Chapter 10

Cell Division

Ch. 10: Section 1

I. Limits to Cell Growth/SizeA. DNA “Overload” – If a cell grows too

large, its DNA could no longer serve the needs of the entire cell

B. Exchanging materials – if a cell is too large, is struggles to move enough nutrients & wastes throughout the cell and to the cell membrane

II. Surface Area to Volume RatioA. Surface Area = length x width x # of sidesB. Volume = length x width x heightC. Surface Area to Volume Ratio = SA/VD. Volume increases more rapidly than

surface area, causing the ratio to decrease

E. 2 lane main street into a town will experience more traffic as town gets bigger, and it takes longer to get to center of town as size of town increases.

II. Surface Area to Volume Ratio (cont)Calculations:

All sides = All sides = All sides =       

Cell Size: 1cm 2cm 3cm              

Surface Area      (length x width x 6)      

              

Volume      

(length x width x height)      

       Ratio of Surface      Area to Volume      

       (SA/V)      

II. Surface Area to Volume Ratio (cont)Calculations:

All sides = All sides = All sides =       

Cell Size: 1cm 2cm 3cm              

Surface Area      (length x width x 6) 6 cm2 24 cm2 54 cm2

              

Volume      (length x width x

height) 1 cm3 8 cm3 27 cm3       

Ratio of Surface      Area to Volume 6/1 = 24/8 = 54?27 =

  6:1 3:1 2:1(SA/V)      

Ch. 10: Section 2

I. Why cells divide/reproduceA. Growth – new cells are needed to grow

tissues and organsB. Replacement & Renewal – old/damaged

cells die & are replaced with newC. Reproduction

1. unicellular organisms divide to make new organisms

2. multicellular organisms divide cells to make sex cells (gametes).

II. Chromosome StructureA. Gene – DNA is a large molecule broken

down into hereditary units called genes• DNA is organized & packaged into

chromosomes

B. Chromosome – DNA wound or coiled tightly around proteins (histones)• Prokaryote Chromosome – a single, circular

loop of DNA• Eukaryote Chromosome – many linear DNA

molecules packaged into chromosomes

C. Structure – fully condensed, duplicated • A chromosome is made of 2 identical

halves. Each half is called a chromatid.• A centromere holds 2 chromatids together

to make a chromosome.• DNA is packaged as a chromosome only

during cell division, after it has been copied.

• When a cell is not dividing, its DNA is packaged more loosely as chromatin.

II. Chromosome #’s - each species has a different number of chromosomes

A. Sex Chromosomes – and X or Y chromosome

1. They determine the sex of the individual

2. Female = XX Male = XY

B. Autosomes – all remaining chromosomes

1. In humans: 44 autosomes + 2 sex chromosomes = 46 total chromosomes

2. The 44 autosomes in a human are actually 22 pairs. An individual gets a copy of each chromosomes from each parent.

C. Homologous Chromosomes – a pair of chromosomes

1. A human has 22 homologous chromosome pairs

2. An homologous pair are the same size, shape, and contain the same types of genes for the same traits. Each chromosome can have

different specific genes than its homologous pair

D. Diploid Cells 1. Are cells having all homologous pairs and

2 sex chromosomes2. All cells except gametes

(gametes = sex cells: egg and sperm cells)3. Diploid cell are abbreviated as 2n, where

n = # of 1 set of chromosomes.4. Also called body cell, or somatic cells.5. The chromosomes of diploid cells can be

arranged and studied using karyotypes.

E. Haploid Cells1. Cells that contain only 1 chromosome

from the pair of homologous chromosomes and 1 sex chromosome.

