Heredity

• Deoxyribose has 5 carbon atoms, which are numbered clockwise

  • The 1’ (one prime) carbon holds the nitrogen base

  • The 3’ (three prime) carbon has a hydroxide that will bond with the P-group of another nucleotide

  • The 5’ (five prime) carbon holds onto the phosphate group

• DNA is antiparallel because complementary strands run in opposite directions. Important because the 3’ and 5’ directions is how DNA is “read” by enzymes. 

• HINT: The O on the deoxyribose sugar “points” to the 5’ end.

• Pyrimidines (T, C, with single rings) always bond with purines (A, G, with double rings) in nucleic acids.

DNA bonds

• Hydrogen bonds (weak attractions) hold bases together

  • T=A (2 bonds)

  • G=C (3 bonds)

• Covalent phosphodiester bonds (strong bonds) hold nucleotides together at the backbone

• DNA polymers: acid bases

• Ligase: covalent bonds

  • Semi-conservative replications

• Helicase: breaks hydrogen bonds, unwinds part of the DNA double helix,

• Topoisomerase: untwist DNA, helps relieve the strain of unwinding by breaking, swiveling, and rejoining DNA strands

• Primase: adds RNA primer so polymerase can attach

Protein Synthesis:

• RNA

  • Ribose sugar

  • Uracil instead of thymine

  • Single stranded

  • Copies the information to take from the inside nucleus to the ribosome

    • mRNA (messenger): carries information from DNA to the ribosome

    • t:RNA (transfer):  carries amino acids to the ribosome

    • rRNA (ribosomal) : building blocks of ribosomes

    • microRNA (inhibit synthesis): small RNA molecules that bind to other RNA molecules to degrade them (more on these later)

  • The nucleotide sequence in the DNA is used to make a complementary sequence in mRNA

  • Uses many of the same enzymes from DNA replication - helicase, topoisomerase, RNA polymerase, etc.

  • RNA polymerase uses a single strand of DNA to make mRNA; works in the 5’ to 3’ direction

  • The DNA strand that is used is called the template strand, noncoding strand, minus strand, or antisense strand

• Post-transactional Modification:

  • Before the mRNA leaves the nucleus - 

    • A poly-A tail is added (Protect the ends from degradation; like aglets on shoelaces)

    • A GTP cap is added

    • Splicing by spliceosomes

      • Introns stay in the nucleus; do not code for proteins

      • Exons exit the nucleus to go to the ribosome; do code for proteins

• Translation:

  • Occurs at ribosomes

    • Free ribosomes in prokaryotes

    • Free ribosomes or bound ribosomes (to rough ER) in eukaryotes

  • In prokaryotes, translation occurs as the mRNA is being transcribed

  • In eukaryotes it occurs after transcription 

  • Three steps - initiation, elongation, and termination

    • Initiation

      • Small ribosomal subunit binds to mRNA and an initiator tRNA

      • Then the large ribosomal subunit attaches

    • Elongation

      • The ribosome moves down the mRNA in the 5’ to 3’ direction

      • For each codon (3 bases on the mRNA), a tRNA with a corresponding anticodon brings an amino acid to the ribosome

      • The amino acid is added to the preceding one by a peptide bond

    • Termination:

      • Elongation continues until the ribosome reaches a stop codon in the mRNA

        • UAG, UAA, or UGA

      • A protein called a release factor that causes the polypeptide chain to separate from the ribosome

• Which amino acid gets added to the polypeptide?

  • Each codon in the mRNA corresponds to one amino acid

  • If the anticodon on the tRNA is complementary to the codon on the mRNA → the correct amino acid is at the ribosome and gets added

  • If the anticodon on the tRNA is not complementary to the codon on the mRNA → the correct amino acid is not at the ribosome; must wait for another tRNA with a complementary anticodon to arrive

  • The polypeptide folds up based on the arrangement of its amino acids (secondary and tertiary protein structure)

  • Some polypeptides combine with others to make larger proteins (quaternary structure)

  • May be packaged at ER or modified and p

    

    ackaged at the Golgi

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