genome organization

Category: Education

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Genome Organization


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Dinesh D. Khedkar Department of Botany A UGC Awarded College with Potential for Excellence NAAC Reaccredited “A” - “Very Good” Grade Shri Shivaji Science College Amravati, Maharashtra - 444 603 Phone No.: 0721-2660855 Fax: 0721-2665485 e-mail : Web site : Genome organizaTION

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Genome The haploid genetic material that an organism possesses Nuclear genome Mitochondrial & chloroplasts genome

Genomic Processes : 

Genomic Processes

Genomics : 


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Facts of Genome Molecular wt of nucleotide pair – 650 Da Wt of chromosome varies greatly No. of chromosome- Bacteria – 01 Human – 46 Garden Pea – 14 Chicken – 78 Maize – 20 Mouse – 40 Frog – 26 Total contour Length – 2 meter / Human cell 1.7 mm / E. coli Cell DNA total length in Human – 2 X 10 11 Km. Distance Sun – Earth – 1.5 X 10 8 Km.

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Facts of Human Genome Human genome = 3 x 109 bp (Cell Size Few Micron) Only 1.5 % Genome is Functional The β-globin gene = 3 x 103 bp Size of an average human chromosome - 130 million bp Rate of replication - ~ 50 bp per sec Fidelity of replication

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How the long DNA is accommodated in cell How the specific genes are active in cells

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Need (movie)

Viruses : 

Virus is infectious particles containing nucleic acid surrounded by a protein capsid Rely on host cell for replication, transcription, translation Exhibit a limited host range Genomes vary from a few thousand to a hundred thousand nucleotides Viruses

Some Virus Structures : 

Some Virus Structures

Bacterial genome : 

In a region called the nucleoid DNA in direct contact with cytoplasm Bacterial genome

Bacterial genome : 

Bacterial genome Chromosomal DNA is compacted ~ 1000 fold to fit within cell

Bacterial Chromosomes : 

Size Escherichia coli ~ 4.6 million bp Haemophilus influenzae ~ 1.8 million bp Composition E coli ~6000 genes Genes encoding proteins for related functions arranged in operons Intergenic regions nontranscribed DNA Single origin of replication (Ori) Bacterial Chromosomes

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Eukaryotic Chromosomes

Anatomical view : 

Anatomical view

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NUCLEOSOME ASSEMBLYFirst level packaging : 

NUCLEOSOME ASSEMBLYFirst level packaging


DNA PACKAGING NUCLEOSOME COMPOSITION DNA - 200 BP (67nm) - 1,30,000 da HISTONES - 4 (2 Each) - 1,08,000 da NON HISTONES - 1 - 24,000 da Total - 2,62,000 da

Histones : 

Histones Small basic protein MW ranging between 11000 – 21000 da Rich in basic amino acid (Lysine, Arginine, etc) 25 Nucleotides can be accommodated per histone TYPES OF HISTONES – Type MW Amino acids H 2 A 13960 129 H 2 B 13774 125 H 3 15273 135 H 4 11236 102 H 1 21130 223


NUCLEOSOME Height – 6 nm Diameter – 11 nm Length of DNA around it – 67 nm (approx. 200 bp) 1.65 turns of DNA around nucleosome A=T rich region mostly attached to histones Histones are forming heterodimer H 2 A and H 2 B; H 3 and H 4 Each heterodimer binds 30 bp DNA at 10 bp interval Phosphate backbone contacts with histones

Further Compaction of the Chromosome : 

Further Compaction of the Chromosome The attachment of radial loops to the nuclear matrix is important in two ways 1. It plays a role in gene regulation 2. It serves to organize the chromosomes within the nucleus Each chromosome in the nucleus is located in a discrete and nonoverlapping chromosome territory

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Compaction level in euchromatin Compaction level in heterochromatin During interphase most chromosomal regions are euchromatic

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In fact in humans only 1.5% of the entire genome length corresponds to coding DNA. This 1.5% codes for about 27,000 genes which in turn code for proteins that are responsible for all the cellular processes.

Heterochromatinization : 

Heterochromatinization Compaction level of interphase chromosomes is not uniform Euchromatin Less condensed regions of chromosomes Transcriptionally active Regions where 30 nm fiber forms radial loop domains Heterochromatin Tightly compacted regions of chromosomes Transcriptionally inactive (in general) Radial loop domains compacted even further

Types of Heterochromatin : 

Types of Heterochromatin Constitutive heterochromatin Always heterochromatic Permanently inactive with regard to transcription Facultative heterochromatin Regions that can interconvert between euchromatin and heterochromatin Example: Barr body

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What is Genome Organization at functional level?

Eukaryotic gene organization : 

Eukaryotic gene organization enhancers silencers

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Peptide Amino acid 360 1021 275 275 MW (Da) 3800 1,25,000 30,000 30,000 Active Protein Tetramer Tetramer Monomer Dimer Function Repressor β- Galactosidase Permease Trans acetylase Lac operon

How ? : 

How ? Introns Extragenic region: gap between genes (spacers) Solitary and Family gene Solitary : Singly in haploid genome (25 – 50%) Family : Set of genes that encode protein with similar but nonidentical amino acid sequence. Pseudogenes: The DNA sequences identical to the actual genes, but nonexpressing Tandemly repeated sequences: rRNA, tRNA and histones. Repeatitive DNA

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Commercial Break GENE EXPRESSION

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