genetics,gene,chromosomes,organization in prokaryotes and eukaryotes

1. Genome organization
Presented by Dr.SIBI P ITTIYAVIRAH,
PROFESSOR,
DIVISION OF PHARMACOLOGY
DEPARTMENT OF PHARMACEUTICAL
SCIENCES,CPAS,CHERUVANDOOR,KERALA,INDIA.
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2. ❖ The term genome was introduced by H.Wrinkler 1920 to
denote the complete set of chromosomal and
extra-chromosomal genes present in an organism, including a
virus.
❖ The genome is the full complement of genetic information in a
cell, and contains the programme required for that cell to
function.
❖
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3. Gene
A gene is a region of DNA that encodes function. A
chromosome consists of a long strand of DNA
containing many genes.
A human chromosome can have up to 500 million
base pairs of DNA with thousands of genes.
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4. Gene
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5. ❖ Cellular organization of genome function occurs at
three hierarchical levels: the spatial and temporal
organization of nuclear processes themselves,
including
❖ transcription,
❖ RNA processing,
❖ DNA replication, and
❖ DNA repair;
❖
❖ the organization of chromatin into higher-order
domains; and the spatial arrangement of chromatin.
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6. Gene Britannica
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7. Gene, unit of hereditary information that occupies a fixed
position (locus) on a chromosome. Genes achieve their
effects by directing the synthesis of proteins.
In eukaryotes (such as animals, plants, and
fungi), genes are contained within the cell
nucleus.
The mitochondria (in animals) and the
chloroplasts (in plants) also contain small
subsets of genes distinct from the genes found
in the nucleus.
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8. In prokaryotes (organisms lacking a distinct nucleus,
such as bacteria), genes are contained in a single
chromosome that is free-floating in the cell cytoplasm.
Many bacteria also contain
plasmids—extrachromosomal genetic elements
with a small number of genes.
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9. The number of genes in an organism’varies
significantly between species.
human genome contains 20,000 to 25,000 genes.
bacterium Escherichia coli -5,416 genes.
Arabidopsis thaliana—the first plant - complete
genome—25,500 genes;
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10. Genes and Chromosomes
Genes are composed of DNA, except in some viruses which
have genes consisting of a closely related compound called
RNA
A DNA molecule is composed of two chains nucleotides that o
resemble a twisted ladder.
The sides of the ladder are made up of sugars and phosphates,
and the rungs are formed by bonded pairs of nitrogenous
bases. These bases are adenine,guanine,cytosine,thymine
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11. Gene transcription and translation
The sequence of bases along a strand of DNA
determines the genetic code
When the product of a particular gene is
needed, the portion of the DNA molecule that
contains that gene will split.
Through the process of transcription, a strand
of RNA with bases complementary to those of
the gene is created from the free nucleotides
in the cell. 11

12. Gene transcription and translation
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13. During translation,
a second type of RNA,
Transfer RNA (tRNA),
matches up the nucleotides on mRNA with
specific amino acids.
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14. Each set of three nucleotides codes for one amino
acid.
The series of amino acids built according to the
sequence of nucleotides forms a polypeptide chain
all proteins are made from one or more linked
polypeptide chains.
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15. Chromosomes
When Gregor Mendel formulated his laws of
heredity, he postulated-units of inheritance.
What exactly these particles were he did not
know.
Now it is well known - physical location and its
molecular composition of genes.
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16. Chromosomes
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17. Each individual in a sexually reproducing species inherits two
alleles for each gene, one from each parent.
The formation of gametes occurs through a process of cell division
called meiosis.
When gametes unite in fertilization, the double dose of hereditary
material is restored, and a new individual is created.
This individual, consisting at first of only one cell, grows via mitosis,
a process of repeated cell divisions.
Mitosis differs from meiosis in that each daughter cell receives a full
copy of all the hereditary material found in the parent cell.
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18. Mitosis Britannica.com
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19. Meiosis
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20. cell nuclei resolve themselves into small rodlike bodies
during mitosis;-chromosomes (coloured bodies).
When the chromosomes condense during cell division,
- replication.
Each chromosome thus consists of two identical
replicas, called chromatids, joined at a point called the
centromere.
During mitosis the sister chromatids separate, one
going to each daughter cell. 20

