select the incorrect matching regarding the following diagram
TRANSCRIPT
Select the incorrect matching regarding the following diagram:
Which of the following possess heterocyclic ring?
(a) Adenine
(b) Guanine and Cytosine
(c) Thymine and Uracil
(d) All of these
Identify the nucleoside from the following:
A. Adenosine
B. Uridylic acid
C. Uridine
D. Cytidylic acid
(a) A and B only
(b) (b) A and C only
(c) C and D only
(d) B and C only
Which of the following acts as a genetic material?
(a) DNA and RNA
(b) Uridylic acid
(c) Adenylic acid
(d) Guanylic acid
Sugar + Nitrogen bases form
(a) Nucleoside
(b) Nucleotide
(c) Peptide
(d) Glycoside
Sugar + Nitrogen bases + Phosphate forms
(a) Nucleoside
(b) Nucleotide
(c) Peptide
(d) Glycoside
How many Nitrogen atoms are present in adenine?
(a) 3
(b) 4
(c) 5
(d) 6
DNA and RNA are
(a) Polypeptides
(b) Polynucleotides
(c) Polysaccharides
(d) All of these
How much percentage of total cellular mass is formed by nucleic acid?
(a) 3
(b) 2
(c) 5 to 7
(d) 10 to 15
Which of the following are purines?
(a) Adenine
(b) Guanine
(c) Cytosine
(d) Both (a) and (b)
Which of the following are pyramidine(substituted)?
(a) Cytosine
(b) Thymine
(c) Uracil
(d) All of these
DNA contains
(a) Ribose
(b) 3’ deoxyribose
(c) 5’ deoxyribose
(d) 2’ deoxyribose
The bond present between two nucleotides is known as
(a) Phosphoester linkage
(b) Phosphodiester linkage
(c) Glycosidic linkage
(d) Peptide linkage
The Watson-Crick Structure of DNA is
(a) 1° structure
(b) 2° structure
(c) 3° structure
(d) 4° Structure
Which of the following is correct about DNA?
(a) Double helical structure in which two strands of polynucleotide runs antiparallel.
(b) Backbone is formed by Sugar–Phosphate–Sugar chain.
(c) N2-bases projected more or less perpendicular to back bone and faces inside.
(d) All of these
Which one of the following is the diagrammatic representation of a nucleotide?
Which one is correct about the following diagram?
Which one is correct about DNA?
(a) DNA exist as double helix.
(b) Two strands of polynucleotide in DNA are antiparallel.
(c) The nitrogen bases are projected more or less perpendicular to this backbone but face
inside.
(d) All the above
At each step of an ascent in a B-DNA double helical structure, the strand turns _________.
(a) 36°
(b) 72°
(c) 90°
(d) 18°
One full turn of B-DNA helix strand would involve how many base pairs?
(a) 12
(b) 8
(c) 10
(d) 20
Select the incorrect statement from the following:
(a) N2-bases (A, G, C, T, U) have heterocyclic rings.
(b) In most of the organisms, the DNA is genetic material.
(c) Adenylic acid is nucleoside.
(d) The rise per base pair in B-DNA is 3.4A°.
There are _____ hydrogen bond between A and T, and _____ hydrogen bond between G and C.
(a) 2, 2
(b) 3, 3
(c) 2, 3
(d) 3, 2
When you take cells or tissue pieces and grind them with an acid in a mortar and pestle, all the small biomolecules dissolves in the acid. Proteins, polysaccharides and nucleic acids are insoluble in mineral acid and get precipitated. The acid soluble compounds include amino acids, nucleosides, small sugars, etc. When one adds a phosphate group to a nucleoside one gets another acid soluble biomolecule called
(a) Nitrogen base (b) Adenine(c) Sugar phosphate (d) Nucleotide
• Structure of DNA
- Primary structure
- Secondary structure of B DNA (and other types)
- Organization of chromosome
- Mitochondrial DNA
• Functions of DNA
• Experiment to show that DNA is genetic material
NUCLEIC ACIDS
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
26www.sblifescience.in
Nucleic Acids
• Nucleic acids are polymers of nucleotides.
Nucleic acid = (nucleotide)n
• Types:
1. DNA and
2. RNA
Deoxyribo Nucleic acid =(Deoxyribonucleotide)n
Ribo Nucleic acid = (Ribo nucleotide)n
Chemistry of nucleotides• Nucleotides have three characteristic
components:
(1) a nitrogenous (nitrogen-containing) base,
(2) a pentose, and
(3) a phosphate (or more in other nucleotides)
Nucleotide = nitrogenous base + pentose sugar + one or more phosphate
Nucleotides Are Nucleoside Phosphates.
