1. Viruses

2. What is a Virus? Non-living particle
WHY? Viruses are considered non-living because they do not carry out metabolism, they do not grow, they do not develop. In fact, they can not even replicate without the help of a living cell (host).

3. Characteristics of Viruses
Only pathogenic (causes disease).
Viruses are specific to certain kinds of cells.
Ex: HIV infects only Helper T cells
Before a virus can replicate, it must attach to and infect a living cell, called the host cell.

4. Virus Structure
A virus has simple structure consisting of an inner core of genetic material (DNA or RNA) and an outer protein layer called a capsid.
This structure is known as a virion.

5. Figure 18.2 Viral structure

6. Figure 18.1 Comparing the size of a virus, a bacterium, and a eukaryotic cell
Viruses are SMALL!!!

7. Scale in Biology
Cell Size and Scale Interactive

8. All living things contain cells. -The Cell Theory

9. Characteristics of cells
All cells contain…
Cell membrane
Cytoplasm
Ribosomes
Genetic material (DNA)

10. Cell Membrane Regulates what goes in and out of the cell (selective)
Composed of lipids and proteins

11. Cytoplasm Jelly-like substance found on the inside of the cell
Enclosed by cellular membrane
Cytoplasm

12. Ribosomes
Site of protein production
Located in cytoplasm
Ribosomes

13. Two Basic Cell Types
All cells are either
prokaryotic or
eukaryotic

14. What is the difference? The location of their DNA
Prokaryote = no nucleus present; DNA is in the cytoplasm
Eukaryote = nucleus present; DNA surrounded by nucleus

15. Prokaryotes a.k.a. Bacteria
Simplest cellular organisms
Unicellular
Contain genetic material but no nucleus
No membrane bound organelles – therefore, not many specialized functions.
Typical bacteria cell

16. Eukaryotes Complex cellular organisms Unicellular and multicellular
Contain a nucleus and many membrane-bound organelles with specialized functions.

17. Nucleus
Controls activities of the cell and holds the genetic information (DNA)
Only found in eukaryotes
Ribosomes, which are used in protein synthesis, are assembled in an area of the nucleus called the nucleolus.

18. Viruses vs. Cells VIRUSES Bacterial CELLS DNA or RNA.
Have no metabolism of their own.
Must be parasitic!
DNA
Can metabolize “food” to produce energy.
Can live on their own and reproduce through binary fission.
Knowledge
“Viruses are genetically distinct entities of nucleic acid, within a protective structure, that can organize its replication within a host cell using the host cell metabolic systems. The virus is the ultimate parasite because it attacks the genetic makeup of a cell. Viruses can only replicated in living cells and are dependent on host cells for energy and protein synthesis. These molecules are very small. In fact, the largest virus is only as big as the smallest bacteria.”
--Dr. Raymond Loan
TEKS: Science-
6.3 Problem Solving
A) Analyze, review, and critique scientific explanations.
D) Evaluate the impact of research on scientific thought, society, and nature.
E) Connect science concepts with the history of science.
7.7 Know that a substance has physical and chemical properties
7.9 Relationships between structure and function
7.10 Understand that traits are contained in genetic material and species can change over time
7.12 (B) Relationship between organisms and the environment
(B) Observe how organisms interact and use resources
8.3 Problem Solving
B) Draw inferences based on data related to promotional materials.
D) Evaluate the impact of research on science, society, and the environment.
E) Connect 8th grade science concepts with history of science and scientists.