Biology  by Bradford
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A2.3 Viruses: revision map

The subtopic in the middle and eight tasks round it: label three diagrams, complete a table, put a process in order and fill 40 gaps. The whole subtopic is higher level. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.

A2.3 practice questionsThe whole A2 map

A2.3

Viruses

Cells ยท Unity and diversityName

A2.3.2HIV up closeHL

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Its outer layer is a piece of the host cell's , taken as each new virus out of the cell.

A2.3.4The lysogenic cycleHL

In the lysogenic cycle, lambda's DNA is into the bacterial chromosome, where it is called a . Most of its genes stay switched off, and it is copied with the host's DNA each time the cell , so every daughter cell inherits it. Stress such as can make it leave the chromosome and enter the .

A2.3.1, A2.3.2Bacteriophage lambdaHL

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All viruses are small and of a size, with no and few or no of their own.

A2.3Viruses

A2.3.5Where viruses came fromHL

Viruses are so varied that they probably arose , from different organisms: some may be cells that lost most of their parts, others genes that escaped from cells. What they share, such as a capsid and no metabolism, could be , shaped by the same extreme way of life: all viruses are parasites. They also use the same as living organisms, which fits an origin from cells.

A2.3.6Fast-evolving virusesHL

Some viruses evolve very fast. They make huge numbers of copies, a new generation within hours or days, and the enzymes that copy the RNA genes of influenza and HIV do no , so their rate is very high. The surface proteins of influenza change so often that a new flu is made every year. HIV evolves inside each patient, so to any single drug soon appears: it is treated with a of antiretroviral drugs.

A2.3.2Three different virusesHL

VirusNucleic acidStrandsEnvelope?
Lambda phagenone
Coronavirusyes
HIVRNA (two copies)

A2.3.3The lytic cycleHL

Number the steps in order.

  1. The host cell's enzymes copy the viral DNA, and its ribosomes build capsid and tail parts.
  2. A phage enzyme breaks down the cell wall: the cell bursts, releasing the new phages.
  3. New phages assemble: DNA is packed into each new capsid and a tail is added.
  4. The phage injects its DNA into the cell; the empty capsid stays outside.
  5. The tail fibre binds to receptors on the surface of an E. coli cell.

A virus has no metabolism of its own: it depends on its host for an supply, for raw materials and for .

A2.3 examAn enveloped virus in sectionHL

An enveloped virus in section1234
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Word bank budscapsidcombinationconvergent evolutioncytoplasmdividesDNAdoubleenergyenvelopeenzymesfixedgenetic codeglycoproteinintegratedlytic cyclemutationnucleic acidobligateplasma membraneproofreadingprophageprotein synthesisresistancereverse transcriptaseRNAseveral timessingletailtail fibreUV lightvaccineyes

Answer key

Every box on the sheet with its gaps filled in, as the subtopic reads in full.

  1. LabelBacteriophage lambda HL

    1. capsid
    2. DNA
    3. tail
    4. tail fibre

    All viruses are small and of a fixed size, with no cytoplasm and few or no enzymes of their own.

  2. LabelHIV up close HL

    1. envelope
    2. glycoprotein
    3. capsid
    4. RNA
    5. reverse transcriptase

    Its outer layer is a piece of the host cell's plasma membrane, taken as each new virus buds out of the cell.

  3. TableThree different viruses HL

    VirusNucleic acidStrandsEnvelope?
    Lambda phageDNAdoublenone
    CoronavirusRNAsingleyes
    HIVRNAsingle (two copies)yes

  4. OrderThe lytic cycle HL

    1. The tail fibre binds to receptors on the surface of an E. coli cell.
    2. The phage injects its DNA into the cell; the empty capsid stays outside.
    3. The host cell's enzymes copy the viral DNA, and its ribosomes build capsid and tail parts.
    4. New phages assemble: DNA is packed into each new capsid and a tail is added.
    5. A phage enzyme breaks down the cell wall: the cell bursts, releasing the new phages.

    A virus has no metabolism of its own: it depends on its host for an energy supply, for raw materials and for protein synthesis.

  5. GapsThe lysogenic cycle HL

    In the lysogenic cycle, lambda's DNA is integrated into the bacterial chromosome, where it is called a prophage. Most of its genes stay switched off, and it is copied with the host's DNA each time the cell divides, so every daughter cell inherits it. Stress such as UV light can make it leave the chromosome and enter the lytic cycle.

  6. GapsWhere viruses came from HL

    Viruses are so varied that they probably arose several times, from different organisms: some may be cells that lost most of their parts, others genes that escaped from cells. What they share, such as a capsid and no metabolism, could be convergent evolution, shaped by the same extreme way of life: all viruses are obligate parasites. They also use the same genetic code as living organisms, which fits an origin from cells.

  7. GapsFast-evolving viruses HL

    Some viruses evolve very fast. They make huge numbers of copies, a new generation within hours or days, and the enzymes that copy the RNA genes of influenza and HIV do no proofreading, so their mutation rate is very high. The surface proteins of influenza change so often that a new flu vaccine is made every year. HIV evolves inside each patient, so resistance to any single drug soon appears: it is treated with a combination of antiretroviral drugs.

  8. Exam diagramAn enveloped virus in section HL

    1. glycoprotein
    2. envelope
    3. capsid
    4. nucleic acid