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Questions and Answers on DNA and MRNA

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  • Rumana Anam

Q1. What is the full forms of the following:

D.N.A Deoxyribonucleic (The Free Dictionary, 2015)

MRNA Messenger Ribonucleic Acid (The Free Dictionary, 2015)

TRNA Transfer Ribonucleic Acid (The Free Dictionary, 2015)

Q2. Complete the following sentences

The synthesis of mRNA from DNA is known as:- Transcription (The Free Dictionary, 2015)

The synthesis of proteins from RNA is known as:- Protein Synthesis (The Free Dictionary, 2015)

Q3. Explain the process of Protein Synthesis detailing the role of DNA, mRNA, tRNA and ribosomes.

The process where individual cells make protein is called protein synthesis. DNA and all RNA are both involved in this process. RNA are made by enzymes in the cell’s nucleus which start the process of protein synthesis by way of unwinding the wanted section of the DNA. A copy of one side of the DNA is formed by the RNA, and then is sent to all the other areas of the cell to help to bring altogether the different amino acids that make up proteins. As proteins are synthesised by mechanical and chemical processes within the cells, this process is called protein synthesis. Within the nucleus when the strand of RNA has been made, it is called messenger RNA MRNA. Through opening in the nucleus called pores the MRNA exits the nucleus and goes into the larger area of the cell which is called cytoplasm. As soon as the MRNA leaves the nucleus, it is attracted to a structure called ribosome, which are the cells work station or factory for protein synthesis. Within this point only one sub unit of ribosome is present. Another strand of RNA called transfer RNA, TRNA are activated as the MRNA start to attach to the ribosome sub unit. The TRNA stand finds the correct place to bind to the MRNA, as soon as it finds the place; it binds itself to the MRNA, which on one end holding amino acid. As this happens the other sub unit of ribosome come to completely form a complete structure. Another strand of TRNA appears as the ribosome encircles the strand of RNA. This strand is different from the first strand as it is carrying another amino acid; again the TRNA finds the correct place to bind to the MRNA. With the amino acid as soon as the second strand of TRNA is placed, both of the amino acid joins together aided by the ribosome, and adenosine triphosphate (ATP) with its cellular energy. As this pattern continues and repeats itself the chain of amino acid grows longer. As soon as all the amino acids have been placed in the correct sequence, a three-dimensional chain is made. Once this has happened the protein is complete. When the proteins have been made the two sub-units of ribosome part to be joined later. In many ribosomes within the cell the process of protein synthesis take place there (Wisegeek, 2015).

Q4.What is Point Mutation? Evaluate its effects.

Point mutation is where there is a change within a gene, where one base pair in the DNA sequenced is changed or altered.Point mutation is most commonly the result of mistakes made during the DNA replication, however if DNA is exposed to x-rays and or ultraviolet radiations, this can also bring on point mutation.

The two types of mutations are transition mutation and transversion mutation. Transition mutation happens when a pyrimidine base which is thymine (T) or cytosine (C) changes for another pyrimidine base, or it is when a purine base which is adenine (A) or guanine (G) changes for another purine base. Within a double stranded DNA each base is paired with a certain partner on the corresponding strand. A always pairs with T and C always pairs with G. For example a transition mutation is a GC base pair that swaps an AT base pair. However transversion mutation happens when a purine base changes for a pyrimidine base or the other way around i.e. when a TA or CG swaps for AT pair (Britannica, 2015).

Point mutation can be put in three groups, nonsense mutation which is a code for a stop this can shorten the protein. Missense mutation which is a code for a different amino acid and silent mutation which is a code for the same or a different amino acid with no purposeful change in the protein itself. Missense mutation for example causes sickle cell disease, as the beta haemoglobin gene converts a GAG code into a GTG. This codes the amino acid valine instead of glutamic acid (Answers, 2015).

The Effects of Point Mutation

As all the cells within the body contain DNA therefore there are many places where point mutation can happen. However not all mutations are passed on to the offspring, these do not matter for evolution purposes. The mutations that matter for evolution purposes are those that can be passed on to the offspring, these happen in the reproductive cells eggs and sperm this type of mutation is called germ line mutation. There are three effects of germ line mutation:-

  1. No change happens in the phenotype, this is where there is no effect on the organism. This can happen in a part of the DNA strand where there is no function, or it can happen in a protein coding area but does not affect the amino acid sequence of the protein.
  2. Small changes happen in the phenotype, a single mutation can cause some cats ears to curl backwards.
  3. Significant changes happen in phenotype, this is where significant changes happen within the organism for example sickle cell disease. A single mutation can cause negative effects for the organism for example mutation that cause death, this is called lethal.

