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 rules in metabolism & energy storage
(e.g. ATP is a nucleotide)

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

8. PURINE RING C 6 N 7 N 1 C 5 C 8 C 2 C 4 N 3 N 9
Purine ring in adenine & guanine

9. Pyrimidine RING N C N C C C 4 3 5 2 6 1
Pyrimidine ring in thymine, cytosine & uracil

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 purines: Sources of atoms of purine ring

14. Synthesis of pyrimidines: Sources 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, the case is called HYPERURICEMIA
Hyperuricemia may lead to GOUT
GOUT is a disease affects joints (arthritis) & kidneys (kidney stones) caused by deposition of uric acid in these tissues

16. Pyrimidine nucleotides are degraded to highly soluble products :
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
DNA molecule is formed of double helical strands.
(Dounble helix)
The two strands are held together by hydrogen bonds
Each single strand is formed of polynucleotides
Polyncleotides are mononucleotides bound to
each other by phosphodiester bonds

20. Structure of Single strand of DNA
Building Units: Polynucleotide sugar: deoxyribose
Base: Purine: A or G OR Pyrimidine: T or C
Phosphoric acid
Mononucleotides are bound together by phosphodiester bonds
In linear DNA Strand : two ends (5` = phosphate & 3` = OH of deoxyribose)
In circular strand: no ends

21. Structure of Single strand of DNA
Sequence
of DNA

22. Structure of double stranded DNA
Hydrogen bonds link
the two single strands together
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 leading to formation of two separate single strands)
Causes of denaturation : heating or change of pH of DNA

23. Linear & Circular DNA 1- Linear DNA 2- Circular DNA
in nucleus of eukaryotes (including human cells)
i.e. DNA of chromosomes
2- Circular DNA
i. in eukaryotes: mitochondria
ii. in prokaryotic chromosomes (nucleoid of bacteria)
iii. in plasmids of bacteria (extrachromosomal element)
iv. in plant chroroplasts

24. DNA Synthesis (Replication)
OLD
DNA
DUPLEX
(PARENTAL)
DNA synthesis (replication) is the synthesis of new DNA (daughter) duplexes using a template of old (parental) DNA duplex
The two strands of the parental DNA double helix are separated, each can serve as a template for the replication of a new
Complementary (daughter) 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
DAUGHTER
DNA
DUPLEXES

25. RNA 1- Structure (differences from DNA) 3- Types
4- Importance of each type

26. Structure of RNA
Building units: Polynucleotides (bound together by PDE)
Single strand
Linear (but may fold into complex structure)
with two ends: `(phosphate) & 3`(-OH end)
Sugar: Ribose
Purine bases: Adenine & Guanine
Pyrimidine bases: Cytosine & Uracil

27. Types & Functions of RNA

28. Ribosomal RNA (rRNA) Function: machine for protein biosynthesis
80% of total RNA in the cell (most abundant RNA)
Location: cytosol
Function: machine for protein biosynthesis
Types:

29. 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

30. Transcription + Translation
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

31. complementary base-pair between DNA & RNA in transcription

32. 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)

33. Eukaryotic mRNA
5`-end: cap of 7-methylguanosine
3`-end: poly-A tail

34. The Genetic Code Each individual word of the 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

35. Genetic Code Table