2. Haploid cells are abbreviated as n.3. Haploid cells are gametes.

Chromosome # Example

A male human has 46 total chromosomes.(A chromosome is made of 2 chromatids, duplicated copies of the same DNA molecule)

• # of autosomes = • # of sex chromosomes = – The sex chromosomes are

• # of homologous pairs = • Diploid # (2n) = • Haploid # (n) =

III. Eukaryote Cell CycleA. Cell Cycle – repeating events of growth

and division during the life of a cellB. Interphase – time when cell is not

dividing1. G1 Phase – cells grows rapidly as it makes

more organelles2. S Phase – DNA/chromosome is copied3. G2 Phase – cell continues to grow and

makes organelles for cell division4. G0 Phase – when cell doesn’t divide

(instead of G1, S, & G2 Phases)

C. Mitosis – division of the nucleus (DNA)1. Prophase – 1st step• DNA is packaged into chromosomes• Nucleolus and nuclear membrane

break apart• Centrioles move to opposite ends of

the cell

2. Metaphase – 2nd step• Spindle fibers coming from the

centrioles attach to the centromeres of the chromosomes

• Chromosomes line up in the middle of the cell

3. Anaphase – 3rd step• Spindle fibers pull chromatids apart

at the centromere• Each chromatid is now considered a

chromosome!

4. Telophase – 4th (last) step• Spindle fibers disappear• Nuclear envelope reforms around

each set of chromosomes

D. Cytokinesis 1. Begins during telophase.2. Is the division of the cell/cytoplasm.• Animal cells: cell membrane pinches

inward making a cleavage furrow. This continues until 2 cells are formed.

• Plant Cells: a cell plate forms between the 2 sets of chromosomes.

***Mitosis happens in somatic cells and makes 2 diploid cells!

Mitosis in a Plant Cell

Mitosis in an Animal Cell

E. Controls on Cell Division1. Physical contact• Cells tend to divide until a space has

been filled.• Once that space has been filled, or the

cells contact each other, they stop dividing.

2. Cell Cycle Regulators• Cyclin – protein that regulates the cell

cycle• High levels of cyclin = cell division• Low levels of cyclin = Interphase

F. Uncontrolled Cell Growth1. Cancer – cells lose the ability to control

cell divison/growth2. Cancer cells do not respond to the signals

that regulate the growth of most other cells.

3. As a result, they form masses of cells, tumors, that can damage the surrounding tissues.

Section 11-2: Meiosis

Meiosis – cell division that halves the number of chromosomes in new cells, making haploid cells

*Recall, haploid cells in human are egg/sperm cells, called gametes, and contain 23 chromosomes.

Stages of MeiosisI. Interphase

A. cells go through G1, S, and G2 phases;

B. DNA is copied and cells grow larger.

II. Meiosis IA. Prophase I

1. DNA is coiled into chromosomes & nucleus breaks down

2. Centrioles move to ends of cell; spindle fibers appear

3. Chromosomes pair up (in homologous pairs) and twist together.– Portions of a chromatid can break off and

reattach to the identical chromatid on its homologous chromosome = crossing over

Prophase I and Crossing Over

B. Metaphase I1. Homologous chromosomes line up

randomly in the center of the cell2. Spindle fibers attach to the centromeres

C. Anaphase I1. Spindle fibers pull homologous

chromosomes apart.2. The direction the chromosomes are pulled

is random = independent assortment

D. Telophase I1. Chromosomes move to opposite ends of

the cell2. Cytokinesis occurs

**Meiosis I results in 2 new haploid cells

III. Meiosis II• Begins immediately after Meiosis I.• Both cells from Meiosis I go through

Meiosis II.• DNA is not copied this time!!!!!!!

A. Prophase II – spindle fibers reform, centrioles move to opposite ends of cell

B. Metaphase II – single chromosomes line up in the middle of the cell

C. Anaphase II – spindle fibers attach at centromeres and pull chromatids apart

D. Telophase II – chromatids move to opposite ends, and nucleus forms around them and cytokinesis occurs

**Meiosis II results in 4 new Haploid cells.

Stages of Meiosis II

IV. Meiosis Forms GametesA. The 4 haploid cells produced in Meiosis

are gametes (sex cells = egg/sperm)B. Spermatogenesis – production of sperm

cellsC. Oogenesis – production of mature egg

cells or ova (singular = ovum)

V. Genetic Variation in MeiosisA. Crossing Over – switching of DNA

between chromatids of homologous pairs; occurs during prophase I

B. Independent Assortment – each homologous pair is separated independent of how the other pairs are separated.

C. Random Fertilization – of the 4 gametes produced in meiosis, any one can fertilize (join) with another gamete