BUILDING AN ORGANISM-STELLA ANGELI
1
BUILDING AN ORGANISM-STELLA ANGELI
Building an organism
All living species, humans, animals and plants are organisms created to
perform different functions, essential for their survival, but they have one
common thing that verifies the rules of nature. Their growth begins from a
single cell which uses the genetic material ( Hershey A. and Chase M 1952)
and throughout specific functions, the genetic code is translated to proteins
which are used for the cell’s enquiries. During time, cells join together and
form tissues, organs and organ systems. This is how an organism, with its
features can be built from the simplest unit of life…the cell.
Cell is the simplest unit of function in a larger system (Campbell and
Reece), which controls the structure of the organism and interacts with the
environment by receiving specific messages that might influence its abilities.
The basic types of cells are: a) the eukaryotic cell and b) the prokaryotic cell.
These cells differ in their structure and functions as it seems in figure 1.
Figure 1: Eukaryotic and Prokaryotic cell
Both eukaryotic and prokaryotic cells have in common basic features
such as the plasma membrane, cytosol with organelles, ribosomes etc. A huge
difference between them is that eukaryotic cell has a nucleus which contains
the chromosomes with the genetic material but in the prokaryotic cell, DNA is
located in the nucleoid, an area without an enclosed membrane .
2
BUILDING AN ORGANISM-STELLA ANGELI
Here are some more differences between these cells:
COMPARISON OF EUKARYOTIC AND PROKARIOTIC CELL
EUKARIOTIC
PROKARYOTIC
FEATURES
TYPES
OF
ORGANISM
LOCATION
SIZE
COMPLEX
SIMPLE
PLANTS
BACTERIA
ANIMALS
ANIMAL CELLS: 10-3O
MICROMETERS
1-10 MICROMETERS
PLANT CELLS: 10-100
MICROMETERS
ATP
SYNTHESIS
MITOCHONDRIA IN
ANIMALS
CHLOROPLASTS IN
PLANTS
3
CELL MEMBRANE
BUILDING AN ORGANISM-STELLA ANGELI
ANIMAL AND PLANT CELL
Animal and plant cells enclose a variety of organelles structured in the
whole cell’s surface; each one of these controls a different function and keeps
the cells well organized. One of the most vital organelles for the cell is the
nucleus which includes the nuclear envelope, the nucleolus (involves in
ribosome production) and the chromatin. By looking at both cells, it is verified
that they have many other similarities such as (Tom Matheson lecture):
o Ribosomes which are responsible for making proteins
o Golgi apparatus which "receives, processes, packages, and shipps
cell products" (Tom Matheson’s lecture 2)
o Mitochondria where ATP is produced
o Cytoskeleton which controls the cell’s shape and contributes in
cell movement
o Endoplasmic reticulum (rough and smooth) which is responsible
for protein traffic and other processes
Figure 2: animal cell
4
BUILDING AN ORGANISM-STELLA ANGELI
Despite all their common features they differ in some of their structures.
Animal cells have also lysosomes, organelles where the hydrolysis of
macromolecules is performed, centrosomes and flagella, which gives to the cell
the ability to move. In contrast, plant cells have a cell wall around the cell
membrane which holds its stable shape, controls communication with other
cells and protects it from any damage. They have also specific organelles for
photosynthesis called chloroplasts, a central vacuole for the storage or waste
products and plasmodesmata which are ‘paths’ that connect the cytoplasmes
between two cells joined together(Campbell and Reece).
Figure 3: plant cell
5
BUILDING AN ORGANISM-STELLA ANGELI
As it is mentioned above, the nucleus is
fundamental for the cell’s survival because it encloses
the most important information, the entire cell’s codes
and all these in the genetic material-DNA. Many
scientists did experiments to prove that DNA was
actually the genetic material such as Mendel and
Morgan, Frederick Griffith, Alfred Hershey and Martha
Chase and many others.
The DNA structure
DNA is a double helix molecule (Meselson-Stahl
1958). Each strand is composed of nucleotides bind
together with phosphodiester bonds and each of the
nucleotides consists a nitrogenous base: T, A, C, G,
(figure 6), the deoxyribose (sugar) and a phosphate
group. Thymine is always opposite of Adenine,( Franklin
R. 1953) (in the complementary strand) bonded with two
hydrogen bonds and Cytosine is bonded with Guanine
Figure 4: DNA molecule
with three hydrogen bonds(Watson and Crick). Theffdirectionality of the DNA
strand is 5’ to 3’ prime.
Figure 5: DNA double helix
6
BUILDING AN ORGANISM-STELLA ANGELI
Figure 6: the nitrogenous bases (A,T,C,G)
The central dogma of molecular biology
DNA
RNA
PROTEINS
(Replication)
Transcription
Translation
7
BUILDING AN ORGANISM-STELLA ANGELI
The central dogma of molecular biology (Francis Crick 1957) indicates
how from DNA, a single cell can build its own proteins throughout a complicate
process. The whole process begins with DNA replication, which is vital for the
perpetuation of genetic information ( Hershey A. and Chase M. 1952).
