3 vocabulary:

• 1. Cyclin,

• 2. Cancer,

• 3. Carcinogen,

• 4. Apoptosis,

• 5. Stem cell

Cell cycle regulation

• The rate of the cell cycle is important.

• Rate varies depending on the cell type.

• Cyclins, proteins, bind to enzymes to start the parts of the cell cycles.

• G1 has a cyclin /CDK complex to to get it started… so do several other places in the cell cycle.

The cell cycle in eukaryotes is controlled by many proteins. Control occurs at three principal checkpoints

• 1. Cell growth (G1) checkpoint

• 2. DNA synthesis (G2) checkpoint.

• 3. Mitosis checkpoint

When Control Is Lost: Cancer

• Cancer is essentially a disorder of cell division. Cancer cells do not respond normally to the body’s control mechanisms.

Cancer cells

• http://www.youtube.com/watch?v=A1Fkdt-2veM&feature=youtube_gdata_player

• There are check points along the way to make sure the processes are working properly.

• If the checkpoints are not working properly uncontrolled growth can occur. This is how cancer can occur.

• Mutations in cell proteins that check the cycle can cause cancer. Carcinogens, substances that cause cancer, can cause damage to the DNA to make faulty proteins.

apoptosis

• Programmed cell death. The cell shrinks and dies.

• Examples include the cells in-between the fingers and toes die at the correct time to prevent webbing.

• Some damaged cells die to prevent damage to the entire organism.

Stem cells

• Unspecialized cells that can develop into specialized cells under the correct conditions.

• 2 types

• Embryonic

• Adult stem cells

• SC.912.L.16.8 Explain the relationship between mutation, cell cycle, and uncontrolled cell growth potentially resulting in cancer.

• 1. What controls the rate at which the cell divides? The types of cell, the regulating proteins of the cell cycle.

• 2. What happens when the control system no longer works? Uncontrolled growth or cancer can result.

• 3. What is cancer? Uncontrolled cell growth. • 4. What types of things can cause cancer? DNA

mutations , chemicals, environmental causes, genetic mistakes

• 5. Does the body have ways to try to prevent cancer from harming it? Yes there are check points and ways to destroy cells with defects.

Section 3 reflections are due:

• Monday!• Include• 1. the benchmark• 2. Your level of understanding, any questions you

still have about this material• 3. The answer to this benchmark, even if you

have to look it up in your notes or the book!• Chapter 10 section 1 vocabulary due Monday s

well…. See the board for the list

• There is little room for variation in this process so the cells are almost like clones of each other!

Asexual reproduction

• http://www.youtube.com/watch?v=DY9DNWcqxI4&feature=youtube_gdata_player

Comparing Mitosis and Meiosis

• Observational activity

• In your groups, use the pictures in the book

• ( pages 249 and 273) to draw the basic diagrams of the phases of mitosis and meiosis side by side on the poster paper.

• Make a chart/vendiagram of what they have in common and what differences they have.

• Be prepared to share your results with the class!

Meiosis

chromosomes

Duplicated and unduplicated

Homologous chromosomes

Homologous chromosomes• Example - an organism is 2n = 4. • This means the organism has a total of 4

chromosomes  • Chromosomes 1 & 2 are homologous chromosomes • Chromosomes 3 & 4 are homologous chromosomes

• Chromosomes 1 & 3 came from the mother

• Chromosomes 2 & 4 came from the father

How many?

karyotype

karyotype

• A quick glance at any karyotype will tell you one of the most important facts about chromosomes:

• They come in pairs. • The members of a pair are the same size and

shape, and they have the same banding patterns. • In other words, each person actually possesses

two copies of chromosome 1, two copies of chromosome 2, and so on.

• Human cells contain 23 pairs of chromosomes.

definitions:

• Allele - alternate forms of the same gene • Homozygous - having two identical alleles for a

given gene • Heterozygous - having two different alleles for a

given gene • Genotype - genetic makeup of an organism • Phenotype - the expressed traits of an organism

Meiosis

• Meiosis Is a Special Type of Cell Division That Occurs in Sexually Reproducing Organisms

• Why is this different?

