Cell Growth & Division What problems does growth pose for cells?

Cell Growth & Division

What problems does growth pose for cells?

DO NOW Why do cells need to be

small?

Why do cells need to be small?

– Trouble moving enough nutrients and wastes across the cell membrane

– Organization– The larger a cell becomes, the more

demands on its DNA

Purpose of cell division?

Chromosomes

Chromosome number is unique to every species

• Humans: 46 chr.• Chimpanzees: 48 chr.• Yeast: 32 chr.• Adders-Tongue Fern: 1440 chr.!

Moral:

Quality of the Genetic Material and NOT the

Quantity give an organism

complexity

23

Chromosomes

• Humans have 46 chromosomes in every cell

• During S-phase of the cell cycle, all 46 are copied

• When the cell splits in half, each new cell has the exact same chromosome # as before

MITOSIS

Parent Cell

Daughter Cells

Checkpoints G1 Checkpoint: - Cell size

- DNA can be replicated

G2 Checkpoint- Cell size

- DNA intact

- DNA duplicated

M checkpoint

- Chromosomes are properly attached to the spindle fibers.

1. Repair the damage

OR

2. Self-destruct APOPTOSIS (Programmed Cell Death)

What happens if the cell cannot pass through the checkpoint?

I. Interphase: 90% of the time!

1. Gap 1 cell grows, doubles organelles

2. Synthesis Duplication of the DNA 3. Gap 2 cell grows

Steps of Mitosis: (PMAT)

Prophase

Metaphase

Anaphase

Telophase

http://www.goldiesroom.org/Note%20Packets/14%20Mitosis%20and%20Asexual/00%20Mitosis--WHOLE.htm

MITOSIS : NUCLEAR DIVISION

During Mitosis the movement of the chromosomes (DNA) are guided by spindle fibers which are long proteins that grow from the centrioles (in animal cells) or the membrane (in plant cells).

1. Prophase-• Chromatin fibers condense• Nuclear membrane breaks down• Spindle of microtubules forms from

centrioles [animals only]

2. Metaphase- “middle”• Spindle fibers from centrioles attach to

centromeres• Spindles move Chromosomes to line up

in the middle

Centriole

Spindle

3. Anaphase: “away phase”, form “A’s”

• Spindle fibers contract• Pull sister chromatids apart• Chromosomes move towards opposite

ends• Each side has own copy of DNAIndividual

chromosomes

4. Telophase- “end phase”• Nuclear membranes reform at each

pole• Chromosomes unwind• Spindle disappears

Cytokinesis (NOT a phase of Mitosis)

During cytokinesis, the cytoplasm cuts in half

Each daughter cell has an identical set of duplicate chromosomes

Cytokinesis in Plants

In plants, a structure known as the cell plate forms midway between the divided nuclei.

Cytokinesis in Animals

Animal cells contract an actin fiber across

middle of cell and “pinch” into 2 new cells. - called

a “cleavage furrow”.

- Do not stop dividing when they contact other cells - Do not respond to signal and divideuncontrollably - Don’t stop at checkpoints and do not do apoptosis- Form masses of cells called tumors- Metastasis: tumor cells break loose and

spread in body

Cancer Cells…

Contact Inhibition

- Normal cells will reproduce until they contact other cells.

- When this happens, they stop growing.

How are cancer cells different from other cells?

Tumors - mass of cancer cells.

The cells attract new blood vessel growth (this is called angiogenesis)

Causes of Cancer/Carcinogens Random Mutations GeneticsChemicals- asbestos, cigarettes, formaldehyde, pesticides, nitrates Radiation Certain viruses (HPV) Poor Diet/ Obesity

Prevention of Cancer

Genetic screening BRCA 1 and BRCA 2 Do not smoke limit alcohol consumption Maintain a proper diet exercise prevent sunburns Get Proper health screenings

Mutations typically happen in two types of genes

1. Proto-oncogenes are normal genes that regulate cell growth Oncogenes are mutated

proto-oncogenes 2. Tumor suppressor genes – genes that stop the cell cycle or promote apoptosis

ex. p53 gene

p53 gene, Tumor suppressor gene "guardian of the genome", usually functions to properly control the cell cycle

p53 is mutated in over 50% of all human cancers.

Biopsy- way to diagnose cancer by surgically removing piece of tissue and examining it

Staging- Describes the severity of a person’s cancer - Aids in planning the treatment

Sperm and egg.

MEIOSIS

Meiosis - the production of haploid cells with unpaired

chromosomes - word means "to diminish".

-process creates gametes (sperm and eggs), cells that are haploid (1N)

-gametes combine to create a zygote which is diploid (2N)

Meiosis is actually TWO divisions, this results in FOUR daughter cells, each with HALF the number of chromosomes.

These cells are HAPLOID!

Homologous Chromosomes

- each chromosome has a match, called a homolog. 

This is why normal organisms always have an even number of chromosomes. 

Chromosomes are numbered and paired according to their size. 

Karyotype showing homologous pairs. 

During Prophase I - homologous chromosomes pair up and exchange DNA. -

this is called CROSSING-OVER

Why Meiosis increases Genetic Variation

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.

This is called INDEPENDENT ASSORTMENT

When gametes combine, offspring show variation due to independent assortment and crossing over

Fertilization = combining the genes of two different parents.

The Phases of Meiosis

Similar in plants and animals.  Plant cells lack centrioles. 

Meiosis creates gametes               (sperm and eggs)

Meiosis ensures variability in offspring

Gametes combine to create a zygote which is diploid (2N) - process of sexual reproduction

Figure 10.9a

During OOGENESIS, cytoplasm divides unevenly during each cytokinesis,

resulting in only ONE viable egg cell.

3 small polar bodies are formed

1 large OOCYTE has potential to be fertilized

Key points of Meiosis

●The process results in 4 daughter cells●Daughter cells are haploid (N)●Daughter cells have unique combinations of

chromosomes

Check for understanding

1.  What phase directly follows metaphase I?

2.  How many cells are present at the end of meiosis I ?

3.  A cell has a diploid number of 60, what is the organism's haploid number? 

4.  Meiosis occurs in what type of cells?

5.  In what phase do homologous chromosomes pair up and crossing-over can occur?

6.  In what phase do the CHROMATIDS separate?

anaphase I

2

30

gametes

prophase 1

anaphase 2

Pg 180

Which of these pictures is metaphase I of MEIOSIS and which is metaphase of MITOSIS?

Mitosis                                              Meiosis

Mitosis Videos • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/cha

pter2/animation__mitosis_and_cytokinesis.htmlhttp://www.youtube.com/watch?v=VlN7K1-9QB0http://www.cellsalive.com/mitosis.htm http://www.youtube.com/watch?v=lf9rcqifx34å

Twilight DOES IT TOO!