2.3. Viruses and membrane structure Flashcards
What are the advantages of cell differentiation?
1| Form can match function more specifically.
2| Specialist performs a function of life more efficiently than a generalist.
What are the advantages of multicellularity?
1| Longer lifespan of the organism (death of one cell does not impact the survival of the whole organism).
2| Larger body size possible (plants competing for light, predatory animals).
3| Effectiveness due to cell differentiation (more complex body forms can develop).
How are viruses similar to each other and how are they different?
Shared features of viruses: non-cellular (no cytoplasm, metabolism, enzymes), obligate intracellular parasites, multiple origins (no shared ancestor), small, fixed size (smaller than the host cell, lack structural features, do not grow), nucleic acid as genetic material (same as host cell - where their proteins are synthesized, same genetic code), have a capsid made of protein subunits
Diversity of viruses: genetic diversity - no genes occur in all viruses, structural diversity (can be enveloped or non-enveloped)
What enzymes do viruses have?
1| For replication of genetic material
2| For infection of the host cells
3| For lysis (bursting host cells)
What type of genetic material can viruses have? What does positive sense mean?
double/single-stranded DNA/RNA which can be circular/linear and can either be positive/negative sense (if it’s single-stranded).
Positive sense can be used immediately as mRNA while negative has to be transcribed before translation.
What is the viral membrane made of? What is its function? Which viruses have it?
- out of phospholipids (from the hosts’ plasma membrane (lysis)) and glycoproteins (from the virus)
- to help the virus make contact and infect the host cell
- only animal/human viruses are enveloped (plant and bacteriophages are mostly not)
What are spike proteins? Which viruses have them?
receptors that initiate the fusion of the virus with the host cell (COVID-19)
Compare and contrast influenza, TMV, bacteriophage, COVID, and HIV based on their host cell, type of genetic info, and the existence of a membrane (add extra).
Influenza: epithelial cells of the respiratory system - eight single-stranded negative-sense RNA – enveloped - has RNA-replicase enzyme
TMV (Tobacco Mosaic Virus) - plant cells - one single-stranded positive-sense RNA - non-enveloped - 1st discovered virus
Bacteriophage – bacteria - one double-stranded DNA - non-enveloped
COVID-19 - epithelial cells of the human respiratory system - single-stranded positive-sense RNA – enveloped - have spike proteins on the capsid
HIV - human T-lymphocyte cells - two single-stranded positive-sense RNA - enveloped - retrovirus, converts RNA to DNA, reverse transcriptase (highest mutation rate)
What is the lytic cycle (the steps in it)?
1| Attachment (to a host cell using tail fibers)
2| Penetration - genetic material entered via tail and pores in the membrane
3| DNA replication (100 copies)
4| Synthesis of viral proteins - using mRNA transcribed from viral genetic material
5| Assembly (of new viruses)
6| Lysis (host bursting)
What is the lysogenic cycle?
the viral genetic material becomes integrated into the host cell’s genetic material and becomes a prophage - virus is temperate in this state because it does not kill its host (causes minimal harm) - daughter cells of the host inherit the undetected and inactive viral genes - stimulus for lysis can come from inside or outside of the host (steps are the same as in lytic but with integration) – it could change to the lytic state at any time and then cause lysis
What is the evidence for several origins of viruses?
1| Obligate parasites - cells evolved before
2| Use the same genetic code as living organisms - evolved from cells by losing cell components and life functions
3| Diverse in structure and genetic constitution (similarities due to convergent evolution)
4| Evolved from cell components (some virus-like cell components)
What are the main reasons for the rapid rates of evolution in viruses?
1| Short generation times (under an hour) in the lytic cycle
2| High mutation rates (RNA viruses)
3| Intense natural selection (host cells defending (antibodies))
Why do influenza and HIV have high mutation rates?
Influenza - RNA replicase replicates genetic material and does not proofread or correct errors - transmission of flu between humans and other species triggers evolution
HIV - reverse transcriptase converts single-stranded RNA genome to DNA - does not proofread or correct errors - enzyme cytidine deaminase made by the host that converts C to U - highest mutation rate produces genetically different strains, becomes resistant to drugs, evades the immune system, chronic infection
What are glycoproteins and glycolipids? What are their roles?
Glycoproteins - polypeptides and carbohydrates
Glycolipids - lipids (1-2 f.a.) and carbohydrates
1| Cell adhesion - form a carbohydrate-rich layer on the outer cell face called glycocalyx – glycocalyx of adjacent cells can fuse
2| Cell recognition - differences in the types of glycoproteins and glycolipids - immune system distinguishing between self and non-self-cells (destroying pathogens)
What makes the PM stable and what makes it fluid?
Interactions between hydrophobic tails, hydrophilic heads, and hydrophobic tails and hydrophilic heads make the membrane stable while lateral movement of protein and phospholipid molecules make it fluid.
