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Unit 11: Genetics and Genetic EngineeringLearning aim: A: To understand the structure and function of nucleic acids and to describe gene
expression and the process of protein synthesis.
A.P1: Explain the structure and function of DNA and various nucleic acids.
A.M1: Discuss the functional role of nucleic acids in DNA in the stages of protein synthesis.
A.D1: Assess the impact of error in the stages of protein synthesis.
Introduction
DNA obtains its name from deoxyribose acid a type of nucleic acid, however, gets a significance from its
unique structure. Nucleic acids are very large molecules which contain two main parts. A backbone of
nucleic acid is made of alternating sugar and phosphate molecules. (Anon., n.d.) Phosphate molecules are
alts which derivative of phosphoric acid and are composed of phosphorus and oxygen, this allows it to play
a major role in biological processes. Nucleic acids are made up of polynucleotide cains which are formed
by many nucleotides bonded together. The sugar is the 3’end, and the phosphate is the 5’end of each
nucleotide. Each nucleic acid contains millions of bases bonded to it. The polynucleotide chain is made of 3
parts: a five-sugar carbon (pentose), an organic base that contains nitrogen and a phosphate group. A
nucleotide has 2 various kinds of sugars deoxyribose and ribose. Deoxyribose sugar present in the
nucleotides form DNA whilst ribose sugar forms RNA in the polynucleotide chain. Consequently, the order
in which these nucleotide bases appear in the nucleic acid is the coding information carried out in the
molecule. Nucleotide bases are the genetic alphabet in which a structure of each protein becomes
encoded. In the nucleotide there are 5 different bases. These bases are adenine (A), cytosine (C), thymine
(T), guanine (G), and uracil (U). Uracil is only found in RNA whilst thymine in only present in DNA. Each
base can be identified by the first letter of its name.
- Adenine is a molecule that transports energy needed for work in cells and is made of carbon,
nitrogen, and hydrogen. Its job is to help stabilize the nucleic acid in molecules, its chemical formula
is C5H5N5.
- Thymine serves as the main stabilizer to ensure that the DNA ‘ladder’ has a solid foundation. Its
chemical formula is C5H6N2O2.
- Cytosine is full of nitrogen atoms. It can be easily converted into other bases, so it is often known as
the wild card base. Its chemical formula is C4H5N3O.
- Guanine performs important functions in the cellular metabolism. Its chemical formula is C5H5N50.
DNA Structure
DNA is made up of two strands of polymer wound into a helix, DNA is made up of molecules, these
molecules are known as nucleotides and each contains a phosphate group, a sugar group, and a nitrogen
base. Adenine, thymine, guanine, and cytosine are the four distinct kinds of nitrogen bases. (Scitable, n.d.)
Genes are formed by the order of nitrogen bases in the DNA sequence, this is known as the language of
the cell and it tells us how proteins are made. Ribonucleic acid also known as RNA is another type of
nucleic acid that translates genetic information from DNA into proteins. (Chatterjee, 13 July 2018)
RNA Structure
Ribonucleic acid, RA, is a complex compound that has high molecular weight. It functions in the cellular
protein synthesis and it also replaces DNA as a carrier of genetic codes in some viruses. Ribose
Nucleotides are in RNA that are attached by phosphodiester bonds, which form strands of different lengths.
In RNS there a nitrogenous bases that are adenine, guanine, cytosine, and uracil which replaces thymine in
DNA. (Chatterjee, 13 July 2018)
The ribosome sugar of the RNA is a cyclical structure, it contains 5 carbons and 1 oxygen. RNA is prone to
hydrolysis due to the presence of a chemically reactive hydroxyl group which is attached to the second
carbon group in the ribose sugar molecule. RNA is a single stranded biopolymer. (Chatterjee, 13 July 2018)
Differences in RNA & DNA
, Unit 11: Genetics and Genetic Engineering
Function: DNA copies and stores all genetic information and is a blueprint for genetic information that is in
an organism. Whilst in the RNA, genetic information is converted in the RNA that is within the DNA to a
format used to build proteins, then it moves to the ribosomal protein factories. (Mackenzie, 2020)
Structure: DNA is made up by a double helix, which is two strands that are made up of subunits that are
named the nucleotides. The nucleotides each have a phosphate high is a 5-carbon sugar molecule and a
nitrogenous base. The RNA is also made up of nucleotides, but only has one strand. DNA strands are
longer than RNA strands, sometimes the RNA may create a secondary double helix structure, however this
only happens intermittently. (Mackenzie, 2020)
Length: A chromosome is a single long DNA molecule. It can be several centimetres in length when
unravelled, which makes it a much longer polymer than RNA. RNA molecules are different in their length
but still smaller than DNA polymers. An RNA molecule may be a few thousand base pairs long.
(Mackenzie, 2020)
Sugar: Deoxyribose is the sugar that is in DNA, it has one less hydroxyl group than RNA’s ribose. Whilst
RNA has ribose sugar molecules and without the hydroxyl modifications of the deoxyribose. (Mackenzie,
2020)
Bases: There are 4 bases in DNA, these are adenine, thymine, guanine, and cytosine. RNA has adenine,
guanine, and cytosine; however, it replaces thymine with uracil. (Mackenzie, 2020)
Base Pairs: For DNA: Adenine and thymine par A-T & Cytosine and guanine pair C-G. For RNA Adenine
and uracil pair A-U, & Cytosine and guanine pair C-G. (Mackenzie, 2020)
Location: The DNA is in the nucleus, and a very small amount of DNA is in the mitochondria. RNA is
formed in the nucleolus, then it is transported to the specialised regions of the cytoplasm, but it depends on
the type of RNA formed. (Mackenzie, 2020)
Reactivity: DNA is more stable than an RNA molecule, this is because of DNA’s deoxyribose sugar that
contains one less oxygen containing hydroxyl group. This is useful for a molecule that has the job of
keeping genetic information safe. Whilst RNA has a ribose sugar, it is more reactive than the DNA, it is not
stable in alkaline conditions. RNA is more easily subject to by attacked by enzymes due to the RNA’s larger
helical grooves. (Mackenzie, 2020)
Ultraviolet Sensitivity: DNA is damaged by ultraviolet light. Whilst RNA does get as damaged by UV light
as it is more resistant to it. (Mackenzie, 2020)
Protein Biosynthesis
When making protein there are two main major processes involved. The first process within the two overall
within the gene expression is known as transcription. This involves the formation of messenger RNA
through the copying of the genes DNA sequence as they are rewritten. The second stage is known as
translation this involves the translation of genetic code, though decoding a mRNA and uses its information
to create a polypeptide amino acid chain.
There is some DNA in the body which does not exit the nucleus. Its primary function is to act as a blueprint
or a template for mRNA production. The template or blueprint can transport the instructions from the
nucleus to the cytoplasm. The cytoplasm is where protein synthesis is carried out Protein synthesis is a
biological function where individual cells build a formation of specific proteins. Assembled proteins and a
suitable surface area for mRNA attachment is due to the ions within ribosomes. Transcription and
translation usually occur in 3 steps: initiation, elongation, and termination.
Transcription
In transcription, a DNA sequence is rewritten, or transcribed, into a similar RNA "alphabet." In eukaryotes,
the RNA molecule must undergo processing to become a mature messenger RNA (mRNA). (Khan
Academy, 2021)
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