Immunity, Infection & Forensics

Question 1

When DNA is read what does it code for?

Answer 1

For a specific proteins

Question 2

In a eukaryotic cell when can gene expression be regulated?

Answer 2

After transcription and before translation.

Question 3

What does post transcriptional modification involve?

Answer 3

Involves modifying mRNA into mature mRNA

Question 4

In eukaryotes what does the process of transcription result in?

Answer 4

The synthesis of pre-mRNA.

Question 5

Why is Prost-transcriptional regulation required ?

Answer 5

Needed because eukaryotic genes contains introns and extrons

Question 6

What are Exons?

Answer 6

Sections of DNA that code for proteins

Question 7

What are Introns?

Answer 7

Sections of DNA that do not code for protein

Question 8

What must be removed before the pre-mRNA can be synthesised into polypeptides?

Answer 8

Introns must be removed

Question 9

Failure to remove introns would result in?

Answer 9

An incorrect sequence and as a direct consequence to the wrong person would get made during translation

Question 10

What is splicing ?

Answer 10

The process in which introns are removed from pre-mRNA and the exons are joined together to form mature mRNA

Question 11

What is the process of splicing catalysed by?

Answer 11

Enzyme - RNA complex - spliceosome

Question 12

Explain why it is difficult to identify the true number of genes that are in the human genome

Answer 12

Primary mRNA cans be spliced and combined in many different ways.
This allows for more protein to be produced than the number of genes in human genome.

Question 13

Explain the advantage of being able to modify the mRNA to produce different proteins.

Answer 13

Being able to modify the mRNA allows an organism to produce alternative proteins without needing an entirely new gene to code for it.

This ensures that the organism’s genome is not too large.

Question 14

Describe some of the modifications that a polypeptide chain undergoes before becoming a functional protein.

Answer 14

modifications include:

1. cleaving the chain to form the functional protein
2. adding carbohydrate or phosphate group to alter the structure or destination of the protein
3. attaching lipids t anchor the proteins in a cell membrane
4. degrading the protein chain once it has served its purpose

Question 15

Explain why changes to the polypeptide are necessary?

Answer 15

changes to the polypeptide determine the poteins structure and function, or determnine where the protein is transported to.

without these modifications, the proetin may not function properly.

Question 16

Does the process of splicing only involve the removal of introns?

Answer 16

No it can also consist of removal of some exons

Question 17

No it can also consist of removal of some exons

Answer 17

Different combinations of mature mRNA will be formed

Question 18

What can one gene produce ?

Answer 18

Many different mRNAs hence different proteins

Question 19

How are humans able to produce more over 100,000 proteins from only 20,000 genes?

Answer 19

Due to alternative splicing

Question 20

Explain the purpose of of PCR

Answer 20

To produce large quantities of ‘cloned’ DNA from very small samples.

Large quantities are needed for effective analysis .

small quantities are often unusable.

Question 21

Describe how the polymerase chain reactions work

Answer 21

1. DNA is heated to 96 to denature the strands and provide single straded templates for replication
2. The reaction is cooled to 60 to allow primers (short lengths of DNA to which free nucleotides attach to) to aneal to the single strand of DNA
3. The reations is heated to 72 so that the Taq Polymerase can work at an optimum condition and rapidly extend the nucleotide chain from the primer
4. This process is repeated 25-35 times and the amount of DNA icreases exponentially with each repeat.

Question 22

Describe 3 situations where only very small DNA samples may be available for sampling and PCR could be used

Answer 22

forensic sample taken at the scene ofthe crime - hair, blood, semen

Archaeological samples from human remains

samples taken from the remains of prehistoric organisms preserved in ice, mummified, preserved in amber, tar pits

Question 23

After two cycles of replication, 4 copies of the double-stranded DNA exists. Calculte how much a DNA sample will have inreased after a. 10 cycles b. 25 cycles

Answer 23

a. 10- cycles = 1024

b. 25 cycles = 33 554 432

Question 24

The risk of contamination in the preparation of PCR is considerable. Explain what the effect would be of having a single molecule of unwanted DNA in the sample prior to PCR

