Introduction to Cell Biology

1. Cell Biology
Presented By: Mahrukh Shehzadi

2. Course Content
• Introduction to prokaryotic and eukaryotic cell differences including cell
wall, membrane structure and chemical constituents of the cell. Composition
and functions of lipid bilayer, transport across cell membrane and role of
glycolipids and glycoproteins as receptors in cellular signaling. The functions,
isolation and molecular organization of cellular organelles specifically the
endoplasmic reticulum, golgi bodies, ribosomes, lysosome, micro-bodies,
mitochondria. The structure and function of chromosomes and role of nucleus in
regulation of metabolism. The concept of cell cycle, mitosis and meiosis and cell
death. Structure and function of cytoskeleton, centriole and function of cilia
and flagella in cell movement.
• Practicals: Microscopy and staining techniques; Study of prokaryotic, eukaryotic
cells; cellular reproduction; Mitosis: smear/squash preparation of onion roots.

3. Introduction to Cell Biology
• Discovery of cell
• In 1665, Robert Hooke used an early compound microscope to look at a nonliving
thin slice of cork, a plant material; termed them as cells in his publication called
Micrographia. In Holland, Anton van Leeuwenhoek used a single-lens microscope to
observe pond water and other things; termed them as animalcules
• Felix Dujardin termed all substances found inside the cell as sarcode. Later,
Jan Evangelista Purkinje, called it as protoplasm. Robert Brown discovered
the nucleus.

4. Cell Theory
By the late 1830s, botanist Matthias Schleiden and
zoologist Theodor Schwann were studying tissues and
proposed the cell theory.
Schleiden and Schwann proposed spontaneous
generation as the method for cell origination, but
spontaneous generation (also called abiogenesis) was later
disproven.
Rudolf Virchow famously stated “Omnis cellula e
cellula”… “All cells only arise from pre-existing cells”.
The unified cell theory states that:
All living things are composed of one or more cells; the cell is the basic unit
of life; and new cells arise from existing cells.

5. Fundamentals of Cell Theory
• The cell is the
fundamental unit of
structure and function
in living things.
• All organisms are
made up of one or
more cells.
• Cells arise from other
cells through cellular
division.

6. The expanded version of the cell theory can also include:
• Cells carry genetic material passed to daughter cells during cellular
division
• All cells are essentially the same in chemical composition
• Energy flow (metabolism and biochemistry) occurs within cells
• Adenosine tri phosphate (ATP)

7. Basic Cell Types
• Prokaryotes
• Eukaryotes
‘Cells’ are considered as the structural and
functional unit of life, whether it’s a single cell
organism like bacteria, protozoa, or multicellular
organisms like plants and animals.

8. Prokaryotic Cells
Pro means ‘old,’ and karyon means ‘nucleus,’
So as the name suggest the history of the
evolution of prokaryotic cells is at least 3.5
billion years old, but they are still important
to us in many aspects like they are used in
industries for fermentation (Lactobacillus,
Streptococcus), for research work, etc. In
comparison to eukaryotic cells, they lack few
organelles and are not advanced as
eukaryotes.

9. Generalized Structure of Prokaryotes
Glycocalyx: This layer function as a receptor, the adhesive also provide protection to the cell wall.
Nucleoid: It is the location of the genetic material (DNA), large DNA molecule is condensed into
the small packet.
Pilus: Hair like hollow attachment present on the surface of bacteria, and is used to transfers of
DNA to other cells during cell-cell adhesion.
Mesosomes: It is the extension of the cell membrane, unfolded into the cytoplasm their role is
during the cellular respiration.
Flagellum: Helps in movement, attached to the basal body of the cell.
(different types of bacterial cells based on the flagella)

10. EXAMPLES

11. Cell Wall: It provides rigidity and support for the cell.
Fimbriae: Helps in attachment to the surface and other bacteria while mating. These are
small hair-like structure.
Inclusion/Granules: It helps in storage of carbohydrates, glycogen, phosphate, fats in
the form of particles which can be used when needed.
Ribosomes: Tiny particles which help in protein synthesis.
Cell membrane: Thin layer of protein and lipids, surrounds cytoplasm and regulate the
flow of materials inside and outside the cells.
Endospore: It helps cell in surviving during harsh conditions.
Permeability:
Impermeable
Selectively permeable
Completely permeable

