human genome gene density 1/100 kb (vary widely); averagely 9 exons per gene 363 exons in titin gene...

HUMAN GENOMEHUMAN GENOME


Gene density 1/100 kb (vary widely); Averagely 9 exons per gene 363 exons in titin gene Many genes are intronsless Largest intron is 800 kb (WWOX gene) Smallest introns 10 bp Largest protein: titin: 38,138 AA


Interferon genes Histone genes Many ribonuclease genes Heat shock protein genes Many G-protein coupled receptors Some genes with HMG boxes Various neurotransmitters receptors and hormone

receptors

Intronless Genes


The human genome is the term used to describe the total genetic information (DNA content) in human cells.

It comprises two genomes, a complex nuclear genome, and a simple mitochondrial genome


Nuclear genome accounts for 99.9995% of the total genetic information.

Mitochondrial genome accounts for the remaining 0.0005%

HUMAN MITOCHONDRIAL GENOMEHUMAN MITOCHONDRIAL GENOME

The human mitochondrial genome is a single circular double-stranded DNA.

Complete nucleotide sequence has been established


16 569 bp in length 44% (G + C). The two DNA strands have significantly

different base compositions: the heavy (H) strand is rich in guanines, the light (L) strand is rich in cytosines.



H strand enriched in G

L strand enriched in C

Very few repeats No introns 93% coding; Recombination not evident


The human mitochondrial genome contains 37 genes.

28 are encoded by the heavy strand, and 9 by the light strand


Of the 37 genes, 24 specify a mature RNA product: 22 mitochondrial tRNA molecules and two mitochondrial rRNA molecules,

The remaining 13 genes encode polypeptides which are synthesized on mitochondrial ribosomes.



Mitochondrial codon table

HUMAN NUCLEAR GENOMEHUMAN NUCLEAR GENOME

The nucleus of a human cell contains more than 99% of the cellular DNA.

23 (XX) or 24 (XY) linear chromosomes each of which has histones and other nonhistone proteins bound to it.


Introns in the most of the genes Genes are transcribed individually Repetitive DNA sequences (45%) Recombination at least once for each chrom. Mendelian inheritance (X + auto, paternal Y)


Chromosome Size (Mbp)1 2492 2373 1924 1835 1746 1657 1538 1359 13210 13211 13212 123


Chromosome Size (Mbp)13 10814 10515 9916 8417 8118 7519 6920 6321 5422 57

X 141Y 60


Group Chromosomes DescriptionA 1–3 Largest; 1 and 3 are metacentric but

2 is submetacentricB 4,5 Large; submetacentric with two arms

very different in size C 6–12,X Medium size; submetacentricD 13–15 Medium size; acrocentric with

satellites E 16–18 Small; 16 is metacentric but 17 and

18 are submetacentric F 19,20 Small; metacentric G 21,22,Y Small; acrocentric, with satellites on

21 and 22 but not on the Y


Metacentric: Chromosome having its centromere in the middle Submetacentric: Chromosomes have short and long arms of

unequal length with the centromere more towards one end

Acrocentric: Chromosomes have a centromere very near to one end and have very small short arms.


Repetitive sequence The human genome is occupied by stretches of DNA

sequences of various length that exist in variable copy number.

These repetitive sequences may be in a tandem orientation or they may be dispersed throughout the genome.

Repetitive sequences may be classified by function, dispersal patterns, and sequence relatedness.


1. Satellite DNA (tandem repeats)typically refers to highly repetitive sequences with no known function

2. Interspersed repeat sequencesTypically the products of transposable element integration, including retrogenes and retropseudogenes of a functional gene.

Satellite DNA

Microsatellites Minisatellites Macrosatellites



Microsatellites Small arrays of short simple tandem repeats. primarily 4 bp or less. Different arrays are found dispersed throughout

the genome, although dinucleotide CA/TG repeats are most common, yielding 0.5% of the genome.