21. the number of chromosomes within the nucleus is
usually constant in all individuals of a given species
—for example, 46 in the human,
40 in the house mouse,
8 in the vinegar fly (Drosophila melanogaster;
sometimes called fruit fly),
20 in corn (maize), 24 in the tomato.
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22. Genome organization in eukaryotes
• Much greater complexity than prokaryotes
● much more DNA in cells
• Many proteins specifically associated with DNA
• DNA in eukaryotes organized into 2 or more chromosomes
• Chromosomes have roughly equal amounts DNA & protein
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23. Genome size
Genome size is the total amount of DNA
contained within one copy of a genome
• It is typically measured in terms of mass in
picograms (pg) or megabases (Mb)
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24. ❖ Genome size is the total amount of DNA contained within
one copy of a single complete genome.
❖
❖ One picogram is equal to 978 megabases.
❖ In diploid organisms, genome size is often used
interchangeably with the term C-value.
❖ An organism's complexity is not directly proportional to
its genome size; total DNA content is widely variable
between biological taxa.
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25. ❖ Having two sets of chromosomes or double the haploid number of
chromosomes in the germ cell, with one member of each
chromosome pair derived from the ovum and one from the
spermatazoon. A diploid organism or cell. Having paired sets of
chromosomes in a cell or cell nucleus.
❖
❖ Diploid Cells These cells have two sets of chromosomes. It is
formed by the fusion of two haploid cells. Most mammals are
diploid, i.e., they have two homologous copies of each
chromosome in the cells.
❖ Haploid is the quality of a cell or organism having a single set of
chromosomes. Organisms that reproduce asexually are haploid.
Sexually reproducing organisms are diploid (having two sets of
chromosomes, one from each parent). In humans, only their egg and
sperm cells are haploid.
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26. C value
• C value means, it’s the total amount of DNA in
haploid genome.
• C value = mass of DNA / haploid genome.
It’s characteristic of each genome of species.
• Its measured using cot technique.
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27. Cot analysis
Cot analysis, a technique based on the principles of DNA
reassociation kinetics, is a biochemical technique that measures how
much repetitive DNA is in a DNA sample such as a genome.
It is used to study genome structure and organization and has also
been used to simplify the sequencing of genomes that contain large
amounts repetitive sequence
Cot=DNA Concentration (moles/L) X renaturation time in seconds X
buffer factor (that accounts for the effects of cations on the speed of
renaturation).
Nucleotide concentration = 0.050 M. Renaturation time = 344 sec. Buffer
factor, 0.5 M SPB = 5.820. Cot value = 0.050X 344 X 5.820=100.000. 27

28. DNA organization in Prokaryotes and Eukaryotes
Prokaryotes are typically haploid, usually having a
single circular chromosome found in the nucleoid.
Eukaryotes are diploid; DNA is organized into multiple
linear chromosomes found in the nucleus. ...
Prokaryotic and eukaryotic genomes both contain
noncoding DNA, the function of which is not well
understood.
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31. Prokaryote genomes
• Example: E. coli
• 89% coding
• 4,285 genes
• 122 structural RNA genes
• Prophage remains
• Insertion sequence (IS) elements
• Horizontal transfers
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33. Genome organization
• Prokaryotes
– Most genome is coding
Small amount of non-coding is regulatory sequences
• Eukaryotes
– Most genome is non-coding (98%)
– Regulatory sequences
– Introns – Repetitive DNA 33

34. PROKARYOTIC GENOME
It is circular, double stranded piece of DNA.
Commonly referred to as NUCLEOID.
Length varies widely but is generally few million
base pairs.million base pairs.
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35. Eukaryotic genome organization
1. Multiple genomes: nuclear, plastid: mitochondria,
chloroplasts
2. Plastid genomes resemble prokaryotic genomes
3. Multiple linear chromosomes, total size 5- 10,000 MB,
5000 to 50000 genes
4. Monocistronic transcription units
5. Discontinuous coding regions (introns and exons)
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36. Eukaryotic genome organization (contd.)
6. Large amounts of non-coding DNA
7. Transcription and translation take place in different
compartments
8. Variety of RNAs: Coding (mRNA, rRNA, tRNA), Non-coding
(snRNA, snoRNA, microRNAs, etc).
9. Often diploid genomes and obligatory sexual reproduction
10.Standard mechanism of recombination: meiosis 36

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39. Nucleoid is composed of 60% DNA and small amounts
of RNA and protein.
Nucleoid proteins help to maintain the supercoiled
structure of DNA.
DNA supercoiling refers to over or under winding of a
DNA strand. It is important for DNA packing within all
cells.
Toroid and plectoneme In prokaryotes,
plectonemic supercoils are predominant because of
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40. EUKARYOTIC GENOME in the form of nucleoprotein complex
called chromatin.
Chromatin is made up of 35% DNA,60%35% DNA,60%
proteins,5% RNA
dispersed in nuclear matrix in form of network of chromatin
threads
Information in DNA is read using histones and non-non-
histones(associated with gene regulation)
Saccharomyces cerevisiae was the 1st eukaryote to have
its complete genome sequence determined. 40

41. Eukaryotic genome
• Example: C. elegans
• 10 chromosomes
• 19,099 genes
• Coding region – 27%
• Average of 5 introns/gene
• Both long and short duplications 41

42. HISTONES: are main structural proteins in eukaryotes.
It has positively charged amino acids which helps
histones to bind to DNA and help in packing of DNA
molecule.
Nucleosome has octamer of histones H2A,H2B,H3,H4 &
a strand of DNA having 146 base pair wrapped tightly
around this. DNA strand linking 1 nucleosome to
another is called linker DNA.
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44. Histone 1 protein is associated with linker DNA.
The nucleosome model was proposed by
R.D.KORNBERG & J.O.THOMAS in 1974 to explain
chromatin structure
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45. Human Mitochondrial Genome
Small (16.5 kb)
circular DNA rRNA,
tRNA and protein encoding genes (37) 1
gene/0.45 kb Very few repeats
No introns 93% coding;
Genes are transcribed as multimeric transcripts
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46. Human mitochondrial gene
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