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NUCLEIC ACIDS STRUCTURE AND FUNCTION RNA DNA MONONUCLEOTIDE PHOSPHATE PENTOSE SUGAR ORGANIC BASE PHOSPHATE PENTOSE SUGAR RIBOSE DEOXYRIBOSE ORGANIC BASES PURINES PYRIMIDINES GUANINE G ADENINE A CYTOSINE C URACIL U THYMINE T NUCEIC ACIDS Found in all cells:- DNA (Deoxyribonucleic Acid) in nucleus. RNA (Ribonucleic Acid) in cytoplasm. Building blocks = NUCLEOTIDES Mononucleotide = Condensation product of:Phosphate Pentose sugar (Ribose/Deoxyribose) Organic/Nitrogenous base (A T G C U) Nucleic acids = Polynucleotides = condensation products of many mononucleotides (i.e. polymers) RIBONUCLEIC ACID (RNA) A POLYNUCLEOTIDE PHOSPHATE RIBOSE ADENINE PHOSPHATE RIBOSE GUANINE PHOSPHATE RIBOSE CYTOSINE PHOSPHATE RIBOSE URACIL POLYNUCLEOTIDE RNA ribosomal RNA (rRNA) Makes up the bulk of the ribosome. Large folded molecule. messenger RNA (mRNA) Carries the genetic message from DNA in the nucleus to the ribosomes where proteins are synthesised (made) accordingly. Long molecule, not folded. Variable in length and base sequence. Readily broken down and remade. transfer RNA (tRNA) Collects amino acids and takes them to the ribosomes for assembly into proteins. AMINO ACID Small molecule. Winds back on itself to form a “clover-leaf” shape. One end carries an amino acid. One loop has a special triplet of bases (ANTICODON) which determines the amino acid carried. ANTICODON RIBONUCLEIC ACID (RNA) Single stranded polynucleotide. Sugar is always ribose. Organic bases are always A, G, C, and U, NEVER T. 3 types :- ribosomal RNA (rRNA) messenger RNA (mRNA) transfer RNA (tRNA) Back DEOXYRIBONUCLEIC ACID (DNA) A POLYNUCLEOTIDE PHOSPHATE DEOXYRIBOSE ADENINE PHOSPHATE DEOXYRIBOSE GUANINE PHOSPHATE DEOXYRIBOSE CYTOSINE PHOSPHATE DEOXYRIBOSE THYMINE HYDROGEN BONDS ANTIPARALLEL What is the difference between deoxyribose and ribose? What type of spiral is DNA? How many bases are there to each turn of the DNA molecule? What three forms of evidence were used to derive the structure of DNA? How many nucleotides (on average) does it take to make a human chromosome set? What are chromosomes made of as well as DNA? SPECIFIC BASE PAIRING PYRIMIDINES PURINES GUANINE CYTOSINE ADENINE THYMINE COMPLEMENTARY SHAPE SPECIFIC BASE PAIRING HYDROGEN BONDS THE DOUBLE HELIX DEOXYRIBONUCLEIC ACID (DNA) Double stranded helix - “THE DOUBLE HELIX” Sugar (Deoxyribose) / Phosphate backbone. Antiparallel Bases are A, G, C and T, NEVER U. Chains are held together by “H” bonds between base pairs. 10 base pairs per turn of the helix. Specific base pairing A:T and G:C (i.e. purine:pyrimidine) Back THE FUNCTION OF DNA REPLICATION DNA GENE EXPRESSION/ PROTEIN SYNTHESIS Transcription m RNA Translation PROTEIN DNA REPLICATION SEMI-CONSERVATIVE HYPOTHESIS DNA REPLICATION Takes place during interphase of the cell cycle (S phase). The DNA helix is unwound and unzipped by the enzyme HELICASE which breaks the weak “H” bonds between the base pairs. The exposed, unpaired bases form a template. Free nucleotides are specifically base paired to the exposed bases by the enzyme DNA POLYMERASE. ATP is required as a source of energy. Two identical DNA molecules are produced. Since each new DNA molecule retains half an old one, this is known as the “SEMI-CONSERVATIVE HYPOTHESIS”. QUIZ Give 3 differences between DNA and RNA. What is the difference in chemical structure between ribose and deoxyribose? Name the three components of a mononucleotide? What is meant by a “condensation” reaction? Name the three different types of RNA. Name the scientists credited with discovering the structure of DNA? What is meant by complementary? Give the two complementary base pairs. What is meant by antiparallel? What is meant by the “Semi-conservative Hypothesis”? ANSWERS DNA is double stranded, has deoxyribose sugar, and bases G, C, A & T. RNA is single stranded, has ribose sugar and the bases G, C, A & U. Ribose has a hydroxyl group (OH) on C atom 2, deoxyribose has a H atom. Phosphate, pentose sugar and organic,nitrogenous base. Joining molecules together with the production of water. rRNA, mRNA and tRNA. James Watson and Francis Crick (1953), though many others paved the way. To fit together perfectly, to make a complete whole. A<->T and C<-> G. To run along side each other but in opposite directions. Each new DNA molecule partially consists of (conserves) the old one. WANT TO KNOW MORE ? THEN VISIT:- “DNA From the Beginning” http://vector.cshl.org/dnaftb THE END J.Minton SWGS 2002
