Download Kaitlyn Kraybill-Voth Period 3 Investigation 2: Scientific Essay: Cells

Kaitlyn Kraybill-Voth
Period 3
Investigation 2: Scientific Essay: Cells
Molecules Make Cells, and How do Cells Function?
Introduction/Cell theory:
Every living thing is made of at least one cell. The discovery of cells was made possible by the
development of the microscope in the early 1600s. In 1665, English scientist Robert Hooke used
a microscope to look at a slice of cork. He wrote “I could exceedingly plainly perceive it to be
perforated and porous,” and he described it as “as great many little boxes” these little boxes
reminded him of the small rooms where monks lived, so he called them cells. What Hooke
observed were actually the remains of dead plant cells. Around a century and a half after the
observation of Hooke and van Leeuwehoek, scientists began to organize these observations into
a unified theory called the cell theory. It has three parts: 1)All living things are made of one or
more cells. 2) Cells are the basic units of s structure and function in an organism. And 3) Cells
come only from the reproduction of existing cells.
Essential Biologic Molecules:
Cells make a huge number of large molecules from a small set of small molecules. There are four
classes of biological molecules. Carbohydrates, Proteins, Lipids, and Nucleic acids.
Monosaccharides are the simplest carbohydrates. Carbohydrates rang from small sugar
molecules called monomers, to large polysaccharides. Monosaccharides are sugar monomers
including glucose and fructose, these can been bonded together to form the polysaccharides. The
purpose of Monosaccharides is to fuel cellular word. They are also used as raw materials to
manufacture other organic molecules. Proteins are essential to the structures and functions of
life. They are polymer built from many combinations of twenty amino acid monomers. They are
involved in nearly all cell activities, have structures that are directly related to their function, and
as enzymes they serve as catalysts and regulate the chemical reactions within a cell. There are
structural proteins, defensive proteins, and receptor proteins. Lipids are water isolable, the are
hydrophobic or water fearing compounds that store energy. They contain twice as much energy
as a polysaccharide. Fats are lipids made from glycerol and fatty acids. Oils are liquid facts and
are water repellants. Fats are lipids that are mostly energy-storage molecules. Nucleic acids are
information-rich polymers of nucleotides. DNA and RNA are made of monomers called
nucleotides. Nucleotide have three parts, a five-carbon sugar, a phosphate group, and a
nitrogenous base.
Cell Organelles
Atoms make up molecules, molecules make up cell organelles, cell organelles make up cells
(which in turn make up tissues, which make up organs, which make up organ systems, which
make an organism.) Cell Organelles are comprised of many different components including: The
Nucleus whose function is to control the center of a cell as it is the most important part of the
cell. The Plasma membrane is an important factor of cellular control. It restricts what can leave
and enter the cell. This is called homeostasis.
Parts of a Cell and Their Functions
Nucleus- The nucleus is enclosed within a double membrane. It communicates with the
surrounding cytosol with nuclear pores. The nucleus houses the DNA that give the cell its unique
characteristics. The DNA in each of the cells in the body are all similar, however it depends on
the particular type of cell, because some genes turn off and on. This is shown the fact that a
muscle cell is different from a liver cell. When a cell divides, the nuclear chromatin (the DNA
and surrounding protein) condenses into chromosomes that can by seen with microscopes.
Nucleolus- The nucleoulus is an important structure in the nucleus. It makes ribsomes that move
out of the nucleus and take positions on the rough endoplasmic reticulum where they are vital in
protein synthesis.
Cytosol- The cytosol is sometimes considered the soup that all the other cell organelles reside in.
It is also where most of the cellular metabolism happens. The cytosol is comprised mainly of
water, it also has proteins. These proteins control cell metabolism. The term for the cytosol and
the organelles suspended within the cytosol is called ‘Cytoplasm.’