12. CELL WALL
CELL
MEMBRANE

13. Eukaryotic Cells
Eu means ‘new,’ and karyon
means ‘nucleus,’ so these are
the advanced type of cells
found in plant, animals, and
fungi. Eukaryotic cells have a
well-defined nucleus and
different organelles to
perform different functions
within the cell, though
working is complex to
understand.

14. Generalized Structure of Eukaryotes

15. Key Difference Between Prokaryotic Cells and Eukaryotic Cells
Prokaryotic cells are the primitive kind of cell, whose size varies from 0.5-3µm, they are generally
found in single-cell organisms
Eukaryotic cells are the modified cell structure containing different components in it, their size
varies from 2-100µm, they are found in multicellular organisms.
Organelles like mitochondria, ribosomes, Golgi body, endoplasmic reticulum, cell wall, chloroplast,
etc. are absent in prokaryotic cells, while these organelles are found in eukaryotic organisms.
Though cell wall and chloroplast are not found in the animal cell, it is present in the green plant
cell, few bacteria, and algae.
The main difference between Prokaryotic cells and the Eukaryotic cell is the nucleus, which is not
well defined in prokaryotes whereas it is well structured, compartmentalized and functional in
eukaryotes.

16. Cell organelles are present which are membrane-bound and have individual functions in
eukaryotic cells; many organelles are absent in prokaryotic cells.
In prokaryotes, the cell division takes place through conjugation, transformation, transduction but
in eukaryotes, it is through the process of cell division.
The process of transcription and translation occurs together, and there is a single origin of
replication in the prokaryotic cell. On the other hand, there are multiple origins of replication and
transcription occurs in nucleus and translation in the cytosol.
Genetic Material (DNA) is circular and double-stranded in Prokaryotes, but in Eukaryotes, it
is linear and double-stranded.
Prokaryotes reproduce asexually; commonly Eukaryotes have a sexual mode of reproduction.
Prokaryotes are the simplest, smallest and most abundantly found cells on earth; Eukaryotes are
larger and complex cells.

18. Characteristics of All Cells (Summary)
• A surrounding membrane
• Protoplasm – cell contents in thick fluid
• Organelles – structures for cell function
• Control center with DNA

19. Representative Animal Cell

20. Representative Plant Cell

21. Chemical Composition of Cells
Cells consist of a collection of simple and complex organic molecules,
inorganic molecules, and ions. There are also organized clusters of these called
supramolecular complexes. The majority of biomolecules are composed of only
6 chemical elements - C, H, O, N, S and P. Cells are mostly water by weight.
Prokaryotes - Small, single cell organisms lacking a
membrane-bound nucleus and other subcellular
compartments. Bacteria and blue-green algae are
examples.
Eukaryotes - Cell or organism with membrane-bound
nucleus and other well-developed subcellular
compartments (organelles). Yeast, fungi, protozoans,
plants and animals are eukaryotes.

22. Basic Components
• Biochemical Functional Groups (alcohol, ketones, aldehydes,
phosphoester, amine etc)
• Proteins
• Amino Acids
• Peptides --- small linear polymers of amino acids (<=50)
• Proteins --- large linear polymers of amino acids
• Primary, secondary, tertiary, quaternary structure
• Structural, globular and membrane proteins
• Nucleic Acids
• Carbohydrates
• Lipids
https://www4.uwsp.edu/chemistry/tzamis/ch260/cellmolecsintro26005.pdf

23. PROKARYOTE STRUCTURE

24. The Capsule
• Sticky outermost layer called the capsule
• Made of polysaccharides (sugar polymers).
• The capsule helps prokaryotes cling to each other and to various
surfaces in their environment, and also helps prevent the cell from
drying out.
• In the case of disease-causing prokaryotes that have colonized the
body of a host organism, the capsule or slime layer may also protect
against the host’s immune system.
• Griffith’s Experiment

25. The Cell Wall
• Cell wall, located underneath the capsule (if there is one).
• Maintains the cell’s shape, protects the cell interior, and prevents the
cell from bursting when it takes up water.
• The cell wall of most bacteria contains peptidoglycan, a polymer of
linked sugars and polypeptides.
• Antibiotics used to treat bacterial infections in humans and other
animals act by targeting the bacterial cell wall.
• Archea have pseudo-peptidoglycan.

