WHAT IS A CELL?
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It is fundamental living unit of any organism.
Metabolism refers to all of the chemical reactions that occur within a cell.
WHAT ARE THE IMPORTANCE OF METABOLISM?
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Growth, reproduction, and irritability.
Mutation pertains to the accidental changes in the genetical material.
Cells are classified as:
1. Prokaryotes
 Do not have complex system of membranes and organelles.
 Bacteria and archaea.
2. Eukaryotes
 More complex cells, containing true nucleus and many membrane bound
organelles.
 Algae, protozoa, fungi, plants, animals, and humans.
Microbes
1. Acellular
2. Cellular
2.1. Prokaryotes
2.2. Eukaryotes
Eukaryotic Cell
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Eu meaning true; karyo meaning nucleus
Have true nucleus, DNA is enclosed by a nuclear membrane.
10x larger than most prokaryotic cells.
Eukaryotic Cell Structures
1. Cell Membrane
 Enclosed and keep the cell intact.
 Composed of large molecules of proteins and phospholipids.
 Selective permeability.
2. Nucleus
 Controls the functions of the entire cell.
 “Command center”
 4 components: nucleoplasm; nuclear membrane; chromosomes; nucleolus
3. Cytoplasm
 Semifluid, gelatinous, nutrient matrix
 Contains the “organelles”
 Organelles has highly specific functions which maintain the cells and allow
it to properly perform its activities.
4. Endoplasmic Reticulum
 Highly convoluted system of membranes that are interconnected to form
transform network tubules and flattened sacs within the cytoplasm.
 It has rough ER and smooth ER.
5. Ribosomes
 18 to 22 nm in diameter.
 Consists of rRNA.
 Play important part in protein synthesis.
 Free or attached in the RER.
6. Golgi Complex
 Stack of flattened, membranous sacs.
 Packages newly synthesizes proteins into small membrane-enclosed
vesicles for storage within the cell or export outside the cell (exocytosis).
 “Packaging plants”
7. Lysosomes and Peroxisomes
 Lysosomes
- Contain lysozyme and other digestive enzymes
- Phagocytosis and Autolysis
o is a cellular process for ingesting and eliminating particles larger
than 0.5 μm in diameter, including microorganisms, foreign
substances, and apoptotic cells. Phagocytosis is found in many
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types of cells and it is, in consequence an essential process for
tissue homeostasis.(Immune system response)
o The enzymatic digestion of cells by the action of its own enzymes,
and it mostly occurs in dying or dead cells. (rotting)
Peroxisomes
- Where hydrogen peroxide is both generated and broken down
- Found in mammalian liver cells
8. Mitochondria
 Where most of the ATP (energy carrying molecules) are formed by cellular
respiration.
 Energy is released from glucose molecules and other nutrients to drive
other cellular functions.
9. Plastids
 Contains various photosynthetic pigments.
 Chloroplasts is one type of plastid, containing a green photosynthetic
pigment called chlorophyll.
 Found in plant cells and algae.
10. Cytoskeleton
 System of fibers present throughout the cytoplasm.
 It strengthens, supports, and stiffens the cell, giving its shapes.
- Microtubules: slender, hallow tubules (tubulins).
- Microfilaments: slender, thread-like contractile structures which
facilitate cell contraction.
11. Cell wall
 External structures that provide rigidity, shape, and protection.
 May contain cellulose, pectin, lignin, chitin, and some mineral salts.
- Cellulose: polysaccharide, present in algae and plants.
- Chitin: present in fungi and exoskeleton of arthropods.
12. Flagella and Cilia
 Flagella
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- Relatively long, thin structure, the organelle of locomotion.
Cilia
- Tend to be shorter (hair-like), thinner, and more numerous.
Prokaryotic Cell
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10x smaller than eukaryotic cells.
Very simple cells than eukaryotic cells.
Do not contain membrane-bound organelles.
Reproduce by binary fission.
Includes bacteria and archaeans.
Prokaryotic Cell Structure
1. Cell Membrane
 Enclose the cytoplasm.
 Similar in structure and function to the eukaryotic cell membrane.
 Consists of proteins and phospholipids.
 Selectively permeable.
There is whole lots of difference between Prokaryotic and Eukaryotic chromosome.
1. Prokaryotes have double stranded mostly circular chromosome while the
Eukaryotes have double stranded linear chromosomes which contain all the
basic information.
