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Title: Introduction to Molecular Biology


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

4
1- NUCLEOTIDES
  • 1- Importance of nucleotides
  • 2- Structure of nucleotides
  • 3- Metabolism of nucleotides
  • i. synthesis
  • ii. degradation

5
  • Importance of nucleotides
  • 1- Building units for nucleic acids (DNA RNA)
  • 2- Other roles in metabolism energy storage
  • (discussed later with metabolic pathways)

6
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
7
(No Transcript)
8
PURINE RING
C 6
N 7
N 1
C 5
C 8
C 2
C 4
N 3
N 9
9
Pyrimidine RING
C 4
N 3
C 5
C 2
C 6
N 1
10
b
11
  • Purines Adenine Guanine
  • Pyrimidines Cytosine, Thymine Uracil
  • DNA contains Adenine Guanine (purines)
  • Cytosine Thymine
    (pyrimidines)
  • RNA contains Adenine Guanine (purines)
  • Cytosine Uracil
    (pyrimidines)

12
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

13
Synthesis of purinesSources of atoms of purine
ring
14
Synthesis of pyrimidinesSources of atoms of
pyrimidine ring
15
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

16
Degradation (catabolism)End products of
pyrimidine ring degradation
  • Pyrimidine nucleotides are degraded to highly
    soluble products
  • b-alanine b-aminoisobutyrate

17
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

18
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

19
Structure of DNA molecule
20
Structure of Single strand of DNA
  • Building Units Polynucleotide sugar
    deoxyribose

  • 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
21
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

22
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)

  • IMPORTANCE ??
  • iv. in plant chroroplasts

23
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)
24
RNA
  • 1- Structure (differences from DNA)
  • 3- Types
  • 4- Importance of each type

25
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

26
Types Functions of RNA
27
Ribosomal RNA (rRNA)
80 of total RNA in the cell (most abundant
RNA) Location cytosol Function machine for
protein biosynthesis Types
28
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

29
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

30
complementary base-pair between DNA RNAin
transcription
31
  • 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)

32
Eukaryotic mRNA
5-end cap of 7-methylguanosine 3-end
poly-A tail
33
  • 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

  • termination (stop) codons

34
Genetic Code Table
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