Biology Chapter 10: Cell Growth and

Division

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Let's start from the beginning...

• A long time ago our ancestors noticed that some things tended to reproduce themselves - traits were inherited. Unfortunately, that's not always a good thing!

What is a chromosome?

• Threadlike structure in nucleus > contains genetic information - passed on from one generation of cells to the next– Genetic information = DNA (“blueprints” of

life)– DNA in form of a code (genes) > dictates

everything from eye color to how long you live

– “It’s in your genes” should actually be “It’s in your DNA

Gene• Sequence of DNA that codes for a

protein and determines a trait– Trait = specific characteristic that varies from

one individual to another– Ex: height, hair and eye color

• Genes are the bands on chromosomes.– The thicker the band, the more information it

holds.

Living things grow by producing cells.

bacteria (0.5 to 1.5 microns)

red blood cell (5 microns)

lymphocyte (5 to 8 microns)

As a cell grows larger, it…• Places more demands on its DNA

– DNA “Overload” – Compare to town library (town

grows, more demand for books)

• Has more trouble moving enough nutrients and wastes across its membrane (in and out of cell)

The cell will eventually divide into two daughter cells.

Cell Division• Process by which a cell

divides into two daughter cells– DNA replicated before division– Each daughter cell gets one

complete set of genetic information

• Two stages:– Mitosis - nucleus divides to

form two identical nuclei– Cytokinesis - cytoplasm

divides to form two identical cells

Chromosomes• Made up of DNA (genetic information) and

proteins > chromatin

• Each chromosome has two identical “sister” chromatids - one goes to each new cell

• Cells of every organism have specific number of chromosomes– Ex: fruit flies 8, carrots 18, humans 46

• Duplicated chromosomes are called dyads

• Duplicates held together by centromere• Homologous pair = 1 of each pair

acquired from one of the parents

The Cell Cycle• Cell grows, replicates its DNA, and

divides into two daughter cells

• Four phases~M phase > Mitosis and

cytokinesis (cell division)~S phase > Synthesis

(chromosome replication)

~G1 and G2 > “Gap” phases (periods of intense Growth and activity)

Interphase• Period of cell cycle between cell

divisions• All phases except M

– Made up of G1, S, and G2 phases – Split because M phase occurs much

more quickly• Includes: DNA replication, protein

synthesis, and synthesis of organelles and materials needed for cell division

•Mitosis > Process in which the nucleus divides to form two identical nuclei

Four Phases of Mitosis

•Prophase

•Metaphase

•Anaphase

•Telophase

Prophase• Chromatin condenses

into chromosomes• Nucleolus disappears• Centrioles separate

– Two tiny “anchors” in cytoplasm near nuclear envelope

• Fanlike fibers extend to form spindle

Pair of Centriol

es

CentromereChromosome (two

sister chromatids)

Metaphase• Chromosomes line up along center

of cell– Each chromosome connected to

spindle at centromere

(Imaginary line)

Anaphase•Sister chromatids separate and

move to opposite sides of cell

Telophase• Chromosomes gather at

opposite ends of cell • Two new nuclear envelopes form

Chromosomes gathering

New nuclear envelopes

forming

Cytokinesis• Cytoplasm pinches in half• Each daughter cell has identical

set of duplicate chromosomes

New individual cell

Uncontrolled Cell Growth• Cancer

– Disorder in which some cells lose ability to control growth

– Cells do not respond to signals that regulate growth of most cells

– Result > divide uncontrollably and form masses of cells called tumors

Results of Mitosis• Mitosis is the division of a

NUCLEUS

• Mitosis produces two new nuclei with the SAME number of chromosomes as original nucleus

• Mitosis is ASEXUAL

– ONE parent = 2 IDENTICAL daughters