A type of RNA virus that reproduces by reverse transcribing i its RNA into DNA then inserting the DNA into the host chromosome
What are some components of viruses
Lipid envelope
Glycoproteins
Reverse transcriptase (retro only)
Reproductive cycle of Retroviruses like HIV (diagrams)
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Explain why viruses can change so quickly and the consequences for human and animal health
Viral genomes change/mutate very rapidly
A large number of viral particles are produced
RNA viruses have a very high rate of mutation (RNA polymerase do not correct mistakes)
Where do enveloped viruses get their envelope from?
They take some of the host's cell membrane before budding off from the host cell
What are the different appearances of viruses
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Give examples of how some bacteria are beneficial to the organisms of the environment
Bacteria can...
Make antibiotics
Clone genes
Fix nitrogen to make plants grow
Break down pollutants
Produce plastics
Produce fuel
Bacteria cell defence against bacteriophages
Some bacteria cells can protect their DNA by cutting up viral DNA with restriction enzymes
CRISPR-Cas
Restriction enzymes
Stores some DNA from previous infections, and they are now immune against these bacteria
Makes cas protein, that will find invader DNA, so that it can cut it up
Describe and distinguish the three primary mechanisms that contribute to horizontal gene transfer in bacteria
* Bacteria evolve by horizontal gene transfer (HGT) as well as by verticle transfer of genes from parents
* Transfer of genes from between cells that are existing at the same time
Transduction
DNA transfer mediated by bacteriophage
Conjugation
DNA transfer mediated by plasmids
Transformation
DNA is taken up from the environment
What is Transduction (as a mechanism of horizontal gene transfer)?
Phage infects bacterial donor cell
Phage DNA is replicated and phage proteins are synthesized
Fragment of bacterial DNA with A+ allele is packaged in a phage capsid
Phage containing A+ allele will infect bacterial recipient cell
The incorporation of DNA from the phage creates recombinant cells
When phages infect and replicate in bacterial cells, errors can occur, and a phage is produced which contains bacterial DNA.
This DNA can then be transferred into another bacterial cell
What is conjugation (as a mechanism of horizontal gene transfer)?
conjugation- Bacterial 'sex'
The ability of gene transfer was shown to be acquired through the F(fertility) plasmid in the 1950s
Different bacteria were mixed to produce bacteria with new gene combinations + phenotypes
F Plasmid + Bacteria = New gene combinations
** Requires cell contact, replicates autonomously in bacterial cell
What is the bacterial advantage of bacterial conjugation?
Can transfer chromosomal genes, with the insertion of the F plasmid
When transferred, the F plasmid also includes the original donor chromosome also transfers new DNA with similar attributes (A+,A-). Recombination, replacement
This occurs at a high frequency ie Hfr is a high-frequency recombination
What is Transformation (as a mechanism of horizontal gene transfer)?
A process in which bacteria can take up and incorporate foreign DNA from their surroundings
During the process, bacterial cells become competent, or capable of taking up extracellular DNA fragments and integrating them into their genetic material
This allows scientists to manipulate the genetic material of bacterial cells and study the functions of specific genes or traits
What induces a physiological change
Can be induced by high calcium or salt concentrations
Transformation (as a mechanism of horizontal gene transfer)
Bacterial cells undergo physiological change to competently take up DNA; This physiological change can be induced by high salt or calcium concentrations
DNA fragments must be single-stranded to bind to receptors on bacterial cell surface
Foreign DNA must be integrated into bacterial cell's genome using recombinases
Integrated DNA can then be expressed by bacterial cells leading to the production of new proteins/other cellular changes
Why are bacteria so diverse?
They can quickly reproduce
Have large population sizes
Have diverse ways of regeneration
lots of genetic variation
Describe the properties of plasmids that allow them to mediate horizontal gene transfer
F plasmids contain genes that produce a pilus that allows the plasmid to be transferred to a recipient cell.
Plasmids are transferred through a mating bridge formed by the pilus
Plasmid- small double-stranded DNA molecule (similar to a chromosome) that sits inside the bacterial cell, has a relatively small number of genes and the plasmid DNA is transferred through a bridge
What is the difference in reproductive methods between a virus and a living cell?
Virus:
Requires host cell
Replicates itself through the host cell and destroys it
Living cell:
Mitosis/cytokenesis
replication/division
limited by nutrient availability
Explain the rapid rate of mutation in viruses and it's consequences for human and animal health
Viral genomes mutate rapidly
Large number of viral particles are produced
RNA viruses have a very high rate of mutation (RNA polymerase does not correct mistakes) compared to DNA
How does horizontal gene transfer contribute to the rise of antibiotic bacteria?
When genes are transferred through HGT, recipient bacterial cells can acquire new traits such as antibiotic resistance
Antibiotic resistance is a major and growing threat to human health and horizontal gene transfer by R (resistance) plasmids is a major driver
HGT helps antibiotic resistance develop quickly
Whats the difference between Asexual and Sexual reproduction ?
Asexual Reproduction
One parent/cell
Genetically identical
By mitosis or binary fission
Sexual Reproduction
Two parents
Genetically different
Gametes and Fertilisation
Distinguish between sister homologous chromosomes and sister chromatids, draw or label chromosome switch alleles to represent these and explain what happens to them in meiosis
Same size and shape
Same genes at the same loci (centrosome)
Each gene at different alleles (2 parents AA, aa)
Describe the role of sex chromosomes in mammalian sex determination and their behaviour in meiosis
XY MALE XX FEMALE
What does the Y chromosome do?
-SRY gene is responsible for 'maleness' and code for regulatory protein TDF (testis determining factor)
During meiosis:
Females (xx) pair up and separate = haploid with one x each
Males (xy) Pair up at the end, can have recombination or crossing over. Resulting in 4 haploid cells, only 1/2 carrying y
***An unusual number of sex chromosomes will result in infertility
What does Aneuploidy mean?
That there is and abnormal number of autosomes or sex chromosomes