Download Advanced Biology\AB U5 Part 1 Cells

Unit 5, Part 1: Cytology
Objectives:
• Describe the accomplishments of Hooke, Leeuwenhoek, Schleiden, Schwann,
and Virchow.
• Discuss the cell theory.
• Distinguish between prokaryotic and eukaryotic cells.
• Describe the purpose and function of each organelle.
• Compare and contrast plant and animal cells.
• Explain the importance of proteins & glycoproteins on the cell membrane
• Explain the huge significance of mitochondria.
Vocabulary:
Ribosomes * Golgi Body/Apparatus * Nucleus * Mitochondria * flagella *
Endoplasmic Reticulum (smooth and rough) * Prokaryote * Eukaryote *
Cell Membrane * Cell Wall * Spontaneous Generation * Cell Theory *
Bacteria * Nucleolus * Lysosomes * Microtubules/filaments * vacuoles *
Cytoplasmic streaming * nuclear pore * nucleoplasm * nuclear envelope
tRNA * mRNA * rRNA * nucleolus * enzymes * cytoplasm * cilia *
peroxisomes * cell membrane * hydrophobic * hydrophilic * respiration *
spindle fibers * microtubules/fibers * vacuoles * chloroplasts * plastids *
chromoplasts * leukoplasts * ATP * endosymbiosis * cellulose * pectin
Robert Hooke was the first to see the dead, therefore empty, cells of
cork through his microscope. He referred to them as cells because they
reminded him of the rather empty “cells” monks retreated to. Antoine van
Leeuwenhoek built microscopes and was the first to notice “animalcules”, or
bacteria in the tartar scraped from his teeth, though he had no idea what they
were.
Matthias Schleiden viewed many plants and declared that the basic unit
of plant life was the cell. Shortly thereafter, Theodore Schwann declared that
all animals are composed of cells. The cell theory combined these
statements with Rudolph Virchow’s declaration that all cells come from preexisting cells. This was in direct opposition to the earlier belief of
spontaneous generation, life being able to generate from non-living things.
The Cell Theory:
• All living things are composed of 1 or more cells.
• Cells are the basic structural and functional units of life.
• All cells come from pre-existing cells.
There are 2 to 3 basic types of cells. Prokaryotes (bacteria) and
eukaryotes have long been accepted as the 2 distinct cell types. But recently,
a third category of cell (Archaean cells) has gained recognition. These have
some similarities to both prokaryotes and eukaryotes.
Characteristics of Prokaryotes:
• lack a true nucleus and membrane bound organelles
• size is between 1 and 10 micrometers
ONLY BACTERIA ARE PROKARYOTIC
Characteristics of Eukaryotes:
• have a true membrane bound nucleus and organelles
• size is between 10 and 100 micrometers
The third cell type, the Archaean cells are similar to prokaryotic cells in size but
have some characteristics similar to eukaryotic cells and some characteristics
found in neither prokaryotes or eukaryotes.
Animals, plants, fungi, everything EXCEPT bacteria and archaean cells, are
eukaryotes. Organelles within eukaryotic cells are like separate compartments
due to membranes surrounding the organelles.
Organelles include:
1) The nucleus is the “control center” of the cell. The chromatin within the
nucleus contains the gene sequences of DNA (deoxyribonucleic acid) which
direct the cell as to which proteins to make. In order to get the directions from
the nucleus to the ribosomes, where proteins are made, mRNA (messenger
ribonucleic acid) must be transcribed from DNA and then travel to the
ribosomes to be translated to make proteins.
Within the nucleus is the nucleolus. This is where ribosome parts are made
and partially assembled before export to the cytoplasm.
The nucleus is filled with a gel-like nucleoplasm and is surrounded by a
nuclear envelope. This membrane is a lipid bi-layer that has nuclear pores
which act as channels for proteins to enter the nuclear area and RNA to leave.
The area outside the nucleus is bathed by the gel-like cytoplasm which is
constantly moving in an effort to nourish the organelles and carry away their
wastes. This movement is called cytoplasmic streaming.
2) The Endoplasmic Reticulum (“endo” = inside, “reticulum” = network, so
it’s the network inside the “plasm” of the cell) folds back and forth extending
from the nuclear envelope to the cell membrane. The “ER” appears rough near
the nucleus because it has numerous ribosomes attached to it. These
ribosomes make proteins that will be exported out of the cell or become part of
the cell’s membrane. Further away from the nucleus, the ER becomes
smooth. Smooth ER synthesizes fatty acids and many membrane
components. It contain enzymes used in detoxification. It acts as a pathway
for the proteins synthesized by the rough ER. At the end of the smooth ER
pathway, proteins and fatty acid lipids are put in vesicles to be carried to the
Golgi apparatus.
3)
The Golgi apparatus, or Golgi bodies, process and finish folding the
proteins made by the rough ER. It also makes simple carbohydrates and
attaches them to proteins or lipids to make glycoproteins or glycolipids. Those
substances for cell export will be put in vesicles that will travel to the cell
membrane. Some proteins will be sent to the lysosomes.
4) Lysosomes (“lyse” means to cut apart) contain enzymes (special
proteins) important for killing bacteria, worn-out cell organelles, and other
debris. Enzymes from lysosomes are also responsible for dissolving the
tissues at the finger and toe buds so that fingers and toes can grow. In
addition, these enzymes can break down fats, carbohydrates, and proteins into
forms usable at the cellular level. The enzymes within the lysosomes are made
by the ribosomes on the rough ER and then sent to the lysosomes by the Golgi
bodies.
