1. Introduction - Cell Biology
Ebonia B. Seraspe
U.P. Visayas
Miagao, Iloilo

2. Cell Biology is the study of cells
Cell Biology is the study of cells. An essential foundation course for all people interested in human health, animal care and animal studies. The cell is the basic unit of life. Its knowledge is most essential to understand how life works for higher animals and plants

3. Living things are constructed of cells.
The Cellular Level of Organization
Living things are constructed of cells.
Living things may be unicellular or multicellular.
Cells are small so they can exchange materials with their surroundings.
Surface area relative to the volume decreases as size of cell increases.
- limits the size of cells
STRUCTURE OF MICOBIAL CELLS

4. Size of Living Things
1 m = 100 cm = 1,000mm = 1,000,000 µm = 1,000,000,000nm
1mm = 1000 µm = nm
1 µm = 1000nm
Diagrams:

5. Two basic types of cells
There are two types of cells:
prokaryotic
eukaryotic
______________
Almost always single-celled (except for prokaryote colonies).
Always reproduces by means of binary fission.
Does not have a cell nucleus or any other organelles contained within a membrane. The prokaryote’s DNA travels openly around the cell.
All bacteria are prokaryotes.
Can either be single-celled or multi-celled.
Can reproduce in one of several ways (e.g. meiosis, mitosis).
Have a cell nucleus within which its DNA is contained.
This presence of a nucleus is the most evident distinction between these two types of cell.
STRUCTURE OF MICOBIAL CELLS

6. Comparison of Eukaryotic and Prokaryotic Cells
Image: k12station.blogspot.com/2006_08_01_archive.html

7. Only Two Types of Cells

8. Two basic types of cells
_____________________
_____________________
Diagrams:
Prokaryotic & Eukaryotic Cell, Mariana Ruiz

9. Prokaryotic Cells Pro-, “before”, karyon, “nucleus”
Believed to be the first cells to evolve.
Lack a membrane bound nucleus and organelles.
Genetic material is naked in the cytoplasm
Ribosomes are only organelle.
Image: Mariana Ruiz

10. Prokaryotes - Cell Wall
Nearly all prokaryoes have a cell wall, but the cell walls of Archaea and the cell walls of Eubacteria (true bacteria) are different in structure as compared to the plant cells.
Diagram:
Mariana Ruiz

11. Bacteria – Cell Wall
__________________ is a huge polymer of interlocking chains of identical peptidoglycan monomers. Only present in bacteria.
Peptidoglycan
- Rigid mechanical support
- Freely permeable to solutes
Image:
Peptindoglycan Structure: NicolasGrandjean

12. Bacterial Cell Wall: Gram-Negative & Gram-Positive
Peptidoglycan makes up as much as 90% of the thick, compact cell wall.
Gram-negative
More chemically complex and thinner.
Peptidoglycan only 5 – 20% of the cell wall.
Peptidoglycan not outermost layer, between the plasma membrane and the outer membrane.
Outer membrane is similar to the plasma membrane, but is less permeable and composed of lipopolysaccharides (LPS).
LPS is a harmful substance classified as an endotoxin,
The space between the cell wall and the plasma membrane is called the periplasm.
Image:
Prokaryotic Cell, Mariana Ruiz
Gram +-, Julian Onions

13. Why are these differences in cell wall structure so important?
Gram-negative bacteria: fewer interpeptide bridges but have an outer membrane made of lipopolysaccharides LPS.
Penicillins and cephalosporins interfere with linking of interpeptides, but can’t easily get to in gram- bacteria.
Cell walls without enough of these intact cross-links are structurally weak, and disintegrate when cells divide. This is how penicillins and cephalosporins work.
Since the eukaryotic cells of humans do not have cell walls, our cells are not damaged by these drugs.
Microorganisms that do not contain peptidoglycan are not susceptible to these drugs.
Images: Sources unknown

