11.1. The immune system
A subsection of Biology, 9700, through 11. Immunity
Listing 10 of 122 questions
During an immune response, only B-lymphocytes with receptors that are specific to the antigens present are activated. Activation occurs when an antigen binds to a receptor of a B-lymphocyte. Activated B-lymphocytes grow in size and then divide by mitosis. Many further mitotic cell divisions occur, increasing the number of B-lymphocytes with receptors specific to the antigen. Eventually, cells produced in this process will develop into either plasma cells that secrete antibodies or memory B-cells. is a summary of B-lymphocyte activation and the events that follow. antigen receptor cell growth mitosis binding of antigen and activation of B-lymphocyte B-lymphocyte that has not yet been activated repeated cycles of cell division by mitosis develops into antibodies plasma cell that produces and secretes antibodies memory B-cell The development of plasma cells and memory B-cells in this process depends on transcription factors. Explain the role of transcription factors in gene expression in eukaryotic cells. Transcription factors are proteins. Genes that code for proteins can become mutated. Describe how different types of gene mutation can cause changes in the protein that is synthesised. BLIMP-1 is a transcription factor that is essential for the development of plasma cells and memory B-cells in the process shown in . BLIMP-1 reduces the synthesis of c-Myc in B-lymphocytes. c-Myc is a protein that is required for the mitotic cell cycle to continue. Suggest and explain how a mutation in the gene coding for BLIMP-1 can prevent the development of plasma cells and memory B-cells. Microarrays can be used to analyse the effect of transcription factors, such as BLIMP-1, on gene expression. Describe how a microarray is used in the study of gene expression. BCL6 is another transcription factor found in B-lymphocytes. The effect of BCL6 on gene expression was compared in two samples of B-lymphocytes. • Sample 1 consisted of B-lymphocytes that were producing BCL6. • Sample 2 consisted of B-lymphocytes that were not producing BCL6. Suggest why a microarray is suitable for identifying the function of the transcription factor BCL6 in these two samples.
9700_m19_qp_42
THEORY
2019
Paper 4, Variant 2
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T-helper lymphocytes and Leydig cells are two types of mammalian cells. The main role of T-helper lymphocytes and Leydig cells is to synthesise and secrete cell-signalling molecules. • T-helper lymphocytes synthesise proteins known as cytokines. • Leydig cells synthesise the steroid hormone testosterone from cholesterol. Leydig cells also synthesise cholesterol. State one way in which cytokines are involved in an immune response. shows part of a mammalian cell. State, with reasons, whether shows part of a Leydig cell or part of a T-helper lymphocyte. Underline the correct name for the type of image shown in and explain your choice. photomicrograph scanning electron micrograph transmission electron micrograph explanation Testosterone molecules and cytokine molecules are transported in the circulatory system to reach their target cells. Testosterone molecules are able to enter their target cells and bind to receptors within the cytoplasm. Outline one way in which testosterone molecules could enter their target cells. Cytokine molecules are not able to enter their target cells. Suggest and explain why cytokine molecules are not able to cross the cell surface membrane to enter their target cells.
9700_m21_qp_22
THEORY
2021
Paper 2, Variant 2
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Questions Discovered
122