Phosphate gp is attached to Ribose by ester bond
NITROGENOUS BASES – PURINE AND PYRIMIDINE BASES
Nitrogenous bases
1. Purine bases
- Adenine (6 – Amino Purine)
- Guanine (2 Amino 6 oxy purine)
2. Pyrimidine bases
- Cytosine (2-oxy, 4- amino pyrimidine)
- Uracil (2,4 Dioxy Pyrimidine)
- Thymine (2,4 Dioxy 5-methyl Pyrimidine)
6 – Amino Purine 2 Amino 6 oxy purine
2-oxy, 4- amino pyrimidine
2,4 Dioxy Pyrimidine
2,4 Dioxy 5-methylPyrimidine
PENTOSE SUGAR – monosaccharide with 5 carbon atoms
Nucleosides
• Nucleosides are formed when a base is linked to a pentose sugar via a glycosidic bond.
Nucleoside = nitrogenous base + pentose sugar
Bond – glycosidic bond
(b/w 1st C of Ribose and N9 of Purine/ N1 of Pyrimidine)
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Examples:RibonucleosidesAdenine + ribose = AdenosineGuanine + ribose = GuanosineCytosine + ribose = CytidiineUracil + ribose = UridineDeoxy ribonucleosidesAdenine + 2-deoxy ribose = 2-deoxy AdenosineGuanine + 2 - deoxy ribose = 2-deoxy GuanosineCytosine + 2-deoxy ribose = 2-deoxy CytidiineThymine + 2-deoxy ribose = 2-deoxy Thymidine
Chemistry of nucleotides• Nucleotides have three characteristic
components:
(1) a nitrogenous (nitrogen-containing) base,
(2) a pentose, and
(3) a phosphate (or more)
Nucleotide = nitrogenous base + pentose sugar + one or more phosphate
Nucleotides Are Nucleoside Phosphates.
Phosphate gp is attached to Ribose by ester bond
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Examples for nucleotides
1. RIBONUCLEOTIDES:
- containing Ribose as pentose
AMP – Adenosine Mono Phosphate, ADP, ATP.
GMP - Guanosine Mono Phosphate, GDP, GTP.
CMP - Cytidine Mono Phosphate, CDP, CTP.
UMP - Uridine Mono Phosphate, UDP. UTP.
Examples for nucleotides
2. Deoxy RIBONUCLEOTIDES.
dAMP – 2’ deoxy Adenosine Mono Phosphate
dGMP - 2’ deoxy Guanosine Mono Phosphate
dCMP – 2’ deoxy Cytidine Mono Phosphate
dTMP – 2’ deoxy Thymidine Mono Phosphate
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Structure of DNA
• DNA is polymer of deoxyribo nucleotides.
Deoxyribo Nucleic Acid= (deoxyribo nucleotide)n
Primary structure of DNA
• DNA is polymer of deoxyribo nucleotides.Deoxyribo Nucleic Acid= (deoxyribo nucleotide)n
• Nucleotides present in DNA are dAMP, dGMP, dCMP and TMP.
• Nucleotides are joined together by 3’5’ phosphodiester bond.
• DNA is double stranded structure.• Each strand has two ends namely 3’ end and
5’end.
Nucleotides present in DNA
Deoxy RIBONUCLEOTIDES.
dAMP – 2’ deoxy Adenosine Mono Phosphate (2’ Deoxy Adenylic acid)
dGMP - 2’ deoxy Guanosine Mono Phosphate (2’ Deoxy Guanylic acid)
dCMP – 2’ deoxy Cytidine Mono Phosphate (2’ Deoxy Cytidylic acid)
TMP – 2’ deoxy Thymidine Mono Phosphate (2’ Deoxy Thymidylic acid)
dA dG dT dC
Deoxyribonucleotides found in DNA
Double Helix model for the structureof DNA
• In 1953
• James Watson and Francis Crick
• Based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin.
Secondary structure of B DNA
1. Two strands are helically coiled. Helix is right handed.
2. The two strands of DNA are antiparallel;
- ie, one strand runs in the 5' to 3‘ direction and the other in the 3' to 5' direction (run in the opposite direction).
3. Two strands are complementary to each other.
A-T, G-C
4. The two strands are held together by hydrogen bonds formed between complementary bases.
A forms 2 bonds with TG forms 3 bonds with C
5. Chargaff’s rule:In a DNA double helix,A= T, G = C,A+ G = C + T
Number of purines = Number of Pyrimidines.Ratios between Adenine and Thymine and Guanine and
Cytosine are constant and equals one
6. A single turn contains ten base pairs.
• Each base pair occupies 0.34nm.