Mutations are sometimes stereotyped as unimportant or the cause of genetic disease. While many mutations do have a negative effect, other mutations can have a small positive effect. Mutations that control genes can have a huge and sometimes positive effect. As some areas of the DNA control other genes, that decide when and where other genes are turned on, mutation in these parts can considerably change the way an organism is built. This can cause flow of effects in the behaviour of the genes under its control. Organisms have control genes that shape how the body is laid out i.e. the Hox gene is found in humans and animals. This gene sets out where the head goes and where limbs grow. These control gene build the bodies units i.e. limbs, head etc, therefore evolving a huge change in basic body lay out can be likely by a change in the Hox gene and natural selection (Understanding Evolution, 2015).

Task 2

Q5. What is the probability of a couple having a boy or a girl?







Female X X

XX = Girl

XY= Boy

The probability of a couple having a boy is 50%, the probability of a couple having a girl is 50%.

Q6 What chromosomal abnormalities occur in the inheritance of Down’s syndrome

Down syndrome is a result from trisomy 21, this is where the 21st chromosome has three chromosome and not the normal 2 chromosome. Therefore the individual will have 47 chromosomes and not the normal 46 chromosome. Down syndrome is cause by chromosomal abnormalities that happens randomly in the development stage of reproductive cells within a parent. This normally happens in the egg, but can sometimes happen in the sperm. The mistake in cell division results in a reproductive cell with abnormal number of chromosome, trisomy 21. This condition brings on intellectual disability, a characteristic facial appearance and weak muscle tone, all individual that are effected have cognitive delay (Genetics Home Reference, 2012).

Q7. Explain inheritance of a sex-linked condition with a relevant example

Hemophilia A and hemophilia B are both inherited sex linked traits, where they are inherited through the X linked recessive pattern. The genes that cause this condition are in the X chromosome, which is one half of the two sex chromosomes, the other being the Y chromosome. As males only have one X chromosome, one changed copy of the gene in the cell is enough to cause this condition. As females have two X chromosomes a mutation would have to have happened in both of the copies of the genes to cause this condition. This is very rare to happen in females as both copies of genes would have to have the same mutation happened to them. Therefore it is rare for females to have hemophilia. Fathers cannot pass on the inherited X linked condition to their sons as this is one of the characteristics of X linked inheritance. Females who have this X linked recessive condition have one mutated gene are called carriers. Female’s carriers have normally half the amount of coagulation factor which is enough for blood clotting. Some female’s carriers have less than half of the normal amount of coagulation factor, these carriers are at risk for abnormal bleeding (About Education, 2015).

Q8. Explain the inheritance of either cystic fibrosis or phenylketonuria

Cystic fibrosis is a disorder that causes respiratory failure and vitamin deficiencies. Cystic fibrosis effects the secretion of the body i.e. saliva, mucus, sweat and digestive juices. As this secretion should be thin and watery, they are thick and sticky. This causes passageways to be clogged up within the body which causes damage to the pancreas and lungs. Cystic fibrosis is caused by inheriting defected gene from both parents, known as recessive gene. Cystic fibrous cannot be inherited by the off spring, if only one parent has the gene. If the off spring has only one defective gene then they are carriers of cystic fibrosis, this means that they will have the potential to pass on the defective gene to their off spring (eHow, 2015).

The cystic fibrosis allele is represented by f. The normal allele is F. Suppose both parents have alleles Ff. The possible combinations of alleles in the children are FF, Ff, Ff and ff. The alleles ff will cause the disease. So, although the parents do not have cystic fibrosis, they can produce children with the disease. The parents are called

The off spring labelled Ff are carriers, they have one defective gene but do not have the disorder themselves. In the diagram above both parents are carriers, they have one in four chances of producing an off spring that has cystic fibrosis (Bitesize, 2014).

The cystic fibrosis allele is represented by f. The normal allele is F. Suppose one parent is FF and the other is a carrier, Ff. The possible combinations of alleles in the children are FF, FF, FF and Ff. So the parents cannot produce children with cystic fibrosis (ff). But they can produce children with alleles Ff, who will be carriers

In the diagram above one parent is a carrier, while the other is not. They will not produce an off spring with cystic fibrosis, but are able to produce off springs that are carriers (Bitesize, 2014).

