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