Post on 14-Jul-2016
description
Nucleic acids are made up of polynucleotides – polymers of nucleotides.
There are two types of nucleic acids◦Deoxyribonucleic acid (DNA)◦Ribonucleic acid (RNA)
Genes◦Are the units of inheritance made up of DNA◦they consist of sequences of DNA nucleotides that
program the amino acid sequence of polypeptides
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Stores information for the synthesis of specific proteins◦Directs RNA synthesis◦Directs protein synthesis through mRNA
Exists as double stranded structure in the form of the double helix in cells and has a long life span
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2
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Synthesis of mRNA in the nucleus
Movement of mRNA into cytoplasm
via nuclear pore
Synthesisof protein
NUCLEUSCYTOPLASM
DNA
mRNA
Ribosome
AminoacidsPolypeptide
mRNA
Relationship between DNA, RNA and proteins
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Nucleic acids are polymers called polynucleotides
Each polynucleotide is made of monomers called nucleotides
Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups
The portion of a nucleotide without the phosphate group is called a nucleoside
Sugar-phosphate backbone5 end
5C
3C
5C
3C
3 end
(a) Polynucleotide, or nucleic acid
(b) Nucleotide
Phosphategroup Sugar
(pentose)
Nucleoside
Nitrogenousbase
5C
3C
1C
Nitrogenous bases
Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA)
Adenine (A) Guanine (G)
Sugars
Deoxyribose (in DNA) Ribose (in RNA)
(c) Nucleoside components
Pyrimidines
Purines
Nitrogenous bases
Cytosine (C)
Thymine (T, in DNA)
Uracil (U, in RNA)
Adenine (A) Guanine (G)
Sugars
Deoxyribose (in DNA)
Ribose (in RNA)
(c) Nucleoside components
Pyrimidines
Purines
Are made up of nucleosides and phosphate groups The phosphate group carries negative charges and as a result both
DNA and RNA are negatively charged The nucleosides are made up of nitrogenous bases and pentose
sugars There are 2 types of pentose sugars – deoxyribose (in DNA) and
ribose (in RNA) Nitrogenous bases contain nitrogen and act as bases by picking up
hydrogen ions The bases can be categorized into 2 groups – purines and
pyrimidines Purines consist of adenine (A) and Guanine (G) while pyrimidines
consist of cytosine (C), thymine (T) and uracil (U) There are 4 types of bases in DNA and RNA In DNA, the type of bases are – A, G, T and C In RNA, the type of bases are – A, G, C and U
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Are made up of nucleotides linked by the –OH group on the 3´ carbon of one nucleotide and the phosphate on the 5´ carbon on the next nucleotide through condensation reactions resulting in the formation of 5´ 3´ phosphodiester linkages
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Sugar-phosphate backbone5 end5C
3C
5C
3C
3 end(a) Polynucleotide, or nucleic acid
(b) Nucleotide
Phosphategroup Sugar
(pentose)
Nucleoside
Nitrogenousbase
5C
3C
1C
The sequence of bases/nucleotides along a nucleotide polymer◦ Is unique for each gene◦ Determines the sequence of amino acids for a
polypeptide chain
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Cellular DNA molecules◦ Have two polynucleotides that spiral around an imaginary
axis◦ Form a double helix held together by hydrogen bonding
The nitrogenous bases in DNA◦ Form hydrogen bonds in a complementary fashion (A
with T only, and C with G only)◦ Between A and T, there are 2 hydrogen bonds while
between G and C, there are 3 hydrogen bonds◦ Each turn of the double helix contains 10 pairs of bases
held together by hydrogen bonds
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Sugar-phosphatebackbonesHydrogen bonds
Base pair joinedby hydrogen bonding
Base pair joinedby hydrogen
bonding
(b) Transfer RNA(a) DNA
5 3
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Base pairing between the bases
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O
–O O
OH
O
–OO
O
H2C
O
–OO
O
H2C
O
–OO
O
OH
O
O
OT A
C
GC
A T
O
O
O
CH2
OO–
OO
CH2
CH2
CH2
5 end
Hydrogen bond3 end
3 end
G
P
P
P
P
O
OH
O–
OO
O
P
P
O–
OO
O
P
O–
OO
O
P
(b) Partial chemical structure
H2C
5 end
O
The DNA double helix◦ Consists of two antiparallel nucleotide strands which
are complementary to each other.
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3’ end
Sugar-phosphatebackbone
Base pair (joined byhydrogen bonding)Old strands
Nucleotideabout to be added to a new strand
A
3’ end
3’ end
5’ end
Newstrands
3’ end
5’ end
5’ end
Generally single stranded Has short life span Consist of the bases A,G,C and U. There are 3 main types of RNA:1. mRNA (messenger RNA) – transcribes the genetic
information from DNA2. rRNA (ribosomal RNA) – combines with proteins to
form ribosomes3. tRNA (transfer RNA) – transfers amino acids to the
growing polypeptide chains attached to ribosomes to aid in translation process
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Molecular comparisons ◦ Help biologists sort out the evolutionary connections
among species ◦ DNA and amino acid sequences can be compared to
establish evolutionary relationships
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