Chapter 20 Classification: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.

They 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

They 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

Other 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

Viral 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

Retroviruses 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.

Prokaryotae 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

Protista 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

Fungi Mushrooms, toadstools,

rusts, molds, yeasts Have cell walls Heterotrophs – cannot make

their own food. Most are decomposers –

get food from dead matter.

Plantae

Eukaryotic AutotrophsHave cell walls and chloroplasts

Nonmotile (can’t move)Most contain chlorophyllUndergo photosynthesisDepend on water & air for nutrients

Animalia Multicellular & very diverse Most are motile Heterotrophs Divided into two main categories –

vertebrates & invertebrates. Invertebrate – no backbone Vertebrates – have backbones