Summary Unit 4 notes biology IAL edexcel, Decomposition and forensics
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Edexcel A level Biology B Student Book 2 ActiveBook
- Biology notes that will help international a level students prepare for their unit 4 exam.
- Consist of Chapter 6C: Decomposition and forensics.
- 100% typed notes.
- Useful tools to help learn and memorise them like emojis, diagrams, tables and shortcuts
,1) Microorganisms and decay
• Decomposers are microorganisms like bacteria and fungi which break down
dead plants and animals. They play a crucial role in recycling chemical
components needed by living organisms.
They secrete enzymes that break large
organic molecules into smaller ones
which can be broken down further
during respiration.
They release CO2 and CH4
• Decomposition releases waste products which provide nutrients to plants
2) Polymerase Chain Reaction
• A person’s DNA sequence can be used to create a DNA profile which is very
useful in forensics as it provides a way to identify individuals
Can also be used to determine the genetic relationship between organisms
(paternity tests, ancestry kits, evolutionary relationship between species)
1. Isolating a sample of DNA (saliva, skin, , ).
2. Producing more copies of DNA using the
polymerase chain reaction (PCR).
3. Carrying out gel electrophoresis on the DNA
produced by PCR.
4. Analysis the resulting pattern of DNA fragments.
The polymerase chain reaction
= molecular biology technique used in application of gene technology (e.g DNA
profiling and genetic engineering)
· in vitro method of DNA replication
· produces many copies of a piece of DNA = DNA
amplification
Used to produce large quantities of specific
thermal cycler (PCR machine) provides
fragments of DNA or RNA from very small optimal temperature and controls
quantities length of time at each stage
, · in each PCR cycle the DNA x2 so in a run of 20 cycles = 1 million molecules
produced
What is required:
DNA or RNA to be amplified
Primers
= short sequence of single-stranted DNA that have base sequence complementary to
the 3’ end of the DNA or RNA being copied
• They define the region that is to be amplified and identifies where the DNA
polymerase needs to bind
DNA polymerase
• Taq polymerase is used which comes form thermophilic bacterium
Does not denature at the high temperature required during first stage
Optimum tempº is high enough to prevent annealing
Free nucleotides
• Enable construction of new DNA or RNA strands
Buffer solution
• ensures the optimum pH for the reactions
Each PCR cycle doubles
Stages of PCR
the amount of DNA
1. Denaturation - double-stranded DNA heated to 95
degrees which breaks the hydrogen bonds that hold the 2
DNA strands together
2. Annealing - temperature decreases to 50-60 degrees so that primers can anneal
to the ends of the stands of DNA
3. Elongation/Extension - temperature increased to 72 degrees which is optimum
temperature of Taq polymerase to build the complementary strand of DNA to produce
the new identical double-stranded DNA molecule
• After PCR the DNA is treated with restriction endonuclease (=recognises and cuts
DNA at a specific sequence of bases)
breaks the DNA up into fragments of different lengths
fluorescent tags enable DNA fragments to be seen under UV light
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