Answer 24

it would be amplified along with the intended DNA sample, thereby contaminating the sample and rendering it unusable

Question 25

Describe the 2 possible sources of DNA contamination in preparing a PCR sample

Answer 25

dirty equipments -from previous treatments → dna molecules left

DNA from the technician - dandruff

spores, viruses + bacteria in the air

Question 26

Describe 2 other genetic engineering/ genetic manipulation procedures that require PCR amplification of DNA

Answer 26

DNA sequencing , gentic cloning

Question 27

Describe the properties of the short tandem repeats that are important to the application of DNA profiling technology

Answer 27

STRs are non-coding nucleotide sequence (2=6 base pairs) that repeat themselves many times over.

THe human genome has numerous different STRs

This property can be used to identify the natural variation found in evey persons DNA since every person will have a different combinations of STRs of different length

Question 28

Explain the role of the PCR in the process of DNA profiling

Answer 28

used to make copies of the STRs. Only the STR sites are amplified by the PCR becausse the primers are used to initiate the PCR are very specific

Question 29

Describe the 3 main steps in DNA profiling using PCR

Answer 29

1. Extract the DNA sample. treat the tissue with chemical and enzymes to extract DNA which is then seperated and purified
2. amplify the sTR sites using PCR. Priers are used to make a large quantities of STR
3. Run the fragments through a gel to separate them. The resulting pattern represents the STR size for that individual

Question 30

Explain why as many as 10 STR sites are used to gain a dNA profile for forensic evidence

Answer 30

To ensure thata the number of STR sites, when compared, will produce a profile that is effectively unique

it provides a high degree of statistical confidence when a match occur

Question 31

Explain the pupose of gel electrophoresis

Answer 31

Gel electrophoresis separates mixtures of molecules on the basis of size ad other physial properties

Question 32

Describe the process of gel electrophoresis

Answer 32

1. The DNA is loaded into wells at one end of a slab of agrose gel and an electric current is passed through
2. The negatively charged (due to the phosphate group) DNA moves through the gel towards the positive electrode, with the smaller fragments moving faster and further
3. The DNA ends up aranged in bands, with similar length strands rouping together.

Question 33

Describe the two forces that control the speed at which framents pass through the gel

Answer 33

the frictional forces of each fragment’s size (larger fragments travel more slowly than smaller ones)

the strength of the electric field (movement is more rapid in stroner fields)

Question 34

Explain why the small fragments travel through the gel the fastest

Answer 34

The gel is full of pores through which the fragments must pass.

Smaller fragments pass through these pores more easily with less resistance and

therefore faster than larger ones

Question 35

what are the controlled variables in this practical?

Answer 35

Voltage applied

Thickness of agarose gel

Temperature

Time allowed for DNA to run

Restriction enzymes used

Question 36

what are restriction endonucleases?

Answer 36

type of enzymes deried from bateria that uts into DNA fragments at speific restriction sites

Question 37

What is the Southern blotting?

Answer 37

alkaline buffer solution is poured over salb after gel electrophoresis

use a dry nylon filter to absorb fragments of stained DNA & proue visible blobs

Question 38

Summarise the process of DNA profiling

Answer 38

1. uses restiction endonucleases to produce DNA fragments
2. use gel electrophoresis to separate fragments
3. label fragments wit fluorescent or radioactive gene probes
4. perform Southern blotting to compare pattern of bandsr

Question 39

How can one gene result in the production of several different proteins?

Answer 39

Post transcriptional modification of pre mRNA splices out all introns and some exons

splicesomes rejoins the fragments. Exons can be joined in vaious sequence producing different versions of functional mRNA

Question 40

What are the 3 stages of PCR?

Answer 40

DENATURATION

ANNEALING

ELONGATION

Question 41

State the difference between alternative splicing and Splicing

Answer 41

Introns removed in splicing

Alternative splicing some exons spliced