Dr. Tarek El Sewedy
Department of Medical Laboratory Technology
Faculty of Allied Medical Sciences
Nucleic Acids
Structure and Function
Intended Learning Outcomes
By the end of this lecture, students will learn:
 Recognize the structure of nucleosides and nucleotide.
 Identify functions of nucleotides.
 Recognize the structure of DNA and RNA.
 Learn Polymerase chain reaction (PCR)
 Identify the biological importance of DNA and RNA.
Lecture Content
• Nitrogenous bases (Purines and Pyrimidines)
• Nucleosides
• Nucleotides
• Nucleic acids (DNA and RNA) Structure and function
• Polymerase chain reaction
Nucleic Acid Structure
A. Nitrogenous
Base
+
Ribose Sugar
=
B. Nucleosides
Nucleosides
Nucleotide
+
+
Phosphate
Nucleotide
=
=
C. Nucleotides
D. Nucleic Acid
DNA & RNA
Purines and pyrimidine
•
Purines and pyrimidine bases are nitrogen-containing heterocycles
compounds whose rings contain both carbon and Nitrogen (hetero
atoms).
•
The smaller pyrimidine has the longer name and the larger purine the
shorter name
• Nucleosides consist of nitrogenous base bound to a ribose (RNA) or
deoxyribose sugar (DNA) via a glycosidic bond.
consists of a nucleoside (Nitrogenous base and sugar)
bonded to one or more phosphate groups.
Base
Nucleoside
Nucleotide
Adenine
Adenosine
Adenosine M.P
Guanine
Guanosine
Guanosine M.P
Cytosine
Cytidine
Cytidine M.P
Thymine
Thymidine
Thymidine M.P
Uracil
Uridine
Uridine M.P
1. Nucleotides are the monomers or building blocks of nucleic acids (DNA and RNA).
2.
Adenosine triphosphates ATP is the central cellular energy source.
3.
Forming important coenzymes such as NAD+, NADP+, FAD and co A.
4.
Intermediates in lipids, carbohydrates and protein biosynthetic reactions.
5.
Cyclic nucleotides are 2nd messenger and regulators of many cellular metabolic
pathways.
Adenosine tri-phosphate (ATP)
energy source for many reactions in living organisms.
Phosphates are well-known high-energy molecules, meaning that high levels of energy
are released when the phosphate groups are removed
They are polymers of nucleotides.
They carry genetic information within cells.
They are usually either single-stranded or double-stranded.
They are made of three components,
1. nitrogenous bases (purines and pyrimidine)
2. 5-carbon sugars (Ribose in RNA or deoxyribose in DNA)
3. phosphate groups.
Adenine, guanine, and cytosine are found in both RNA and DNA, while thymine
occurs only in DNA and uracil only in RNA.
*
Ribose Sugar
Deoxyribose Sugar
(1) In RNA, the sugar moiety to which the phosphates and purine and pyrimidine bases are
attached is ribose rather than the 2′-deoxyribose of DNA.
(2) The pyrimidine components of RNA differ from those of DNA. Although RNA contains the
ribonucleotides of adenine, guanine, and cytosine, it does not possess thymine. Instead of
thymine, RNA contains the ribonucleotide of uracil.
(3) RNA exists as a single strand, whereas DNA exists as a double-stranded.
(4) Since the RNA molecule is a single strand its guanine content does not necessarily equal its
cytosine content, nor does its adenine content necessarily equal its uracil content.
• Base pairing between Adenosine (A) and Thymidine (T) involves the formation of
two hydrogen bonds.
• Three hydrogen bonds are formed between Cytosine (C) and Guanosine (G)
* Double helix
* The bases occupy the centeral
core of helix
* Sugar –phosphate
run along
external backbone.
* Complementary base pairing
(G binds C),(A binds T)
* The length of DNA
by bp and Kb.
is measured
-The Main Function of DNA can be summarized in:
Carrying the genetic information for all
biological functions of the cell.
RNA plays essential role in Protein Biosynthesis
Through the 3 types mentioned above
* Although the structure of DNA is the same throughout all species of plants,
animals and microorganisms, each individual organism looks different. This
is due to the DNA base pairs sequence. Not only does this order make you a
human rather than a dog or a monkey, it also makes each person unique.
* Sequences of DNA differ from person to person, but every cell within the
same person contains the same sequence of DNA. So, your hair, blood, skin
and all of the other cells in your body are exactly the same at the
molecular level.
* Inside cells During DNA replication the two strands of the DNA must be separated
from one another by enzymes called helicases that uses chemical energy (from ATP).
* In the laboratory, DNA can be disrupted by heating DNA. The heating disrupts the
hydrogen bonds between base pairs and thereby causes the strands to separate.
* Separated complementary strands of nucleic acids spontaneously reassociate to
form a double helix when the temperature is lowered below T m. This renaturation
process is sometimes called annealing.
* The ability to denature and reanneal DNA in the laboratory provides a powerful tool
for some molecular biology techniques such as Polymerase chain reaction (PCR).
•
PCR allows scientists to amplify and analyze bits of DNA from trace
amounts of DNA samples.
•
PCR is an essential element in DNA fingerprinting and in the
sequencing of genes and entire genomes. Basically, It’s like a
technique to photocopy pieces of DNA. In a matter of a few hours, a
single DNA sequence can be amplified to millions of copies.
*
* Typically, PCR consists of a series of 20-40 repeated
temperature changes, called cycles, with each cycle
commonly consisting of 3 discrete temperature steps
1. Denaturation.
2. Annealing.
3. Extension.
* Stage one is a hot stage
called denaturation At 90◦C
temperature opens up the
DNA for copying.
* Stage two is a cooling or
annealing that permits the
DNA to attach to chemicals
needed to copy it.
*
Stage three is a warm
temperature cycle called the
extension. It encourages the
growth of the DNA strand.
* DNA template that contains the DNA region (target) to be
amplified.
* Two primers
that are complementary to the 3' (three prime)
ends of each of the sense and anti-sense strand of the DNA
target.
* Taq polymerase or another DNA polymerase with a
temperature optimum at around 70 °C.
* Deoxynucleoside triphosphates dNTPs, the building blocks
from which the DNA polymerases synthesizes a new DNA
strand.
* Buffer solution, providing a suitable chemical environment
for optimum activity and stability of the DNA polymerase.
* Medicine: Detection of mutations in genes causing tumor.
* Infectious disease: early diagnosis of viruses such as AIDS.
* Forensic: Human DNA fingerprinting.
* Research: identification of certain DNA or RNA regions.
*
* Write three points about :
* i-Function of nucleotides
* 1* 2* 3* Correct the incorrect word:
* Nucleosides are made from a ring of nitrogen, carbon and
oxygen atoms together with a six-carbon sugar.
* DNA is polymer of nucleotides and contains ribose sugar.
Choose:
1-Nucleotide consists of
* a-Sugar+ Nitrogenous base+phosphate group
* B- Nitrogenous base+phosphate group.
* C- Sugar+ Nitrogenous base
2- DNA is polymer of
 a-Nucleoside
 b-Nucleotides
 c-Nitrogenous base
Principles of Biochemistry, Donald J. Voet, Judith
G. Voet, Charlotte W. pratt; Willey, 3rd ed.