Questions

1. Are the cells of the small plant larger or smaller than those of the larger plant? Are the cells of the small animal larger of smaller than those of the large animal.

2. Can you make a general statement that compares the number and size of cells in small organisms to those in large organisms.

10 – 1: Cell Growth and Division

How do living things grow?

• Grow by producing more cells. (Cells do not increase in size)

– A human adult has about 10 trillion – 100 trillion cells in their entire body.

– About how many cells does a newborn baby have?

Answer: Much less

Cells Dividing

Blood Lily

Limits to Cell Growth

• 2 reasons why cells divide rather than grow?1. The larger cell has more trouble moving

nutrients and waste across the cell membrane.

2. The larger the cell, the more demand the cell places on its DNA.

DNA “Overload”

• DNA is found in the nucleus of the cell

• Why can’t a cell grow without limit?

When a cell grows, it does not make more copies of its DNA. If the cell grew continuously, there would be information crisis.

Exchanging Material

• What substances may move through the cell membrane?

Answer: Food, oxygen and water enters.

Waste leaves the cell.

• The rate materials exchange depends on the surface area of the cell

• The rate materials are used depends on the cell’s volume (size).

Ratio of Surface Area to Volume • Surface to volume ratio

• Volume increases faster than surface– The cell uses materials faster

than it can get them in

• Town analogy: A small town has only a 2 lane street. As the town grows there is more traffic on the 2 lane street.

Asexual Reproduction– Asexual reproduction - a single parent

producing an offspring. The offspring produced are, in most cases, genetically identical to the parent.

– Asexual reproduction is a simple, efficient, and rapid way for an organism to produce a large number of offspring.

– Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually. Ex. hydra, bacteria, yeast

Sexual Reproduction– In sexual reproduction, offspring are

produced by the fusion of two sex cells – one from each of two parents.

– The offspring produced inherit some genetic information from both parents, therefore they are genetically different.

– Most animals and plants, and many single-celled organisms, reproduce sexually.

• Cells divide to form two new cells called daughter cells

• This process is called cell division (mitosis)• Before it can occur, what has to happen? The cell

replicates, or copies, all its DNA• DNA is condensed into a manageable form

(chromosome) so it can be divided precisely

10.2 The Process of Cell Division

Section 10-2: Cell Division• Prokaryotes – less complicated division

– Replicate DNA – divide everything up between 2 cells.

• Eukaryotes – more complicated division

2 Main Stages1. Mitosis – division of the nucleus

2. Cytokinesis – division of cytoplasm

Chromosomes• Chromosomes – bundled packages of DNA that contain

genetic information• Every organism has a specific number of chromosomes

– Fruit flies – 4

– Dog - 78

– Carrots – 18

– How many chromosomes do humans have? 46 (23 pairs)

Chromosomes• Chromosomes are only visible when

the cell divides.• Why is this?

DNA and protein molecules are spread throughout the nucleus in the form of Chromatin. Chromatin condenses during cell division.

• Before division, the chromosome (DNA) is replicated

• The replicated chromosome consists of 2 identical “sister” chromatids.– One chromatid goes to each new cell– Held together near the center by

centromere

TE

M

36,0

00

Centromere

Sister chromatids

Exact copies of each other

Chromosomes (a closer look)• Chromatin is a complex of DNA coiled around proteins called

histones

• The DNA and histone molecules then form beadlike structures called nucleosomes.

• The chromosome “X” shape we usually see drawn is a duplicated chromosome made of supercoiled chromatin

Eukaryotic Cell CycleThe cell cycle represents the events in the

life of a cell.

InterphaseInterphase Growth Phase most time Growth Phase most time spent in this phasespent in this phase

G1 G1 Cell growthCell growthS S Replication of DNAReplication of DNAG2 G2 Final growth and prepare for Final growth and prepare for

divisiondivision

Mitosis Mitosis (M phase) (M phase) Division of the Division of the nucleus (can last hours to a few days)nucleus (can last hours to a few days)

4 Phases:4 Phases:1.1. ProphaseProphase2.2. MetaphaseMetaphase3.3. AnaphaseAnaphase4.4. TelophaseTelophase

Mitosis – Prophase first and, longest phase

• DNA condenses into chromosomes

• 2 centrioles (microtubules) take positions on opposite sides of the nucleus

• Spindle begins to form

• What is a spindle?A fanlike microtubule structure that

helps separate chromosomes.

Cytokinesis• Division of the cytoplasm

• Occurs at the same time as telophase

Actin (blue) and microtubules (orange) at the end of cytokinesis in a green urchin zygote.

Cytokinesis - Animal

• Animal cells are surrounded by a cell membrane

Animal Cell Formation of a cleavage furrow

Cleavagefurrow

SE

M 1

40

Daughter cells

Cleavage furrow Contracting ring ofmicrofilaments

Cytokinesis - Plant

• Plant cells are surrounded by a Plant cells are surrounded by a cell wallcell wall

Plant CellPlant Cell Formation of cell Formation of cell plateplate

TE

M 7

,500

Cell plateforming

Wall ofparent cell

Daughternucleus

Cell wall New cell wall

Vesicles containingcell wall material

Cell plateDaughter cells

Mitosis Animation

Cell Division - ProkaryotesProkaryote unicellular bacteria with no nucleus

Binary Fission DNA is replicated, cell doubles in size and splits

10-3 Regulating the Cell Cycle

• Cell growth and division is very controlled

• True or False – All cells move through the cell cycle at the same rate.

Controls of Cell Division• What happens when cells are grown in a petri

dish? Cells will grow until they form a thin layer covering the bottom of the dish.

• What does this experiment show? Controls of cell division can be turned on and off.

• What happens in our body that is similar? Cells at the edge of an injury are stimulated to divide rapidly.

Cell Cycle Regulators• Scientists have been trying to determine

what regulates the cell cycle.

• Found a protein – if they inject it into a non-dividing cell, the cell enters mitosis

• What is the protein called? Cyclin

Why? regulates cell cycle

• Cyclins regulate the timing of the cell cycle in eukaryotic cells.

Internal Regulators• Proteins that respond to events inside the cell

Ex: Don’t allow mitosis to start until all chromosomes are replicated.

External Regulators• Proteins that respond to events outside the cell.

Ex: Growth Factors found on the outside of cells can speed up or slow down cell division

Uncontrolled Cell Growth = CANCER

• Cancer cells do not respond to cycle regulators

• Results– Divide uncontrollably– Form tumors (masses of

cells) that can damage the surrounding tissue

Uncontrolled Cell Growth = CANCER

– Cancer cells may break loose from tumors and spread throughout the body disrupting normal activities.

• What are some causes of cancer?

smoking tobacco, radiation exposure, viral infection

Uncontrolled Cell Growth = CANCER

5.4.3.

2.

1.

4.3.2.1.

Cleavagefurrow

Haploid daughter cellsforming

Sister chromatidsseparate

4.3.2. 5.1.

Questions for whiteboards:

• Show how a cell looks normally while it’s doing it’s job as a tissue, muscle, bone or nerve cell. Focus on what genetic material looks like in nucleus

Questions for whiteboards:

• Show how a cell would look as it’s getting ready to divide. Again, focus on nucleus and genetic material

Questions for whiteboards:

• Using two circles, “X”s and a mitochondria show why efficiency is different between large and small cells.

Questions for whiteboards:

• List some problems that cells might encounter if they were to grow to large.