2. Prokaryotic cells usually have only one chromosome while the Eukaryotic cells
can have multiple chromosomes.
3. Since Prokaryotic cells have only one chromosome, it doesn’t have
homologous pair. On the other hand, Eukaryotic chromosomes are usually
paired called homologous pair. These paired chromosomes are also called as
their sister chromosomes.
4. Chromosomes in the Prokaryotic cells are found in cytoplasm in a sport called
as nucleoid since there is no specified organelle. But in the case of Eukaryotic
cells, chromosomes are found in membrane bound organelle called nucleus.
This is also a basic difference between prokaryotic and eukaryotic cells.
5. Prokaryotic chromosome is very simple compared to the Eukaryotic one.
Prokaryotic chromosome lack telomeres and centromeres sequences which is
found in the Eukaryotic chromosomes.
6. The packaging of chromosome in Prokaryotic cell is rather simpler than the
Eukaryotic cell. Prokaryotic chromosome is packed with the help of nucleoid
associated proteins which helps in packaging. Eukaryotic chromosomes are
much larger in size and requires special proteins called histone proteins which
forms a special structure called nucleosomes when DNA is wrapped around it.
7. Replication of the chromosome in the Prokaryotes occurs at the beginning of
the cell division while the replication in the Eukaryotic cells occurs in the S
phase of the cell cycle.
8. Prokaryotic chromosomes have only one origin of replication while Eukaryotic
chromosomes have multiple origin of replication. Origin of replication is the site
or sequences on the chromosome where the replication is the site or sequence on
the chromosome where the replication process is initiated.
9. Prokaryotic chromosome encodes for fewer proteins as compared to larger
Eukaryotic chromosomes which codes for thousands of different proteins.
10. Prokaryotic chromosome achieves genetic recombination through horizontal
gene transfer while genetic recombination in Eukaryotes is achieved by meiosis
or fusion of different gametes.
2. Plasmid
 Small, circular molecules of double-stranded DNA that are not part of the
chromosome.
 May contain 10 to hundred genes.
 May or may not be present in bacterial cell.
3. Cytoplasmic Particles
 Many tiny particle in the bacterial cytoplasm.
 Most of these are of clusters of ribosomes-polyribosomes or polysomes.
4. Bacterial Cell Wall
 Rigid exterior cell wall that defines the shape of bacteria.
 Consist of a complex macromolecule known as peptidoglycan.
5. Grain Stain
 The most widely used procedure for staining bacteria.
 Developed over a century ago by Dr. Hans Christian Gram.
 Bacteria are grouped as Gram-negative and Gram-positive.
6. Glycocalyx
 Slimy, gelatinous material produced by the cell membrane and secreted
outside the cell wall.
- Slime layer: not highly organized and is not firmly attached to the cell
wall.
- Capsule: highly organized and firmly attached to the cell wall.
7. Flagella
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Thread-like, protein appendages that enable the
bacteria to move.
Flagellated bacteria are said to be motile
- (a) Monotrichous
- (b) lophotichous
- (c) amphitrichous
- (d) peritrichous
8. Pili (Fimbriae)
 Hair-like structures, most often observed on Gram-negative bacteria.
 Kinds:
- Pili that enables transfer of genetic material from one bacterial cell to
another (conjugation).
- Pili that enables bacteria to anchor themselves to surfaces.
9. Endospores
 Formed by a few bacteria when the environment in unfavorable for their
survival. Firmucute Phylum
 Sporulation pertains to the process of forming endospore.
 Resistant to heat, cold, drying, and most chemicals.
 The discovery of Endospores:
- John Tyndall concluded that certain bacteria can be killed by simple
boiling, while others cannot be killed. Tyndallization.
- Ferdinand Cohn called the small bodies in the bacteria “spores”. He
concluded that spores are heat resistant.
Prokaryotic Cell Reproduction
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Prokaryotic cells reproduce by binary fission.
One cell (parent cell) splits into half to become two daughter cells.
Before a prokaryotic cell can divide into half, its chromosomes must be duplicated.
Generation time varies from one bacterial species to another (ex. E. coli, 20
mins.)
Eukaryotic Cell Reproduction
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Eukaryotic cell reproduce in a process called mitosis.
Mitosis is the type of division that gives rise to daughter cells for the purpose of
tissue growth, regeneration or asexual (vegetative) reproduction.