DNA and Replication

Anchoring Phenomenon: Why do We Age?

Google Slides: DNA

Student Handout

Chapter 14 - Openstax

Short Film: The Double Helix

Slides Outline

The Establishment of DNA as the molecule of heredity:

• able to store information that pertains to development and structure
• stables so that it can be replicated
• able to undergo changes (mutations)

*At the time, some scientists felt that amino acids / proteins stored genetic information

Nucleic Acids (DNA and RNA)

• consists of a sugar, phophate, nitrogen base
• DNA has the sugar deoxyribose; RNA has ribose
• Four bases in DNA: adenine, thymine, guanine and cytosine
• RNA has uracil instead of thymine

Experiments to Support Hypothesis the DNA was the molecule of heredity

• Griffith experiment on S and R strained bacteria (transformation)
• Hershey and Chase experiment on radioactive bacteriophage

Establishing the Structure (shape) of DNA

• Rosalind Franklin's X ray of DNA (photograph 51)
• Chargaff's Rule (adenine and thymine had the same percentage in a sample; guanine and cytosine also same)
• Watson and Crick determining the structure was a helix, with paired bases in the center

DNA Structure

• Sides are antiparallel, running 5' to 3' (prime)
• The prime ends are whre the phosphates are located
• Adenine always pairs with thymine - held together by a pair of hydrogen bonds
• Cytosine pairs with guanine - three hydrogen bonds
• Adenine and guanine have two rings (purines)
• Thymine and cytosine and uracil have one ring (pyrimidines)

DNA Replication

Replication is the process by which DNA makes a copy of itself

It is semi-conservative (half of the original strand is saved in each copy)

Steps in Replication

• DNA helicase unwinds DNA, creating a replication fork
• DNA polymerase ads nuclotides, traveling from the 3' to 5' (template strand, leading strand)
• Nucleotides are added in the opposite direction on the lagging strand, creating fragments
• Okazaki fragments are bound together by DNA ligase

*DNA Replication Handout | DNA replicaiton Model

DNA and Mutations

Mutation - change in DNA

• Substitution (missense) - one base is switched, results in a new protein
• Insertion or deletion (frameshift) - alters reading frame, changes most of the protein
• Duplication - sections are repeated, can amplify a gene product
• CNV - copy number variation (type of duplication)

HTT mutation - cause of Huntington's disease, results from repeating CAG trinucleotides (CAGCAGCAGCAG...)

Copy Number Variant in amylase gene - increased copy numbers increase salivary amylase for starch digestion

Telomeres

Caps at the end of DNA strands; these shorten with each duplication

Telomeres act as the aging clock of the cell, eventually the DNA can no longer replication

**Likely the cause of senescene (aging) **