viruses Flashcards
DNA viruses
The genetic material is DNA.
The viral DNA acts as a template for both new viral DNA and for the mrnas needed to induce synthesis of viral proteins for exmaple lambda phage
RNA viruses
RNA is the genetic material.
RNA viruses do not produce DNA as part of their life.
The majority of RNA viruses contain a single strand of rna known as ssrna
Positive ssrna
Has RNA that can directy act as MRNA and be translated at the ribosomes.
E.G tobacco mosaic virus
Negative ssrna
Cannot be directly translated. The rna strand muust be trasncribed before it is trasnlated at the ribosome.
E.G Ebola
RNA retrovirus
Have a protein caspid and a lipid envelope. Single strand of viral RNA dircts the synthesis of reverse transcriptase. This goes on to make DNA molecules corresponding to teh viral genome. This DNA is then incorporated into the host cell DNA and used as a template for new viral proteins and a new viral RNA genome
Outline the lytic cycle of a virus
Viral RNA is injected in cilliated epithelial cell. Virl RNA hijacks cell biochemistry, producing virions. The cell lysis releasing teh virions.
Outline Latency
Lysogenic virus injects viral DNA in the form of provirus into the host cells DNA allowing it to replicate every tme cell divides. The provirus can remian dormant if the virus produces repressor proteins, preventing mRNA from being produced by mking it impossible to trnslate the rest of teh viral genetc material. During this period of lysogeny, when thevirus is part of the reproducing host cell, the virus is latent.
How do antivirals work?
Know that viruses are not living cells and so antivirals must work by inhibiting
virus replication.
Ethical implications of drug testing
Some people feel that it is not ethical to use untested drugs not completed through full human trials
If an untested drug produces unexpected side effect it can make teh situation worse
Decidign who takes the drug is ddificult
Informed onsent is difficult: Depends on a evel ofeducation to understand the durg
Issues of trust between indivudlas, communites and helath workers
How do antivirals treat viral infections/ target virus replication
Target receptors by which viruses recognise their host cells
Target enzymes which translate or replicate the viral DNA/RNA
Inhibit protease enzymes which enable new virus particles to bud from host membranes
How to control disease
Rapid identification of the disease by effective testing
Isolation
Preventing transmission from one individual to another: hand washing
Sterilising and disposal of equipment and bedding: main transmission cause of Ebola.
PPE: protective clothing.
Identifying contacts – monitor/treat/rapidly isolate.
Define the cell cycle
a regulated process in which cells divide into two
identical daughter cells, and that this process consists of three main stages:
interphase, mitosis and cytokinesis.
Give another explanation lysogenic cycle
The retrovirus attacks an animal cell
Virus RNA enters the host cell. This RNA cannot be used as mRNA.
Viral RNA is trasnlated into viral DNA by reverse transcriptase in the cytoplasm
Viral DNA is incorporated into teh host DNA in the nucleus. It directs the production of new viral genome RNA, mRNA and coat proteins
New viral proteins are assembled and leave teh host cell by exocytosi. Viral DNA remains in the nucleus so teh process is repeated
How does a virus work?
Viruses only reproduce inside a living cell.
To do this the virus must first enter the cell through
the plasma membrane and (if present) the cell wall.
Viruses do so by either attaching to a receptor on the
cell’s surface or by simple mechanical force.
The virus then releases its genetic material (DNA or
RNA) into the cell.
How do DNA viruses work?
Lytic cycle
Lysogenic cycle
Ethical implications when fast tracking drugs
Severity of diseases
Availability of other treatments
Effectiveness of standard disease control measures
Transparency of the process and informed consent of those given the treatment
Freedom of choice
Involvement of the affected community.
Clear clinical data of the new medicines and on-going assessments of safety and efficacy.
Interphase
A period of non division when the cells increase in size and mass, carry out normal cellular actvities and replicae their DNA ready for division
Mitosis
The process by which a cell divides to produce two gentically identical daughter cells
Cytokinesis
Division of the cytoplasm at teh en dof mitosis to form two geneticlly idenitcal cells
Why are viruses non living
Viruses are not living becuase they are acellular which means they have no cytoplasm, no metabolism and no self replicating
Viruses have no metabolism = difficult to treat infection after initial contact.
