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BIO 111 > Chapter 13 > Flashcards

Chapter 13 Flashcards

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Biology 101 flashcards
1
Q

Viruses

A

Obligate intracellular parasitic molecules; replication can only occur within another living cell, considered non-living; 5,000 known to man

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2
Q

Central Core of a Virus

A
  • Genome: The nucleic acids found inside a virus will store information that will direct the host cell to replicate the viral parts (numerous times)
  • Enzymes: Some are carried along with the nucleic acid; used to allow entry to a cell or to replicate its own nucleic acids (e.g., DNA and RNA polymerase)
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3
Q

Capsid

A

Outer protein coat found on all viruses; constructed from identical building blocks (capsomeres) which are composed of smaller protein molecules

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4
Q

Capsomeres

A

Form viral capsids spontaneously, forming viruses into nearly perfect geometric shapes; rod-shaped form a helical capsid

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5
Q

Icosahedron

A

Capsid shape; 3-dimensional, 20-sided polygon with 12 evenly spaced corners

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6
Q

Spikes

A

Proteins that project outward into the environment and are essential for viruses to attach to a host cell

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7
Q

Enveloped Viruses

A

Viruses that have a bilayer surrounding their capsid

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8
Q

Naked Virus

A

Type of virus that does not have an envelope

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9
Q

Functions of Capsids and Envelopes

A
  • Both protect the nucleic acid from various enzymes and chemicals outside the host cell
  • Both allow the virus to attach to host cells and help the virus penetrate the host cell
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10
Q

Host Range

A

The organisms or cell types a virus can infect; usually limited to only a few cell types or species or even strains

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11
Q

Productive State

A

New viruses are being produced by the host cell:

  • Host cell destroyed by lysis when new viruses are released (lytic cycle)
  • Host cell continues to divide while releasing viruses
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12
Q

Latent State

A

No new viruses are produced by host cell:

  • Viral nucleic acid is incorporated into host chromosome
  • Host cell continues to divide, replicating viral DNA with each new cell (lysogenic cycle)
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13
Q

Superfamilies

A

Broadest category into which viruses are divided into:

  • Those that contain DNA (7 families)
  • Those that contain RNA (13 families)
  • Family names end with Latin root: viridae (capitalized and underlined)
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14
Q

Characteristics Used to Classify Viruses into Families

A
  • Shape of capsid
  • Overall viral size
  • DNA/RNA viruses
  • Presence of cell envelope
  • Type of host cell it will infect
  • How the virus effects the host cell (e.g., productive, latent)
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15
Q

Bacteriophages

A

Viruses that infect bacteria

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16
Q

Adsorption (Bacteria)

A

The bacteriophage’s spikes on the capsid (all are naked) attach to bacterial receptor proteins; viruses are not capable of locomotion, they must collide with a host cell by chance; this must occur before any other productive phase of infection can occur

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17
Q

Penetration (Bacteria)

A

Entrance of viral nucleic acids into cytoplasm of bacterial host cell:

  • The enzyme lysozyme digests its way through a small portion of bacterial cell wall
  • Viral nucleic acids are injected through the cell membrane of the host
  • Viral nucleic acid enters cytoplasm but capsid remains on the outside of the cell
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18
Q

Transcription of Viral DNA and Production of New Viral Parts (Bacteria)

A
  • DNA of virus is transcribed and translated using the machinery of the host cell
  • Phage-induced proteins are produced
  • The phage DNA is replicated and phage capsid is produced
  • All virus particles are produced independently of one another, including all DNA, capsomeres, binding proteins, etc.
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19
Q

Phage-Induced Proteins

A

Contain new genes that are unique to the virus and not the host cell; code for the production of proteins that perform specific viral functions

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20
Q

Nuclease

A

An enzyme that breaks apart and destroys host cell DNA; essential for the replication of viral DNA and capsid

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21
Q

Maturation (Bacteria)

A

Assembling virus particles into mature viruses:

  • Some particles spontaneously assemble themselves
  • Others use enzymes to join the particles together
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22
Q

