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genome structure and repetitive sequence.pdf
The document discusses the differences in genome structure between prokaryotes and eukaryotes, highlighting that eukaryotic genomes are more complex, with linear DNA molecules and features like repetitive DNA. It explains that genome size does not correlate with an organism's complexity, providing examples to illustrate this point. Additionally, the presence of various forms of DNA, including non-repetitive and repetitive sequences, is explored in relation to the genetic diversity and functional requirements of different organisms.
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genome structure and repetitive sequence.pdf
- 1.
- 2. Difference between prokaryotes andeukaryotes In eukaryotes: 1. The nuclear genome is split into a number of individual DNA molecules 2. The DNA molecules are linear 3. there are two copies of each chromosome in most cells Human chromosomes
- 3. In eukaryotes: 4. Theintegrity of individual genes can be interrupted . 5.There may be multiple and identical copies of particular sequences . 6.There may be large blocks of DNA that do not code for protein. 7.The arrangements for gene expression in eukaryotes must bedifferent from those in prokaryotes .
- 4. C-value • Means Constantor Characteristic value • is the amount of DNA in the haploid genome of an organism • Measured in picogram
- 5. False idea: complexity ofan organism is directly proportional with its genome size There is no direct correlation between: ➢ Genome size and organism’s complexity ➢ Genome size and chromosome number
- 6. • Ex: Thetoad Xenopus and man have genomes of essentially the same size , but we assume that man is more complex in terms of genetic development 1-genome size not related to genetic complexity
- 7. 2-There is nocorrelation between genome size and chromosome number Saccharomyces cerevisiae • Genome = 12.1 MB • Split into 16 chromosome Human • Has DNA more about 150 times (3200MB) • Haploid complement of only 23 chromosomes
- 8. kinetics of thereassociation or reannealing reaction • in molecular biology and genetics refers to the process of two complementary single-stranded DNA molecules coming together and forming a double-stranded DNA molecule. • biochemical studies on purified eukaryotic DNA purified nucleic eukaryotic DNA Heat The 2 strands separate Allow to cool DNA started coming together much faster than was expected onthe basis of separated strands of single genes finding each other. Observation
- 9. “Fast reassociating DNAis low complexity” • Repetitive DNA: a class of DNA that was present in many copies in the genome • Repetitive frequency (f): The number of copies present per genome So, Do large genomes contain a greater number of different genes or instead more copies of the same genes? • a substantial part of the eukaryotic genome is made of repetitive DNA or individual sequence elements that are repeated many times over , either in tandem arrays or interspersed throughout the genome. conclusion
- 10. “There is anincrease in the minimum genome size found in each group as the complexity increases” • Minimum Genome Size: It represents the minimal set of genes necessary for the basic biological processes of that organism. • Groups: (e.g., different species, genera, families, or orders) or other criteria like ecological roles or lifestyles. • Complexity: More complex organisms typically have more specialized cell types, tissues, organs, and behaviors. They often perform a wider range of functions and have more sophisticated life strategies. • Increase in Minimum Genome Size: more complex organisms generally require a larger set of genes to support their complex functions and traits. Therefore, It is necessary to increase the genome size in order to make insects , birds , amphibians and mammals.
- 11. Eukaryotic DNA Non repetitiveor single copy DNA sequences or functional genes Repetitive DNA functional sequence Noncoding functional sequence Telomeres Families of coding (and related pseudogenes) Dispersed gene families Tandem gene families “tandem array” sequence with no known function Repeats in centromeric heterochromatin “satellite” Variable Number Tandem Repeats “VNTRs” Transposonses sequence Transposons Retro transposons Spacer DNA
- 13. (1) Non repetitiveor single copy DNA sequences. • Present in single or low copy numbers. • Includes coding sequence for structural genes (up to 1400 bp in size),which account for 3% of the genome. • The remainder is intrinsic sequence or spacer DNA • portion of the genome that does not consist of repetitive elements or sequences • R= 1 or 2 • contains the genetic information necessary for encoding proteins and regulating gene expression. • plays a central role in determining an individual's traits, functions, and overall biology
- 14. The organism Thepresence of non repetitive sequences Prokaryotes only non repetitive DNA Lower eukaryotes most of the DNA is non repetitive , < 20% falls into one or more moderately repetitive components. plants and amphibians the non repetitive DNA may be reduced to a minority of the genome , with the moderately and highly repetitive components accounting for up to 80% animal cells up to half of the DNA often is occupied by moderately and highly repetitive components. (1) Non repetitive or single copy DNA sequences.