Runs of As and Ts are common as well. Microsatellites have no known functions.


Minisatellites Tandemly repeated sequences of DNA of

lengths ranging from 1 kbp to 15 kbp. For example, telomeric DNA sequences contain

10–15 kb of hexanucleotide repeats. Most commonly TTAGGG in the human

genome, at the termini of the chromosomes.


Macrosatellites Very long arrays, up to hundreds of kilobases,

of tandemly repeated DNA.


Transposable Elements (Interspersed repeat sequences)

Can be divided into two classes based on the mode of transposition;1. The class I elements2. The class II elements


1. The class I elements They are TEs which transpose by replication that

involves an RNA intermediate which is reverse transcribed back to DNA prior to reinsertion.

These are called retroelements and include LTR transposons, non-LTR elements (LINEs and SINEs), and retrogenes.


2. The class II elements Class II elements move by a conservative cut-and-

paste mechanisms. The excision of the donor element is followed by its

reinsertion elsewhere in the genome.


Integration of Class I and Class II transposable elements results in the duplication of a short sequence of DNA, the target site.

There are about 500 families of such transposons. Most of transposition has occurred via an RNA intermediate,

yielding classes of sequences referred to as retroelements (more than 400 families, e.g. Alu, L1, retrogenes, MIR).

However, there is also evidence of an ancient DNA-mediated transposition (more than 60 families of class II (DNA) transposons, e.g. THE-1, Charlie, Tigger, mariner).


Retroelements (LINEs) long interspersed repetitive elements and

(SINEs) Short interspersed repetitive elements are the two most abundant classes of repeats in human.

Represent the two major classes of mammalian retrotransposons.


LINEs (long interspersed repetitive elements) L1, L2, L3 LINE is ~21% of human DNA A full-length LINE (or L1 element) is approximately 6.1 kbp There are about 100000 copies of L1 sequences in our genome. Approximately 1% of the estimated 3500 full-length LINEs have

functional RNA polymerase II promoter sequences along withtwo intact open reading frames necessary to generate new L1 copies.


SINE (Short interspersed nuclear elements) Alu is ~10.7% of human DNA (1,200, 000 copies) MIR, MIR3 is 3% of hum DNA (500,000 copies) Each Alu element is about 280 bp


LTRs (Long terminal repeats) ERV and MalR are 8% of human DNA (500,000 copies)

HUMAN NUCLEAR GENOME HUMAN NUCLEAR GENOME

Class II elements contain inverted repeats (10–500 bp) at their termini and encode a transposase that catalyses transposition.

They move by excision at the donor site and reinsertion elsewhere in the genome by a non-replicative mechanism.

MER1 (Charlie), MER2 (Tigger), others (350, 000 copies) 2.8% of human DNA

The Human Genome Project is one of the most enterprising and challenging aspects of modern genetic research.

Funded primarily by the US Government, This project was created to map and sequence the

entire human genome--that is, to locate every gene on every human chromosome.

It is estimated that anywhere from 100,000 to 300,000 genes exist! And scientists not only plan to map the genes, but also intend to sequence the 3 billion DNA amino acid “building blocks” that make each gene!

HUMAN GENOME PROJECTHUMAN GENOME PROJECT

Human genome project was conceived in 1984 and begun in 1990.

Human genome project draft completed in 2001. These drafts representing only 83-84% of the entire

genome. The Human Genome Project could easily be the most

important organized scientific effort of mankind.


The project involves so many people, and not only geneticists; rather the Human Genome Project relies on all scientific and technological backgrounds from physics and chemistry to engineering and robotics to computer science.

Even sociologists, ethicists, and theologians are involved. Never before in the history of humanity have so many professionals united under a single scientific endeavor.

The estimated total cost of the Human Genome Project is a staggering $3 billion

The US government provides most of the funds (other funds coming from big companies and other countries).


human genome gene density 1/100 kb (vary widely); averagely 9 exons per gene 363 exons in titin gene...

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