G1
Time between the end of the previous round of mitosis and the start of chromosome duplication. Cell assimilates material, grows and develops. This may also involve duplicating organelles and making proteins
G1 simpler terms
ATP is produced for the energy intensive process of cell division about to occur
S
Chromosomes replicate and become double stranded chromatids (this happens at the end) This also involves DNA synthesis where the strands of the DNA is replicated and genome is doubled. The DNA is being doubled so that each of the new cells will have its own set of DNA
S simpler terms
The genetic material is copied
Chromosomes replicate and become double stranded chromatids
G2
G2: This is the time where all the organelles and other materials needed for cell division is synthesised (two of each organelle). The organelles begin to divide. It starts to condense the genetic material
G2 simpler terms
The organelles duplicate
More cytoplasm is produced as the cell grows further ready for division
DNA is checked for errors
What is teh cyclins
Cyclins: Involved in the control of the cell cycle by their attachment to cyclin dependant kinases.
What happens to teh cell mass as the cell cycle progresses
The mass of the cell will increase during the cell cycle as it makes more proteins, organelles and DNA.
What is teh role of mitosis
Growth
Repair
Aesexual reproduction
How is mitosis involved in growth
Growth: Mitosis is the splitting of cells. It increases the number of cells within your body which enables you to grow
How is mitosis involvwdin repair
When part of a tissue breaks, then there are cells lost. So, mitosis will create tons of new cells in periods of time to fill the gap and make the tissue bigger again. This ensures that the tissue is back to normal and can function properly. It’s like a wound healing.
How is mitosis involedin aesexual reproduction
Asexual reproduction uses the process of mitosis to create the identical copies (clones) of the parent cell. It therefore leads to offspring that show no genetic variation. It shares the genetic material of the parent cell between the two daughter cells.
Sporulation
Involes mitosis and teh prouctionofaesexual spores that re capableof growing itn o new indviduals
They can survive harmful conditions
Regeneration
Organisms replacing lost body parts
Fragmentation
The use of mitosis to regenerate whole organism from a fragment of teh original
Budding
The production by mitosis of an outgrowth fromt he parent organism that devlops into a small independt organism
Vegetaive propagation
The process by which a plant forms a strcuture by mitosis that devlops ito a fully differentiated genetically idneitcla new pant
Parthenogenesis
The process by which an unfertilised egg cell develops into a new individuals
Mitosis in plants
Takes plae at teh meristem
Just behin teh tip of teh steem and the root where the cell continuously divide actvily
Prophase
Chromosomes arecoieup ad onsst of two daughter chromatids joined by a centromere. The nucelolus breaks down and the nucear envelope dissappers.
Spindle fibre forms
Metaphase
Chromosome line up on teh metaphase platen
Anaphase
Centromeres split so chromatids become new chromosomes. They are moved to opposite poles of cells, centromere first, by contraction of the spindle fibre
Telophase
Nuclear memrbne forms around two sets fo chromsoes, chromosomes unravela dn teh spinle fibre breaks down
First phase of meisosi
Prophase 1: Each chromosomes appears in condensed form with two chromatids. Homologous pairs of chromosomes associate with each other. Crossing over occurs
Metaphase: Spindle fibre forms and pairs of chromosomes line up on metaphase plate
Anaphase; Centomeres dont divide. One chromosome from each homologous pairs moves to each end of the cell. As a result, the chromosoome number in each cell is half the original
Telophase: Nuclear membrane reforms and cells begin to divide.
Second phase of meiosis
Prophase 2: New spindles form
Metaphase: Chromosomes line up on metaphase plate
Anaphase: Centromeres divide and chromatids move to opposite ends of the cell
Telophase: Nuclear envelope reforms, chromosomes return to their interphase state and cytokinesis happens
Four daughter cells with half the chromosome number of the original diploid cell.
The four daughter cells are h aploid as they contain half the number of chromosome of teh diploid parent cell.
How does meiosis result in genetic variation
Crossing over and idenpendent asortment
