18 7 Streptococcus pneumoniae is a bacterium that causes pneumonia. (a) When Streptococcus pneumoniae is grown on a culture plate, the bacterial cells produce:  either smooth, shiny colonies (S‑strain)  or rough colonies (R‑strain). The S‑strain bacteria produce a smooth capsule but the R‑strain bacteria do not. (i) Explain why the R‑strain bacteria are not able to produce the capsule present in the S‑strain bacteria. 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(ii) In an investigation, mice were injected with either the S‑strain or the R‑strain. The results are shown in the table. Strain of Streptococcus pneumoniae injected into mice Injected mice S‑strain died R‑strain lived The S‑strain bacteria were then killed by heating them. Mice were then injected with either heat killed S‑strain bacteria or a mixture of heat killed S‑strain bacteria and live R‑strain bacteria. The results are shown in the table. Strain of Streptococcus pneumoniae injected into mice Injected mice S‑strain (heat killed) lived S‑strain (heat killed) and R‑strain (live) died 19 Turn over Analyse the data to explain why the mice died when they were injected with a mixture of heat killed S‑strain and live R‑strain bacteria. 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(b) In another investigation, heat killed S‑strain bacteria were treated with one type of enzyme:  protein digesting enzymes (proteases)  RNA‑digesting enzymes (RNAases)  DNA digesting enzymes (DNAases)  lipid digesting enzymes (lipases). Each type of enzyme treated S‑strain bacteria was then mixed with live R‑strain bacteria and injected into mice. Complete the table to predict whether the mouse lives or dies. Write dead OR alive in the spaces in the table. (3) Enzyme used to treat the heat killed S‑strain bacteria Mouse injected with live R‑strain and enzyme treated S‑strain [dead or alive] protease RNAase dead DNAase lipase 20 (c) Another investigation used radioactively labelled phages. Phages are viruses that consist of DNA contained within a protein head. DNA Protein Phages inject their DNA into a host bacterial cell, but leave the protein heads (called phage ghosts) on the outside of the infected cell. Two different types of phage were developed by growing the phages in cultures of bacteria in two separate media. Medium (A) contained radioactive phosphorus (32P). Medium (B) contained radioactive sulfur (35S). Type A phage had DNA that included the 32P. Type B phage had proteins that included the 35S. (i) State why radioactive carbon, nitrogen or oxygen were not used in this experiment. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 21 Turn over (ii) Separate cultures of the bacteria E. coli were infected with either type A or type B phage. After infection the empty phage heads (phage ghosts) were separated from the bacterial cells. Each was tested for radioactivity. Complete the table to show where radioactivity was present (Y) or absent (N). (1) Phage type (label) Bacterial cells Phage ghosts A (32P) B (35S) (Total for Question 7 = 10 marks)