• The distance spanned by one turn(pitch) is 3.4nm. Angle between 2 neighbouring basepairs is 360
• The width ( diameter) of the helix is 2 nm.
7. There are two grooves
Major and minor
In these grooves, proteins interact with nucleotides.
8. Stability of helical structure is maintained by:
- H bonds formed between complementary bases
- Plane of one base pair stacks over the other in double helix.
Watson and Crick proposed a schemefor replication of DNA
• ‘‘It has not escaped our notice that
• the specific pairing we have postulated immediately suggests
• a possible copying mechanism for the genetic material’’
• (Watson and Crick, 1953).
Rosalind Franklin and Maurice Wilkins
• used x-ray diffraction to analyze DNA fibers
• From this it was deduced that DNA molecules are
- helical with two periodicities along their long axis,
• A primary one of 3.4 Å and a secondary one of 34 Å.
B DNA and other types of DNA
• There are many types of DNA based on secondary structure.
A DNA B DNA Z DNA
Z DNA
Left-handed double helix• Seen in the 5’ end of chromosomes• Longer and thinner than B-DNA• 12 bp per turn• Particularly seen in sequence of alternating
purine and pyrimidine- d(GC)n sequence• Sequences that are not strictly alternating
purine andpyrimidine also form Z DNA on methylation• Z-DNA influences gene expression and
regulation
Length of DNA double helix
6.6 × 109 bp × 0.34 × 10-9m
Total number of
Base pair
Distance between two
consecutive base pairxLength of
DNA =
= 2.2 metres.
Length of E. coli DNA is 1.36 mm. Calculate the number of
base pairs in E.coli?
Total number of
Base pair
Distance between two
consecutive base pairxLength of
DNA =
Total number of
Base pair Distance between two
consecutive base pair
---------------------
Length of DNA
=
0.34 × 10-9m
---------------------
1.36 x 10 -6 m
= = 4000
Organization of DNA in prokaryotes(such as E coli)
• Prokaryotes do not have a defined nucleus. • DNA is not scattered throughout the cell.• DNA is negatively charged.• DNA is held with some positively charged
proteins • DNA is present in a region termed as
‘nucleoid’. • The DNA in nucleoid is organised in large
loops held by proteins.
Nucleoid
How is it possible to keep long DNA inside nucleus?
• Length of DNA double helix in a human cell is 2.2 metres.
• Dimension of a typical nucleus is 10–6 m.
• Possible because of folding.
(Levels of) Organisation of DNA
• Nucleosome
• 10 nm chromatin fibril
• 30 nm chromatin fiber
• Chromosome (made up of DNA, Proteins and small amount of RNA)
Nucleosome (histones + 200 nucleotide pairs)
Types of histones
• Five types of histones have been identified:
• H1 - the linker histone,
• H2A, H2B,
• H3 and
• H4.
• Histones are rich in basic amino acids such as Lysine and Arginine.
Formation of nucleosome
• The core histones (H2A, H2B, H3, and H4), associate with DNA to form nucleosomes.
• There are about 200 nucleotide pairs in each nucleosome.
• Nucleosomes constitute the repeating unit of a structure in nucleus called chromatin.
• The nucleosomes in chromatin are seen as ‘beads-on-string’ structure when viewed under electron microscope (EM).
Nucleosomes inchromatin (Beads on string)
Beads = Nucleosomes string = chromatin
Theoretically how many such beads (nucleosomes) do you
imagine are present in a mammalian cell?
Total number of
Beads Number of base pairs in a
nucleosome
----------------------------------------
Total number of base pairs in
DNA in a mammalian cell
=
200
6.6 × 109 bp
---------------------= = 3.3 × 107
10 nm chromatin fibril
Many Nucleosomes form 10nm fibrils.
chromatin are threadlike Stained /coloured bodies seen in
nucleus.
30 nm chromatin fibers
Supercoils of Fibrils form 30nm chromatin fiber.
Chromosome structure
• DNA is supercoiled in a left-handed helix over histone octamer called Nucleosome.
• Many Nucleosomes form 10nm fibrils.
• Supercoils of Fibrils form 30nm chromatin fiber.
• Chromatin fibers are further supercoiled in chromosomes (100 folds)
NUCLEOSOME(HISTONE + DNA)
CHROMATIN FIBRIL
CHROMOSOME WITHSISTER CHROMATIDS
DNA
• Nucleosome is formed using DNA and histones.
• The beads-on-string structure in chromatin (firil)
• Chromatin fibril is packaged to form chromatin fibers.
