Introduction to Molecular Biology

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Introduction to Molecular Biology
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MOLECULAR BIOLOGY
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• 1- Nucleotides
• 2- DNA
• 3- RNA

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1- NUCLEOTIDES

• 1- Importance of nucleotides
• 2- Structure of nucleotides
• 3- Metabolism of nucleotides
• i. synthesis
• ii. degradation

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• Importance of nucleotides
• 1- Building units for nucleic acids (DNA RNA)
• 2- Other roles in metabolism energy storage
• (discussed later with metabolic pathways)

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Structure of nucleotides
Nucleotides nitrogenous base sugar
phosphate (1,2 or 3) Nitrogenous base Purine
OR Pyrimidine Sugar Ribose OR
Deoxyribose Purine Adenine OR
Guanine Pyrimidine Thymine, Cytosine OR
Uracil
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(No Transcript)
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PURINE RING
C 6
N 7
N 1
C 5
C 8
C 2
C 4
N 3
N 9
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Pyrimidine RING
C 4
N 3
C 5
C 2
C 6
N 1
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b
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• Purines Adenine Guanine
• Pyrimidines Cytosine, Thymine Uracil
• DNA contains Adenine Guanine (purines)
• Cytosine Thymine
  (pyrimidines)
• RNA contains Adenine Guanine (purines)
• Cytosine Uracil
  (pyrimidines)

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Metabolism of nucleotides

• 1- Synthesis (anabolism)
• i. sources of purine ring atoms
• ii. sources of pyrimidine ring atoms
• 2- Degradation (catabolism)
• i. end products of purine ring
• ii. end product of pyrimidine ring

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Synthesis of purinesSources of atoms of purine
ring
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Synthesis of pyrimidinesSources of atoms of
pyrimidine ring
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Degradation (catabolism)End products of purine
ring degradation

• In human cells purine nucleotides is finally
  degraded to URIC ACID
• Uric acid is transported in blood to kidneys
• Finally, Uric acid is excreted in urine
• If uric acid is increased in blood ---
  HYPERURICEMIA (CAUSES??)
• Hyperuricemia may lead to --------- GOUT
• GOUT is a disease affects joints (arthritis)
  kidneys (kidney stones) caused by deposition of
  uric acid in tissues

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Degradation (catabolism)End products of
pyrimidine ring degradation

• Pyrimidine nucleotides are degraded to highly
  soluble products
• b-alanine b-aminoisobutyrate

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DNA

• 1- Importance of DNA
• 2- Location of DNA in human cells
• 3- Structure of DNA molecule
• - Structure of a single strand of
  DNA
• - Structure of double stranded DNA
• - Linear circular DNA

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Importance of DNA

• 1- Storage of genetic material information
• (material of GENES)
• 2- Transformation of genetic information to new
  cells
• (template for REPLICATION)
• i.e. synthesis of new DNA for new cells
• 3- Transformation of information for protein
  synthesis
• in cytosol (template for TRANSCRIPTION)
• i.e. synthesis of mRNA in nucleus

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Structure of DNA molecule
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Structure of Single strand of DNA

• Building Units Polynucleotide sugar
  deoxyribose
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  Purine A G Pyrimidine T C
• Polynucleotides are bound together by
  phosphodiester bonds
• If linear DNA two ends (5 phosphate 3
  OH of deoxyribose)
• If circular no ends

Sequence of DNA
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Structure of double stranded DNA

• Two strands are anti-parallel (in opposite
  directions)
• Hydrogen bonds between bases of opposite strands
  (A T , C G)
• Denaturation breakdown (loss) of hydrogen
  bonds between two strands
• (melting) leading to formation of
  two separate single strands)
• Causes of
  denaturation ?? IMPORTANCE ?? e.g. PCR
• heating or change
  of pH of DNA

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Linear Circular DNA

• 1- Linear DNA
• in nucleus of eukaryotes (include. Human
  cells)
• i.e. chromosomes
• 2- Circular DNA
• i. in eukaryotes mitochondria
• ii. in prokaryotic chromosomes (nucleoid of
  bacteria)
• iii. in plasmids of bacteria
  (extrachromosomal element)
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  IMPORTANCE ??
• iv. in plant chroroplasts

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Replication
Semiconservative replication When the two
strands of the DNA double helix are separated,
each can serve as a template for the replication
of a new complementary strand. Each of the
individual parental strands remains intact in one
of the two new Duplexes (i.e. one of the parental
strands is conserved in each of the two new
dublexes)
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RNA

• 1- Structure (differences from DNA)
• 3- Types
• 4- Importance of each type

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Structure of RNA

• Building units Polynucleotides (bound
  together by PDE)
• Single strand
• Linear (but may fold into complex structure)
• with two ends 5(phosphate) 3(-OH
  end)
• Sugar Ribose
• Purine bases Adenine Guanine
• Pyrimidine bases Cytosine Uracil

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Types Functions of RNA
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Ribosomal RNA (rRNA)
80 of total RNA in the cell (most abundant
RNA) Location cytosol Function machine for
protein biosynthesis Types
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Transfer RNA (tRNA)

• Smallest of RNAs in cell 4S
• Location cytosol
• At least one specific tRNA for each
• of the 20 amino acids found in
• proteins
• with some unusual bases
• with intrachain base-pairing (to
• provide the folding structure of
• tRNA)
• Function
• 1- recognizes genetic code word on
• mRNA
• 2- then, carries its specific amino
• acid for protein biosynthesis

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Messenger RNA (mRNA)

• synthesized in the nucleus (by transcription)
• DNA (the gene) is used a template for mRNA
  synthesis
• mRNA is synthesized complementary to DNA
  but in RNA
• language i.e. U instead of T
• So, if A in DNA it will be U in RNA , if T
  in DNA it will be A in
• mRNA.etc
• Carries the genetic information from the nuclear
  DNA (gene) to the
• cytosol
• In the cytosol, mRNA is used as a template for
  protein biosynthesis by ribosomes (with help of
  tRNA). This is called Translation or Protein
  Biosynthesis)
• Transcription Translation
• GENE EXPRESSION

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complementary base-pair between DNA RNAin
transcription
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• Types of mRNA
• Polycistronic mRNA
• One single mRNA strand carries information
  from more than one gene (in prokaryotes)
• Monocistronic mRNA
• one single mRNA strand carries information
  from only one gene (in eukaryotes)

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Eukaryotic mRNA
5-end cap of 7-methylguanosine 3-end
poly-A tail
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• The Genetic Code
• is a dictionary that identifies the
  correspondence between a sequence of nucleotide
  bases a sequence of amino acids
• Each individual word of the code
• is called a codon
• a codon is composed three nucleotide bases
• in mRNA language (A, G, C U)
• in 5-3 direction e.g. 5-AUG-3
• The four bases are used by three at a time to
  produce 64 different combinations of bases
• 61 codons code for the 20 common amino
  acids
• 3 codons UAG, UGA UAA do not code for
  amino acids but are
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  termination (stop) codons

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Genetic Code Table