Ch 3 and Ch 9 DNA

  • View

  • Download

Embed Size (px)



Text of Ch 3 and Ch 9 DNA

  • Chromosomes are found in the nucleus of the cell. Chromosomes are made of DNA. DNA = Deoxyribonucleic acid A DNA molecule has 2 strands. DNA strand made of nucleotides.

  • Nucleotide:

  • Nucleotides on the same strand are held together by a strong chemical bond. The bond forms between the sugar and phosphate. This is called the sugar-phosphate backbone.

  • 4 different bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

  • A and T join together, and G and C join together. They are complementary to each other.Bases are held together by weak hydrogen bonds.

  • The resultant molecule is DNA. The 2 strands twist together to form a double helix.Fig. 3.3 p.19

  • RNA = ribonucleic acid.Made of nucleotides of the same structure, joined in the same way. 3 differences from DNA : - Uracil instead of thymine Single-stranded Ribose sugar instead of deoxyribose

  • 2 types of RNA: Messenger RNA (mRNA) carries code for a gene from DNA to ribosome. Transfer RNA (tRNA) carries specific amino acids to growing protein.

  • For the following strands of DNA, write the complementary bases on the next DNA strand.G A G A C A T T T A C G

    C T T G C C A A T A C G

    3. A G C T T G A C C A T G C T C T G T A A A T G C G A A C G G T T A T G C T C G A A C T G G T A C

  • For the following strands of DNA, write down their complementary strands of RNA .1. G A G A C A T T T A C G

    2. C T T G C C A A T A C G

    3. A G C T T G A C C A T G

    C U C U G U A A A U G C G A A C G G U U A U G C U C G A A C U G G U A C

  • chemical components of DNA same from species to species. sequence of bases unique bases make up genetic instructions which control inherited characteristics.

  • DNA can reproduce itself exactly process called DNA replicationDNA helix unwinds. Weak H bonds between bases break => 2 DNA strands separate with bases exposed.Fig. 9.4 p.70

  • 3. Free DNA nucleotides align with complementary nucleotides on open chain.4. Weak H bonds form between complementary pairs.5. Strong chemical bond forms between nucleotides to form a chain. Controlled by DNA polymerase.

  • 6. Daughter DNA molecules wind back up into double helix. in simplified replication diagram.

  • For replication to occur, nucleus must contain: DNA (for template) Nucleotides Enzyme ATP (energy)2 new molecules formedOne new strand, one from parent molecule=> semi-conservative

  • replication allows new genetic information to be formed 2 DNA molecules coil up, and become 2 identical chromatids held by centromere. replication ensures exact copy of genetic information is passed from cell to cell.

  • inherited characteristics are controlled by enzymes. enzymes are made of protein a proteins function depends on correct sequence of amino acidsOrder of amino acids is controlled by base sequence of DNA. =>DNA determines inherited characteristics.

  • DNA carries the genetic code Each triplet of bases is called a codonEach codon codes for one amino acid.Protein synthesis 2 stages: 1. Transcription Fig. 3.6 p.21 2. Translation Fig. 3.8 p.22

  • This stage makes a copy of the DNA code to take to the ribosomes. Copy = messenger RNA (mRNA)

    *Fig. 3.6 p.21*

  • 1. DNA strands unwind.2. Weak H bonds break => DNA strands separate.3. Free RNA nucleotides line up with complimentary bases on DNA.4. Weak H bonds form between bases.5. Strong chemical bonds form between RNA nucleotides. Controlled by RNA polymerase.

  • 6. H bonds between RNA and DNA bases break => strands separate. 7. mRNA moves to cytoplasm, and attaches to a ribosome.8. H bonds form between DNA bases, strand winds up into double helix. in simplified transcription diagram.

  • Each triplet of bases on mRNA = codon.Transfer RNA (tRNA) each tRNA molecule has a triplet of bases => anticodon. each anticodon codes for one amino acid. each cell ~ 20 tRNA molecules (one per amino acid). tRNA transports amino acid to site of protein synthesis, and ensures amino acids align in correct order.

  • 1. Ribosome attaches to one end of mRNA.2. 2 tRNA anticodons align with complimentary mRNA codons.

  • 3. Strong peptide bond forms between 1st 2 amino acids, when 1st 2 anticodons are aligned.4. 1st tRNA leaves ribosome.

  • 5. Ribosome moves along mRNA so 3rd tRNA anticodon can align.6. Peptide bond forms between 2nd and 3rd amino acids.

  • 7. 2nd tRNA leaves ribsosome, and so on, until polypeptide chain is complete. in simplified translation diagram.

  • 8. Peptide chain undergoes folding/rearrangement to become complete protein in the Golgi apparatus. Protein made in free ribosome used within the cell.Protein made in ribosomes attached to RER for export.After protein synthesis mRNA re-used, tRNA re-joins with amino acid.