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.
DNARNA
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 # sides 1 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 = Interphase
Prophase, Metaphase, Anaphase, Telophase = Mitosis
I Passed My Algebra Test
Mitosis Overview
www.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 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
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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.
Interactive Eye, LLC (1997)
Cytokinesis
Animal Cell - Mitosis
Plant 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 PEA HUMAN
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.