14. Eukaryotic Cells (eu-, “true”, karyon, “nucleus”)
Genetic material contained in a nuclear membrane.
Membrane bound organelles.
Evolved from prokaryotic cells.
Image: Mariana Ruiz

15. Animal Cell (Eukaryote)
Image: Mariana Ruiz

16. Plant Cell (Eukaryote)
Image: Mariana Ruiz

17. ORGANELLES Animal and plant cells have organelles.
Organelles compartmentalize functions within the cell.
The organelles of animal and plant cells are similar to each other except that __________ are present only in animal cells, and ___________ are present only in plant cells.
Image: Mariana Ruiz

18. All living things are composed of one or more cells.
So … what are viruses?

19. Cellular organisms vs Acellular particles
1. Cellular microorganisms are:
_____________
Archaea
Bacteria
Eukarya
2. Acellular particles:
______________
So small can only be seen with an electron microscope.
Images:
ProkEuk Cell:
BacteriophageBacteria : GrahamColm, Pub domain, Wiki

20. Sizes of Viruses Images:
RelativeScale : Created by TimVickers, vectorized by Fvasconcellos
VirusSize : lifescienceblogs.com/

21. How Do Viruses Differ From Living Organisms?
Viruses are not living organisms because they are incapable of carrying out all life processes.
Viruses
are not made of cells
can not reproduce on their own
do not grow or undergo division
do not transform energy
lack machinery for protein synthesis
Living Unicellular Organism: Amoeba
How Do Viruses Differ From Other Organisms?
Viruses are distinct from living organisms. They are not alive. Because of their small size, they do not encode enough genetic information to perform all the functions of life. They can reproduce only within a living host cell, where they usurp the cellular components they need to reproduce. Because viruses are not cells, they do not undergo normal cellular processes, such as cell growth and division. They are incapable of transforming energy on their own or of producing and assembling the complex machinery needed for protein synthesis. Viruses carry only the minimal information (four to several hundred genes) needed to take over a host cell and create more viruses.
References:
Cann, A.J. (2005). Principles of Molecular Virology (4th Ed.). Elsevier, Inc.
Flint, S.J., Enquist, L.W., Krug, R.M., Racaniello, V.R., and Skalka, A.M. (2000). Principles of Virology: Molecular Biology, Pathogenesis, and Control. ASM Press.
Image Reference:
CDC. Illustration of rabies virus in cross section, # 971. Retrieved from Image #971
Images:
Chaos diffluens, an amoeba. Dr. Ralf Wagner under the GFDL.
Coronaviruses : US Gov PHIL
Coronavirus

22. What Are Viruses Made Of?
Nucleic acid, proteins, and sometimes, lipids.
Nucleic acid can be either DNA or RNA. Encodes the genetic information to make virus copies.
Nucleic acid surrounded by a protective protein coat, called a __________.
An outer membranous layer, called an ___________, made of lipid and protein, surrounds the capsid in some viruses.
What are Viruses Made Of?
Viruses are particles of nucleic acid surrounded by a protective protein coat; some viruses also have a membranous outer layer containing lipids. Genetic material consisting of the nucleic acid DNA or RNA makes up the core of a virus. The nucleic acid contains the genetic code that holds the instructions to make more copies of the virus. The nucleic acid core is surrounded by a shell made of protein, called a capsid, surrounds the genome and protects the genetic information. In addition to capsid proteins, other proteins may be included in a virus particle to facilitate its entry into cells and aid the early steps of replication.
Certain viruses have an outer membranous layer, called an envelope, that is derived from the lipid bilayer of the host cell and into which viral glycoproteins (proteins that are covalently linked to carbohydrates) are inserted. Key proteins on the envelope surface help these viruses recognize and invade their hosts. Examples of viruses with envelopes are HIV and influenza.
The diagram illustrates the structure of an enveloped virus particle (in cross-section). The genetic material is shown in the center in black. The capsid, composed of multiple copies of the same protein, is shown in red. And an envelope studded with viral glycoproteins (yellow) is present at the outer surface.
References:
Campbell, N.E., & Reece, J.B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.
Flint, S.J., Enquist, L.W., Krug, R.M., Racaniello, V.R., and Skalka, A.M. (2000). Principles of Virology: Molecular Biology, Pathogenesis, and Control. ASM Press.
Image Reference:
Herrmann, C. (2006). Diagram of a virus.
Image: VirusStructure :

