CHAPTER 1: BIOMOLECULES PART 4- NUCLEIC ACID
Nucleic Acid:
- Nucleic acids are the
most essential macromolecules in cells, constituting the foundation of life's
fundamental dogma.
- The molecular
reservoirs of genetic information are deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA).
- Heredity/Genes-Unit of
Heredity DNA is the master molecule responsible for heredity.
- Every protein's
structure, and hence every biomolecule and cellular component, is a result of
information encoded in the nucleotide sequence of a cell's DNA.
- Nucleotides are nucleic
acid's monomeric units or building components.
Nucleic Acid:
- Nucleic acids are the
most essential macromolecules in cells, constituting the foundation of life's
fundamental dogma.
- The molecular
reservoirs of genetic information are deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA).
- Heredity/Genes-Unit of
Heredity DNA is the master molecule responsible for heredity.
- Every protein's
structure, and hence every biomolecule and cellular component, is a result of
information encoded in the nucleotide sequence of a cell's DNA.
- Nucleotides are nucleic
acid's monomeric units or building components.
Building Blocks of
Nucleic Acid:
1.Nitrogenous bases:
- Purines and Pyrimidines are two kinds of
nitrogenous bases that can be found in nucleic acids.
- In cells, there
are five main bases. Adenine and guanine are purines, while thymine, cytosine,
and uracil are pyrimidines.
- A, G, T, C, and
U are popular acronyms for these five bases.
- A, G, C, and T
are the bases in DNA, whereas A, G, C, and U are the bases in RNA.
2. Sugar:
- Nucleic acids include two sugars: ribose
and deoxyribose. 2 -deoxyribose is found in the repeating deoxyribonucleotide
units of DNA, whereas ribose is found in the ribonucleotide units of RNA.
- These are
present in nucleotides in their furanose (closed five-membered ring) form.
3. Phosphoric Acid:
- Phosphoric acid attaches to the sugar's
C-5 OH group.
- The base along
with sugar is called “nucleoside”. The bond between them is called the
beta-glycosidic linkage.
- Cytidine,
uridine, adenosine, guanosine, and thymidine are examples of nucleosides.
- The three
components of nucleotides are nitrogenous bases, pentose sugar, and the
phosphate group.
- The phosphate is
linked to the sugar portion of the nucleoside's 5' CH2OH group.
- The base of a
nucleotide is covalently linked to the 1 carbon of the pentose in a glycosyl
bond (at N-1 for pyrimidines and N-9 for purines), and the phosphate is
esterified to the 5 carbon.
- A water molecule
is removed to produce the N-glycosyl bond.
Polynucleotides:
- Polynucleotides are made up of
nucleotides linked together by phosphodiester bonds.
- A phosphodiester bond
is formed when the alcohol of one nucleotide's 5'-phosphate and the 3'-hydroxyl
of the next nucleotide come together.
- Polynucleotides include
DNA and RNA.
DNA-STRUCTURE, PROPERTIES AND FUNCTION
- Structure: The discovery of DNA
structure is one of the most significant achievements of contemporary molecular
biology. In 1953, James Watson and Francis Crick presented a model for the
structure of DNA based on Chargaff's base ratios and X-ray Diffraction Analysis
by Maurice Wilkins and Rosalind Franklin.
- They discovered
that DNA is made up of two complementary antiparallel polynucleotide strands
that are wrapped around each other in a rightward orientation.
- The helix's backbone
is sugar-phosphate, and the bases are in the inside of the helix, extending at
90 degrees perpendicular to the helix's axis.
- It has a helical
structure with two helices. One strand is made up of one polynucleotide
chain.
- A double helix
is formed by two such strands.
- The bases are
placed perpendicular to the chain and have a sugar phosphate backbone.
- Each helix turn
is 34 A long, with 10 base pairs discovered each turn and a rise of 3.4A.
- The major and
minor grooves are two deep grooves located on the surface of the double helix.
- Along the axis,
Helix is right-handed.
