DNA Structure.pptx

DNA STRUCTURE LEARNING INTENTION UNDERSTAND THAT DEOXYRIBONUCLEIC ACID (DNA) IS A DOUBLE-STRANDED MOLECULE THAT OCCURS BOUND TO PROTEINS (HISTONES) IN CHROMOSOMES IN THE NUCLEUS, AND AS UNBOUND CIRCULAR DNA IN THE CYTOSOL OF PROKARYOTES, AND IN THE MITOCHONDRIA AND CHLOROPLASTS OF EUKAR...

DNA STRUCTURE LEARNING INTENTION UNDERSTAND THAT DEOXYRIBONUCLEIC ACID (DNA) IS A DOUBLE-STRANDED MOLECULE THAT OCCURS BOUND TO PROTEINS (HISTONES) IN CHROMOSOMES IN THE NUCLEUS, AND AS UNBOUND CIRCULAR DNA IN THE CYTOSOL OF PROKARYOTES, AND IN THE MITOCHONDRIA AND CHLOROPLASTS OF EUKARYOTIC CELLS RECALL THE STRUCTURE OF DNA, INCLUDING nucleotide composition complementary base pairing weak, base-specific hydrogen bonds between DNA strands DNA - OVERVIEW DNA – Deoxyribonucleic Acid A large biomolecule with a double helix structure – double strand that twists Composed of monomers called nucleotides 4 different types of nucleotides Mostly contained within the nucleus of a eukaryotic cell, small amounts in mitochondria and chloroplasts Form long strands called chromatin CHROMOSOMES In eukaryotes DNA is packaged into structures called chromosomes It consists of a long strand of DNA wrapped around proteins called histones into a strand called chromatin The chromatin can be further looped and folded to compact the DNA into a tight chromosome Chromatid refers to one side of the replicated chromosome (‘X’ shaped during metaphase) PROKARYOTE & EUKARYOTE FORMS In prokaryotic cells DNA is located in the cytosol in an unbound, circular form In eukaryotic cells DNA is located in the nucleus, bound to proteins and packaged into a linear form called chromatin NUCLEOTIDES Each nucleotide is composed of a sugar (deoxyribose), a phosphate and a nitrogen base There are 4 different nitrogen bases – Adenine, Thymine, Guanine & Cytosine NUCLEOTIDE BASE PAIRING The double helix structure is the result of specific base pairing Each side of the DNA has a spine formed by the phosphate & sugar and are held together by hydrogen bonds between matching DNA DNA is too large to leave the nucleus of the cell This creates a problem as the instructions held in the DNA are required in the cytoplasm in order to be used This problem is overcome with the use of the second type of nucleic acid - RNA RNA RNA – Ribonucleic Acid A single strand molecule Created in the nucleus Small enough to pass out of the nucleus into the cytoplasm Three main types – ribosomal, messenger & transfer RNA Composed of nucleotides Similar to DNA but contain a different sugar (ribose) and nitrogen base Uracil instead of Thymine (U  A to form RNA) RNA TYPES rRNA – Ribosomal RNA: two separate subunits (large & small) form a ribosome which assembles amino acids into peptide chains mRNA – Messenger RNA: transcribed copy of DNA from the coding section of a gene which will provide the correct order of amino acids in a peptide chain tRNA – Transfer RNA: involved in transferring specific amino acids to the ribosome for assembly of a peptide chain * there are other RNA types that may be mentioned later in the unit DNA COMPARED TO RNA