DNA replication
The replication begins at some parts of the DNA molecule called origins
of replication, which have a specific sequence of nucleotides. DNA helicases,
are enzymes that cause the unwinding and separation of the two parent
strands in both directions, in order to form two Y-shaped replication forks.
Topoisomerase is a protein that prevents DNA strands to brake, swivel and
rejoin. At this point, the synthesis of the complementary strands begins.
Nevertheless, the DNA polymerases, enzymes that synthesize DNA, cannot
begin a new DNA chain. They can attach nucleotides to the end of a preexisting strand. Therefore, a RNA nucleotide chain, the primer, is produced
during the DNA synthesis by the enzyme primase, which adds RNA nucleotides,
opposite the DNA nucleotides on the parent strand. Afterwards, DNA
polymerase III replaces the primase and is able to add DNA nucleotides to the
RNA primer with 5’to 3’ direction, each strand in opposite direction because
the two parent strands are antiparallel. In addition, DNA polymerase II replaces
the RNA nucleotides of the primer with DNA nucleotides and DNA ligase, joins
together the fragments of the lagging strand. Finally the two complementary
strands are synthesised (nature education Pray, L 2008).
8
Figure 7: DNA replication
BUILDING AN ORGANISM-STELLA ANGELI
Transcription
Transcription is the process of RNA synthesis by using the DNA strand as
a template by the enzyme RNA polymerase. This enzyme attaches to the
promoter, the DNA strands unwind and the enzyme synthesizes RNA at the
beginning of the template strand (initiation). Afterwards, the RNA polymerase
moves along the strand, unwinds DNA and continues the RNA transcription in a
5’to 3’ direction (elongation). Finally, the pre-mRNA is released and the
polymerase disconnects from the DNA (termination). The pre-mRNA is
composed by introns, areas that cannot be translated and exons, areas that
can be translated into amino acids. Introns are unnecessary and must cut off
with some proteins, called spliceosome and the help of SnRNA. At the same
time the exons join together and the mature RNA is released, ready to be
translated.
Figure 8: Stages of transcription
9
Figure 9: Mature mRNA
BUILDING AN ORGANISM-STELLA ANGELI
Translation
Translation is the synthesis of a polypeptide chain using the mature
mRNA. All the information from the genes to proteins depends on the triplet
code. The sequence of three bases is a codon (Crick 1958) which specifies an
amino acid. The whole process is based on the translation of the base language
to the amino acids language. Essential elements for the process are: mRNA,
tRNA, and ribosomes.
Figure 11: ribosome units
Figure 10: DNA-RNA-protein
Figure 12: tRNA
10
BUILDING AN ORGANISM-STELLA ANGELI
Figure 13: Translation process
Figure 14: The genetic code
11
BUILDING AN ORGANISM-STELLA ANGELI
At the end of the translation process, a polypeptide chain is produced.
The amino acid sequence is important for the formation of specific proteins.
Proteins are vital molecules for all living organisms because they take part in
many different functions:
 Speed up biochemical reactions, as enzymes
 Give support (e.g. collagen,keratin)
 Transfer other substances (e.g. hemoglobin-transfers oxygen
from the lungs to all the parts of the body)
 Control many activities, as hormones
 Work as receptors at the cell membranes for communication
with other cells
 Responsible for the body movement as contractile proteins
 Protection from pathogenic microorganisms and disease as
defensive proteins (e.g. antibodies)
Figure 15: hemoglobin-transfer protein
12
BUILDING AN ORGANISM-STELLA ANGELI
This whole process of flowing information from genes to proteins is
made by the cells of almost all living organisms. To build an organism, millions
and billions of cells are needed to coordinate for its survival.
Each type of cell has specific proteins in the cell membrane which are
responsible for the recognition of cells that belong to the same type. When a
cell is recognised as a same type cell, is placed next to the original cell and that
happens in a continuous basis. The result is the creation of tissues.
Human body has three types of specialized tissues:
1. The epithelial tissue
It is divided in two other:
-Squamous: It forms the alveoli of respiratory membrane and the
endothelium of capillaries
-Columnar: It covers the small intestine and has unicellural glands, the
goblet cells which release mucus.
Figure 17: Squamous tissue
Figure 16: Squamous tissue
Figure 18: Columnar tissue
13
Figure 19: Columnar tissue
BUILDING AN ORGANISM-STELLA ANGELI
2. The muscle tissue
It is divided in three other:
-Skeletal muscle: It is responsible for the skeletal movement and reacts
to conscious control
-Smooth muscle: It is found in organs’ walls and has involuntary
movement
-Heart muscle: It is found only in heart and has involuntary movement
Figure 20: Types of muscle tissue
Figure 21: Skeletal, smooth and cardiac muscle structure
14
BUILDING AN ORGANISM-STELLA ANGELI
3. Nervous tissue
It is divided in three other:
-Unipolar neurones: They are sensory neurons which divide close to the
cell body into two main branches, the axon and dendrite
-Bipolar neurones: They are spindle shaped and have a dendrite and an
axon at their end
-Multipolar neurones: They are motor neurones which have numerous
cell processes
Figure 22: Neuron types
Specialized tissue comes together in order to form the organs. Organ is a
complex system of tissues working together to subserve human needs.