• Normal body cells have a complete set of chromosomes

• If normal body cells from mom and dad fused to form a baby, the fertilized egg would have twice as many chromosomes as it should.

• Meiosis is sometimes called "reduction division" because it reduces the number of chromosomes to half the normal number

• so that when fusion of sperm and egg occurs, the offspring will have the correct number.

•

• Meiosis reduces the chromosome number by half, enabling sexual recombination to occur.

• Meiosis of diploid cells produces haploid daughter cells, which may function as gametes.

• Gametes undergo fertilization, restoring the diploid number of chromosomes in the zygote

The Role of Sexual Reproduction in Evolution

• Sexual reproduction in a population should decline in frequency relative to asexual reproduction. – Asexual reproduction—No males are needed, all

individuals can produce offspring. – Sexual reproduction—Only females can produce

offspring, therefore fewer are produced.

• Sexual reproduction may exist because it provides genetic variability that reduces susceptibility of a population to pathogen attack.

purpose

• the purpose of meiosis is to produce gametes; the sperm and eggs

Meiosis• Interphase I: Identical to

Interphase in mitosis.

• Prophase I: Identical to Prophase in mitosis

Metaphase I:• Instead of all chromosomes pairing up along the

midline of the cell as in mitosis, homologous chromosome pairs line up next to each other.

• This is called synapsis.• Homologous chromosomes contain the matching

alleles donated from mother and father. This is also when meiotic recombination, also know as "crossing over" (see below) occurs. This process allows for a genetic shuffling of the characteristics of the two parents, creating an almost infinite variety of possible combinations. See the close-up diagram below.

Metaphase I:

• This is also when meiotic recombination, also know as "crossing over" occurs.

• This process allows for a genetic shuffling of the characteristics of the two parents, creating an almost infinite variety of possible combinations.

crossing over

Anaphase I

• Instead of chromatids splitting at the centromere,

• homologous chromosome pairs (now shuffled by crossing over) move along the spindle fibers to opposite poles.

Telophase I

• The cell pinches and divides

Prophase II:

• It is visibly obvious that replication has not occurred.

Metaphase II:

• The paired chromosomes line up.

Anaphase II:

• The chromatids split at the centromere and migrate along the spindle fibers to opposite poles.

Telophase II:• The cells pinch in the center and divide

again.

• The final outcome is four cells,

• each with half of the genetic material found in the original.

Telophase II

Results

• In the case of males, each cell becomes a sperm.

• In the case of females, one cell becomes an egg and the other three become polar bodies which are not used.

Some questions to ponder• 1. How does the number of daughter cells

produced from mitosis and meiosis differ?

• 2. How does the ploidy of the daughter cells produced from mitosis and meiosis differ?

• 3. Do the daughter cells produced from mitosis contain identical genetic complements?

• 4. Do any of the daughter cells produced from meiosis contain identical genetic complements?

• 5. When do the homologous chromosomes separate during mitosis?

• 6. When do the homologous chromosomes separate during meiosis?

• 7. When do sister chromatids separate during mitosis?

• 8. When do sister chromatids separate during meiosis?

answers• 1. How does the number of daughter cells produced from

mitosis and meiosis differ?• When mitosis is complete, there are two daughter cells.

When meiosis is complete, there are four. • 2. How does the ploidy of the daughter cells produced

from mitosis and meiosis differ?• Mitosis produces diploid (2n) cells. Meiosis produces haploid

(n) cells.• 3. Do the daughter cells produced from mitosis contain

identical genetic complements?• Yes, the purpose of mitosis is to produce two identical cells • 4. Do any of the daughter cells produced from meiosis

contain identical genetic complements?• No, the genetic information swapped between homologous

chromosomes during crossing over insures that each daughter cell produced during meiosis will be unique

• 5. When do the homologous chromosomes separate during mitosis?

• Never, they are never joined during mitosis (no tetrads are formed)

• 6. When do the homologous chromosomes separate during meiosis?

• Homologs separate during Anaphase I, when the tetrads break

• 7. When do sister chromatids separate during mitosis?

• Sister chromatids separate during Anaphase. • 8. When do sister chromatids separate during

meiosis?• Sister chromatids separate during Anaphase II.