A Level Biology Revision Lesson 160: How DNA is Stored
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★ AQA A Level Biology Specification Reference: - 3.1.5 Nucleic acids are important information-carrying molecules. 22.214.171.124 Structure of DNA. 3.4.1 DNA, genes and chromosomes: In prokaryotic cells, DNA molecules are short, circular and not associated with proteins. In the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones. Together a DNA molecule and its associated proteins form a chromosome. The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein. A gene is a base sequence of DNA that codes for: the amino acid sequence of a polypeptide a functional RNA (including ribosomal RNA and tRNAs). A gene occupies a fixed position, called a locus, on a particular DNA molecule. A sequence of three DNA bases, called a triplet, codes for a specific amino acid. The genetic code is universal, non-overlapping and degenerate. In eukaryotes, much of the nuclear DNA does not code for polypeptides. There are, for example, non-coding multiple repeats of base sequences between genes. Even within a gene only some sequences, called exons, code for amino acid sequences. Within the gene, these exons are separated by one or more non-coding sequences, called introns.
★ CIE A Level Biology Specification Reference: - 6 Nucleic acids. 6.1 Structure of DNA. 1.2 Cells as the basic units of living organisms: d) outline key structural features of typical prokaryotic cells as seen in a typical bacterium (including: unicellular, 1–5μm diameter, peptidoglycan cell walls, lack of membrane-bound organelles, naked circular DNA, 70S ribosomes). a) describe the structure of a chromosome, limited to DNA, histone proteins, chromatids, centromere and telomeres. mitochondria (including small circular DNA). Chloroplasts (including small circular DNA).
★ Edexcel A Level Biology (Biology A – Salters-Nuffield) Specification Reference: - Topic 2: Genes and Health: 2.8 Know that a gene is a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain. Topic 3: Voice of the Genome: 3.4 Know the ultrastructure of prokaryotic cells, including cell wall, capsule, plasmid, flagellum, pili, ribosomes, mesosomes and circular DNA.
★ Edexcel A Level Biology (Biology B) Specification Reference: - Know that a gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain. v Know the ultrastructure of eukaryotic cells and the functions of organelles, including: nucleus, nucleolus, mitochondria.
★ OCR A Level Biology (Biology A) Specification Reference: - The Structure of DNA. The structure of a chloroplast: The components of a chloroplast including outer membrane, lamellae, grana, thylakoid, stroma and DNA. The structure of the mitochondrion - The components of a mitochondrion including inner and outer mitochondrial membranes, cristae, matrix and mitochondrial DNA.
★ OCR A Level Biology (Biology B) Specification Reference: - 2.1.1 Cells and microscopy (i) the ultrastructure of a typical eukaryotic plant cell such as a palisade mesophyll cell and a prokaryotic cell, as revealed by an electron microscope. To include the structure and function of the mitochondria, nucleus and nucleolus. The ultrastructure a prokaryotic cell, as revealed by an electron microscope. The structure and function of chloroplasts, circular DNA.
★ WJEC A Level Biology Specification Reference: - DNA contains the code for proteins and that between the exons are regions of non-coding DNA called introns. The structure and function of the mitochondria; chloroplasts.