Nucleic Acids and Genome Organisation

Study Notes

Nucleic Acids and Genome Organisation

Nucleic acids, DNA and RNA, are crucial for carrying genetic information. DNA carries the genetic code, while RNA plays diverse roles in gene expression and protein synthesis.
DNA structure is a double helix composed of nucleotides, with specific base-pairing rules (Adenine-Thymine, Guanine-Cytosine).
The sequence of nucleotides along a DNA strand dictates the genetic information.
Genome organization refers to the arrangement of genetic material (DNA) within a cell. Different organisms have distinct methods of packaging, such as bacteria versus eukaryotes.

Bacterial Chromosome Organisation

Bacterial genomes are typically circular, single-stranded DNA molecules.
They are not enclosed within a nucleus but exist in the cytoplasm.
Often have extrachromosomal DNA called plasmids, which can replicate independently.
Supercoiling plays a critical role in compacting the bacterial chromosome.
Typically one circular chromosome per cell.

Eukaryotic Chromosome Organisation

Eukaryotic genomes are linear DNA molecules, often highly fragmented and found at more than one location, organized in chromosomes within the nucleus.
Chromosomes are organized around histone proteins, forming chromatin. The degree of compaction varies during the cell cycle.
Different chromosome types exist in the genome with different levels of expression.
Multiple chromosomes per cell, which can differ in morphology and size.

DNA Reassociation Kinetics

DNA reassociation kinetics provides information about the complexity and repetitiveness of DNA sequences.
It involves separating strands of DNA and allowing them to re-anneal.
The rate of reassociation depends on the number of copies of each sequence present.
This allows researchers to determine the amount of unique and repetitive DNA sequences within a genome.
Reassociation rates vary according to DNA complexity. More complex DNA reassociates slower.

Satellite DNA

Satellite DNA is a type of repetitive DNA sequence that differs from the bulk of chromosomal DNA in base composition.
Often highly repetitive, making up a significant portion of the genome, especially in eukaryotes. This can be tandem repeats or interspersed repeats.
Frequently found in heterochromatin regions, and plays a role in chromosome structure and genetic stability.
Functions are largely unknown, although some evidence suggests a structural role in centromeres or telomeres.

DNA Methylation and Imprinting

DNA methylation is a process where a methyl group is added to a cytosine base in DNA.
This process plays a vital regulatory role in gene expression. Transcription is usually repressed after Methylation.
DNA methylation patterns can be inherited, thus contributing to epigenetic inheritance.
Imprinting refers to a phenomenon where the expression of a gene depends on its parental origin. (gene expression triggered by one copy of a gene but not both)
Methylation is often associated with imprinting. A specific methylation pattern in a parental-specific copy of DNA often determines which gene is expressed.
DNA methylation patterns can be influenced by environmental factors, and abnormal methylation patterns have been linked to various diseases.

Description

Explore the fundamentals of nucleic acids, focusing on DNA and RNA structure and function. Understand how genome organization differs between bacteria and eukaryotes, and learn about concepts like plasmids and supercoiling in bacterial chromosome organization.