Centrosom- The centrosome is an area in the cell where microtubules are produced. Plant and
animal cell centrosomes play similar roles in cell division, they also both include collections of
microtubules. However the plant cell centrosome is not as complicated as the animal cell
centrosome and does not have centrioles.
Centriole- Centrioles pertain only to animal cells. Each centriole is a ring of nine groups of fused
microtubules. There are three microtubules in each group. Microtubules and centrioles are part of
the cytoskeleton. In the complete animal cell centrosome, the two centrioles are arranged so that
they are perpendicular to each other.
Golgi- The Golgi apparatus is a stack of membrane-bound vesicles that are important in packing
macromolecules for transport somewhere else in the cell. The stack of larger vesicles is
surrpounded by many smaller vesicles that contain macromolecules.
Lysosome- Lysosomes contain hydrolytic enzymes that are necessary for intracellular digestion.
They are common in animal cells however they are rare in plant cells. Hydrolytic enzymes of
plant cells are more often found in the vacuole.
Peroxisome- Peroxisomes are membrane-bound packets of oxidative enzymes. In plant cells
preodisomes convert fatty acids to sugar. In animal cells they protect the cell from its own
production of toxic hydrogen peroxide. For example, white blood cells produce hydrogen
peroxide to kill bacteria. The oxidative enzymes in peroxisomes break down the hydrogen
peroxide into water and oxygen.
Secretory Vesticle- Cell secretions (hormones) are held in secretory vesicles at the Golgi
apparatus. The secretory besicles are transported to the cell surface to be released.
Cell Membrane- Every cell is enclosed in a membrane which is a double layer of phosolipids
(lipid bilayer). The exposed heads of the bilayer love water, so they are compatible with water
within the cytosol and outside the cell. The hidden tails of the phosopholipids fear water, so the
cell membrane acts as protective barrier to the controlled flow of water. The numerous proteins
that are crucial to cell activity complicate the membrane. These proteins include receptors for
odors, tastes, and hormones, as wel as pores that control entry and exit of ions like sodium,
potassium, calcium, and chloride.
Mitochondrion- Mitochondria provide the energy that a cell needs to move, divide, produce
secretory products, contract. They are the POWER CENTERS of the cell. They are membranebound organelles and have a double membrane.
Vacuole- A vacuole is a membrane-bound sac that plays roles in intracellular digestion and
releasing cellular waste products. In animal cells vacuoles are usually small. They tend to be
large in plant cells however. They store nutrients and waste products, they increase cell size
during growth. The plant cell vacuole regulates tugor pressure in the cell (this occurs when water
collects in cell vacuoles which presses outward against the cell war and causes the plant to
become rigid.) Without sufficient water, turgor pressure drops and the plant wilts.
Cell Wall- (Are only in plant cells.) Plant cells have a rigid, protective cell wall that is made of
polysaccharides. The cell wall provides and maintains the shape of these cells and serves as a
protective barrier. Fluid collects in the plant cell vacuole and puses out against the cell wall. This
turgor pressure is why fresh vegetables are crisp.
Chloroplast- (Also only in plant cell.) Chloroplasts are specialized organelles in higher plant
cells. They contain the plant cell’s chlorophyll that makes the plant’s green color. Chloroplasts
have a double outer membrane.
Smooth Endoplasmic Reticulum- In the eukaryotic cell, this a large network of membrane-bound
vesicles and tubules called endoplasmic reticulum (ER.) The ER is a continuation of the outer
nuclear membrane and has varied functions. It is named because it looks smooth by electron
microscopy. ER functions depend of the specific cell type, it includes hormone synthesis,
breakdown of lipid-soluble toxins in liver cells, and control of calcium release in muscle cell
contraction.
Rough Endoplasmic Reticulum- Rough endoplasmic reticulum looks ‘pebbled’ by electron
microscopy because of the many ribosomes of its surface. Proteins synthesized on these
ribosomes collect in the endoplasmic reticulum for transport throughout the cell.
