10.2. Antibiotics
A subsection of Biology, 9700, through 10. Infectious diseases
Listing 10 of 82 questions
Bacteria may be classified according to differences in cell wall structure. The differences are shown by using the Gram stain. • A Gram-positive bacterium has a cell wall mainly composed of a thick layer of peptidoglycan . • A Gram-negative bacterium has a more complex cell wall. This wall is composed of a much thinner layer of peptidoglycan and an outer layer known as the outer membrane. Escherichia coli is a Gram-negative bacterium. is a diagram through the cell surface membrane and the cell wall of E. coli. external environment cell wall cell surface membrane outer membrane peptidoglycan lipopolysaccharide core polysaccharide lipid A porin O antigen (O polysaccharide) periplasm (watery fluid containing proteins) cytoplasm The antibiotic penicillin kills bacteria by causing them to lyse . It is more effective in treating diseases caused by Gram-positive bacteria than diseases caused by Gram-negative bacteria. Outline how penicillin acts on bacteria and use to suggest why penicillin has little or no effect at treating diseases caused by Gram-negative bacteria, such as some strains of E. coli. The outer membrane contains transport proteins called OmpF porins. These porins allow the passive movement of water, ions and small, polar molecules across the outer membrane. Each OmpF porin is formed from three identical polypeptides. Explain what is meant by the term passive. Suggest and explain the features of an OmpF porin as a membrane transport protein. E. coli can regulate the number of OmpF porins in the outer membrane to adapt to changing conditions. One control mechanism used by E. coli involves the production of a small mRNA molecule known as micF. MicF binds to the part of the mRNA molecule containing the START codon for the OmpF polypeptide. Suggest and explain how the presence of micF prevents production of OmpF porins. shows that the outer membrane of the cell wall of E. coli contains lipopolysaccharides. These are not present in the cell surface membrane. Each lipopolysaccharide (LPS) consists of a lipid and a polysaccharide portion. The O antigen is the outer part of the polysaccharide portion of the LPS. It faces the aqueous external environment. Define the term polysaccharide. Some strains of E. coli are pathogenic. Different pathogenic strains have different O antigens. Suggest and explain why infection with one pathogenic strain of E. coli does not provide immunity to a different pathogenic strain.
9700_s18_qp_22
THEORY
2018
Paper 2, Variant 2
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The antibiotic teixobactin was discovered in January 2015. Teixobactin kills some bacteria such as Staphylococcus and Mycobacterium. Most antibiotics work by binding to proteins. Teixobactin binds to lipids that are used in the synthesis of bacterial cell walls. This means that it is unlikely that bacteria will quickly develop resistance to teixobactin. Which statements explain why bacteria are unlikely to quickly develop resistance to teixobactin?
9700_s20_qp_11
MCQ
2020
Paper 1, Variant 1
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When bacteria are grown in a Petri dish containing discs with antibiotics, there will be zones of inhibition of bacterial growth. antibiotic disc zone of inhibition area of bacterial growth The chart shows the size of the zones of inhibition when a species of bacteria was incubated on five different plates of agar, each containing a disc with a different antibiotic. zone of inhibition / mm antibiotic Which conclusions can be made about the most and least effective antibiotics on this species of bacteria?
9700_s23_qp_11
MCQ
2023
Paper 1, Variant 1
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Questions Discovered
82