6.1.3
Polynucleotides
Structure of DNA and RNA
Structure of DNA and RNA
A DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs. RNA, on the other hand, is made up of only one polynucleotide.


DNA structure
DNA structure
- DNA is made up of two polynucleotide chains arranged in a double helix structure.
- The sugar and phosphate lie on the outside of the helix and form the DNA's backbone.
- The nitrogenous bases are stacked in the inside of the helix, like a pair of staircase steps.
- Hydrogen bonds hold the base pairs together.


RNA structure
RNA structure
- An RNA molecule is a relatively short polynucleotide chain.
- RNA only has one polynucleotide chain.
- RNA is comprised of ribonucleotides that are linked by phosphodiester bonds.
Specific Base Pairing
Specific Base Pairing
Only certain types of base pairing are allowed.
 - Edited (1)-min,h_400,q_80,w_640.png)
 - Edited (1)-min,h_400,q_80,w_640.png)
Base pairing in DNA
Base pairing in DNA
- Adenine (A) can pair with thymine (T).
- Guanine (G) can pair with cytosine (C).
- This means that there is always an identical number of adenine and thymine bases and of guanine and cytosine bases in DNA.
 - Edited (1)-min,h_400,q_80,w_640.png)
 - Edited (1)-min,h_400,q_80,w_640.png)
The base complementary rule
The base complementary rule
- The base complementary rule states that the DNA strands are complementary to each other.
- If the sequence of one strand is AATTGGCC, the complementary strand would have the sequence TTAACCGG.


Types of bonding in DNA and RNA
Types of bonding in DNA and RNA
- Base pairing holds the two DNA polynucleotides together by hydrogen bonding.
- The single polynucleotide chain is held together by phosphodiester bonds between nucleotides.


Antiparallel
Antiparallel
- The two polynucleotide strands are antiparallel because they run in opposite directions.


Uracil
Uracil
- The RNA base sequence is complementary to the DNA's coding sequence from which it has been copied.
- If the DNA strand has a sequence AATTGCGC, the sequence of the complementary RNA is UUAACGCG.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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