Ribosomes- Ribosomes are packets of RNA and protein that are important in prokaryotic and
eukaryotic cells. They are where protein synthesis occurs. Each ribosome is made of two parts, a
large subunit and a small subunit. Messenger RNA from the cell nucleus is moved along the
ribosome where transfer RNA adds amino acid molecules to the developing protein chain.
Cytoskeleton- Cytoskeleton helps maintain cell shape. Its primary significant is in cell motility.
The internal movement of cell organelles and cell locomotion and muscle fiber contraction could
not happen without the cytoskeleton. It is an organized network of three main protein filaments.
Microtublules, actin filaments, and intermediate fibers.
Types of Cells
There are two main types of cells. The Prokaryote Cell and the Eukaryote Cell. The Prokaryote
Cell is a single celled organism that does not have a nucleus so their genetic material is not
stored in the nucleus. They have some organelles but not many. They are less complicated that
eukaryotes. All bacteria are prokaryotes. Bacteria might be small, but they are powerful. In the
14th century, one fourth of the entire European population was killed by a bacteria called the
Bubonic Plague, also called the Black Death. This bacteria was spread through fleas and rodents.
Paradoxically, we also need bacteria to live. Bacteria are decomposes and without them all other
organisms would not survive. We use bacteria in our digestive system to help digest our food.
There are about then times as many bacterial cells as human cell in the human body. Also more
importantly, the production of cheese and yogurt would be impossible without bacteria.The
Eukaryote Cell is a more complex cell with a nucleus and more organelles. They have a nucleus
where the genetic material of the cell is stored. They have many organelles (explained above)
that work together to help the cell to function. Eukaryotic cells are much more complex than
prokaryotic cells. They can be just one cell, or they can make up more complex multi-cellular
organisms. All plants, animals, fungi, and protists are eukaryotic cells. The main difference is the
nucleus. Prokaryotic cells do have a nucleus and eukaryotic cells do. This allow eukaryotic cells
to make multi-cellular organisms and perform more complex functions.
Cell Division
Cell division is the process that cells go through to divide. They divide for several reasons, and
there are two types of cell division, depending on the purpose. The cell division associated with
sexual reproduction is called meiosis. The cell division associated with growth and cell
replacement or repair is called mitosis. In both types, the nucleus splits and DNA is replicated.
The cell division mitosis produces daughter cells that have al the genetic material of the parent
cell (a complete set of chromosomes.) The cytoplasm and cell membrane divide also. The
process of diving the cytoplasm and the cell membrane is called cytokinesis. The two process
make up the mitotic phases of the cell cycle. The phases of cell division are prophase,
metaphase, anaphase, and telophase and these occur in mitosis and meiosis. Meiosis reduces the
number of chromosomes by half (for example, the human egg and sperm cells each have 23
chromosomes and can join to produce a zygote with 46 chromosomes. It has two division phases
where mitosis only has one.) Meiosis works to combine the genetic material of two individuals.
When there is only one parent in the reproductive cycle (like in ferns) the daughter
cell has to have the full genetic material (all the chromosomes) of the parent cell.
Conclusion
The cell is one of the most basic units of life. There are millions of different types of cells. There
are cells that are organisms onto themselves like microscopic amoeba and bacteria cells. There
are cells that only function when part of a larger organism like the cells that make up our human
bodies. In the body there are brain cells, skin cells, liver cell, stomach cells, and many others. In
the next investigation I will explore how these cells make organs.
Sources
Books
Bryson, Bill. A Short History of Nearly Everything. New York: Broadway Books, 2003.
Websites
”Cells Alive.” Quill Graphics. 1994. Web. 9 Oct. 2010.
< http://www.cellsalive.com/cells/cell_model.htm>
“What is Cell Division?” Wise Geek. Conjecture Cooperation, 2003. Web. Oct 8. 2010.
< http://www.wisegeek.com/what-is-cell-division.htm>