IB DP Biology HL A2.3 Viruses Flashcards

[q] 

Capsid

[q] Bacteriophage

[a] A virus that infects bacteria.

[q] Lytic Cycle

[a] cycle of viral infection; results in replication of virus and cell destruction.

[q] Lysis

[a] The breakdown of a cell caused by damage to its plasma (outer) membrane.

[q] Metabolism

[a] All of the chemical reactions that occur within an organism.

[q] Lysogenic Cycle

[a] a viral reproductive cycle in which the viral DNA is added to the host cell’s DNA and is copied along with the host cell’s DNA.

[q] Prophage

[a] the viral DNA that is embedded in the host cell’s DNA.

[q] Lysogen

[a] a bacterium containing a prophage.

[q] Parasite

[a] An organism that feeds on a living host.

[q] Obligate Parasite

[a] unable to grow outside of a living host.

[q] Convergent

[a] Process by which unrelated organisms independently evolve similarities when adapting to similar environments.

[q] Evolution

[a] Change in a kind of organism over time; process by which modern organisms have descended from ancient organisms.

[q] Antibodies

[a] Specialized proteins that aid in destroying infectious agents.

[q] Antigens

[a] Foreign material that invades the body.

[q] Immunity

[a] Resistance to disease.

[q] Antigenic drift

[a] a mechanism for variation in viruses that involves the accumulation of mutations within the genes that code for antibody-binding sites.

[q] Antigenic shift

[a] the process by which two or more different strains of a virus, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains.

[q] Structural features common to viruses

[a] Relatively few features are shared by all viruses: small, fixed size; nucleic acid (DNA or RNA) as genetic material; a capsid made of protein; no cytoplasm; and few or no enzymes.

[q] Diversity of structure in viruses

[a] Students should understand that viruses are highly diverse in their shape and structure. Genetic material may be RNA or DNA, which can be either single- or double-stranded. Some viruses are enveloped in host cell membrane and others are not enveloped. Virus examples include bacteriophage lambda, coronaviruses and HIV.

[q] Lytic cycle of a virus

[a] Students should appreciate that viruses rely on a host cell for energy supply, nutrition, protein synthesis and other life functions. Use bacteriophage lambda as an example of the phases in a lytic cycle.

[q] Lysogenic cycle of a virus

[a] Use bacteriophage lambda as an example.

[q] Evidence for several origins of viruses from other organisms

[a] The diversity of viruses suggests several possible origins. Viruses share an extreme form of obligate parasitism as a mode of existence, so the structural features that they have in common could be regarded as convergent evolution. The genetic code is shared between viruses and living organisms.

[q] Rapid evolution in viruses

[a] Include reasons for very rapid rates of evolution in some viruses. Use two examples of rapid evolution: evolution of influenza viruses and of HIV. Consider the consequences for treating diseases caused by rapidly evolving viruses.

[q] Virus

[a] A tiny, nonliving particle that invades and then reproduces inside a living cell.

[q] structural features common to all viruses.

[a] – capsid surrounds genetic material
– small size – 200nm diameter
– fixed size
– nucleic acid (DNA/RNA) as genetic material
– no cytoplasm
– few/no enzymes

[q] differences between viruses

[a] DNA or RNA (single or double).
– (absence/presence of) surrounding envelope.
– different glycoproteins which affect virus’ ability to attach + infect specific host cell.
– polyhedral, threadlike or spherical.

[q] why do viruses rely on host cells

[a] Because they lack enzymes/cellular machinery for replication.

[q] two cycles of a virus

[a] lytic and lysogenic.

[q] lytic cycle

[a] A type of viral (phage) replication cycle resulting in the release of new phages by lysis (and death) of the host cell.

[q] lysogenic cycle

[a] a viral reproductive cycle in which the viral DNA is added to the host cell’s DNA and is copied along with the host cell’s DNA.

[q] stages of the lytic cycle

[a] attachment
phage DNA entry into host cell
DNA replication
protein synthesis
assembly of new phage viruses
lysis
spread

[q] what happens to a lambda bacteriophage in lytic cycle

[a] virus reproduces and bursts out of the host cell to kill it.

[q] Stages of the Lysogenic cycle

[a] attachment
entry
integration into host genome
dna replication
cell division

[q] Lambda bacteriophage in lysogenic cycle

[a] virus assimilates its genome within host cell’s genome to achieve replication without killing the host.

[q] differences between lytic and lysogenic cycles

[a] Lytic cycle: replicate, assemble, and release copies of the virus. Causes the host cell to lyse, and die.
Lysogenic: DNA is incorporated into host DNA, doesn’t happen immediately – virus can stay inside and unnoticed for years. Cell divisions produce populations of the bacteria with the virus inside it’s DNA.

[q] possible origins of viruses

[a] – estimated to have been on earth 3.5bn years before humans evolved.
evidence of coevolution of viruses ~8% of human genome contains small segments of viral DNA from ancient infections.

[q] reasons for rapid evolution in viruses

[a] short generation time
large population size

[q] rapid evolution in HIV and influenza

[a] HIV and influenza have high mutation rates as they have RNA. mutations can occur during the process of converting viral RNA into DNA during viral replication.
They have large populations and short generation times

[q] convergent evolution

[a] Process by which unrelated organisms independently evolve similarities when adapting to similar environments.

[q] divergent evolution

[a] when two or more species sharing a common ancestor become more different over time.

[q] is mRNA produced in transcription

[a] yes

[q] Differences of Lytic and Lysogenic cycles

[a] – lytic cycle causes host cells to lyse whereas lysogenic doesn’t.
– in lytic, host bacteria genetic material is inserted into host chromosome, phage DNA is not inserted in lysogenic.
– genes are expressed immediately in lytic, and not expressed in lysogenic.
– in lytic the host is harmed immediately whereas in lysogenic there is no harm for an extended period of time.

[q] similarities in lytic and lysogenic cycles

[a] – both are mechanisms of phage reproduction.
– require genetic information.
– requires phage proteins to bind to specific receptors on surface of host bacterium.

[q] what does hiv affect

[a] human liver cells

[q] Discuss the evidence supporting that the diversity of viruses exists as a result of convergent evolution.

[a] ​→​ convergent evolution is the appearance of similar traits in unrelated organisms in response to different selection pressures.
→​ presence of capsid surrounding genetic material[1].
→​ presence of specific protein receptors OR spikes[1].
→​ viruses share the same genetic code OR use DNA and RNA OR nucleic acids[1].
→​ viruses require host cells to replicate, OR viruses are obligate parasites.

[q] structure of coronavirus vs HIV

[a] – both spherical in shape
– both contain viral envelope
– both contain RNA as genetic material
– both contain spikes
– both contain capsids
– both spikes are made of glycoproteins
HIV contains two (single) strands of RNA, WHILE the coronavirus contains one single strand of RNA.
HIV genome is within enveloped capsid, WHILE coronavirus genome is a nucleocapsid/not in envelope.

[a] human liver cells

[q] forms of genetic information in viruses

[a] ​ single-stranded RNA
→​ single-stranded DNA
→​ double-stranded RNA
→​ double-stranded DNA
→​ nucleic acid OR DNA OR RNA