Something to think about...

(1)

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?

(2)

Cell Growth and Reproduction

(3)

What Limits Cell Size?

Why can’t organisms be just one giant cell?

1

Diffusion

2

DNA Content

3

Surface Area to Volume Ratio

(4)

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?

(5)

DNA Content



Most cells contain only one nucleus

responsible for programming all metabolism.

DNARN A



If the ribosomes don’t receive enzyme and

protein-making instructions from the RNA, guess what? So long, big cell!

(6)

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 # sides 1 cm³

8 cm³ 27 cm³

6 cm²

54 cm² 24 cm²

27 X 9 X

You Know!

So long, big cell!

(7)

So, what must the cell do?

DIVIDE

(8)

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

(9)

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

(10)

Binary Fission

Division of a prokaryotic cell into two

offspring cells

(11)

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

(12)

Eukaryotic Cell Reproduction

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

(13)

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

(14)

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

(15)

Chromosome numbers of various species

(16)

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 = Interphase

Prophase, Metaphase, Anaphase, Telophase = Mitosis

I Passed My Algebra Test

(17)

Mitosis Overview

www.biologycorner.com/images.html

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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

(19)

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

(20)

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.

(21)

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Prophase

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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.

(23)

Metaphase

(24)

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.

(25)

Anaphase

(26)

Telophase



Chromatids arrive at opposite poles of the 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

(27)

Telophase

(28)

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.

(29)

Cytokinesis

(30)

Animal Cell - Mitosis

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Plant Cell - Mitosis

(32)

Mitosis Video Review

•Video Link #1 - Youtube

•Video Link #2 – Cells Alive

•Video Link #3 – DNAtube

(33)

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

14

14 14

GORILLA GARDEN PEA HUMAN

(34)

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.

(35)

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

(36)

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

(37)

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)

(38)

During which stage does DNA replication occur?

A. Prophase.

B. Anaphase.

C. Metaphase.

D. Interphase.

(39)

Name the Following Stages

Anaphase

Telophase Prophase

Metaphase

(40)

Which stage of mitosis is seen in the pictured cell?

A. Anaphase.

B. Prophase.

C. Telophase.

D. Interphase.

(41)

Which diagram most

correctly represents the

process of mitosis?

(42)

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.