Molecular Genetics: DNA, RNA, and Protein Synthesis

Transcription and Translation

• Location:
• Transcription occurs in the nucleus.
• Translation occurs in the cytoplasm.
• Significance of Spatial Separation:
• In eukaryotic cells, transcription and translation occur in separate compartments and cannot happen simultaneously.
• In contrast, prokaryotic cells lack this spatial separation, enabling simultaneous transcription and translation.

Structure and Function of DNA

• DNA serves as the instruction manual for building proteins.
• The sequence of DNA encodes traits, also known as phenotypes.
• Humans have approximately 25,000 genes, which collectively influence traits.
• Certain traits are controlled by a single gene, while most traits are influenced by multiple genes (polygenic traits).
• Example: The trait for ear lobe attachment can be examined to show genetic variation among individuals.

Bacterial Experiment with Mice

• S bacteria: possess a capsule that is harmful to mice.
• An experiment showed that:
• Live S bacteria killed mice due to their virulence from the capsule.
• Live R bacteria (which lack the capsule) did not harm the mice.
• Heat-killed S bacteria (non-viable) also did not kill mice.
• Mixing heat-killed S bacteria with live R bacteria resulted in the death of mice, suggesting that genetic information was transferred.

Bacteriophage Structure

• A bacteriophage consists of a protein coat and a genome.
• It injects its genome into a bacterial cell, subverting the cell's machinery to replicate itself.
• Viral proteins remain outside; only the viral DNA enters the bacterial cell.
• The bacterial cell’s machinery cannot differentiate between viral and bacterial DNA, allowing for viral replication.

Radioactive Labeling Experiments

• P32 labeled DNA: radioactive form of phosphorus used to tag DNA but not proteins.
• S35 labeled proteins: radioactive form of sulfur used to tag proteins.
• Findings:
• Bacteriophages with radioactive proteins produced non-radioactive viruses, indicating proteins are not the genetic material.
• This indicates DNA carries genetic information.

Nucleotide Structure

• A DNA nucleotide consists of a phosphate, sugar, and a nitrogenous base.
• Four nitrogenous bases in DNA:
• Adenine (A)
• Thymine (T)
• Cytosine (C)
• Guanine (G)
• DNA has a double-stranded structure that is antiparallel: one strand runs in the 5' to 3' direction, while the other runs 3' to 5'.
• Phosphodiester bonds create strong covalent links between nucleotides.

Base Pairing Rules

• Adenine pairs with Thymine (A-T)
• Cytosine pairs with Guanine (C-G)
• Specific base pairing allows for accurate copying during DNA replication.

Properties of DNA and RNA

• DNA generally exists as double-stranded, while RNA is mostly single-stranded.
• DNA is highly stable; it can survive intact for thousands of years under proper conditions.
• Applications: Ancient DNA analysis is used to study human migration patterns.
• Stability allows for accurate sequencing and analysis over long timeframes.