Cell Growth Does an animal get larger because each cell increases in size or because it produces more of them?

Cell GrowthDoes an animal get larger because each cell increases in size or because it produces more of them?

Cell Growth• As you might have guessed, living things grow

by producing more cells.

• The koalas have the same size cells, just one has more then the other.

Limits to Cell growth• The larger a cell becomes, the more demands

the cell places on its DNA. In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane.

• The cell can’t grow. It must reproduce!

Cell Division• The process by which a cell divides into two

new daughter cells is called cell division.

• Before cell division occurs, the cell replicates, or copies, all of its DNA. This replication solves the info. problem.

Cell Division• What do you think would happen if a cell

were simply to split into two without any advance preparation?

Chromosomes• In eukaryotic cells, the genetic

information that is passed on from one generation of cells to the next is carried by chromosomes.

• The cells of every organism have a specific number of chromosomes.

• Each chromosome consists of two identical “sister” chromatids. When the cell divides, the “sister” chromatids separate and go to each of the new cells.

Chromosome• Each pair of chromatids is attached at an area

called a centromere.

• Centromeres are usually located near the middle of the chromatids, although sometimes can be found at each end.

The Cell Cycle• The cell cycle is the series

of events that cells go through as they grow and divide.

• During the cell cycle:

- A cell grows

- Prepares for division

- And divides to form to daughter cells

Events of the Cell Cycle p)245• There are four phases of the Cell Cycle.

• G1 phase – period where cell does most of their growing

• S phase – chromosomes are copied and the synthesis of DNA molecules takes place.

(DNA Replication)

• G2 phase – usually the shortest of the phases. The phase where essential organelles are constructed.

• and M phase – Cell Division.

I P on a MAT C *preparation between split

Interphase

*mitosis

Prophase

Metaphase

Anaphase

Telophase

*cells split

Cytokenesis

Steps of Cell Division

Interphase• Stage between cellular

division.

• Also known as the G1, S, and G2 stages of the cell cycle.

• In Interphase the cell is allowed to grow, copy its DNA and check for crucial genetic mistakes.

Mitosis• Mitosis (M phase) steps which include the

process for asexual cell division.

• Biologists divide the events of mitosis into four phases:

- Prophase

- Metaphase

- Anaphase

- Telophase

Depending on the type of cell, the four phases may last anywhere from a few minutes to several days.

Prophase- The first and the longest phase of mitosis, prophase can take as much

as 50 to 60 percent of the total time required to complete mitosis.

- During prophase in animal cells, the centrioles separate and take up positions on opposite sides of the nucleus.

- The centrioles help organize the spindle, fanlike microtubule structure that helps separate the chromosomes.

Prophase

• chromosomes appear-chromatin condenses to form chromosomes

• the nucleolus disappears

• the cell membrane begins to break down

Metaphase

• chromosomes align along the equator of the cell pulled by the spindle fibers

• Spindle fiber that are attached to the poles connect to the centromeres

• Short Phase

Early Anaphase

• chromosomes are pulled to the poles by the contraction of the spindle fibers chromatids are separated at the centromere

Late Anaphase

• chromosomes begin to move to the opposite poles

• Karyokinesis• the energy for this

process is provided by the mitochondria

Early Telophase

• the new cell wall begins to form to separate the new cell the chromosomes begin to form a nucleus

Late Telophase

• the chromosomes start to uncoil and become less dense

• Nuclear membrane reassembles

• Nucelolus reappears• Plasma membrane

begins to separate• Cell plate forms• two new identical

cells are formed

• Cytokinesis is the division of the cytoplasm of a parent cell.

• Microfilaments form a ring around the equator. When the microfilaments contract-pinches makes a furrow

Cytokinesis

• You may either consider it the end of Mitosis or the beginning of Interphase.

• While each daughter cells gets identical sets of DNA, the cytoplasm and organelles are only roughly divided equally between the two cells.

• Parent chromosome #= Daughter chromosome#

Cytokinesis

Mitosis • all four

stages of mitosis can be seen in this picture. note the process by which the red and blue chromosomes separate.

MITOSIS

://www.youtube.com/watch?v=VlN7K1-9QB0

Regulating the Cell Cycle• If we grow by cell division, then why do we stop

growing?

• Multi-cellular organisms cell growth is controlled.

• For example, in the human body, most muscle and nerve cells don’t divide at all once they have developed, whereas skin cells and blood cells divide rapidly.

Controls on Cell Division• Look at Fig 10-7 on page 250. What is

happening in this figure? What would happen if the cells continued to divide?

• When cells come into contact with other cells, they respond by not growing.

• How does this relate to how your body responds to a cut or a bone fracture?

Cell Cycle Regulators• Scientists discovered

that cells in mitosis contain a protein called cyclin when injected in a non-dividing cell, would cause a miotic spindle to form.

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

Other Cell Cycle Regulators

• Internal regulators- proteins that respond to events inside the cell.

For example: several regulatory proteins make sure that a cell does not enter mitosis until all its chromosomes have been replicated.

- External regulators- proteins that respond to events outside the cell.

For example: external regulators direct cells to either speed up or slow down the cell cycle.

Uncontrolled Cell Growth• Why is cell growth regulated so carefully?

• Cancer- a disorder in which some of the body’s own cells lose the ability to control division. Cancer cells do not respond to the signals that regulate the division of most cells.

Skin Cells