Chapter 10:Cell Growth and Division

The blue whale is the largest mammal in the world. The pygmy shrew is one of he

smallest mammals in the world. How does the size of an average cell compare

between the two?

A. the average cell of a blue whale is A. the average cell of a blue whale is smallersmaller then the average cell of a then the average cell of a pygmy shrew. pygmy shrew.

B. the average cell of a blue whale is B. the average cell of a blue whale is larger larger then the average cell of a then the average cell of a pygmy pygmy shrew. shrew.

C. the average cell of a blue whale is C. the average cell of a blue whale is about the about the samesame size as the size as the average cell average cell of a pygmy shrew. of a pygmy shrew.

Cell Growth

When an organism grows, the number of cells increase but the size of each cell remains small.

Limits to cell growthLimits to cell growth1.1. DNA “DNA “overload”overload”:: The larger a The larger a

cell becomes, the more cell becomes, the more demands the cell places on its demands the cell places on its DNA.DNA.

a.a. WWhen a cell is small, DNA hen a cell is small, DNA can easily control the cell’s can easily control the cell’s functions and meet its functions and meet its needs.needs.

b.b. When a cell is large, it still When a cell is large, it still only has one copy of DNA, only has one copy of DNA, so it is more difficult for the so it is more difficult for the cell to perform its functions. cell to perform its functions.

2.2. ExExchanging materialschanging materials: :

• Large cells have more trouble moving Large cells have more trouble moving substances across the cell membrane.substances across the cell membrane.

• If a cell is too large, it is difficult to get If a cell is too large, it is difficult to get enough oxygen and nutrients in and waste enough oxygen and nutrients in and waste products outproducts out

Limits to cell growth

Division of the CellDivision of the Cell

When a cell gets When a cell gets too large, it : too large, it :

1. makes a copy of its DNA (replication),1. makes a copy of its DNA (replication),

and then…and then…

2. divides to form two “daughter” cells.2. divides to form two “daughter” cells.

Surface area to volume ratios

• 1 X 1 X 1 cube SA:______ volume: _____

• 2 X 2 X 2 cube SA:______ volume: _____

• 10X10X10 cube SA:______ volume: _____

• So when volume doubles, the surface area cannot “keep up” with it

6 1

24 8

600 1,000

Cell Division1. Cell division in eukaryotes is more complex than in

prokaryotes.2. There are two stages of eukaryotic cell division

a. Mitosis: Division of the cell nucleusb. Cytokinesis: Division of the cell cytoplasm

3. Unicellular organisms reproduce asexually by mitosis or something similar to mitosis (prokaryotes cant do mitosis!)

a. The daughter cells are identical to the parents cells

Asexual Reproduction

• Is one cell reproducing by itself

• Two types:

1. Binary Fission: organism replicates its DNA and divides in half, producing two identical daughter cells

• Example: bacteria

2. Budding: asexual process by which yeasts increase in number

Budding Binary Fission

Chromosomes1. Chromosomes are made of condensed

chromatin.2. Chromatin consists of DNA and the

proteins it is wrapped around.3. The cells of every organism have a specific

number of chromosomes 1. Ex. humans have 46 chromosomes

Chromatin v. chromosomes

4. Chromosomes are only visible during cell division, when they are condensed. The rest of the time the chromatin is spread throughout the nucleus.

5. Before cell division, each chromosome is replicated (meaning copied)a) When a chromosome is replicated, it consists of

two identical “sister” chromatids.b) When a cell divides the chromatids separate,

and one goes to each of the two new cells.

c) Sister chromatids are attached to each other at the spot called the centromere.

6. At the ends of each chromatid is an area called the telomere.

- The telomere is filled with non-coding DNA- Like a protective cap- Gets shorter during each cell division- Shortening is believed to be linked to aging

Telomeres

The Cell Cycle• When a cell is NOT dividing, it is said to be

in interphase.

• The series of events that a cell goes through as it grows and divides is called the cell cycle.

Events of the cell cycleInterphase, when the cell is NOT dividing, has three

phases: G1, S, and G2.

1.  G1 phase: period of activity in which cells do most of their growing.

a.     Cells increase in size

b.     Cells synthesize (make) new proteins and organelles

2. S phase: DNA (chromosomes) is replicated

3. G2: organelles and molecules required for cell division are produced

M phase is the phase of cell division. This includes:

1. Mitosis, the division of the cell nucleus, which is made up of four segments

including prophase, metaphase, anaphase, and telophase.

