Biology topic 6

Describe the structure of a DNA primer

Short single stranded section of DNA, attach to start and end of a fragment, complimentary to the template

Explain the role of a DNA primer

Binds to the template strand

Defines region of dna to be copied or amplified, as it bind to the start and end of a sequence

How can large quantities of RNA be made

If RNA is double stranded heat to 95 degrees to break h bonds to create a template strand

attach 2 primers on start and end of the template strand 50-65 degrees

Heated to 72 degrees free nucleotides join to template strand via complimentary base pairing using dna polymerase to catalyse phosphodiester bonds

Repeats the amount of rna doubles each time

How do the structures of DNA polymerase make it thermostable

dense ionic network, strong secondary structure

List the stages involved in DNA profiling/fingerprinting

DNA sample collected

cut into fragments using restriction enzymes isolating strs

str sequences are amplifies using pcr

amplified strs are then separated using gel eloctophoresis ehich separated dna fragemnts acording to base pair length

stained with uv light

Define the terms introns and exons

Introns - don’t code for proteins

Extrons - code for proteins

proteins exit the cell instructuctions dont

Explain why introns are useful for DNA profiling/fingerprinting

this is what makes up the dna fragemnts (strs) which we can separeate and are inhertied by individuals

DNA profiling requires the DNA to be cut into fragments of different lengths. Explain the role of restriction enzymes in this process

they bind to dna bases, break both hydrogen bonds and phosphodiester bonds, cut dna into fragments

State the full name of the technique for amplifying DNA

polymerase chain reaction

List the equipment and materials needed for PCR

dna template, free nucleotides, dna primers, dna polymerase

PCR is divided into 3 stages. Name the three stages, state the temperatures necessary and describe what is happening at each stage 

Denaturation

heat DNA to 95 degrees to break h bonds to create template strands

Annealing

attach 2 primers on start and end of the template strand 50-65 degrees

Extension

Heated to 72 degrees free nucleotides join to template strand via complimentary base pairing using dna polymerase to catalyse phosphodiester bonds

Repeats the amount of rna doubles each time

State the name of the technique for separating out DNA fragments

gel electrophoresis

Describe how to carry out this technique

dna is loaded into gel wells

current is applied across so DNA moves to thev + end

DNA radioactively labelled so its visable

compare bands between different samples

matching between the bands indicated samples are closely related

Explain why DNA moves to the positive electrode in gel electrophoresis

DNA has phosphate ions so is negatively charged = moves to the opposite

Explain how the size of the DNA fragment determines the distance it moves in the gel

shorter = moves further and faster than a long fragment

An antelope is found dead in Kruger National Park. The park rangers suspect that the antelope was killed by a cheetah, they take a sample of saliva from the wounds in the antelope. Explain how the park rangers could use gel electrophoresis to identify whether the antelope was killed by a cheetah or not

• Collect DNA from the saliva found in the antelope's wounds.

• Collect a DNA sample from a cheetah for comparison.

• Use restriction enzymes to cut both DNA samples into fragments.

• Load the DNA fragments into wells in a gel.

• Apply an electric current so the DNA fragments move through the gel (smaller fragments travel further).

• The fragments separate, forming a DNA banding pattern.

• Compare the banding pattern from the saliva sample with the cheetah DNA sample.

• If the patterns match, the saliva came from a cheetah, indicating the antelope was likely killed by a cheetah.

• If the patterns do not match, the killer was not a cheetah.

Explain why DNA can be used to create unique DNA profiles for individuals (2)

DNA contains regions that don’t code for amino acids/contains introns

STRs in introns are highly variable between individuals/STRs vary in number of repeats

DNA band position on profile therefore different for everyone

Compare and contrast the structure of viruses, prokaryotes and eukaryotes  dna, double, linear, membrane, histones etc.

