Human Molecualr Genetics. Luqman Sulaiman MD, MSc, PhD Candidate Molecular & Medical Surgey Karolinska Hospital CMM Chapter One Fri.14-11-08. Aims. Motivate and Encourage Starting point Refresh and boost knowledge How to prepare presentations Have Fun!!!. DNA. Overview
MD, MSc, PhD Candidate
Molecular & Medical Surgey
is a polymer,
Nucleoside and Nucleotide are
Base Pairs (Nitrogen bases: Purine and Pyrmaidine)
Covalent, phosphodiester bonds
National Health Museum
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DNA is made of chemical building blocks called nucleotides. These building blocks are made of three parts: a phosphate group, a sugar group and one of four types of nitrogen bases. To form a strand of DNA, nucleotides are linked into chains, with the phosphate and sugar groups alternating.
The structure of DNA is illustrated by a right handed double helix, with about 10 nucleotide pairs per helical turn. Each spiral strand, composed of a sugar phosphate backbone and attached bases, is connected to a complementary strand by hydrogen bonding (non- covalent) between paired bases, adenine (A) with thymine (T) and guanine (G) with cytosine (C). Adenine and thymine are connected by two hydrogen bonds (non-covalent) while guanine and cytosine are connected by three.
A B Z
James Watson and Francis Crick,
Science Museum, UK
SSBP (Single Stranded Binding Proteins)
DNA Holoenzymes (Polymeraze)
DNA Polymerase, can only synthesize new DNA from the 5’ to 3’ (of the new DNA). Leading Strand
DNA ligase, is used to connect the so-called Okazaki fragments. Lagging StrandTerminationThe sticking out 3’ end consists of noncoding DNA called the telomere, which can be simply cut off.
Genetic information is encoded by the linear sequence of bases in the DNA strands (the primary structure). Consequently, two DNA strands of a DNA duplex are said to have complementary sequences (or to exhibit base complementarity) and the sequence of bases of one DNA strand can readily be inferred if the DNA sequence of its complementary strand is already known. It is usual, therefore, to describe a DNA sequence by writing the sequence of bases of one strand only, and in the 5′ → 3′ direction. This is the direction of synthesis of new DNA molecules during DNA replication, and also of the nascent RNA strand produced during transcription . However, when describing the sequence of a DNA region encompassing two neighboring bases (really a dinucleotide) on one DNA strand, it is usual to insert a ‘p' to denote a connecting phosphodiester bond [e.g. CpG means that a cytidine is covalently linked to a neighboring guanosineon the same DNA strand, while a CG base pair means a cytosine on one DNA strand is hydrogen-bonded to a guanine on the complementary strand .