2. Cytokinesis, or the division of cytoplasm.

M phase

G2 phase

S phase

G1 phase

MitosisThere are four phases in mitosis:

1.     Prophase

a. Longest phase in mitosis (take 50- 60% of total time mitosis requires)

b.     Chromosomes become visible because they are

condensed

c.    Centrioles become visible on opposite sides of the nucleus

i. The centrioles help organize the spindle, a structure made of microtubules that helps

separate the chromosomesii. Chromosomes attach to the spindle

fibers near the centromereiii.      Plant cells to not have centrioles but do

have mitotic spindles

d.     Nucleolus disappearse.    Nuclear envelope breaks down

2. Metaphasea.     Chromosomes line up in the center of

the cellb. Microtubules connect to the

centromeres

3. Anaphasea.     Centomeres split and the sister

chromatids separateb.     The sister chromatids become

individual chromosomes

c.      Chromosomes move and separate into two groups

near the spindled. Anaphase ends when the

chromosomes stop moving

4. Telophase

a. Chromosomes change form being condensed to dispersed

b. A nuclear envelope forms around each cluster of chromosomesc.   Spindle breaks apartd. Nucleolus is visible in each daughter nucleus

Telophase in the midbodies of two daughter cells

Cytokinesis• Mitosis occurs within the cytoplasm of one cell.• Cell division is complete when the cytoplasm

divides.• In plants, a structure called the cell plate forms

between the two daughter nuclei. The cell plate develops into a cell membrane and cell wall.

• In animal cells, the cell membrane is drawn inward until the cytoplasm is pinched into two equal parts. Each part has a nucleus and cytoplasmic organelles.

Cytokinesis

The cleavage of daughter cells is almost complete; this is visualized by microtubule staining

Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomesMetaphase

Centriole

Spindle

CentrioleChromosomes (paired

chromatids)

Prophase

Centromere

Spindle forming

What are some reasons that cells undergo mitosis?

• Growth

• Repair

• Maintenance

• Asexual reproduction

Regulating the Cell Cycle Chapter 10-3

Different cell types divide at different rates.

Examples:– Muscle cells and nerve cells do not divide once

they have developed. – Skin cells and cells in the bone marrow that

make blood cells divide rapidly.

Proteins called Cyclins are present when the cell is dividing and are absent when the cell is not dividing.

They regulate the timing of the cell cycle

Controls on cell division• Cell growth and cell division can be turned

on and off.

• When you are injured your cells divide rapidly to repair the injury. When the injury has healed, the cells stop dividing.

Uncontrolled cell growthWhen cells in your body CANNOT control cell growth and division, cancer may form.

1. Cancer cells cannot respond to the signals that regulate the division of cells.

2. When cancer cells have been dividing uncontrollably, tumors form.

3. Tumors can damage surrounding tissue.4. Cells from tumors can break free and travel to

other parts of the body, forming new tumors.

Regulating Cell Divisions

• Internal regulators – Signals from within the cell to regulate the cell cycle. – They make sure everything is complete

before moving on.

Regulating Cell Divisions

• External regulators – Stimulate or suppress cell growth by recognizing the surrounding situation. – Injury repair– Embryonic stem cell differentiation

Cancer• Cancer cells tend to have a damaged

oncogene. – This gene possess the information needed to

respond to internal and external regulators.

During the Reading

Define the following

1. Metastasis :

2. Benign:

3. Malignant:

The process or condition of abnormal cell migration and tissue invasion.

Cells that stay where they are usually considered as a Tumor. (Not Cancer)

Cells can break off and infect other areas of the body (Cancer)

There are several reasons that cells may lose the ability to control growth.

Examples:1. smoking2. radiation exposure3. viral infection

Scientists who study cancer are researching how cells divide.

Reviewing Mitosis

When does the following occur?

(Name the phase of the cell cycle. If it is in mitosis, name the phase of mitosis)

1. Sister chromatids separate.

2. Chromosomes line up across the center of the cell.

3. The cell’s DNA molecules are copied.

4. The cytoplasm pinches in half.

5. A spindle forms.

Mitosis - Anaphase

Mitosis - Metaphase

S Phase

Cytokinesis

Mitosis - Prophase

What are the structures shown?

How many copies of the cell’s DNA are

shown here?

A. Sister chromatids

B. Centromere

2

Cell Cycle

Interphase ? Phase

Mitosis Cytokinesis

? ? ??

M Phase

Prophase

Metaphase

Anaphase Telophase

A

B

C

What is the name of the structure labeled:

A? __________________

B? __________________

C? __________________

Chromosome

Centriole

Spindle fiber

If your were to examine a sample of 1000 cells undergoing mitosis, in which of the phases listed below would you expect to find most of the cells?

