Immunity, DNA and forensics

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Topic 6: Immunity, Infections and Forensics
DNA Profiling
Polymerase is the.... enzyme used in the Polymerase Chain Reaction to amplify DNA in a small
sample of blood taken from a crime scene.
Gel Electrophoresis is the .....process used to separate DNA fragments to create a DNA profile
Describe how gel electrophoresis can be used to analyse DNA. (3)
*First, a DNA sample will be collected from blood, saliva or semen etc; *these small samples of
DNA can then be amplified by PCR. DNA profiling then takes place which uses *restriction enzymes
to break the DNA and then *uses electro potential difference, with the DNA in a gel, to draw the
bands apart. *The DNA is stained so it can be seen and will *show up as bands/bars. *The number
of bands that match indicates the similarity of the DNA.
Name substances X, Y and Z:
Substance X ...........DNA Primers
Substance Y......... (mono)nucleotides
Substance Z ..........DNA Strands
What are the temperatures for?
T1: Heated to 90­95 °C
T2: Cooled to 55­60 °C
T3: Heated to 75 °C
Using DNA profiling explain how a suspect is found guilty. (5)
A DNA match is needed, this means that *all of the bands in the sample are the same as the ones
shown in the evidence sample. *DNA profiling assumes every individual's DNA is unique/different;
*apart from identical twins. *DNA profiling analyses the introns/noncoding blocks/STR parts of
DNA as the *non-coding areas are hypervariable because *there are a large number of
introns/non-coding blocks and so there can be *many combinations of STRs at each locus.
Suggest how DNA profiling could be useful to scientists who examine fossils of animals and
plants. (2)
*Comparisons could be made between DNA from fossils and other organisms *to find genetic
relationships/how closely related they are. It may also be *used in taxonomy/classification *to
understand evolutionary lines/to determine a common ancestor.

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Explain how the results of DNA profiling of tissue samples from the two sub-species could be
used to provide evidence that they share common ancestry. (3)
DNA profiling will *produce bands that will have spread to *certain positions. *Common/similar
bands will contain similar DNA fragments; *the more similar these patterns, the closer the
relationship/more likely the sub-species will have a recent common ancestor. *There will still be
very few differences between the DNA of sub-species.
Suggest how DNA analysis could give further evidence for evolution.…read more

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Describe the role of microorganisms in the recycling of the carbon from compounds in a dead
animal. (3)
Decomposition/putrefaction occurs by microorganisms, they may digest the carbon in the animal
and then release the carbon into the atmosphere by *respiration where the *carbon dioxide is
used for photosynthesis. *Methane is released in anaerobic conditions and is *available as fuel.
Suggest three factors that could influence the rate at which a body cools after death.…read more

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This sequence codes for 7 amino acids during protein synthesis T
Thymine can't be found in.................... mRNA
A cistron is..............the sequence of triplets on a section of DNA used to form a strand of
A Peptide Bond.............. links the amino acids in the primary structure of a protein
Reverse transcriptase is the...... enzyme is used to produce DNA from viral RNA in an infected
Transcription takes place......... In the nucleus
The amino acids in a primary structure are linked together in the ........…read more

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Explain the function of the codons at each end of a strand of mRNA, during the process of
translation. (2)
*They function as start/stop/nonsense codons. The *start (codon) is needed to begin the
Polypeptide/protein synthesis and *the stop/nonsense (codon) is needed to end polypeptide
Suggest why a variety of different protein structures could be formed from the polypeptides
synthesised using the mRNA molecules from a single gene.…read more

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Explain why the processes shown in the flow diagram will only happen in response to some
types of bacteria. (3)
Because the protein nature of antigens/antibodies is different, the *antigens are specific to each
bacteria strain and the *antibodies need to be complementary/specific to the antigen so that
binding can take place. *Some bacteria will have different/changed antigens to another, they may
also have different *slime/mucus capsules or be *inside body cells, this changes the effectiveness
of the antibodies.…read more

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When MRSA enters the blood it can stimulate the production of several different clones of
plasma cells. These produce a variety of antibodies (polyclonal antibodies). Suggest an
explanation for this. (4)
Because the *bacterium is made of many different polymers/chemicals *which can act as different
antigens, *individual B-lymphocytes will recognise specific antigens/antibodies are specific and so
only certain *B-lymphocytes are activated by T-lymphocytes. These cells of *B-lymphocytes will
then divide by mitosis *to form genetically identical plasma cells that secrete specific antibodies.…read more

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Suggest why health authorities in the USA are encouraging the reduction in the number of
prescriptions of antibiotics. (2)
Because *some bacteria can resist/are resistant to the antibiotics and this *resistance is
genetic/can be passed on. *MRSA, for example is already resistant to many antibiotics.
Explain why doctors have been advised to limit the prescription of antibiotics. (2)
Because *antibiotics act as a selective pressure, *some bacteria are already resistant to some
antibiotics.…read more

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A specific/humoral immune response to the synthetic antigen will be stimulated, i.e. *Effector B
cells will be produced by clonal expansion of B cells, involving cytokines or T helper cells will
activate B cells. These will then *produce B memory cells that will cause (2G12) antibodies to be
produced faster/in greater concentration on reinfection (secondary immune response).
Describe how a vaccine gives active immunity against PWMS.…read more

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Name two types of cell that HIV enters in the immune system.
*T helper/CD4 positive cell/lymphocytes; *phagocytic cells e.g. macrophages, dendritic cell
State how the genetic material in HIV differs from the genetic material in the Mycobacterium
tuberculosis that causes TB. (2)
*RNA is found in HIV/ virus and DNA in the bacterium/TB, *the nucleic acid in the bacterium is
circular whereas it is linear in HIV. *There are also plasmids in bacterium and no plasmids in HIV.…read more


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