27. Gram Positive or Gram Negative
• Bacteria are classified according to the change in peptidoglycan
concentration.
• Process of gram staining:
• Slide preparation (de-greasing, smear preparation and heat fixing)
• Crystal violet for 1 minute (Primary stain)
• Gram’s Iodine for 30 seconds (mordant  forming complex with crystal
violet)
• Ethanol for washing (till the droplets from the slides are colorless)
• Safranin for 45seconds (counter stain)

29. The Plasma Membrane
• Underneath the cell wall.
• The basic building block phospholipid.
• A lipid composed of a glycerol molecule attached a hydrophilic (water-
attracting) phosphate head and to two hydrophobic (water-repelling) fatty acid
tails.
• Plasma membranes of archaea differ from bacteria and eukaryotes.
• Opposing phospholipid tails are joined into a single tail, forming a
monolayer instead of a bilayer (as in bacteria and prokaryotes).
• Stabilize the archeal membrane at high temperatures, allowing them to
survive in boiling hot springs.

32. The Appendages
• Prokaryotic cells often have appendages (protrusions from the cell
surface) that allow the cell to stick to surfaces, move around, or
transfer DNA to other cells.
• Thin filaments called fimbriae (singular: fimbria) used for
adhesion— help cells stick to objects and surfaces in their
environment.
• Longer appendages, called pili (singular: pilus). For instance, a sex
pilus allows DNA to be transferred between bacterial cells via
conjugation.
• Type IV pili, help the bacterium move around its environment.

33. • The most common appendages used for getting around, however,
are flagella (singular: flagellum).
• These tail-like structures whip around like propellers to move cells
through watery environments.

34. Chromosomes and Plasmids
• Prokaryotes have single circular chromosome.
• Genome size is much smaller than eukaryotic genome.
• Nuclear material dispersed in the cytoplasm, called as the nucleoid.
• Plasmids, small rings of double-stranded extra-chromosomal ("outside
the chromosome") DNA.
• Plasmids carry a small number of non-essential genes and are copied
independently of the chromosome inside the cell.
• Can be transferred to bacteria and can have special genes for survival.
(antibiotic resistance genes  R genes)

36. EUKARYOTE STRUCTURE

37. The plant cell has a cell wall, chloroplasts,
plastids, and a central vacuole—structures not
found in animal cells. Plant cells do not have
lysosomes or centrosomes.

38. The Plasma Membrane
• Phospholipid bilayer with embedded proteins that separates the
internal contents of the cell from its surrounding environment.
• Controls the passage of organic molecules, ions, water, and oxygen
into and out of the cell.
• Wastes (such as carbon dioxide and ammonia) also leave the cell by
passing through the plasma membrane, usually with some help of
protein transporters.

40. The Cytoplasm
• Entire region of a cell between the plasma membrane and the nuclear
envelope.
• Composed of organelles suspended in the gel-like cytosol, the
cytoskeleton, and various chemicals.
• 70 to 80 percent water.
• Proteins, simple sugars, polysaccharides, amino acids, nucleic acids,
fatty acids, ions and many other water-soluble molecules are all
competing for space and water.

41. The Nucleus
• Stores chromatin (DNA plus proteins) in a gel-like substance called
the nucleoplasm.
• Nuclear membrane is continuous with the endoplasmic reticulum.
• Nuclear pores allow substances to enter and exit the nucleus.

42. The Nuclear Envelope
• Boundary is called as the nuclear envelope.
• Boundary is composed of two phospholipid bilayers: inner and outer.
• Protein-based pores that control the passage of ions, molecules, and
RNA between the nucleoplasm and cytoplasm.
• Nucleolus  where the ribosome synthesis occurs.

