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What is DNA composed of?

What is DNA composed of?. The DNA molecule is a very long polymer , or chain of repeating units. The small units, or monomers, that make up DNA are called nucleotides . Phosphate group – one phosphorus with 4 oxygens A ring-shaped sugar called deoxyribose A nitrogen-containing base.

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What is DNA composed of?

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  1. What is DNA composed of? • The DNA molecule is a very longpolymer, or chain of repeating units. • The small units, or monomers, that make up DNA are called nucleotides. • Phosphate group – one phosphorus with 4 oxygens • A ring-shaped sugar called deoxyribose • A nitrogen-containing base

  2. Bases: • One molecule of human DNA contains billions of nucleotides, but there are only four types of nucleotides in DNA. These nucleotides differ in their nitrogen-containing bases. • Adenine (A) – double-ring structure • Cytosine (C) – single-ring structure • Thymine (T) – single-ring structure • Guanine (G) – double-ring structure

  3. The Double Helix: James Watson and Francis Crick hypothesized that DNA might also be a helix. Rosalind Franklin and Maurice Wilkins took x-ray photographs of DNA that showed an X surrounded by a circle. Watson and Crick used this evidence to build a model to figure out DNA structure.

  4. The Double Helix (cont.): Watson and Crick found that if they paired double-ringed nucleotides with single-ringed nucleotides, the bases fit like a puzzle. Double helixmodel – two strand of DNA wind around each other like a twisted ladder.

  5. Nucleotide Pairings: • The bases of two DNA strands always pair up in the same way. • Thymine (T) = Adenine (A) • Cytosine (C) = Guanine (G)

  6. What would be the correct pairing? • TTCA • ACTC • ACGT • CTAT • 5. CTCA AAGT TGAG TGCA GATA GAGT • AGTC • AAGT • GGCA • CAGA • 10. CATC TCAG TTCA CCGT GTCT GTAG

  7. Replication: Watson and Crick realized that a single DNA strand can serve as a template, or pattern, for a new strand. Replication – the process by which DNA is copied during the cell cycle DNA only stores genetic information. Enzymes and proteins do the actual work of replication.

  8. Replication (cont.): • Process of replication: • Enzymes begin to unzip the double helix at numerous places along the chromosome. • Free-floating nucleotides pair, one by one, with the bases on the template strands as they are exposed. • Two identical molecules of DNA result.

  9. Transcription: Information flows in one direction, from DNA to RNA to proteins. This is known as the central dogmaof molecular biology. Cells cannot make protein directly from DNA. They must convert the DNA into an intermediate molecule called RNA, or ribonucleic acid. You can think of RNA as a temporary copy of DNA that is used and then destroyed.

  10. Transcription (cont.): • RNA differs from DNA in three ways: • The sugar in RNA is ribose, which has one additional oxygen atom not present in DNA’s sugar (deoxyribose). • RNA has the base uracil (U) in place of thymine. • RNA is a single strandof nucleotides, in contrast to DNA’s double-stranded structure.

  11. Transcription (cont.): • Transcription produces three major types of RNA molecules: • Messenger RNA (mRNA) – an intermediate message that is translated to form a protein • Ribosomal RNA (rRNA) – forms part of ribosomes • Transfer RNA (tRNA) – brings amino acids from the cytoplasm to a ribosome

  12. Translation: Translation is the process that converts, or translates, an mRNA message into a polypeptide. The “language” of nucleic acids uses four nucleotides – A, G, C, and T in DNA; A, G, C, and U in RNA. The “language” of proteins uses 20 amino acids.

  13. Codons: A codon is a three-nucleotide sequence that codes for an amino acid. In addition to the codons that code for amino acids, three stop codons signal the end of the amino acid chain. There is also one start codon, which signals the start of translation and the amino acid methionine.

  14. Codons (cont.): For the mRNA code to be translated correctly, codons must be read in the right order. Codons are read, without spaces, as a series of three nonoverlapping nucleotides. This order is called the reading frame. Changing the reading frame completely changes the resulting protein.

  15. Becoming Proteins: A cell translates a codon into an amino acid using ribosomes and tRNA molecules. The tRNA acts as a sort of adaptor between the mRNA and amino acids. The tRNA molecules fold up in a L shape. One end of the L is attached to a specific amino acid. The other end (anticodon) recognizes a specific codon.

  16. Becoming Proteins (cont.): Anticodon – a set of three nucleotides that is complementary to an mRNA codon.

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