Uploaded by Kristelle Dae Pagunsan

CELLS

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Kristelle Dae B. Pagunsan 11 HUMSS - SOCRATES
 Cell Theory
The study of cell started about 300 years ago with the help of one powerful instrument called the
‘microscope’ invented by Hans and Zacharias Janssen, the cell has begun to be known to humans. The
development and refinement of magnifying lenses and light microscopes made the observation and
description of microscopic organisms and living cells possible.
Revised Cell Theory
1. Cells are the basic units of structure and function in an organism.
2. All living things are made up of cells.
3. Cells came from pre-existing cells by division.
Continued advances in microscopy allowed observation of cell organelles and structure.
Proponents and Contributors of the Cell Theory
 Robert Hooke – An English Scientist who coined the term ‘cell’. He observed that a cork has
small regular boxes in it that he called “cells.” He is the inventor of the compound microscope.
 Anton van Leeuwenhoek “Father of Ancient Microbiology” - He’s a Dutch business man and
scientist who was the first to see bacteria and protists. He described cells in a drop of pond water
that he called “animalcules”.
 Matthias Schleiden – A German botanist who concluded that all plant tissues are composed of
cells.
 Theodor Schwann – A German Zoologist. He concluded that all animal tissues are composed of
cells. He is one the proponents of the Cell Theory.
 Rudolph Virchow – A German Scientist who discovered that all cells came from pre-existing cells.
He completed the cell theory by expounding his famous “omnis cellula e cellula” which means
“cells develop from pre-existing cells.” According to Schwann, 1.) The cell is the unit of structure,
physiology, and organization in living things. 2.) The cell retains a dual existence as a distinct
entity and a building block in the construction of organisms. 3.) Cells form by free-cell formation,
similar to the formation of crystals (Spontaneous Generation).
 Robert Brown – English botanist who discovered the nucleus in plant cells (orchid).
 Hans and Zacharias Janssen – Credited for the production of lenses.
 Differences of Plant and Animal Cell
Plant Cell
Animal Cell
1. Rectangular/Box-like shape
1. Spherical/Round shape
2. Relatively larger in size
2. Relatively smaller in size
3. Covered by a thick cell wall
3. No Cell wall. Only covered by a thin cell
membrane.
4. Vacuole is big, prominent, and
permanent
4. Vacuole is small, not so prominent, and
temporary
5. Plastids are only present in plant cell
5. Plastids are absent
6. Absence of Centrosome
6. Centrosome is present in Animal cell
7. Number of Mitochondria is less in plant
cell than animal cell
8. Cell division occurs by cell plate
9. Have 9 parts composed of; Cell
membrane, cell wall, chloroplasts,
chromosomes, cytoplasm, mitochondria,
nuclear membrane, nucleus, and
vacuoles
7. Number of Mitochondria is
approximately more in animal cell
8. Cell division occurs by furrow in spite of
cell plate
9. Only have 7 parts which are; Cell
membrane, chromosomes, cytoplasm,
mitochondria, nuclear membrane,
nucleus, and vacuoles
 Prokaryotic and Eukaryotic Cells
Prokaryotic Cells
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have no nucleus or organelles enclosed within membranes
a single cell organism that does not have a nucleus
do not have nucleus, and their genetic material is not stored in the nucleus
less complicated than eukaryotes
all bacteria are prokaryotes
Eukaryotic Cells
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a more complex cell with a nucleus and many organelles
they all have a nucleus where the genetic material of the cell is stored
have many organelles that work together to help the cell function
can be just one cell or can make up more complex multi-cellular organisms
all plants, animals, fungi, and protists are eukaryotic cells
 Parts of a Cell and their Functions
1. Cell Membrane – holds the cell together and lets substances pass in and out of the cell;
separates the cell from other cells ; allows molecules to pass through
2. Nucleus – controls the cell’s activities
3. Cell Wall – gives a stiff and rigid shape to the cell; gives protection and support
4. Cytoskeleton – structural support; cell movement
5. Flagella – motility or moving fluids over surfaces
6. Plasma Membrane – regulates what passes into and out of the cell
7. Endoplasmic Reticulum (ER) – connects the nuclear membrane to the cell membrane;
passageway for material moving through the cell; participates in protein and lipid synthesis
8. Golgi – packages proteins for export from cell; forms secretory vesicles
9. Lysosomes – contain enzymes which are used in digestion; play role in cell death
10. Micro bodies – isolate particular chemical activities from the rest of the cell
11. Mitochondria – “power house”/ “power plants” of the cell; releases energy for cell function
12. Chloroplasts - sites of photosynthesis; they contain chlorophyll, a chemical that allows plants to
store solar energy
13. Chromosomes – contain hereditary information; made up of genes
14. Nucleolus – assembles ribosomes
15. Nuclear Membrane – allows substances to pass in and out of the nucleus
16. Ribosomes – sites of protein synthesis; help make proteins
17. Vacuoles – store food and chemicals
 Cytoplasmic Organelles
By definition, organelles are the membrane-bound structures in a cell. The nucleus is an example. Other
organelles are located in the cytoplasm such as mitochondria, chloroplasts, endoplasmic
reticulum, Golgi apparatus, peroxisomes, lysosomes, vacuoles and glyoxisomes.
