Summary TOPIC 6 A LEVEL BIOLOGY EDEXCEL - A* NOTES
13 views 0 purchase
Course
Immunity, Infection and Forensics
Institution
PEARSON (PEARSON)
This bundle contains EVERYTHING you need to know in year 1 Edexcel (A) Biology (Salters-Nuffield) for topic 6 - Immunity, infection and forensics.
I have included the most important information from the book, MARK SCHEMES and revision sheets. I wrote these notes after solving all past papers and ...
1. DNA PROFILING (fingerprinting)
- Used to study DNA
- Obtain tissue/cell sample from source ‘X’ – e.g. blood, saliva, samen
- Cells are broken down in buffer solution
- Protease enzymes used to remove proteins and ethanol is added to precipitate out the DNA
- DNA profiling assumes that every individual is unique – apart from identical twins
- It analyses the introns and non-coding DNA (very reliable)
- There is a large number of introns and non-coding blocks, so many combinations of
genes/DNA/alleles at locus.
2. PCR – Polymerase chain reaction
- Multiple copies of DNA are made
- Denature the DNA – separate the DNA double helix into 2 separate strands – 90-95
- DNA primers and nucleotides are needed
- Primers attach to the 2 separate strands (1 on each strand) – 50-65
- 2 polymerase molecules attach to the 2 primers on the 2 separate strands and move along
the strand – 70-75
- This cycle needs to be repeated several times to make several multiple copies of DNA –
amount large enough to be examined
3. Creating DNA fragments
- Restrictions enzymes are used to break the DNA
- They cut the DNA at specific places of sequences known as restriction sites
- To produce DNA fragments
4. Separation of DNA fragments
- Load the DNA fragments onto agarose gel plate
- Electric current is applied across the gel plate – potential difference is used
- DNA (negatively charged) moves towards the anode/positive terminal
5. Southern blotting
- Transfer the profile to a more durable material such as nylon membrane
- The samples will be drawn by the flow of water diffusing into a drier material into the nylon
sheet
- The DNA fragments show up as bands
- DNA bands can be visualised by using gene probes or fluorescent staining, which can be seen
with UV light
,6. How are 2 DNA profiles compared?
- Compare the total number of bands
- Position of bands
- Size/width of bands
- Common bands contain similar DNA
7. Similarities in DNA of ‘A’ and ‘B’ using PCR. What do these similarities suggest?
- Same number of chromosomes
- Number of bands that match indicate similarities in DNA
- Common bands contain similar DNA
- Similar DNA indicates closeness of relationship because genes are sections of DNA and genes
are codes for proteins
- More similar patterns à more likely to have a common ancestor
8. DNA polymerase from human sources is not suitable for use in PCR. Why?
- Human enzymes will not work at high temp, which is above 37 – denaturation of proteins
9. Plants cannot be identified using PCR and DNA profiling. Why?
- Xylem is made from dead material/tissue – no DNA – no nucleus
10. Suggest why DNA profiles may not be conclusive
- DNA profiling has several stages
- Contamination can arise at any stage
- Only a small portion of the DNA is analysed
- There might be a possibility of 2 identical profiles from unrelated individuals
11. Suggest how DNA profiling could be useful to scientists who examine fossils of animals and
plants
- Comparison of the DNA profiles/made between DNA from fossils and other organism
(number/width/size of bands) used to find genetic relationship between the two organisms
and DNA similarities to show how closely related they are
- DNA profiling could be used in taxonomy to understand evolutionary lines and to determine
common ancestor
, DETERMING TIME OF DEATH
1. BODY TEMPERATURE
- Average body temperature is between 36.2 and 37.6
- Temperature of body drops after death – linked to time after death
- Chemical reactions that produce heat stop causing the body to cool
- Factors, which affect temperature are: environmental temp, body size, clothing
- It is useful because time of death can be calculated if the ambient temperature is known
- Ambient temp – average air temp around body
- Only useful for a short period of time following death – 24 hours
- This is because, the extent of temp depends on ambient temp
- Ambient temp fluctuates over time – does not stay constant
- Sooner after death that the temp is taken, the more accurate the estimate of time of death
- Calculations of time of death based on the average body temp – 37
- This also depends on the time of the day
2. RIGOR MORTIS
- The oxygen dependent reactions in the body will stop
- There is not enough oxygen in the body that is required for aerobic respiration
- So respiration in the cells become anaerobic – produces lactic acid
- No ATP produced needed for muscle contraction
- Muscles cannot contract – they become fixed/stiff
- The environment becomes too acidic for enzymes – enzyme activity decreases – PH drops
3. FORENSIC ENTOMOLOGY
- Used to determine time of death
- Insects occur in the succession of the decomposing body
- Forensic entomologists record the type of insect found on the body (fly, wasp)
- Identify the species of the insect and the stage of lifecycle that they are in
- External factor that affects forensic entomology is temperature
- This can be compared to current data to estimate time of death
4. DECOMPOSITION
- Micro-organisms such as bacteria act as decomposers
- Environmental temperature increases the rate of decomposition
- This is because temp increases the kinetic energy of molecules – increases the number of
collisions between enzymes and substrates – more enzyme-substrates formed – increases
enzyme activity
- Also increases the rate at which bacteria grow (bacteria contains enzymes)
- So, tissues begin to denature due to action of enzymes and bacteria
- Above a certain temp rate (optimum temp), decomposition decreases
- Enzymes denature and bacteria are killed
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller lindaalsalti. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.80. You're not tied to anything after your purchase.
