Post on 30-Dec-2020
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5.1 DNA Organization
Organization of Genetic Material
Genome: the total genetic material of an organism
Gene: the functional unit of DNA (a specific DNA sequence that codes for RNA and then made into proteins)
Non-coding regions: no genes, may contain regulatory sequence
Prokaryotic Cells
Bacterial chromosome:
Circular, double-stranded DNA
No nucleus – not separated
in the nucleoid
Tightly packed supercoiling
Supercoilinglooped
proteins
Formation of
additional coils due to
twisting forces
Controlled by enzymes
topoisomerase I and II
Antibacterial drugs
block these enzymes
DNA of Prokaryotic Cells
Haploid:
• Have only one set of chromosomes
• Carry only one copy of each gene
Genome contains:
• Genes
• Regulatory sequences (control gene activity)
• has very little non-essential DNA
E. Coli
genome
Plasmid
in some prokaryotes
Small, circular or linear DNA
Often carry non-essential genes
Not part of nucleoid
Can be copied and transmitted between cells
Can be incorporated into chromosomal DNA and reproduced in cell division
DNA of Eukaryotic Cells
Double-stranded
Linear
Total amount much greater than in prokaryotic cells
inside nucleus
2m DNA fits into a 4μm nucleus Greater compacting
(protein)
Solenoid
DNA Organization in Eukaryotic Cells
“Beads-on-a-string
Chromatin
DNA Organization in Eukaryotic Cells
Chromosome
Variation in the Eukaryotic Genome
1. Diploid vs Haploid
• Most are diploid
• Some haploid (ferns, algae)
• Some triploid (seedless watermelon)
2. Genes are not evenly spaced, and not equally divided
• Chr19 : 72 million base pairs with 1450 genes
• Chr4 : 1.3 billion base pairs with 200 genes
Variation in the Eukaryotic Genome
3. Size of genome
4. Number of genes
• Vary greatly
• No correlation to organism’s
complexity
(A) Lungfish have 40 times more DNA
per cell than a human cell.
(B) Rice has 30 000 more protein-
coding genes than a human.
(C) C. elegans has the same number
of genes as humans but less DNA.
Variation in the Eukaryotic Genome
5. Coding:
• Can code for proteins
• Can code for RNA molecules (for cellular
processes, not protein-making)
increase biological complexity without
increasing the number of protein-coding genes