Molecular Genetics Overview

Histones

• H1, H2A, H2B, H3, and H4 are all involved in the packaging of DNA into nucleosomes.

Griffith's Experiment

• Heat-killed virulent S-cells transformed the living non-virulent R-cells into virulent S-cells, killing the mice they were injected into.
• This experiment demonstrated that genetic material can be transferred between bacteria.

Nucleic Acids

• Adenine and Guanine are double-ringed purines.
• Cytosine, Thymine, and Uracil are single-ringed pyrimidines.

Chargaff's Rule

• The number of purines is always equal to the number of pyrimidines in a DNA molecule.
• This is because adenine pairs with thymine (A-T), and guanine pairs with cytosine (G-C).

Meselson and Stahl Experiment

• Meselson and Stahl used the heavy isotope nitrogen-15 (15^{15}15N) during DNA replication to demonstrate that DNA replication is semiconservative.
• This means that each new DNA molecule consists of one original strand and one newly synthesized strand.

DNA Replication

• DNA polymerase is the enzyme responsible for synthesizing new DNA strands.
• Single-stranded binding proteins (SSBPs) prevent the separated strands of DNA from recoiling during replication.

Transcription

• mRNA is a copy of a gene sequence from DNA.
• tRNA is a small RNA molecule that carries amino acids to the ribosomes.
• The genetic code is degenerate, meaning that multiple codons can code for the same amino acid.
• The wobble hypothesis explains how some tRNA molecules can recognize multiple codons.

Translation

• The sigma factor helps RNA polymerase bind to the promoter region of a gene.
• The sigma factor is released during elongation of the polypeptide chain and is reused.
• Peptidyl transferase is the enzyme responsible for forming peptide bonds between amino acids during translation.

RNA Splicing

• Exon segments are separated by non-coding introns.
• RNA ligase joins the exons back together after splicing.

Lac Operon

• The lac operon is a group of genes that are involved in the metabolism of lactose in bacteria.
• Lactose acts as an inducer of the lac operon, meaning it causes the operon to be turned on.
• The repressor protein binds to the operator gene, blocking transcription of the lac operon in the absence of lactose.

DNA Structure

• Each nucleotide consists of a phosphate group, a sugar (deoxyribose), and a nitrogenous base.
• Phosphate groups link nucleotides together to form DNA strands.