Download 1E Nucleic Acid

NUCLEIC
ACIDS
The roles of nucleic acid
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Made up of C,H,O,N,P
Most complex & largest molecule in living things. (Note
packing in the DNA)
There are two types of nucleic acids:
- deoxyribonucleic acid (DNA)
- ribonucleic acid (RNA)
Both found
in the
nucleus of
the cell
NUCLEIC ACIDS
2 types
Deoxyribonucleic Acid
(DNA)
Ribonucleic Acid
(RNA)
Nucleic Acids
• Nucleic acids are polymers called polynucleotides.
• Each polynucleotideis made of monomers called
nucleotides.
• Each nucleotide consists of a nitrogenous base, a
pentose sugar, and a phosphate group.
• The portion of a nucleotide without the phosphate
group is called a nucleoside.
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Fig. 5-27ab
5' end
5'C
3'C
Nucleoside
Nitrogenous
base
5'C
Phosphate
group
5'C
3'C
(b) Nucleotide
3' end
(a) Polynucleotide, or nucleic acid
3'C
Sugar
(pentose)
Fig. 5-27
5□ end
Nitrogenous bases
Pyrimidines
5□ C
3□C
Nucleoside
Nitrogenous
base
Cytosine (C)
Thymine (T, in DNA)
Uracil (U, in RNA)
Purines
Phosphate
group
5□ C
Sugar
(pentose)
Adenine (A)
3□ C
Guanine (G)
(b) Nucleotide
Sugars
3□ end
(a) Polynucleotide, or nucleic acid
Deoxyribose (in DNA)
(c) Nucleoside components: sugars
Ribose (in RNA)
NUCLEOTIDE
Pentose Sugar
Ribose
Deoxyribose
Nitrogenous
Base
Purine
Phosphate Group
Pyrimidine
Nitrogenous base
• Contain nitrogen atoms that give the basic nature of the
base.
• The nitrogenous bases in nucleotides consist of two
general types:
• Based on the number of C ring:
2 groups
Double rings
Single ring
Pyrimidine
Cytosine (C)
Purine
Uracil (U)
Thymine (T)
In RNA
In DNA
Guanine (G)
Adenine (A)
Learning Outcomes :
(a) Describe the structure of nucleotide as the basic composition of nucleic acid (DNA and
RNA)
Nitrogenous base
• Nitrogenous base in DNA:
i. Guanine
ii. Adenine
iii. Thymine
iv. Cytosine
• Nitrogenous base in RNA:
i. Guanine
ii. Adenine
iii. Uracil
iv. Cytosine
Pentose Sugars
• There are two related pentose sugars (5C):
- RNA contains ribose (C5H10O5).
- DNA contains deoxyribose (C5H10O4).
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Phosphate Group
• Joined by condensation to the pentose sugar–gives the
nucleic acids their acidic property.
Nucleotides
• Nucleotide – an organic compound composed of 3
sub-units namely sugar unit, phosphate unit &
nitrogenous base joined together by condensation.
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Nucleotides
• ATP is another type of nucleic acid and
hence it is structurally very similar to the
nucleotides that make up DNA and RNA.
• Adenosine triphosphate (ATP) is the
energy-carrying molecule that provides
the energy to drive many processes inside
living cells
• Adenosine (a nucleoside) can be
combined with one, two or three
phosphate groups
• One phosphate group = adenosine
monophosphate (AMP)
• Two phosphate groups = adenosine
diphosphate (ADP)
• Three phosphate groups = adenosine
triphosphate (ATP)
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Reading Primary Structure
• A nucleic acid polymer has
a free 5’-phosphate group
at one end and a free 3’OH group at the other end
• The sequence is read from
the free 5’-end using the
letters of the bases
• This example reads
5’—A—C—G—T—3’
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Example of DNA Primary Structure
• In DNA, A, C, G, and T are linked by 3’-5’ ester bonds
between deoxyribose and phosphate.
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Polymerization of Nucleic Acids
Nucleic acid is a polynucleotide that consists
of a chain of nucleotides such as DNA and
RNA.
❖ Nucleotides form polynucleotides through
condensation/dehydration reaction with the
formation of phosphodiester bonds.
❖
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Formation of a polynucleotide chain.
