C HAPTER 20 C LASSIFICATION : Kingdom Overview and Virus Notes

VIRUSES Noncellular, infectious agents composed of a nucleic acid inside a protein coat. They lack many features of living cells, so they are in a category of their own somewhere between living and nonliving. A virus cannot reproduce itself; it can only be reproduced inside of a host cell.

T HEY ARE LIKE LIVING ORGANISMS IN THAT : They possess genetic material They are composed of nucleic acids, which can be DNA or RNA They are capable of mutation – they can evolve and adapt to their environment

T HEY ARE UNLIKE LIVING ORGANISMS IN THAT : They are not made of cells They have NO ribosomes (for protein synthesis) They have NO metabolic machinery for protein synthesis or energy generation

O THER CHARACTERISTICS : Viruses take over and use a cell’s machinery Viruses do not grow They are not considered living and are not in any of the kingdoms

V IRAL MULTIPLICATION (5 STEPS ) Attachment - virus attaches to a host cell Penetration - either the virus or its genetic material will enter the cell

Replication and Synthesis - the genetic material directs the host cell into producing copies of viral nucleic acids and proteins

Assembly - viral nucleic acids and proteins are assembled into new viruses Release - new viruses release from the cell

R ETROVIRUSES The genetic material of retroviruses consists of ribonucleic acid (RNA), instead of deoxyribonucleic acid (DNA).

Retroviruses are unique in that they reproduce by transcribing themselves into DNA. Reverse transcriptase, an enzyme within a retrovirus, makes it possible for the retrovirus’ RNA to perform as a template of sorts for the transcription process.

Once transcription has taken place, the viral DNA gains access to the DNA of a cell, reproducing along with the cell and its offspring. Within the cell’s offspring, referred to as daughter cells, the viral DNA creates RNA replicas of itself.

Finally, the RNA replicas leave the daughter cells after coating themselves with a protein.

Have been known to lead to cancer Also the cause of HIV which leads to AIDS.

Retroviruses are prone to mutation. For this reason, viruses in this family often become resistant to antiviral drugs within a relatively short period of time. This level of mutability is one of the reasons cited for the difficulty scientists face in trying to develop a safe and effective HIV vaccine.

P ROKARYOTAE Lack nuclear membranes, mitochondria, chloroplasts, and other membrane bound organelles. Divide & reproduce without meiosis. DNA is one circular double helix called a plasmid. Has no chromosomes Example: Some bacteria

P ROTISTA Microscopic organisms common in fresh & salt water. Live most places that are moist. Cause diseases such as malaria, dysentery, & sleeping sickness Most protista are harmless. They are eukaryotes. Some bacteria fall in this category along with amoebas, euglenas, and diatoms

F UNGI Mushrooms, toadstools, rusts, molds, yeasts Have cell walls Heterotrophs – cannot make their own food. Most are decomposers – get food from dead matter.

P LANTAE Eukaryotic Autotrophs Have cell walls and chloroplasts Nonmotile (can’t move) Most contain chlorophyll Undergo photosynthesis Depend on water & air for nutrients

A NIMALIA Multicellular & very diverse Most are motile Heterotrophs Divided into two main categories – vertebrates & invertebrates. Invertebrate – no backbone Vertebrates – have backbones