44. Chromatin and Chromosomes
• Chromosomes are structures within the nucleus that are made up of
DNA, the hereditary material.
• Eukaryotes have linear chromosomes.
• Clearly visible during the dividing stage.
• Chromatin is used to describe chromosomes (the protein-DNA
complexes) when they are both condensed and de-condensed.

46. The Nucleolus
• Some chromosomes have sections of DNA that encode ribosomal
RNA.
• A darkly staining area within the nucleus called the nucleolus (plural =
nucleoli)
• aggregates the ribosomal RNA with associated proteins to assemble
the ribosomal subunits
• Transported out to the cytoplasm through the pores in the nuclear
envelope.

48. The Ribosomes
• Responsible for protein synthesis
• Appear as (polyribosomes) clusters called bind form.
• Or can also appear as single dots called free form.
• May be attached to the cytoplasmic side of the plasma membrane or
the cytoplasmic side of the endoplasmic reticulum and the outer
membrane of the nuclear envelope

49. • Large complexes of protein and RNA, consist of two subunits, called
large and small subunits.
• At the nucleus, the DNA is transcribed into messenger RNA (mRNA).
• mRNA travels to the ribosomes, which translate the code provided by
the sequence of the nitrogenous bases in the mRNA into a specific
order of amino acids in a protein.

50. The Mitochondria
• Power house or energy factories of the cell.
• Primary site for the metabolic respiration in eukaryotes.
• Number of mitochondria depends on the energy need.
• Inner and outer membranes are phospholipid bilayers embedded with
proteins that mediate transport across them and catalyze various other
biochemical reactions.
• The inner membrane layer has folds called cristae increase the surface
area into which respiratory chain proteins can be embedded.
• The region within the cristae, called the mitochondrial matrix—having
enzymes of the metabolic cycle.

52. The Peroxisomes
• Small, round organelles enclosed by single membranes
• Carry out redox reactions that oxidize and break down fatty acids and
amino acids.
• Detoxify many toxins that may enter the body.
• Many of these redox reactions release hydrogen peroxide, H2O2,
which would be damaging to cells; however, enzymes safely break
down into oxygen and water.
• Glyoxysomes, which are specialized peroxisomes in plants, are
responsible for converting stored fats into sugars.

53. Vesicles and Vacuoles
• Membrane-bound sacs that function in storage and transport.
• Vacuoles are larger than vesicles.
• Membranes of vesicles can fuse with either the plasma membrane or
other membrane systems within the cell.
• Enzymes within plant vacuoles break down macromolecules.
• The membrane of a vacuole does not fuse with the membranes of other
cellular components.

54. The Centrosome
• Microtubule-organizing center found near the nuclei of animal cells.
• A pair of centrioles, two structures that lie perpendicular to each other.
• Each centriole is a cylinder of nine triplets of microtubules.
• Replicates before cell division
• Play a role in pulling chromosomes during cell division but role
remains still unclear.
• Animal cells without centrioles and plant cells lacking centrioles still
are able to divide.

56. The Lysosomes
• In animal cells and not in plant cells
• Aid the breakdown of proteins, polysaccharides, lipids, nucleic acids,
and even "worn-out" organelles.

57. The Cell Wall
• Present in plant cells only.
• Rigid  provides protection, structural support and gives shape.
• Made of cellulose.
• Fungal cell wall made of chitin.

58. The Chloroplasts
• Plant cell organelles carry out photosynthesis.
• Have their own DNA and ribosomes.
• Chloroplasts have outer and inner membranes, but within the space
enclosed by a chloroplast’s inner membrane is a set of interconnected
and stacked fluid-filled membrane sacs called thylakoids.
• Each stack of thylakoids is called a granum (plural = grana). The fluid
enclosed by the inner membrane that surrounds the grana is called the
stroma.
• Contains chlorophyll.

60. The Central Plant Vacuole
• Plays a key role in regulating the cell’s concentration of water in
changing environmental conditions.