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Chemical structures of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
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DNA
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Deoxyribonucleic acid
Found in nucleus, mitochondrion, & chloroplast.
Carries the instructions for cell activities
Established by James Watson and Francis Crick
DNA has two polynucleotides chain twisted to
form a double helix.
The two strands are anti-parallel with opposite
direction.
It has a uniform diameter of 2 nm.
Each polynucleotide is composed of millions of
nucleotides in which the sugar is deoxyribose and
the bases are A, C, G and T.
Nucleotides are joined together by
phosphodiester linkage.
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What are these instructions?
•GENES
WHAT DO OUR GENES
GIVE US? Our characteristics or traits
Cleft Chin
Dominant (1 copy)
Recessive- 2 copies
Dimples
Dominant
Recessive
Free earlobes
Dominant
Attached Earlobes
Recessive
Face freckles
dominant
No face freckles
recessive
No Hitchhiker's
thumb dominant
Hitchhiker's
thumb recessive
Widow's peak
dominant
No Widow's
peak recessive
HOW MANY GENES
DO WE HAVE?
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Thousands on ______
chromosomes
How does DNA carry the genes?
• The structure of DNA
allows it to carry the
genetic code
• It is a double helix made
of repeating nucleotides
What make
up the DNA ladder sides?
• Sugar-phosphate forms the backbone.
• The 2 backbones are on the outside,
the nitrogenous bases are paired
inside the helix.
What bases make
up the DNA ladder
steps?
• Adenine
• Thymine
• Guanine
• Cytosine
DNA Structure
• Both chains are held together by
5'
3'
hydrogen bonds between
complementary base pair;
• Adenine with Thymine, Cytosine
with Guanine
• Between Adenine & Thymine ~ 2
hydrogen bonds
• Between Cytosine & Guanine ~ 3
hydrogen bonds
• Specific base-pairing rule
~ the numbers of A=T, G=C
3'
5'
DNA Structure
5'
• 2 polynucleotide chains are
3'
arranged in opposite
direction (antiparallel).
• One strand ends with a 3’
hydroxyl group while the
other strand ends with a 5’
phosphate group.
3'
5'
Think of the bases of DNA like letters.
Letters form words....
Words form sentences....
*endless
combinations
How the Code Works
The combination of A,T,G,C determines what
traits you might have, for ex.
C A T C A T = purple hair
T A C T A C = yellow hair
WHAT PART OF DNA CARRIES THE
GENETIC CODE?
The base sequence holds the genetic
code.
• An important observation was made by Chargaff : the
the amount of guanine is equal to cytosine and the
amount of adenine is equal to thymine
• This led to the realisation that the hydrogen bonding
interactions between specific base pairs was important
:
A=T and G≡C
• These interactions are shown below:
Chargaff’s Rule
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RNA
• Ribonucleic acid
• Found in nucleus & cytoplasm (associated with
ribosomes)
• Nitrogenous bases are A, G, C, and U.
• Sugar in RNA is ribose
• Exist as single strands
• Hydrogen bonds are formed between pairs of A
with U and between pairs of C with G.
• RNA function in the polypeptide synthesis.
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Example of RNA Primary Structure
• In RNA, A, C, G, and U are linked by phosphodiester
bonds between ribose and phosphate
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Types of RNA
• 3 types: (involved in protein synthesis)
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mRNA
Function :
• Carries genetic information copied from
DNA which act as a template for protein
synthesis.
Transcription (formation of messenger RNA).
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rRNA
Function :
• Forms ribosomal subunits (together with proteins).
tRNA
Function :
• Transfer specific amino acids to ribosome during protein
synthesis
The cloverleaf structure for
tRNA molecules.
Structural elements include
three loops formed by hairpin
turns and double-helix regions
stabilized by hydrogen bonding
between complementary bases.
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Let's Review What We Know About DNA
1. DNA stands for: De _____ ribo ______ acid
2. What is the shape of DNA? _______________
3. Who established the structure of DNA? ____________
4. Adenine always pairs with _______________
5. The sides of the DNA ladder are deoxyribose and _____
6. Guanine always pairs with _____________
7. What is the complimentary sequence: A A T G C A
8. The two sides of DNA are held together by _______
bonds.
9. DNA is composed of repeating subunits called
______________________
10. What are the 4 bases that make up the rungs of the DNA
ladder? _______________________________________