Enzymes from lysosomes can only function under acidic (low pH)
conditions. Certain cells, like white blood cells, have more lysosomes because
their enzymes are needed to break apart bacteria and debris. Liver cells also
have numerous lysosomes to break down cholesterol and toxins.
There are more than 40 enzymes in lysosomes. If one is missing, it can
lead to a “storage disease” where a body product is not broken down or
removed properly. With Pompe’s disease, glycogen in the liver can not be
broken down so the liver becomes damaged. In Tay-Sachs disease, the brain
is damaged as fats begin to accumulate due to a missing lysosomal enzyme.
5) The ribosomes are the most numerous of all of a cell’s organelles. This
is where proteins are made. Ribosomes attached to the rough ER make
proteins that will be exported by the cell for use elsewhere. Ribosomes loose
in the cytoplasm make proteins that will stay in the cell. Ribosomes are made
of protein and ribosomal RNA (rRNA). When proteins are being made, transfer
RNA (tRNA) carries the amino acids to the ribosome to add to the chain.
6) Microfilaments and microtubules are long, slender protein structures that
help maintain the shape of a cell by creating the cytoskeleton. Spindle fibers
are specialized microtubules that help chromosomes move during cell division.
A weak or broken spindle fiber may cause a birth defect, such as trisomy 21,
because sister chromatids may not be separated to opposite areas in the egg
or, possibly, the sperm cell during meiosis.
7) Peroxisomes help protect cells from toxins. They use catalase to convert
H2O2 to water. Liver and kidney cells contain a lot of these organelles to help
disarm toxins in the blood. In adrenoleukodystrophy (ALD) - the disease in
“Lorenzo’s Oil” - there is a defect in one of the proteins in the peroxisome’s
membrane. This protein normally helps transport an enzyme that breaks down
a very long chain fatty acid. Without this protein, the fatty acid builds up in the
brain and spinal cord. This causes behavioral problems, loss of muscle
strength/control, and death if not treated correctly.
8) The cell membrane is a lipid bi-layer. The carboxyl and phosphate,
“head” end of the 2 lipid layers point away from each other, forming both the
inner and outer portion of the membrane. Therefore, the innermost and
outermost portion of the cell membrane is hydrophilic (water loving) because it
is polar. The hydrocarbon chains, or “tails” of the lipids are turned inward,
sandwiched between the carboxyl heads. The tails are hydrophobic (fear
water) because they are nonpolar. The cell membrane also has numerous
proteins imbedded along its length. Some proteins act as channels for
transport of substances into and out of the cell. Some glycoproteins help mark
the cell as “self” so that it can be recognized from foreign substances and will
not be attacked by the immune system. These glycoproteins are also important
for distinguishing between blood types: A, B, AB, and O and for letting the
body know that this is a “bone” cell or a “skin” cell, etc..
9) Cilia are short, numerous, hair-like structures that extend out from the cell
membrane of some cells. For example, cells of our respiratory tract. The cilia
help mucus and irritants get coughed out of the body. Unicellular organisms,
such as paramecium use cilia for movement.
10) Flagella are longer whip-like structures found on some cells, usually in
small numbers, used for movement by sperm cells and some unicellular
organisms like Euglena,Trypanosomes, Giardia, Trichomonas, etc.
11) The mitochondria are the cell’s energy providers. Here, energy from the
foods we eat is converted into a form of energy our cells can use, that is ATP
(adenosine triphosphate). This process is called respiration. This is probably
the single most important process going on at the cellular level! Cells requiring
more than usual amounts of energy, for example, the liver for detoxification
purposes and the muscles for contraction/strength, have far more mitochondria
than other cells. The mitochondria also have their own DNA! ***This DNA is
inherited 100% from the mother!*** Very few structures besides the nucleus
ever contain their own DNA. In plants, the best example of an organelle
containing DNA, other than the nucleus, would be the chloroplasts.
Some scientists believe more advanced eukaryotic cells were created when
one prokaryote ingested another, but instead of digesting it, a symbiotic
relationship occurred where the ingested prokaryote started producing energy
for its host. This is how eukaryotic organelles like mitochondria and
chloroplasts arose. This evolution from prokaryote to eukaryote is called
endosymbiosis.
Plant cells have several organelles not usually found in animals. They include:
12) A cell wall. The cell wall is made of a long chain polysaccharide called
cellulose. This is strengthened by pectin and lignin. Since these are not
Digestible by humans, we consider them “fiber” or roughage which helps clean
out the digestive tract. Pectin, usually from apples or other fruit, is used to set
jelly, for example. The cell wall surrounds the cell membrane, adding shape
and support to the cell structure. Primary cell walls form in young growth.
Wood is formed when primary cells stop growing and lignin fills in, thus forming
secondary cells which can no longer grow. So wood is made of secondary cell
walls.
13) Vacuoles in plants store enzymes, toxins, and wastes. Usually, the older
the cell, the larger the vacuole.
14) Plastids are primarily storage and photosynthesis areas. Chloroplasts
are green from chlorophyll, the primary plant pigment that traps sunlight for
photosynthesis. Chromoplasts make and store secondary plant pigments
(orange = carotenes, yellow = xanthophylls, etc.) used to catch different light
wavelengths and leukoplasts store starch as well as proteins and lipids. (Think
potatoes)