• They are further coiled and condensed at metaphase stage of cell division to form chromosomes.
Non histone chromosomal proteins
• Packaging of chromatin at higher level requires Non-histone Chromosomal (NHC) proteins.
Euchromatin and heterochromatin
• Some region of chromatin are loosely packed (and stains light) and are referred to as euchromatin.
• The chromatin that is more densely packed and stains dark are called as Heterochromatin.
• Euchromatin is said to be transcriptionallyactive chromatin, whereas heterochromatin is inactive
Function of DNA
• DNA contains genetic information
- Contains information about primary structure of proteins (number and sequence of amino acids).
• DNA molecule serve as a template for
- transcription of the information into RNA and
- replication.
What percentage of DNA carries information?
• In total, only about 1.5% of human DNA is “coding” or exon DNA, carrying information for protein or RNA products.
• However, when the much larger introns are included in the count, as much as 30% of the human genome consists of genes.
Introns and exons
• Nontranslated DNA segments in genes are called intervening sequences or introns,
• The coding segments are called exons.• Few prokaryotic genes contain introns.• Another 3% or so of the human genome consists
of highly repetitive sequences, referred to as simple-sequence DNA or simple sequence repeats (SSR).
• These short sequences, generally less than 10 bplong, are sometimes repeated millions of times per cell.
How many base pairs and genes present in DNA of
human beings?
Haploid content of human DNA is 3.3 × 109 bp.
Where do we find DNA
• Nucleus in the form of chromosomes and
• In mitochondria.• Mitochondrial DNA codes for the
mitochondrial tRNAs and rRNAs and for a few mitochondrial proteins.
• In Chloroplast (in plants)
MitochondrialDNA (mtDNA)
• In human cells, mtDNA contains 16,569 bp and is a circular duplex.
• Each mitochondrion typically has two to ten copies of this mtDNA molecule,
• The number can rise to hundreds in certain cells • In a few organisms (trypanosomes, for example) each
mitochondrion contains thousands of copies of mtDNA,
• Organized into a complex and interlinked matrix known as a kinetoplast.
• Mitochondrial DNA codes for the mitochondrial tRNAs and rRNAs and for a few mitochondrial proteins.
• More than 95% of mitochondrial proteins are encoded by nuclear DNA.
• Mitochondria and chloroplasts divide when the cell divides.
• Their DNA is replicated before and during division, and the daughter DNA molecules pass into the daughter organelles.
Structure of RNA
Structure of RNA
RNA is polymer of ribonucleotides.
RNA = (ribonucleotides)n
Nucleotides present in RNA are AMP,GMP,CMP and UMP.
They are joined together by 3’5’ phosphodiesterbond.
RNA is single stranded. It has 2 ends namely 3’ end and 5’end.
Classes of RNA
Four main classes
1. messenger RNA (mRNA)- (3 - 5%),
2. transfer RNA (tRNA) – (15%),
3. ribosomal RNA (rRNA) highest – (70 – 88%), and
4. small RNAs.
Structure of mRNA
mRNA is polymer of ribonucleotides.
mRNA = (ribonucleotides)n
Nucleotides present in mRNA are AMP,GMP,CMP and UMP.
They are joined together by 3’5’ phosphodiesterbond.
mRNA is single stranded. It has 2 ends namely 3’ end and 5’end.
5’ 3’
7- METHYL GUANOSINE TRI PHOSPHATE
POLY ‘A’ TAIL
CODED REGION NCS(UTR)
NCS(UTR)
(200 -300)
• The 5' terminal is "capped" by a 7-
methyl guanosine triphosphate.
• Cap is involved in the recognition of mRNA by the translation machinery,
• helps stabilize the mRNA by preventing the attack of 5'-exonucleases
• the 3‘ end, has a tail made up of 200-300 adenylate residues known as poly(A) "tail“
• prevents the attack of 3'-exonucleases
• facilitates translation
• At the centre there is coded region.
• It carries information about the primary structure of protein (polypeptide).
• It starts with initiation codon ‘AUG’ and ends with one of the termination codons (UAA, UAG or UGA)
• On either side of coded region untranslatedregions (UTR) are present.
• The UTRs are present at both 5' -end (before start codon) and at 3' -end (after stop codon).
• They are required for efficient translation process.
Function of mRNA
• Carries information in a gene to the protein synthesizing machinery.
• as a template for protein synthesis (translation)
Total number of nucleotides in the coded region is equal to
the number of codons (plus one termination codon).
Each codon has 3 nucleotides. Therefore,
Total number of nucleotides
in coded region= Total number of amino acids x 3
Structure of tRNA
• Yeast alanine tRNA (tRNAAla) was the first to be completely sequenced,
• by Robert Holley in 1965.
