DNA, Genes and Genomics

Prokaryotic DNA The prokaryotes usually have only one chromosome, and it bears little morphological (physical) resemblance to eukaryotic chromosomes. Consists of single, circular DNA molecule located in the cytosol. Bacterial cells may also contain multiple plasmids - small circular fragments of DNA separate from the main chromosome.

Eukaryotic DNA Structure DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix. A molecule of DNA is made up of millions of tiny subunits called Nucleotides. Each nucleotide consists of: Phosphate group Deoxyribose sugar Nitrogenous base

Nucleotides (e.g. DNA) Phosphate Nitrogenous Base Deoxyribose Sugar

Nucleotides The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”. There are four types of nitrogenous bases.

Nucleotides A Adenine T Thymine C Cytosine G Guanine

Nucleotides Each base will only bond with one other specific base. Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Form a base pair. Form a base pair.

DNA Structure A C T G G A T C Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

DNA Replication unfolding and unwinding of the DNA double helix at hundreds of points, known as replication origins, along the chromosome. The enzyme helicase separates the two DNA strands, separating them like opening a zipper, with the point of opening being termed the replication fork. Where the DNA strands are separated, a short length of RNA binds to each DNA strand (RNA primer). This RNA allows DNA polymerase to add nucleotides to it.

DNA Replication A DNA polymerase enzyme can then proceed to build new DNA strands using each of the old strands as a template. Replication of DNA can occur only in the 5´ to 3´ direction (the code is read in the 3´ to 5´ direction). This is no problem with the so-called leading strand because its new complementary strand can be built continuously in the 5´ to 3´ direction. The other strand, known as the lagging strand, can be built only backwards and in short discontinuous pieces (Okazaki fragments). When finished, the RNA primers are removed, the gaps are filled by another DNA polymerase and the pieces are joined by the enzyme, DNA ligase.

DNA Replication DNA replication is semiconservative the final copies contain one original and one new DNA strand

DNA Replication

DNA Replication http://highered.mheducation.com/sites/0072943696/student_view0/chapter3/animation__dna_replication__quiz_1_.html

Mitochondrial DNA Mitochondria contain mtDNA, a double stranded circular molecule. Replication is bidirectional (both directions at the same time)

Mitochondrial DNA (mtDNA) http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120073/micro03.swf::Bidirectional%20Replication%20of%20DNA