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1 BIOLOGY PRESENTATIONS FOR A-LEVEL, IN MULTIMEDIA JAMES BOWLES, 2001 LEFT CLICK OR PRESS SPACE BAR TO ADVANCE, PRESS P BUTTON TO GO BACK, PRESS ESC BUTTON TO END 2 ‘A’ Level Biology Nucleic Acids Nucleotides 3 A nucleotide contains: Phosphate Group Pentose Sugar Base O 4 Nucleotides The phosphate group gives the nucleotide an acidic nature O O P OO 5 Nucleotides The pentose sugar may be either Ribose (RNA) or Deoxyribose (DNA) O H OH Ribose O H H Deoxyribose Nucleotides There are five bases Adenine Purines Guanine Cytosine Thymine Pyramidines Uracil 6 Polynucleotides O O 7 Bonds can form between carbon 3 of the pentose sugar and the phosphate group on carbon 5 of an adjacent nucleotide Polynucleotides O 8 O O O O O O Long chains can be built up in this way Polynucleotides 9 5’ OPolynucleotides The ends of O these chains are O named on the O basis of which O carbon is not O involved in bonding O 3’ DNA 10 Deoxyribonucleic Acid Sugar is Deoxyribose Bases are: O H H Cytosine Thymine Adenine Guanine 11 O O DNA O O O O O O O O O O O O Two chains of polynucleotide run anti-parallel to one another DNA The chains are arranged as a DOUBLE HELIX with 10 bases to each complete turn 12 DNA 13 Base pairing is complimentary Adenine Thymine Guanine Cytosine The bonds are hydrogen bonds RNA 14 Ribonucleic Acid Sugar is Ribose Bases are: Cytosine Uracil O H OH Adenine Guanine Messenger RNA 15 Messenger RNA 16 mRNA U A AGC G UA U UGGC A UG Single-stranded, uncoiled polynucleotide Messenger RNA 17 mRNA U A AGC G UA U UGGC A UG mRNA is a copy of the DNA code which is exported from the nucleus Transfer RNA 18 tRNA Single-stranded RNA arranged in a ‘clover leaf’ shape Transfer RNA 19 tRNA Amino Acid binding site tRNA attaches to amino acids in the cytoplasm Transfer RNA 20 tRNA Anticodon The anticodon lines up alongside the appropriate codon on mRNA during protein synthesis Ribosomal RNA 21 rRNA This is a long length of RNA produced in the nucleolus Ribosomal RNA 22 rRNA It has areas of single and double helices Ribosomal RNA 23 rRNA In the cytoplasm it combines with proteins to form ribosomes DNA vs. RNA DNA RNA 24 DNA vs. RNA 25 DNA RNA Always a double helix May have single or double helix DNA vs. RNA 26 DNA RNA Always a double helix May have single or double helix Sugar is deoxyribose Sugar is ribose DNA vs. RNA 27 DNA RNA Always a double helix May have single or double helix Sugar is deoxyribose Sugar is ribose Bases are A, T, G & C Bases are A, U, G & C DNA vs. RNA 28 DNA RNA Always a double helix May have single or double helix Sugar is deoxyribose Sugar is ribose Bases are A, T, G & C Bases are A, U, G & C Permanent May be temporary DNA vs. RNA 29 DNA RNA Always a double helix May have single or double helix Sugar is deoxyribose Sugar is ribose Bases are A, T, G & C Bases are A, U, G & C Permanent May be temporary Chemically very stable Chemically less stable 30