Feature of genetic material	Eukaryotic cell	Prokaryotic cell	Viral particle
DNA or RNA or either?	DNA	DNA	Either
Double stranded or single stranded or either?	Double-stranded	Double-stranded	Either
Linear or circular?	Linear	Circular	Linear
Membrane-bound or not?	Membrane-bound	Not membrane-bound	Not membrane-bound
Associated with histone proteins or not?	Associated with histones	Not associated	Not associated

Compare and contrast the structure of viruses and prokaryotes

Differences

• Viruses contain DNA or RNA; prokaryotes contain DNA only.

• Viruses lack cytoplasm and ribosomes; prokaryotes have both.

• Viruses replicate only inside a host cell; prokaryotes reproduce by binary fission.

Similarities

• Both contain genetic material.

• Both are microscopic.

• Both can mutate and evolve.

• Both can act as pathogens.

List the ways in which time of death can be determined

• Body temperature → body cools gradually after death.

• Rigor mortis → muscles stiffen due to lack of ATP.

• Stage of decomposition → degree of tissue breakdown.

• Forensic entomology → age and life cycle stage of insects (e.g., blowfly larvae) on the body.

• Stomach contents → extent of digestion can indicate time since last meal.

Explain how the rate of cooling of a body can be used to determine time of death 

the body drops in temperature roughly 1.5-2.5 degrees per hour

we can see the internal and external body tempertaure to estimate roughly what time

this is only useful if the body temperature is higher than ambient temperature

Describe the stages of rigor mortis

• Muscles become stiff after death as ATP is no longer produced, lactic acid build up.

• Stiffening begins in small muscles (e.g. face and jaw) and gradually spreads to larger muscles.

• The body eventually becomes fully rigid.

• As decomposition occurs, stiffness disappears and muscles relax again.

Explain why the rate of decomposition can be impacted by environmental temperature 

Enzyme controlled reaction

bacteria release digestive enzymes to the body

they break down the polymers via hydrolysis reactions

higher temps give enzymes more kinetic energy, more successful enzyme substrate complexes

Compare and contrast the process of succession in an ecological setting with succession that takes place on a corpse 

both start with pioneer species

in the corpse nothing is outcocmpeted

no climax community is reached in the corpse

Microorganisms use polymers in organic matter as a source of glucose for respiration. Explain how microorganisms break down cellulose and lignin in plant material 

consume cellulose. digestive enzymes catalyse hydrolysis reactions to glucose by breaking glycosdic bonds, this can be used in repiration, released via respiration as co2

Explain why decomposition can contribute to the greenhouse effect

decomposition means that decomposers release carbon locked in plants and animals

it does this by breaking polyemrsdown to monomers in hydrolysis reactions

they then respire releasing the co2 into the atmosphere

more co2 int he atmosphere

co2 is a green house can

more energy is trapped in earths atmosphere

State the major routes pathogens may take when entering the body 

• Through the respiratory tract (inhaled in air droplets)

• Through the digestive tract (contaminated food or water)

• Through the urogenital tract (sexual contact)

• Through breaks in the skin (cuts, wounds, insect bites)

• Via direct contact with infected individuals or contaminated surfaces

Explain how the structure of skin and the skin flora (bacteria found on skin) prevents infection

• Physical barrier: outer layer of skin consists of dead, keratinised cells that are difficult for pathogens to penetrate.

• Continuous surface: healthy skin forms an unbroken barrier, preventing pathogens from entering underlying tissues.

• Skin flora: harmless bacteria on the skin compete with pathogens for nutrients and space.

• Skin flora: some skin bacteria produce antimicrobial substances that inhibit pathogen growth.

Explain how stomach acid prevents infection

• Hydrochloric acid (HCl) in the stomach creates a very low pH (around 1–2).

• This acidic environment kills many pathogens that enter the body in food and drink.

• It denatures proteins and enzymes in microorganisms, preventing them from functioning and reproducing.

• As a result, fewer pathogens reach the intestines and cause infection.

Explain how gut flora (bacteria found in the gut) prevents infection

• Gut flora are harmless bacteria that naturally live in the intestines.

• They compete with pathogens for nutrients and space, making it harder for pathogens to establish themselves.

• Some gut bacteria produce antimicrobial substances that inhibit the growth of pathogens.

• This reduces the likelihood of harmful microorganisms causing infection