A. Prophase

B. Metaphase

C. Anaphase

D. Telophase

Meiosis (Gametogenesis) Chapter 11-4

Chromosomes

• You have 23 different pairs of chromosomes, for a total of 46 chromosomes.

• One chromosome in each pair came from your mother and one from your father.

Each chromosome in a pair is said to be homologous, meaning that the chromosome from the father has a corresponding chromosome from the mother.

• Cells that contain both sets of homologous chromosomes are called diploid (2N).

• All of your cells except the sex cells (sperm and eggs; also called gametes) are diploid (2N).

• Gametes are haploid (N), meaning they contain only one copy of each chromosome.

• When one sperm and one egg combine their DNA, there are two versions of each chromosome.

haploid haploid

diploid

We use “N” to represent the haploid number of chromosomes and “2N” to represent the diploid number of chromosomes.

1. For humans, the haploid number is 23. We write this as N = 23. The

diploid number is 46, which we write as 2N = 46.

2. In fruit flies, N = 4 and 2N = 8.

Practice with haploid and diploid: Practice with haploid and diploid:

In fruit flies, N (______) = 4 andIn fruit flies, N (______) = 4 and 2N (______) = ___2N (______) = ___8.8.

haploidhaploid

diploiddiploid

If elephants have a diploid number of 56, what is their haploid number?

28

Meiosis

Meiosis is the process that divides one diploid (2N) cell to form four haploid (N) cells.

This process is a reductional division because the number of chromosomes per cell are cut in half.

Meiosis is how gametes are formed.

There are two divisions that occur in meiosis: Meiosis I and Meiosis II. 1. Before meiosis I begins, cells go through

Interphase I.

2. This involves DNA replication, forming a duplicate copy of each chromosome.

3. Each chromosome is made of two sister chromatids.

cell

centriolesNucleus with duplicated DNA that is not condensed.

Meiosis I is similar to mitosis.

a.     Prophase I:i.      Centrioles are visible on

opposite sides of the nucleus

ii.      Nucleolus disappears

iii.      Nuclear envelope breaks down

centrioles

spindle

DNA condensed as chromosomes

iv. Homologous chromosomes pair1. When a pair of chromosomes aligns a

tetrad is formed.

2.      When chromosomes form a tetrad, they exchange portions of their

chromatids in a process called crossing-over.

3. Crossing-over produces new combinations of DNA. tetrad

b.     Metaphase I:i.      Spindle fibers attach to the chromosomes at

the centromere

centrioles

spindle

chromosomes (DNA)

centromere

c.     Anaphase I:i. Spindle fibers pull the homologous chromosomes toward opposite ends of the cell.

ii. Chromosomes move and separate into two groups near the spindle

iii. Anaphase ends when the chromosomes stop moving

centrioles

spindle

chromosomes (DNA)

d. Telophase Ii.      Nuclear membranes form around

chromosomes

ii.      Daughter nuclei form

e. Cytokinesis

i. Cytoplasm divides

centrioles

chromosomes (DNA)

Nucleus

Nucleus

Meiosis I produces two haploid (N) daughter cells that have only one copy of each chromosome. Each chromosome is made of two sister chromatids.

Meiosis II

After Meiosis I, cells enter Meiosis II.

No DNA replication occurs between Meiosis I and Meiosis II.

Meiosis II separates the sister chromatids.

a.     Prophase II:

i. Centrioles are visible on opposite sides of the nucleus

ii. Nucleolus disappears

iii. Nuclear envelope breaks down

centrioles

chromosome

b.     Metaphase II:

i. Chromosomes align like they do in mitosis

ii.Chromosomes are attached to the spindle at the centromere.

centrioles

chromosome

spindle

c. Anaphase II:

Sister chromatids separate and move towards opposite ends of the cell.

centrioles

chromosome

spindle

d. Telophase II: i. Nuclear membranes

form around chromosomes

ii. Daughter nuclei form

e.  Cytokinesis: i. Division of the

cytoplasm

f.  Meiosis II - produces four haploid (N) daughter cells

nucleus

chromosome

centrioles

Gamete formation

• In male animals, the haploid gametes are called sperm.

• In female animals, the haploid gametes are called eggs.

• When the male and female gametes join, this is called fertilization and a zygote is formed.

Comparing mitosis and meiosis• Mitosis produces two genetically identical

diploid (2N) somatic (body) cells. Mitosis allows an organism’s body to grow and to replace cells. In organisms that reproduce asexually, new organisms are produced by mitosis.

• Meiosis (or gametogenesis) produces four genetically different haploid (N) cells. Meiosis produces gametes for use in sexual reproduction.