When you see a newborn baby, is it hard for you to imagine that just nine months ago, that baby was a single cell?

Something to think about...

When you see a towering oak tree, can you believe that it was once a measly acorn?

When you mow the lawn on Saturday, can you believe that by next Saturday, you have to do it again?Can you believe that every second, your body makes 25 million new cells?

Cell Growth and Reproduction

What Limits Cell Size?

Why can’t organisms be just one giant cell?

1 Diffusion

2 DNA Content

3 Surface Area to Volume Ratio

Diffusion

= Mitochondrion

Oxygen

Glucose

Waste

Waste

Cells can metabolize only as quickly as they receive raw materials. An average-sized cell with a diameter of 20um will receive supplies in a fraction of a second.

So long, big cell!

What if the cell were 20cm in diameter?

DNA Content

Most cells contain only one nucleus responsible for programming all

metabolism.DNA

RN

A

If the ribosomes don’t receive enzyme and protein-making instructions from the RNA, guess what?So long, big cell!

Surface Area-to-Volume Ratio

As a cell’s size increases, its volume increases much faster than its surface area.

3 cm

1 cm

2 cm

Volume l x w x h

Surface Area l x w x #

sides1 cm3

8 cm3

27 cm3

6 cm2

54 cm2

24 cm2

27 X 9 X

You Know!So long, big cell!

So, what must the cell do?

DIVIDE

Functions of Cell Division

In multicellular eukaryotes:– Growth and development– Replace old, worn-out and dying cells and

tissues– Sexual reproduction – making of gametes,

or sex cells (sperm and egg)

In unicellular prokaryotes:–Asexual reproduction

Types of Reproduction

Asexual Reproduction– Formation of offspring from one parent– Offspring are genetically identical to the parent– Leads to lack of genetic diversity among offspring

~ disadvantage in changing environment– Types include:

Binary fission – bacteria Fragmentation – starfish, Planaria Budding - sponges

Binary Fission

Division of a prokaryotic cell into two offspring cells

Types of Reproduction

Sexual Reproduction– Formation of offspring by uniting gametes

from two parents– Offspring are genetically different from the

parents– Increases variation in the population by

making possible genetic recombination

Eukaryotic Cell Reproduction

Before cell division, DNA coils tightly around histones (proteins) and forms chromosomes

Chromosomes (rod-shaped structures made of DNA and protein) must be duplicated in order for each daughter cell to receive identical copies of the parental chromosomes; each chromosome consists of two identical halves called sister chromatids held together by a centromere

Chromosome Structure

Sex Chromosomes and Autosomes

Humans’ somatic, or body cells, have 23 pairs of chromosomes (46 = diploid or 2n number) – first 22 pair are autosomes; last pair are sex chromosomes

XX=female

XY=male

The two copies of each autosome are called homologous chromosomes, or homologues (same size and shape and carry genes for same traits

Chromosome numbers of various species

Cell Cycle – Cell Division in Eukaryotes

G1 -- Period of cell growth before DNA is duplicated

S -- period when DNA is duplicated

G2 -- period after DNA is duplicated; cell prepares for division; end of interphase

Telophase

Anaphase

Metaphase

Prophase

G1, S, and G2 = InterphaseProphase, Metaphase, Anaphase, Telophase =

MitosisI Passed My Algebra Test

Mitosis Overviewwww.biologycorner.com/images.html

Interphase – G1, S, G2

The cell is engaged in metabolic activity and performing its preparation for mitosis.

Chromosomes are not clearly visible in nucleus, but the nucleolus may

be visible. Centrioles (or microtubule organizing centers) may be visible during this

phase.

nuclear membrane

nucleus

chromatin

Interphase – G1, S, G2 In G1 or first growth phase, cells mature and increase

in size by making more cytoplasm and organelles

S or Synthesis phase follows G1 and results in the replication of genetic material Cell makes all structures needed to divide in G2 or second growth phase

nuclear membrane

nucleus

chromatin

Prophase

Chromatin in the nucleus begins to condense and becomes visible in light microscope as

chromosomes.

Nucleolus disappears. Centrioles in animal cells begin moving

to opposite ends of the cell and fibers extend from the centromeres.

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Prophase

Metaphase

Spindle fibers align the chromosomes along the middle of the cell nucleus, or equatorial plate.– This organization ensures that in the next phase,

each new nucleus will receive one copy of each chromosome.

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Metaphase

Anaphase

The paired chromosomes separate at the centromere and move to opposite sides of the cell; after chromatids separate, they are considered to be individual chromosomes.

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Anaphase

Telophase

Chromatids arrive at opposite poles ofthe cell and new membranes form around the daughter nuclei.

Chromosomes uncoil and are no longer visible under the light microscope.

Cytokinesis begins. Cell Plate or Cleavage Furrow

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Telophase

Cytokinesis

In animal cells, cytokinesis results when a cleavage furrow forms and

pinches the cell in two.

In plant cells, cytokinesis occurs when vesicles from the Golgi apparatus fuse to form a cell plate.

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Cytokinesis

Animal Cell - Mitosis

Plant Cell - Mitosis

Mitosis Video Review

•Video Link #1 - Youtube

•Video Link #2 – Cells Alive

•Video Link #3 – DNAtube

Cell Reproduction Following the completion of the cell cycle, two

daughter cells result, with the same number of chromosomes as the parent cells.

46

46

46

46

46

46

46 46

14

14

14 14

GORILLA GARDEN PEAHUMAN

So… What Are The Results?

Genetic continuity, i.e., two new cells with chromosome sets identical to the parent cell.

Daughter cells will carry out the same cellular processes and functions as their parent cell and will grow until the limitations of cell size force them to divide.

Control of Cell Division

Three checkpoints control division– Cell growth (G1) checkpoint: proteins control

whether the cell will divide– DNA synthesis (G2) checkpoint – DNA repair

enzymes check results of DNA replication;if checkpoint is passed, proteins will signal the cell to begin mitosis

– Mitosis checkpoint – if a cell passes, proteins signal the cell to exit mitosis and enter G1 again

When Control is Lost

If mutation occurs in one of the genes (p53 gene) that regulates cell growth and division, proteins may not function properly– This may lead to cancer, or the

uncontrolled growth of cells – Environmental influences may also play a

role, e.g., UV rays, radiation, X-rays– ONCOLOGY – study of cancer

To Review...

Limits of Cell Size– Diffusion– DNA Content– Surface Area-to-Volume Ratio

Cell Cycle– Interphase– Mitosis (Nuclear Division)

Prophase, Metaphase, Anaphase, Telophase

– Cytokinesis (Cytoplasmic Division)

During which stage does DNA replication occur?

A. Prophase.

B. Anaphase.

C. Metaphase.

D. Interphase.

Name the Following Stages

Anaphase

Telophase

Prophase

Metaphase

Which stage of mitosis is seen in the pictured cell?

A. Anaphase.

B. Prophase.

C. Telophase.

D. Interphase.

Which diagram most correctly represents the process of mitosis?

Which answer gives the stages of mitosis in proper chronological order?A. Anaphase prophase metaphase

telophase.

B. Metaphase anaphase telophase prophase

C. Prophase metaphase anaphase telophase.

D. Interphase prophase metaphase anaphase telophase.