BCH4024 Douma Exam 4 - Lecture 1

Adenine

Guanine

Cytosine

Uracil

Thymine

Nitrogenous Bases in DNA and RNA

Adenine, Guanine, Cytosine, and Thymine (DNA); Uracil replaces Thymine in RNA. Purines (A, G) have double rings; Pyrimidines (C, T, U) have single rings.

Repeating Units of DNA

2'-deoxyribonucleoside 5'-monophosphates (dNMPs) are the monomers of DNA.

Structure of a Nucleotide

Each nucleotide has a sugar, phosphate group, and nitrogenous base.

Directionality of DNA and RNA

Sequences are written 5' to 3', from the free 5' phosphate to the 3' hydroxyl.

DNA Backbone

Alternating sugar and phosphate groups forming the outer structure of the DNA helix.

Hydrogen Bonding and Base Pairing

A pairs with T via 2 H-bonds; G pairs with C via 3 H-bonds, allowing strand separation.

Base Stacking

Hydrophobic interactions between bases that stabilize the DNA helix.

Melting Temperature (Tm)

The temperature at which DNA is 50% denatured; higher in GC-rich sequences.

Denaturing and Annealing DNA

Denaturing separates strands by breaking H-bonds; annealing reforms them if complementary.

Main Characteristics of B-DNA

Right-handed helix; 10.5 base pairs per turn; major and minor grooves; bases stacked inside.

Major Groove vs Minor Groove

Major groove exposes bases for protein binding; minor groove is narrower.

Definition of DNA

Deoxyribonucleic acid; a double-stranded polymer carrying the genetic blueprint.

Central Dogma of Molecular Biology

Describes flow of information: DNA replication, transcription into RNA, and translation into protein.

Purpose of DNA Replication

To duplicate DNA for inheritance by daughter cells.

Purpose of Transcription

To produce RNA as a temporary working copy of genetic information.

Purpose of Translation

To synthesize proteins using information carried by mRNA.

Reverse Transcription

Synthesis of DNA from an RNA template by specific enzymes.

Key Features of Prokaryotic Cells

DNA located in cytoplasm; no nucleus.

Key Features of Eukaryotic Cells

DNA housed inside the nucleus.

Bacterial Transformation

Uptake of external DNA by a bacterial cell, changing its characteristics.

Streptococcus pneumoniae

Bacteria used in Avery's experiment to identify DNA as genetic material.

Smooth Cells (S cells) vs Rough Cells (R cells)

S cells have a protective capsule (virulent); R cells lack it (non-virulent).

Cell-free Extract

Lysed cell contents used in transformation experiments.

Purpose and Findings of Avery's Experiment

DNA was identified as the genetic material because DNase destroyed transformation ability.

Polynucleotide

A polymer of many nucleotides linked by phosphodiester bonds.

Phosphodiester Bond

Covalent bond between the 3' OH of one nucleotide and the 5' phosphate of another.

Chargaff's Rules

A=T and G=C; base composition varies across species but is constant within an organism.

Significance of Rosalind Franklin's Photo 51

Provided key evidence of DNA's double helical structure and periodicity.

Antiparallel Orientation of DNA Strands

Two DNA strands run in opposite directions (5'->3' and 3'->5').

Definition of Gene

DNA sequence encoding a functional RNA or protein with regulatory elements.

Definition of Genome

Complete set of genetic material in an organism (e.g., 46 chromosomes in humans).