-Epithelial tissue comes together to form the lining of the lungs, the blood
vessels and the intestines.
-Muscle tissue comes together to offer protection and support to the skeleton,
as a result of the body movement.
-Nervous tissue comes together to form the central nervous system and is
essential for the control of behaviour and the processes of the human body.
15
BUILDING AN ORGANISM-STELLA ANGELI
Figure 23: human organs
16
Figure 24: human organs
BUILDING AN ORGANISM-STELLA ANGELI
All the organs together create organ systems which perform a certain
task to keep the organism alive.
Some organ systems of the human body are:
 Digestive system: responsible for the food processing, absorption and
excretion of waste
 Muscular system: responsible for body movement
 Skeletal system: responsible for the body support and protection
 Respiratory system: controls the absorption of oxygen and the
elimination of carbon dioxide
Figure 25: organ systems
17
BUILDING AN ORGANISM-STELLA ANGELI
In conclusion, building an organism, is a really complicate process,
starting by a single cell, where the flowing of the genetic information reaches
to proteins and then the same procedure happens to billions of cells which join
together to form tissues, organs and the final organism. The importance of this
is huge because if that single cell was damaged, the world would be without
animals, plants and human beings, thus life would not exist...
REFERENCES
1. Campbell and Reece, 2008, Biology: The structure and function of large biological
molecules unit 2, pp.77-78, concept 5.4
2. Campbell and Reece, 2008, Biology: A tour of the cell unit 2,pp.94-99
3. Campbell and Reece, 2008, Biology: The Molecular Basis of Inheritance unit 3 pp.305318, concept 16.1,16.2
4. Campbell and Reece, 2008, Biology: From Gene to Protein unit 3, pp.328-339,concept
17.1, 17.2, 17.3, 17.4
5. Farabee J. Michael, (2007), Animal cells and tissues
6. Gilbert F.S. (2000). Morphogenesis and cell adhesion. In Developmental biology, sixth
edition
7. Gilbert F.S. (2000). The developmental mechanics of cell specification. In
Developmental biology, sixth edition
8. Stryer L. 1995. Biochemistry: Flow of genetic information, chapter 5, pp.95-99
9. Stryer L. 1995. Biochemistry: Protein structure and function, chapter 2, pp.17-18
10. http://www.daviddarling.info/encyclopedia/E/eukarycell.html
11. http://en.wikipedia.org/wiki/Cell_(biology)#column-one
12. http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg13.html
13. http://www.daviddarling.info/encyclopedia/E/eukarycell.html
14. http://en.wikipedia.org/wiki/DNA
15. http://www.accessexcellence.org/RC/VL/GG/protein_synthesis.php
16. http://en.wikipedia.org/wiki/Biological_tissue#column-one
17. www.daviddarling.info/.../P/plant_cell.html
18
BUILDING AN ORGANISM-STELLA ANGELI
IMAGES
Figures 1, 10 taken from: http://en.wikipedia.org/wiki/Cell_(biology)#column- one,
http://www.daviddarling.info/encyclopedia/E/eukarycell.html
Figure 2 taken from: http://www.uvm.edu/~inquiryb/webquest/fa06/mvogenbe/AnimalCell.jpg
Figure 3 taken from:
http://www.molecularexpressions.com/cells/plants/images/plantcell450.jpg
Figure 4, 6, 7 taken from: http://en.wikipedia.org/wiki/DNA
Figure 5 taken from: http://tigger.uic.edu/classes/phys/phys461/phys450/ANJUM04/
Figure 8 taken from:
http://porpax.bio.miami.edu/~cmallery/150/gene/c7.17.7b.transcription.jpg
Figure 11 taken from:
http://www.modares.ac.ir/elearning/Dalimi/Proto/Lectures/week2/ribosome_1%5B1%5D.g
if
Figure 12 taken from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/tRNA2.gif
Figure 13, 14 taken from:
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPROTSYn.html
Figure 15 taken from: http://www.bloodless.it/hemoglobin.jpg
Figure 16 taken from: http://media-2.web.britannica.com/eb-media/37/92937-0341E4EA526.jpg
Figure 17, 19 taken from: www.stegen.k12.mo.us/.../TissueSlides.htm
Figure 18 taken from:
http://www.udel.edu/biology/Wags/histopage/colorpage/cep/cepcpe.GIF
Figure 20 taken from:
http://apps.uwhealth.org/health/adam/graphics/images/en/19917.jpg
Figure 21 taken from: http://www.dkimages.com/discover/previews/740/76722.JPG,
http://www.web-books.com/eLibrary/Medicine/Physiology/Muscular/muscle_structure.jpg,
http://webanatomy.net/histology/muscle/smooth_muscle_arrangement.jpg
Figure 22 taken from: 4ever-n-4whatever.blogspot.com
Figure 23 taken from: http://universe-review.ca/I10-35-organs.jpg
Figure 24 taken from: http://aaeclinics-site.web4.pbstaging.com/content/images/Backwith-organs.gif
Figure 25 taken from: http://universe-review.ca/I10-82-organs.jpg
19