DNA Structure & Function study guide

Mr. Blanchette

Griffith's Experiment

Demonstrated transformation in bacteria.

Avery's Experiment

Identified DNA as the material for transformation.

Hershey & Chase Experiment

Confirmed DNA as the genetic material using bacteriophages.

Watson, Crick & Franklin

Proposed the double helix structure of DNA; built on Franklin's data.

Chargaff's Rule

• A = T (Adenine equals Thymine

• C = G (Cytosine equals Guanine)

Parts of a DNA Molecule

• Nucleotides:
    - Phosphate
    - Deoxyribose sugar
    - Nitrogen bases

• Antiparallel strands

• 5’ and 3’ ends

• Hydrogen bonds between bases

• Covalent bonds in the sugar-phosphate backbone.

DNA Replication Process

• Unwinding DNA

• Binding complementary nucleotides

• Proofreading for errors

• Leading and lagging strands with Okazaki fragments

• RNA primers added by primase (5’→3’ direction).

Enzymes in DNA Replication

• Helicase: unwinds DNA

• DNA polymerase: synthesizes new strands

• Ligase: joins Okazaki fragments

• Primase: adds RNA primers.

Semi-Conservative Replication

Each new DNA molecule has one old strand and one new strand.

Differences between RNA and DNA

• RNA: single-stranded, ribose sugar, contains uracil (U)

• DNA: double-stranded, deoxyribose sugar, contains thymine (T).

RNA Synthesis (Transcription)

• Occurs in the nucleus

• Makes mRNA copy of a gene

• Steps:
    - Initiation
    - Elongation
    - Termination

• RNA polymerase builds mRNA with A–U and C–G pairing.

Protein Synthesis (Translation)

• Occurs in ribosome

• Steps:
    - Initiation
    - Elongation
    - Termination

• Involves mRNA codons, tRNA, and amino acids.

Mutations

Changes in DNA sequences:

• Affect protein function

• Types:
    - Substitution
    - Insertion
    - Deletion

• Insertions/deletions can cause frameshifts.

Effects of Mutations on Proteins

Can change protein structure/function; may lead to diseases or metabolic disorders.

Central Dogma

Flow of genetic information: DNA → RNA → Protein.

Helicase

Enzyme that unwinds the DNA double helix during DNA replication.

Primase

Enzyme that synthesizes short RNA primers needed for DNA replication.

DNA Polymerase

Enzyme that adds complementary nucleotides to the growing DNA strand during replication.

Ligase

Enzyme that joins Okazaki fragments on the lagging strand by forming covalent bonds.

Leading Strand

The DNA strand that is continuously synthesized in the 5' to 3' direction during replication.

Lagging Strand

The DNA strand that is synthesized discontinuously in short segments called Okazaki fragments.