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- 16. complexity is amultifaceted concept influenced by various genetic and non-genetic factors. • There is an increase in the minimum genome size found in each group as the complexity increases • It is necessary to increase the genome size in order to make insects , birds , amphibians and mammals.
- 17. (2) Repetitive DNAsequences. • Functional coding sequence a. Families of coding genes : ➢Dispersed gene families ❑Gene families are the representation of all those genes which are originated from 1 ancestor gene due to duplication ❑Those genes are scattered rather than clustered and this scattered distribution occurs due to gene duplication followed by gene movement or transpostioins ❑several types of proteins are encoded by families of homologous genes spread throughout the genome
- 18. families may compriseonly a few genes or very many Gene family Number of genes Actin from 5 to 30 genes Keratin > 20 genes Tubulins 3-15 genes Histones 100-1000 genes (2) Repetitive DNA sequences.
- 19. ➢Tandem gene familyarrays: ▪ Tandem copies of rRNA genes in the nucleolar organizer are essential for the efficient production of ribosomal RNA, which, in turn, supports the cell's ability to synthesize proteins. Since ribosomes are fundamental to protein synthesis, the nucleolar organizer plays a crucial role in cellular processes related to growth and protein production. (2) Repetitive DNA sequences.
- 20. ➢Tandem gene familyarrays: ▪ One human Nucleolar Organizer (NO) has about 250 copies of rRNA genes . ▪ For ensuring a large amount of rRNA per cell because Cells need large amount of the products of some genes (2) Repetitive DNA sequences. NOR
- 21. b. Non-coding functionalsequences: ➢Telomeres: ▪ They are specialized structures located at the ends of linear chromosomes in eukaryotic cells. ▪ consist of repetitive DNA sequences that are repeated hundreds to thousands of times. ▪ Human telomeric sequence is 5’-TTAGGG-3’ ▪ solve a functional problem that is inherent in the replication of the ends of linear DNA molecules (end replication problem). (2) Repetitive DNA sequences.
- 22. • Non-Functional repetitive sequence •20% of the human genome consists of nonfunctional repetitive sequences of one kind or another a. Highly repetitive centromeric DNA (2) Repetitive DNA sequences.
- 23. • b. VNTRs: •A special class of tandem repeats which shows variable number at different chromosomal positions and in different individual members of a species. • This type of repeat is called " Variable Number Tandem Repeat " ( VNTR), and sometimes called " Minisatellite DNA“. • The VNTR loci in humans are 1-5 kb sequences. • Consisting of variable numbers of repeating unit from 15 to 100 nucleotides long. • These minisatellite DNA are very useful as "DNA fingerprints " . They are used extensively in forensic medicine. (2) Repetitive DNA sequences.
- 24. • b. VNTRs: •Another class of dispersed repetitive DNA is composed of few nucleotides (1-6) . • This class of repetitive DNA is called " Microsatellite DNA " . • Microsatellites are in fact dispersed regions composed of variable numbers of few nucleotides repeated in tandem . • Because the numbers of repeats varies between individuals, this type of DNA has been most useful in providing a dense array of molecular mark for genome mapping . (2) Repetitive DNA sequences.
- 25. • c. Transposedsequences • A large proportion of a eukaryotic genome is composed of repetitive elements that have propagated within the genome by making copies of themselves , which can move into new locations . • These element collectively called transposed sequences (2) Repetitive DNA sequences.
- 26. (3) Spacer • Thefinal (class/category) of DNA is spacer DNA , which is basically what is the left after all the recognizable units have been identified. • Possibly its function is to space , but no studies have yet been performed to delete such DNA and observe the consequence. • The amount of repetitive DNA is probably the main factor that determines the size of an organism's genome Packaging / Organization of DNA into Chromosome