Mature Viruses are Released (Bacteria)

A
  • Lysozyme is produced and begins to digest cell wall from inside out
  • Osmotic pressure causes the cell to rupture expelling the mature viruses
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23
Q

Burst Size

A

The number of phages released per cell when it lysis due to viral infection (approximately 200)

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24
Q

Adsorption (Animal)

A

A recognition process between a virus and a host cell that results when the virus attaches to the external surface of the host cell

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25
Q

Receptor Sites

A

Specific proteins found on the cell membrane of a host that a virus attaches to; may have to attach to two (virus may have more than one type of spike); normally used by the host cell for other functions

26
Q

Penetration/Uncoating (Animal)

A

Entrance of the virus into the host cell

27
Q

Endocytosis

A

Process by which cells take up particles by enclosing them in a vesicle pinched off from the cell membrane; virus is engulfed in a vesicle of the host cell’s making

28
Q

Uncoating

A

A process in which enzymes found within the host cell will dissolve the capsid and envelope (if present) and release the nucleic acid strands into the cytoplasm

29
Q

Fusion

A

The viral envelope fuses with the cell membrane of the host; only occurs with enveloped viruses; only capsid and genome enters host’s cytoplasm; capsid is uncoated releasing the nucleic acid

30
Q

Transcription of Viral DNA and Production of New Viral Parts (Animal)

A

The copying and expression of the viral genome using the hosts equipment that results in the production of various virus components:

  • The viral genome is expressed and copied
  • Viral enzymes, necessary for the production of viral parts, are produced
  • Viral parts are constructed, including capsomeres and spikes
31
Q

Maturation (Animal)

A

Assembly of individual viral parts into a whole virus:

  • Viral enzymes and nucleic aced strands are surrounded by capsomere components
  • If the virus is enveloped, then spikes are placed within the cell membrane of the cell
32
Q

Release (Animal)

A

Escape from the host cell to the environment; burst size - 3,000 to 50 million from one cell

33
Q

Budding

A

Process enveloped viruses use to escape a cell:

  • A vesicle (cell membrane) is placed around the virus by the cell (membrane contains spikes)
  • Viruses are released slowly without the sudden destruction of the cell
  • Can be destructive (not always) to the cell because of the accumulation of damage to cell membrane or the membrane of organelles; can shut down metabolism and genetic expression; toxicity of viral components
34
Q

Virulent Viruses

A

Viruses that will always be productive and cause cell lysis; a rapid, severe, and destructive virus

35
Q

Latent Virus

A

A nonactive virus which is in a dormant state within a cell; do not lyse host cells; incorporate their DNA directly into the chromosomes of the host cell (lysogenic cycle); e.g., herpes virus

36
Q

Prophage

A

A bacteriophage that is latent (lamda virus infects E. coli)

37
Q

Provirus

A

An animal virus that is latent (HIV, herpes)

38
Q

Temperate Viruses

A

Viruses that are capable of causing lysis or becoming latent; whether the virus will lysis the cell or become latent is usually due to chance but modifying environmental conditions may play a role in which type is more often expressed

39
Q

Lysogenic Conversion

A

With a latent virus, some genes are expressed and the living host cell acquires new proteins, and hence, new characteristics that it does not normally have

40
Q

Repressor Gene

A

A viral gene that is expressed by a latent virus; codes for a repressor protein that prevents transcription of a gene that produces an excise enzyme

41
Q

Excise Enzyme

A

An enzyme that has the ability to remove viral DNA from a host chromosome; once viral DNA is removed from the host DNA, the virus becomes virulent and new viruses are produced and assembled

42
Q

Induction

A

The process of converting a latent virus into a virulent one; Lysogenic cycle —-> Lytic cycle

43
Q

Acute Infections

A

Viral infections that cause disease symptoms for short periods of time:

  • Are productive
  • Can cause extensive tissue damage and cell death, but usually localized
  • Host organism can recover and does not usually die from exposure
  • Much of the damage can be repaired after recovery
  • The body can develop life-long immunity
  • Ex. mumps, measles, influenza (flu), cold viruses
44
Q