23. Capsid Morphology
Protein coat provides protection for viral nucleic acid and means of attachment to host’s cells.
Composed of proteinaceous subunits called capsomeres.
Some capsids composed of single type of capsomere; others composed of multiple types.
______________
Image: TobaccoMosaicVirusStructure : Y tambe, Wiki

24. Characteristics of Viruses
_____________ state
Called virion (vie-ree-on)
Protein coat (capsid) surrounding nucleic acid
Some have phospholipid envelope
Outermost layer provides
protection and recognition sites for
host cells
Capsid removed
Virus exists as nucleic acid (genetic material)
Image:
BacteriophageAnimation :
BacteriophageBacteria : GrahamColm, Pub domain, Wiki

25. How Do Viruses Reproduce?
Viruses reproduce via three basic steps:
1. Viruses deliver their genomes into a host cell.
Viruses commandeer the host cell transcription and translation machineries and utilize host cell building blocks to
copy viral genomes and synthesize viral proteins.
3. Viral genomes and proteins are self-assembled and exit host cells as new infectious particles.
Details of each of these steps vary among different virus groups.
Replication
Transcription and Translation 1 2 3
How Do Viruses Reproduce?
Although details of the mechanisms vary widely among different virus groups, all viruses must follow three basic steps to reproduce. First, they must gain entrance and deliver their genomes into cells. Bacteriophages attach to cells and inject their DNA into the host bacteria cell. Other viruses bind to specific receptors (protein molecules) on the surface of host cells. Binding of the virus can trigger the cellular process of endocytosis, essentially tricking the cell into letting the virus inside. Enveloped viruses (viruses surrounded by a lipid bilayer) use the glycoproteins, contained in the envelope, to bind to a cellular receptor. Next, the envelope fuses with the plasma membrane of the cell and the viral contents are released inside the cell. If the viral genome is still surrounded by a layer of protein after it enters the cell, the virus undergoes an “uncoating” step to make the genetic material accessible.
Second, the virus commandeers the machinery of the host cell so that it can make copies of its viral genome and synthesize viral proteins. In addition to the manufacturing machinery, the virus needs building blocks for its nucleic acid and proteins. It utilizes the host cell’s nucleotides to make copies of its genetic material and the cell’s amino acids to make proteins. At the most basic level, all viruses need to replicate their genome and produce capsid proteins. Many viruses encode additional proteins, that enhance their abilities to take over a cell, replicate to higher levels, or to evade host immune responses. RNA viruses often provide their own enzyme, a polymerase, to replicate their genome, because the host cell does not provide some the necessary enzymes. Virus-encoded polymerases are especially important for RNA viruses that need to make a DNA copy of their genome or for (-) strand RNA viruses to synthesize a (+) strand that can be translated. DNA viruses usually use the host cell DNA polymerase, which normally copies cellular DNA. Viruses use the transcription and translation machinery of the cell to manufacture virus proteins. Some viruses produce proteins that modify the cellular transcription and translation apparatus to ensure preferential synthesis of viral proteins over cellular ones, and some viruses even can completely shut down the synthesis of host cell proteins or destroy the host cell’s DNA.
Finally, the nucleic acid and protein components are synthesized, the virus particle is assembled with the protein capsid surrounding the genome. There are various mechanisms by which a virus can exit a cell. Some viruses lyse, or burst open cells to release the virus particles. This process immediately destroys the host cell. Other viruses will bud out of the cell through the plasma membrane and acquire an envelope. In any case, hundreds or thousands of infectious virus particles are released from an infected cell. These newly made virus particles then go on to infect new host cells and continue the cycle of virus reproduction.
It is constructive to keep in mind that unlike a cell, which duplicates its DNA and reproduces from a preexisting cell by dividing to form two daughter cells, a virus can use a single nucleic acid template to make hundreds or more copies of its genome. A useful analogy is that a virus genome can be reproduced multiple times from a single copy, much like a piece of paper can be reproduced numerous times in a copy machine.
Note: The relative sizes of the virus particles and the cell in the diagram are not to scale. The viruses actually are much smaller, relative to cells, than indicated.
References:
Campbell, N.E., & Reece, J.B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.
Flint, S.J., Enquist, L.W., Krug, R.M., Racaniello, V.R., and Skalka, A.M. (2000). Principles of Virology: Molecular Biology, Pathogenesis, and Control. ASM Press.
Image Reference:
Herrmann, C. (2006). Virus replication.