• It contains 76 nucleotide residues,
• 10 of which have modified bases.
Structure of tRNA
tRNA is polymer of ribonucleotides.
tRNA = (ribonucleotides)n
Nucleotides present in tRNA are dAMP,dGMP,dCMP and dTMP.
They are joined together by 3’5’ phosphodiesterbond.
tRNA is single stranded. It has 2 ends namely 3’ end and 5’end.
tRNA molecule contains 76 -95 ribonucleotides.
Secondary structure of tRNA
• tRNA molecules contain four main arms.
• The acceptor arm terminates in the nucleotides CCA (CCA -5’ to 3’).
• The tRNA appropriate amino acid is attached, or "charged" onto, the 3'-OH group of the A moiety of the acceptor arm.
2. Anticodon arm – decides which amino acid is attached
3. The D (Di Hydro Uracil) arm,
4. TΨ C arm (TMP, Pseudo UMP, CMP), and
5. Extra arm (in most of the cases)
tRNAs compose roughly 20% of total cellular RNA.
Tertiary structure of tRNA
Tertiary structure resembles inverted “L”
Function of tRNA
• Transports amino acid to the ribosomes (to the site of protein synthesis)
tRNA– the Adapter Molecule
• Francis Crick postulated the presence of an adapter molecule
- that would on one hand read the code and
- on other hand would bind to specific amino acids. The tRNA, then called sRNA (soluble RNA) acts as an adapter molecule.
initiator tRNA
• For initiation of translation:
- there is a specific tRNA that is referred to as initiator tRNA (anticodon is UAC).
• There are no tRNAs for stop codons.
How many types of tRNA?
• Eukaryotic cytosol: 40 to 60 types of tRNAs
• Human mitochondria: 22 different tRNAsand
• Plant chloroplasts: about 30.
• The tRNAs, which accept the same amino acid are known as isoaccepting tRNAs.
Structure of rRNA
rRNA is polymer of ribonucleotides.
rRNA = (ribonucleotides)n
Nucleotides present in rRNA are AMP, GMP, CMP and UMP.
They are joined together by 3’5’ phosphodiester bond.
rRNA is single stranded. It has 2 ends namely 3’ end and 5’end.
Types of rRNA
• In Eukaryotes:1. 5S ribosomal RNA (rRNA), 2. 5.8S rRNA3. 18S rRNA; 4. 28S rRNA. 5.8 S ribosomal RNA, 18S ribosomal RNA, and
28 rRNA genes are typically organized as a co-transcribed operon.
In Prokaryotes:1. 16S, 2. 23S and3. 5S.Bacterial 16S ribosomal RNA, 23S ribosomal
RNA, and 5S rRNA genes are typically organized as a co-transcribed operon.
Function of rRNA
• Constituent of Ribosome.
Ribosome (rRNA + proteins)
• The mammalian ribosome contains two major nucleoprotein subunits—a larger one 60S sub unit and a smaller subunit 40S.
• The 60S subunit contains
a 5S ribosomal RNA (rRNA), a 5.8S rRNA, and a 28S rRNA;
there are also more than 50 specific polypeptides.
The 40S subunit is smaller and contains
a single 18S rRNA and approximately 30 distinct polypeptide chains.
Ribosome
80 S
Ribosome
40 S Ribosome
60 S Ribosome
5S ribosomal RNA (rRNA),
5.8S rRNA,
28S rRNA; and
more than 50 specific polypeptides
18S rRNA and
30 distinct polypeptide chains.
SMALL RNA
• Range in size from 20 to 300 nucleotides.
• Complexed with proteins to form ribonucleoproteins
• Distributed in the nucleus, the cytoplasm, or both.
Types of small RNA
1. Small Nuclear RNAs (snRNAs)
involved in rRNA and mRNA processing and gene regulation.
2. Micro-RNAs (miRNAs)
3. Small Interfering RNAs (siRNAs)
• miRNAs and siRNAs cause inhibition of gene expression and cause translation arrest.
Which is the first genetic material?
• RNA was the first genetic material.
• Essential life processes (such as metabolism, translation, splicing, etc.) evolved around RNA.
• RNA used to act as a genetic material as well as a catalyst (important biochemical reactions are catalysed by RNA catalysts).
•
Evolution of DNA from RNA
• RNA being a catalyst was reactive and hence unstable.
• Therefore, DNA has evolved from RNA with chemical modifications that make it more stable.
Why DNA resists changes?
• Because it is
1. Double stranded,
2. Having complementary strand,
3. Can undergo a process of repair.
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