Q9 Describe the process of genetic screening explaining the application of DNA recombinant technology in the treatment of a named medical condition. 

Genetic testing is a medical test that can indicate any changes in the chromosomes, genes and proteins. The result of genetic testing can help to confirm or reject an alleged genetic condition, disease that the individual may have suspicion of, or help verify their chances of developing and or passing on a genetic disorder to their off spring.

Some of the methods of genetic testing can be of these. Molecular genetic testing, this is where the medics study a single gene or short lengths of DNA to find defectiveness or mutation that may lead to a genetic disorder. Chromosomal genetic testing, this is where a whole chromosome and or long lengths of DNA to see if there are any sizable genetic changes i.e. extra copy of chromosome. Biochemical genetic testing, this is where the activity level or the amount of proteins are studied; any abnormalities that are detected can indicate genetic disorder (Genetic Home Reference, 2015).

DNA recombinant technology, is a technology that produces DNA artificially. The DNA in living organism has been changed today due to this procedure. This procedure involves taking DNA from two difference sources and merging it together for it to become one single molecule. However this only works when the artificially created DNA has been reproduced, this is known as DNA cloning. The two types of cloning that DNA recombinant technology is used for are, therapeutic cloning and reproductive cloning. The reproductive cloning produces an organism with the exact same genetic information from the one that already is living. This type of cloning has been done with Dolly the sheep. Dolly was the first mammal to be reproduced as a genetic copy. Therapeutic cloning, reproduces tissues and or organ and not the whole organism.

Therapeutic cloning has a great deal of benefit, i.e. if an organ has cancer it can be replaced with one made from the individuals own DNA. This reduces any likely hood of organ rejection within the body when a tissue or organ transplant is preformed (Wisegeek, 2015).

Q10 Discuss the moral and ethical issues raised by DNA recombinant technology

Not everyone is in favour of DNA recombinant technology, as they feel that science is playing god by reproducing unnaturally organisms that are not meant to be. And that science is devaluing the uniqueness of life itself. Also that some DNA work involves destroying embryos, this angers some social activist as this death is bought on intently this could be classed as murder. However scientist, argue that the purpose of DNA recombinant technology is to benefit and save human life, and not to destroy it (Wisegeek, 2015).


The free Dictionary 2015, DNA, [online] available at http://acronyms.thefreedictionary.com/DNA, Last Accessed 18/05/15

The free Dictionary 2015, MRNA, [online] available at http://acronyms.thefreedictionary.com/mRNA, Last Accessed 18/05/15

The free Dictionary 2015, TRNA, [online] available at http://acronyms.thefreedictionary.com/tRNA, Last Accessed 18/05/15

WiseGeek 2015, What is Protein Synthesis, [online] available at http://www.wisegeek.org/what-is-protein-synthesis.htm, Last accessed 19/05/15

Encyclopaedia Britannica 2015, Point Mutation, [online] available at http://www.britannica.com/EBchecked/topic/54744/point-mutation, Last accessed 19/05/15

Answers 2015, What is point mutation, [online] available at http://www.answers.com/Q/What_is_point_mutation, Last accessed 20/05/15

Understanding Evolution 2015, The effects of Mutation, [online] available at http://evolution.berkeley.edu/evolibrary/article/mutations_05, Last accessed 20/05/15

Genetics Home Reference 2012, Down Syndrome, [online] available at http://ghr.nlm.nih.gov/condition/down-syndrome, Last accessed 20/05/15

About Education 2015, Sex linked traits, [online] available at http://biology.about.com/od/genetics/ss/sex-linked-traits.htm, Last accessed 23/05/15

eHow 2015, How is Cystic Fibrosis Inherited, [online] available at http://www.ehow.com/how-does_5049940_cystic-fibrosis-inherited.html, Last accessed 23/05/15

Bitesize 2014, Cystic Fibrosis, [online] available at http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/celldivision/inheritance4.shtml, Last accessed 23/05/15

Genetic Home Reference 2015, What is genetic testing, [online] available at http://ghr.nlm.nih.gov/handbook/testing/genetictesting, Last accessed 23/05/15

WiseGeek 2015, What is Recombinant DNA Technology, [online] available at http://www.wisegeek.org/what-is-recombinant-dna-technology.htm, Last accessed 23/05/15

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