A-LevelBiologyImmunity9700/21 · May/June 2017 · Q311 Marks

Fig. 3.1 is a diagram that shows the structure of an antibody molecule. [Figure 3.1]

(a)State why the antibody molecule shown in Fig. 3.1 has quaternary structure.[1]
(b)(i)Use Fig. 3.1 to explain how the structure of the variable region of an antibody molecule is related to its function.[3]
(b)(ii)State the role of the constant region of an antibody.[1]
(c)(i)Outline how monoclonal antibodies are produced.[4]
(c)(ii)Suggest the advantages of using monoclonal antibodies in diagnosis of disease.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

(antibody has) more than one polypeptide ; A four polypeptides
R two / two or more / two types of /many / AW, polypeptides
allow epitope for antigen
1 (two) antigen-binding, site(s) / region(s);
A binds to / AW, antigens
R active site
2 (shape / structure is) complementary to antigen;
3 idea of specificity / AW;
4 ref. to, primary structure / sequence of amino acids ;
5 ref. to R-groups / (amino acid) side chains, and interactions with antigen / giving specific shape;
binds to (receptors on), phagocytes / macrophages / neutrophils;
A other correct named cell of the immune system
AVP; e.g. gives class of antibody (e.g. IgM, IgG, IgA, IgE)
1 antigen, introduced / AW, into, (small) mammal ; A named small mammal
2 B-lymphocytes / B cells / plasma cells / splenocytes / antibody-producing lymphocytes, are taken / are isolated (from the spleen/lymph nodes);
3 (these) cells are fused / AW, with, myeloma / cancer, cells ;
4 hybridoma cells / hybridomas, formed ; R hybridised cells / hybrid cells
5 hybridoma cell, is cloned / AW ;
6 screening / testing, for hybridoma that produces desired antibody;
7 ref. to scaling up / large-scale production / grow in a fermenter ;
8 AVP; e.g. fusion using, fusogen / polyethylene glycol / PEG / electric current (electrofusion) / (Sendai) virus HAT medium, for, hybridoma growth / inhibiting myeloma growth humanisation of monoclonal antibody
I suggestions for treatment
1 monoclonal antibodies used all have the same specificity;
R 'are specific' unqualified
2 detect only one, antigen / epitope;
3 can distinguish between different, pathogens / strains of, pathogens; A types of cancer cells
4 can be, labelled / tagged / marked / AW ; e.g. with fluorescent label
5 monoclonal antibodies can detect location of, tissues expressing antigen / cancer cells / blood clots; A idea of locating areas of infection
6 fast(er) (diagnosis);
7 can detect antibody levels (e.g. HIV);
8 AVP; e.g. some pathogens cannot be cultured I ref. to cost