Infections&diseases CAQ

😷 Infections and diseases Created Tags Describe the process of antigen presentation APC engulfs pathogen (bacterial cell) via phagocytosis where pseudopodia are formed and extended outwards to engulf bacteria when it encounters a pathogen Ends of pseudopodia fuse and vesicle pinched off and enters into cytoplasm , forming a phagosome The phagosome fuses with lysosomes to form phagolyosome The hydrolytic enzyme, lysosome breaks down the antigens on the surface of bacterial cell into short peptides The peptides are transported via vesicles to the cell surface of the antigen- presenting cell where they are presented on major histocompatibility complexes MHC which is synthesised in the endoplasmic reticulum Other components of the bacterial cell that are not presented are released from the cell via exocytosis. Explain how affinity maturation occurs Affinity maturation is the result of somatic hypermutation of immunoglobulin genes in B cells. B cells with B cell receptors that bind to introduced antigen with higher affinity are fed survival signals and so they undergo clonal expansion in a process called clonal selection August 4 , 2025 1156 AM Inf ections and dise ases 1

B cells with B cell receptors showing lower affinity are not fed survival signals and so they die from apoptosis. Plasma cells differentiated from selected B cells produced antibodies with higher affinity to the antigen. explain how somatic recombination during B cell development results in the formation of millions of different antibody molecules Different segments of V, D, J being ligated to form gene encoding different variable regions in heavy chain of the antibody refer to only one segment from each V, D and J segments is chosen and remaining gene segments removed / excised refer to different arrangement / combination of V, D, J segments being transcribed to give different mRNA sequences leading to different amino acid sequences, and subsequently different specific 3D conformation of variable region / code for different antibody molecules Tip: Describe the process in the DNA,RNA and then protein level How do influenza virus damageʼs epithelial cells Virus destroys epithelial cells after budding newly formed viruses leads to extensive plasma membrane loss Replication of influenza virus leads to usage of RNA nucleotides to make viral genome and amino acids used to make viral proteins, depriving host cell of these monomers for their own use How does this damage lead to increase risk of bacterial infection Influenza virus infect the epithelial cells and destroy them, causing build up of dead epithelial cells and mucus in airways causing symptoms of running nose and sore throat Weakening of epithelial layer caused by viral replication can make respiratory passage more susceptible to secondary bacterial infections as it creates Inf ections and dise ases 2

environment for bacteria to grow With secondary bacterial infections, this can lead to