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Mitochondria
An eukaryotic cell contains many mitochondria, occupying up to a quarter of the cytoplasmic
volume. The size of a mitochondrion is about 1.5-2 μm in length, 0.5-1 μm in diameter,
approximately the same as E. coli. It has two membranes: outer membrane and inner
membrane. Mitochondria also have their own DNA (represented as mtDNA), which encodes
some of the proteins and RNAs in mitochondria. However, most proteins operating in
mitochondria still originate from nuclear DNA. The major role of mitochondria is to
produce ATP (adenosine triphosphate), which carries high energy to power most cellular
processes. Such energy is stored in the phosphoanhydride bonds of ATP. During ATP hydrolysis,
the bond is broken, releasing 7.3 kcal/mole of energy. Many cellular processes can utilize the
released energy by coupling with the ATP hydrolysis.
Chloroplasts
Like mitochondria, a chloroplast also contains both outer and inner membranes on its surface.
Inside the chloroplast, there are many thylakoids, each is enclosed by a
membrane. Chlorophylls are located on the thylakoid membrane to absorb light for
photosynthesis.
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Endoplasmic reticulum
Endoplasmic reticulum (ER) can be divided into rough ER and smooth ER. The major role of
rough ER is to process the newly synthesized peptides from ribosomes. Therefore, the surface of
rough ER is usually associated with ribosomes and thus appears "rough". Smooth ER is involved
in the synthesis and metabolism of lipids. Hepatocytes are abundant in smooth ER.
Golgi apparatus
Golgi apparatus is a major site for sorting and modifications of proteins and lipids. After proteins
are sorted at rough ER, they are enclosed in transport vesicles and carried to the Golgi
apparatus. Some proteins could be modified into glycoproteins and then transported to other
destinations.
Peroxisomes
Peroxisomes contain enzymes for degrading amino acids and fatty acids. These reactions
produce harmful hydrogen peroxide. Hence, peroxisomes also contain catalase to convert
hydrogen peroxide into water and oxygen
Lysosomes
The major function of lysosomes is to degrade various macromolecules in the cell. They
contain nuclease for degrading DNA and RNA, protease for degrading proteins and other
enzymes for degrading polysacchrides and lipids. Lysosomes exist only in animal cells. Although
plant cells do not have lysosomes, their vacuoles are also capable of degrading macromolecules.
Vacuoles
Vacuoles store small molecules such as water, ions, sucrose and amino acids. They can also hold
waste products which will be slowly degraded. They typically occupy more than 30% of the cell
volume, but may expand up to 90%.
Glyoxisomes
Glyoxisomes are found mainly in plant seeds. Their major function is to convert fatty acids into
acetyl CoA for the glyoxylate cycle where two acetyl-CoA molecules are converted to a 4-carbon
dicarboxylic acid. Peroxisomes and glyoxisomes are also called microbodies.
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