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Chapter 20 Classification:Kingdom Overview and Virus Notes
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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.
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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
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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
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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
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Viral multiplication (5 steps) Attachment - virus attaches to a host cell
Penetration - either the virus or its genetic material will enter the cell
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Replication and Synthesis - the genetic material directs the host cell into producing copies of viral nucleic acids and proteins
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Assembly - viral nucleic acids and proteins are assembled into new viruses
Release - new viruses release from the cell
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Retroviruses The genetic material of retroviruses consists
of ribonucleic acid (RNA), instead of deoxyribonucleic acid (DNA).
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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.
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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.
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Finally, the RNA replicas leave the daughter cells after coating themselves with a protein.
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Have been known to lead to cancer Also the cause of HIV which leads to AIDS.
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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.
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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
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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
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Fungi Mushrooms, toadstools,
rusts, molds, yeasts Have cell walls Heterotrophs – cannot make
their own food. Most are decomposers –
get food from dead matter.
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Plantae
Eukaryotic AutotrophsHave cell walls and chloroplasts
Nonmotile (can’t move)Most contain chlorophyllUndergo photosynthesisDepend on water & air for nutrients
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Animalia Multicellular & very diverse Most are motile Heterotrophs Divided into two main categories –
vertebrates & invertebrates. Invertebrate – no backbone Vertebrates – have backbones