Highlights Lecture #15 Spring 2017

Highlights Nucleic Acids

1. Chromatin is a complex of DNA and proteins. The proteins are called histones and they are positively charged.

2. Histones are proteins that associate with DNA and allow it to coil up. DNA-histone complexes are called nucleosomes. When you put many nucleosomes together, you get chromatin. Chromosomes contain chromatin. Each “ball” of histones contains four pairs of proteins – H2a, H2b, H3, and H4.

3. DNA strands can easily be separated by heat, acid, or base.

4. Single strands of nucleic acid (DNA or RNA) absorb light at 260 nm more strongly than double strands of nucleic acid in the same quantity. Thus, one can monitor the denaturation of nucleic acid by monitoring its absorbance at 260 nm as the denaturation proceeds.

5. The transition temperature (Tm) for a nucleic acid denaturation is the mid-point of the Tm transition

6. RNA differs from DNA in having ribose (instead of deoxyribose) and uracil (instead of thymine).

7. There are three main types of RNA found in all cells. They are transfer RNA (tRNA), ribosomal RNA (rRNA), and messenger RNA (mRNA). We will talk about these later. For now, you should know that mRNAs carry the genetic code necessary for making proteins, tRNAs carry amino acids for translation and rRNAs are components of ribosomes that make proteins.

8. Catalytic RNAs are called ribozymes. Ribosomes contain a ribozyme that catalyzes the formation of peptide bonds.

9. tRNAs carry an amino acid at the 3′ end and a three base sequence called an anti-codon loop at the other. A sequence in the anti-codon loop determines which amino acid gets attached at the 3′ end.

10. Ribosomal RNA is found in ribosomes and helps the ribosome by catalyzing the formation of peptide bonds during protein synthesis. We’ll see at least one other function soon.

11. mRNAs are copied from the DNA. They contain the instructions for making proteins. They are called messenger RNA because they are carrying information from the DNA to the place where protein is made.

Highlights DNA Synthesis

1. Information in cells flows from DNA to RNA (called transcription) and from RNA to Protein (called translation). This is known as the Central Dogma. Some retroviruses have an enzyme called reverse transcriptase that allows them to make DNA from RNA. This last process is called reverse transcription.

2. DNA replication is catalyzed by enzymes called DNA polymerases. They catalyze the formation of phosphodiester bonds.

3. The place within DNA where replication occurs is called a replication fork.

4. The place where DNA replication begins within a DNA is called an origin.

5. Proteins involved in DNA replication (which starts as a replication origin) include DNA helicase (peels apart strands at 6000 rpm), DNA gyrase (a topoisomerase ahead of the replication fork that untangles the tension put into DNA by the helicase), primase (starts the synthesis process) and SSB (single-strand binding protein).

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