Persistent Infections

A

A specific virus is present within the host for long periods of time (life-long in some cases):

  • Can be productive or latent depending on the state of the disease
  • Disease symptoms may not be apparent
  • The host is a persistent source of infective viruses
  • Ex. hepatitis C, HIV
45
Q

Late Complications Following Acute Infection

A

A chronic infection where a person develops an acute viral disease, recovers, and years later will relapse (possibly with other disease symptoms); e.g, acute measles, 1-10 years later some develop subacute sclerosing panencephalitis (SSPE), which is a fatal brain disorder

46
Q

Latent Infections

A

A chronic infection where a person develops an acute viral disease, recovers, and days, months, or years later will develop another, similar infection:

  • Cannot be detected until disease onset
  • e.g., herpes simplex virus 1 causes cold sores, fever blisters; as the virus heals, some viruses leave the mucous membrane of the mouth and enter neurons (will not harm); viruses are prevented from replicating
  • Stress, menstruation, fever, sunburn, can all trigger the movement of viruses from the neuron, reentering the mucosa and cause more blisters``
47
Q

Chronic Infections

A

The virus is present at all times, where the person may or may not show symptoms of the disease, but the host is continually affected; e.g., hepatitis B & C, after an acute phase (nausea, fever) the virus persists and can slowly cause cirrhosis of the liver

48
Q

Slow Infections

A

The virus number slowly increases over a long period of time, finally accumulating to a lethal point where the fatal disease is caused; e.g., HIV… no symptoms… AIDS

49
Q

Cancer

A

Abnormal condition of unregulated cell division

50
Q

Tumor

A

A mass of newly dividing cells:

  • Benign: cells remain within a localized region
  • Malignant: the cells migrate to other locations (metastasize)
51
Q

Proto-Oncogenes (accelerator)

A

Type of regulatory gene that activates gene transcription and increases the rate of cell division; if this gene is always turned on then the cell can become a cancer cell

52
Q

Tumor Suppressor Genes (brake)

A

Type of regulatory gene that suppresses cell division; if this gene is turned off, then a cell can become a cancer cell

53
Q

How Regulatory Genes are Altered

A
  • Mutation: cause 80% of all human cancer (50% on tumor suppresor, 30% on proto-oncogenes)
  • Viruses: cause 15% of all human cancers (probably more)
  • The rest may result from genetic predisposition
54
Q

Oncoviruses

A

Viruses that invade a host and transform it into a cancer cell; latent and will incorporate its genetic material into the DNA of the host cell

55
Q

Oncogenes

A

Genes of viral DNA that disrupt the normal functioning of proto-oncogenes in host cells and produce cancer cells (proto-oncogenes permanently turned on)

56
Q

Retroviruses

A

Cancer causing virus; single strand of RNA; uses enzyme reverse transcriptase to form a double stranded DNA molecule and then it is incorporated into host chromosome; these viral proteins can modify host cell function

57
Q

Viroid

A

A circular molecule of RNA without a capsid:

  • Don’t produce proteins
  • Cause several economically important plant diseases
  • None known to infect animals
  • 1/10 the size of the smallest plant virus
  • How they cause disease is a mystery but one theory is that it interacts in some way with the host genome, changing the expression of the host genes to cause disease
58
Q

Prions

A

Infectious agent composed only of protein:

  • Affect the central nervous system
  • Normal cellular protein are destroyed by the host cell proteases
  • Infectious agent’s proteins are not easily broken down and accumulate in the cell
  • Not known exactly how it causes disease but one theory is that the infectious agent’s proteins attach to normal proteins and convert their shape into the agent’s shape
59
Q

Protease

A

An enzyme that breaks down proteins

60
Q

Induction Triggers

A

Often unknown, but usually related to:

  • decreased immunity
  • stress
  • fever
  • UV exposure

BIO 111 (15 decks)

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