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DNA structure, RNA structure

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Molecular biology basic- DNA, RNA structure, chargaff rule, nucleic acids, ATP, watson and crick model, types of DNA- A DNA, B DNA. Z DNA, types og rna – PowerPoint PPT presentation

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Title: DNA structure, RNA structure


1
Molecular biology
  • Unit 2
  • By Pallavi Bohra

2
Nucleic acid
  • Nucleic acids allow organisms to transfer genetic
    information from one generation to the next. 
  • First discovered by Friedrich Miescher from the
    nuclei of the pus cell from discarded surgical
    bandages and called it nuclein.
  • There are two types of nucleic acids
    deoxyribonucleic acid, better known as DNA and
    ribonucleic acid, better known as RNA.
  • When a cell divides, its DNA is copied and passed
    from one cell generation to the next generation.

3
Nucleic acid continue..
  • Nucleic acids are composed of nucleotide
    monomers.
  • Nucleotides contain three parts.
  • A Nitrogenous Base
  • A Five-Carbon Sugar
  • A Phosphate Group
  • DNA consists of the four nitrogenous
    bases adenine (A), guanine (G), cytosine (C),
    and thymine (T).

4
Nucleic acid continue.
  • DNA and RNA each consists of four different
    nucleotides.
  • All nucleotides have a common structure
    a phosphate group linked by a phosphoester bond
    to a pentose (a five-carbon sugar molecule) that
    in turn is linked to an organic base.
  • In RNA, the pentose is ribose in DNA, it
    is deoxyribose.
  • The bases adenine, guanine, and cytosine are
    found in both DNA and RNA thymine is found only
    in DNA, and uracil is found only in RNA.

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Nucleosides and nucleotides
Base Ribonucleoside Deoxyribonucleoside
Adenine Adenosine (A) deoxyadenosin (dA),
Guanine Guanosine (G) deoxyguanosine (dG)
Cytosine Cytidine (C) deoxycytidine(dC)
Uracil Uridine (U) deoxyuridine(dU)
Thymine Ribothymine (T) Deoxythymidine(dT)
Base Ribonucleotide Deoxynucleotide
Adenine AMP,ADP,ATP dAMP,dADP,dATP
Guanine GMP,GDP,GTP dGMP,dGDP,dGTP
Cytosine CMP,CDP,CTP dCMP,dCDP,dCTP
Uracil UMP,UDP,UTP dUMP,dUDP,dUTP
Thymine rTMPTDP,TTP dTMP,dTDP,dTTP
8
Chemical structure of ATP
ATP -gt ADP P energy, orATP -gt AMP 2P
energy
9
Polynucleotide
  • Polynucleotide formed by condensation of two or
    more nucleotides.
  • Occurs between the alcohol of a 5 phosphate of
    one nucleotide and 3-hydroxyl of a second with
    the elimination of H2O, forming a phosphodiester
    bond.
  • The primary structure of DNA and RNA proceeds in
    5 to 3 direction.
  • Common presentation 5-pGpApTpC-3

10
Polynucleotide
11
Watson and crick model
  • In 1953 using x-ray diffraction
  • Nobel prize
  • Watson and crick ds helix model describe the
    features of B form of DNA
  • Other forms are A and Z

12
Watson and crick model
13
DNA double helix
14
Types of DNA
15
Types of DNA
  • B- DNA
  • The B-form of DNA is the most common form of
    DNA. 
  • The B-DNA when compared to the A-DNA is more
    narrower and elongated. 
  • The major groove is wider and is more accessible
    to proteins. 
  • The minor groove is narrow.  
  • Helix diameter  23.7 Å
  • Rise per Base pair  3.4 Å 
  • Base-pair per helical turn 10 

16
Types of DNA
  • A- DNA
  • A-form of DNA are shorter and wider than the
    B-DNA.
  • Most of the RNA and RNA-DNA duplex are found
    in this form. 
  • The major groove is deep and narrow and is not
    easily accessible to proteins. 
  • The minor groove is wide, shallow is accessible
    to proteins. 
  • The base pairs are tilted to the helical axis. 
  • Helix diameter 25.5 Å
  • Rise per base pair 2.3 Å
  • Base pair per helical turn  11

17
Types of DNA
  • Z-DNA
  • Z-form of DNA has left handed sense. 
  • This structure of DNA is more narrower and
    elongated than A or B helix. Major groove is not
    prominent.
  • The minor groove is narrow. 
  • The base pairs are nearly perpendicular to helix
    axis. 
  • Helix Diameter 18.4 Å
  • Rise per base pair 3.8 Å 
  • Base pair per helical turn  12

18
Types of DNA
19
DNA Biological Functions
  • Proteins
  • DNA carries the codes for proteins. However, the
    actual protein differs a lot from the codes
    present on the DNA. The basic steps include
  • Transcription
  • Translation
  • DNA replication
  • DNA inheritance

20
RNA
  • RNA- Ribonucleic acid, a nucleic acid present in
    all living cells. Its principal role is to act as
    a messenger carrying instructions from DNA for
    controlling the synthesis of proteins, although
    in some viruses RNA rather than DNA carries the
    genetic information.

21
RNA structure
22
RNA type Functions
mRNA Carries genetic information copied from DNA in form of three base code
tRNA Transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation.
rRNA In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis. 
SnRNA Found with nucleus of eukaryotic cells. Involve in RNA splicing and maintain the telomeres.
23
RNA type Functions
Small silencing RNA 20-30 nt. First discovered in 1993 Regulate biological pathways Types-SiRNA, miRNA, and Piwi-interacting RNA
Tm RNA Only found in bacteria Recognizes ribosomes that have trouble translating or reading an mRNA, unfinished protein that may detrimental to the cell. TmRNA help in destructing or proteolysis of these unfinished RNA or protein .
24
rRNA
25
mRNA
26
tRNA
27
RNA silencing
  • RNA interfence- RNA silencing-post-transcriptional
    gene silencing or RNA interference  gene
    silencing, effects by which the expression of one
    or more genes is down regulated or entirely
    suppressed by small RNAs- si,mi and pi RNA

28
Function of SiRNA
  • Potential to be used for therapeutic purposes
    where disease-causing genes are selectively
    targeted and suppressed.
  • Eg. Cancer, HIV infection and hepatitis.

29
Ribozymes
  • Ribozymes (ribonucleic acid enzymes), also
    termed catalytic RNA, are RNA molecules that are
    capable of catalyzing specific biochemical
    reactions, similar to the action of
    protein enzymes.
  • 1982 discovery
  • Ribozymes demonstrated that RNA can be both
    genetic material (like DNA) and a
    biological catalyst (like protein enzymes).
  • Contributed to the RNA world hypothesis, which
    suggests that RNA may have been important in the
    evolution for its self-replicating systems.
  • Discovered by Sidney Altman and Thomas Czech, who
    were awarded the Nobel Prize in Chemistry in
    1989.

30
Ribozymes
  • Function
  • Ribozymes function (as part of the large subunit
    ribosomal RNA) to link amino acids during protein
    synthesis.
  • Includes  RNA splicing- spliceosome
  • Hammerhead ribozymes
  • VS ribozymes
  • Leadzymes
  • Hairpin ribozymes

31
spliceosome
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