- The base pairs
form hydrogen connections with one another, ensuring the structure's stability.
G and C base pairs have three H-bonds, whereas A and T base pairs contain two
H-bonds.
- Because G-C base
pairs are stronger than A-T base pairs, DNA with more GC base pairs will be
more stable than DNA with more AT base pairs.
- In the double
helix, bases are piled on top of each other.
- The DNA is
additionally stabilised by hydrophobic interactions between stacked
nucleotides. Each strand's sugar phosphate backbone is negatively charged.
- Various Conformation of
DNA: One of the characteristics of DNA is that it is conformationally
flexible and may take on many structural shapes. B-form DNA, or B-DNA, is the
Watson-Crick structure.
- In crystal
structures, two additional structural variations of DNA have been thoroughly
described.
- The A-DNA and
Z-DNA are the two types of DNA.
- The helical
sense, diameter, base pairs per helical turn, helix rise per base pair, base
tilt normal to the helix axis, sugar conformation, and glycosyl bond
conformation of these DNA variations differ.
Structure of RNA:
- RNA is a single-stranded polynucleotide,
unlike DNA.
- Because uracil
is used instead of thymine, RNA has four bases: A, U, G, and C. In the cell,
there are three kinds of RNA:
1.
Messenger RNA,
2. Transfer RNA,
3. Ribosomal RNA
Messenger RNA:
- The letters m-RNA stand for messenger
RNA.
- Secondary
structure of m-RNA is not well structured.
- In general, the
polypeptide is linear, with the exception of certain hairpin structures formed
by base pairing between complimentary base pairs in the chain.
- A process called
transcription produces messenger RNA in the nucleus as the complimentary copy
of DNA strand.
- It contains the
genetic information of the DNA that will be utilised to make proteins
Transfer RNA:
- t-RNA stands for trans-ribonucleic
acid. Clover leaf structure is clearly characterised in them. It is made up of
four arms:
1. dihydrouridine (DHU) (D
Loop),
2. anticodon, and
3. pseudouridine (T Loop)
2. anticodon, and
3. pseudouridine (T Loop)
- It performs the function of an
adaptor molecule.
- During the protein synthesis
process, anticodons on the anticodon arm create complementary base pairs with
codons.
- As a result, t-function RNA's is to
transfer amino acids for protein synthesis.
Ribosomal RNA:
- It performs the function of an
adaptor molecule.
- During the protein synthesis
process, anticodons on the anticodon arm create complementary base pairs with
codons.
- As a result, t-function RNA's is to
transfer amino acids for protein synthesis.
miRNAs:
- Micro RNAs (miRNA) are
single-stranded RNA molecules ranging in length from 21 to 23
nucleotides.
- MiRNAs are post-transcriptional
regulators that bind to complementary regions on mRNA transcripts, causing
translation to be slowed or genes to be silenced.
- Genes transcribed from DNA but not
translated into protein (non-coding RNA) encode miRNAs.
- The primary function of mature
miRNA molecules appears to be gene expression control.
- Victor Ambros and his colleagues
originally identified this phenomenon in the worm C.elegans in 1993.
siRNA:
- Short-interfering RNAs (siRNAs) present in plants work to inhibit viral RNA from being transcribed.
- The mechanism of action of siRNA is identical to that of miRNA, despite the fact that it is double stranded.
- Cellular genes are also regulated by siRNAs.
dsRNA:
- RNA with two complementary strands is referred to as double-stranded RNA (dsRNA).
- Some viruses' genetic material is made up of dsRNA (double-stranded RNA viruses).
- In eukaryotes, double-stranded RNA, such as viral RNA, has been shown to cause RNA interference.
BIOLOGICAL ROLE OF NUCLEIC ACIDS
·
DNA is responsible for the storage
of genetic information.
·
Transfer of genetic
information:
·
RNA is responsible for the transfer
of genetic information necessary for protein production.
·
The template for protein synthesis
is mRNA.
· The ribosome, which is the site of protein synthesis, is made up of rRNA and proteins.
~1.webp)