26. Are There Infectious Agents Simpler Than Viruses?
Like viruses, viroids and prions are not made of cells.
________ and _______ are even simpler than viruses.
Viroids and prions can cause disease.
Are There Infectious Agents Simpler Than Viruses?
Viroids and prions are even more simple than viruses. Viroids have only nucleic acid without a protein coat, while prions are composed of protein but do not contain any associated nucleic acid. Viroids can cause plant diseases, such as potato tuber spindle disease and apple scar skin disease. Prions cause mad cow disease and related diseases in humans and animals.
References:
Black, J.G. (2005). Microbiology (6th ed.). John Wiley & Sons, Inc.
Campbell, N.E., & Reece, J.B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.

27. Characteristics of Viroids
The smallest known agents of infectious disease.
Conventional viruses are made up of _______ ________ encapsulated in protein (capsid).
Viroids are uniquely characterized by the absence of a capsid.
So, viroids have genetic material but no protein coat.
In spite of their small size, viroid ribonucleic acids (RNAs) can replicate and produce characteristic disease syndromes when introduced into cells.
Viroids thus far identified are associated with plants.
Images:

28. Prions
Prions may be made of __________ but have no nucleic acid.
Responsible for fatal neurodegenerative diseases called transmissible spongiform encephalopathies (TSE).

29. Good Protein Gone Bad?
Abnormal form of a normally harmless protein found in mammals and birds.
Can enter brain through infection, usually after being ingested, or can arise from a mutation in the gene that encodes the protein.
In the brain, causes normal proteins to refold into abnormal shape. As prion proteins multiply, neurons are
destroyed and brain tissue
becomes riddled with holes.
Prions are unlike all other known
disease-causing organisms in that
they appear to lack nucleic acid
(DNA or RNA

30. Prions Arguments against a Prion Cause of TSE The problem…
Prions not always found when TSEs
are diagnosed. And researchers aren’t
sure what “good” vs “bad” protein
shape is and how proteins transform.
Neuropathologist Laura Manuelidis argues an undiscovered virus, not prions, are the cause of TSEs.
Manuelidis found 25-nanometer particle that looks viral, found in tissue samples with two different types of TSEs.

31. Diseases thought to be caused by prions include:
- Creutzfeldt-Jakob (kroits-felt
yock-ub) disease
- mad cow disease
- scrapie (neuro disease of sheep
& goats.
It appears that prions
can only be destroyed
through incineration.

32. Key to Blanks P2: prokaryotes, eukaryotes P6: nucleosome, plasmid
P7: cytoplasm, granules
P8: ribosomes, cytoskeleton
P9: peptidoglycan
P13: prokaryotes, eukaryotes, viruses
P16: rhinovirus
P17: capsid, envelope
P19: nucleic acid, capsomere, capsid
P19: extracellular, intracellular
P23: viroids, prions
P24: nucleic acids
P25: protein