BIO5101 Notes

BIO5101 (Introduction To Biotechnology) Notes Topic 31-90

Topic 31: Organization of Genetic Material in Eukaryotes

Eukaryotic cells have a complex genetic organization compared to prokaryotes. DNA is contained within a membrane-bound nucleus and is associated with histone and non-histone proteins, forming a highly organized chromatin structure. This organization enables efficient packaging, gene regulation, and accurate replication.

1. General Features of Eukaryotic Genetic Material

1. Location Mostly in the nucleus (nuclear DNA) Also present in mitochondria (mtDNA) and chloroplasts (cpDNA in plants)

2. Chromosome Structure

Linear DNA molecules Each chromosome contains one long DNA molecule with associated proteins

3. Genome Size

Varies widely: Yeast: ~12 Mbp Humans: ~3,200 Mbp Some plants: >100,000 Mbp

4. Ploidy Most eukaryotes are diploid (two copies of each chromosome) Haploid gametes are formed during meiosis

2. Chromatin Structure

Chromatin is the complex of DNA and proteins that forms chromosomes.

A. Histone Proteins

Core histones: H2A, H2B, H3, H4 (form nucleosome core) Linker histone: H1 (stabilizes nucleosome and higher-order structure)

B. Nucleosome

DNA (~146 bp) wrapped around histone octamer Repeating unit of chromatin

C. Higher-order Chromatin Structures

30 nm fiber: nucleosomes folded into solenoid or zig-zag structure Loops and domains: attached to nuclear scaffold or matrix Mitotic chromosomes: highly condensed chromatin during cell division

3. Organization of Eukaryotic

1. Telomeres

Repetitive sequences at chromosome ends Protect DNA from degradation and fusion

2. Centromeres

Region essential for proper segregation during mitosis and meiosis Contains specific DNA sequences and kinetochore proteins

3. Origin of Replication

Multiple origins on each chromosome for efficient replication

4. Introns and Exons

Protein-coding genes often interrupted by introns Exons encode proteins

5. Non-coding DNA

Regulatory sequences, repetitive DNA, transposable elements

4. Gene Arrangement in Eukaryotes

1. Single-gene transcription units (monocistronic)

2. Complex regulation

Promoters, enhancers, silencers