Deoxyribose Nucleic Acid DNA Structure DNA is made
Deoxyribose Nucleic Acid
DNA Structure • DNA is made up of chains of nucleotides • Each nucleotide contains: – A 5 carbon Sugar (deoxyribose) – A phosphate group – An organic base
DNA Structure Cont • Adenine, Guanine, Thymine and Cytosine • A-T C-G • DNA consists of 2 strands of nucleotides, running in opposite directions. • The bases on each strand are complimentary , i. e. match up
DNA Structure Cont • The two strands of DNA are coiled to form a double helix (like a twisted ladder) • The Double helix backbone is made of the sugars and phosphate groups. • The rungs on the “ladder” are made by the bases.
Functions Of DNA • Carries the genetic code for the proper functioning or organisms. • Able to self replicate to continue life • Very long – consists of thousands of genes at set places called loci. • Each gene codes for a polypeptide chain • One or more polypeptides make up proteins.
Functions Of DNA • DNA controls the cell by controlling protein synthesis. DNA RNA transcription Polypeptide translation
Packaging of DNA • Prokaryote DNA is formed into a ring, and the nucleoid it forms is so small that it can only be seen under an electron microscope. • Eukaryote DNA is so long that it has to be packaged. (estimated that each chromosome has about 2 x 108 nucleotide pairs. )
DNA Replication • Zygotes have to be able to divide to form multicellular beings, each cell must carry a copy of the original blueprint of the chromosome. • For this reason DNA must be able to replicate. • It does this during Interphase.
DNA Replication • The enzyme Helicase unwinds and unzips the DNA. • Both sides of the DNA act as a template to make a new strand. • The nucleotides are assembled in the 5’ to 3’ direction using DNA Polymerase. • The leading strand is synthesized continuously.
DNA Replication • The lagging strand is synthesized in fragments which are later joined. • DNA synthesis is “Semi-conservative”. This means that each new DNA is made up of an old strand a new strand. • In cell division these 2 new DNA strands appear as sister chromatids, joined at a centromere.
Semi-conservative Replication
Okazaki Fragments • The sides of the DNA molecule are antiparallel. • DNA polymerase can only join new nucleotides to the 3’ end – the leading strand. • On the lagging strand small sections of complimentary DNA called Okazaki fragments are synthesized and assembled by DNA polymerase.
Okazaki Fragments • These okazaki fragments are joined together into a single DNA strand by the enzyme Ligase.
DNA Replication
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