This document discusses the organization of DNA in chromosomes. It explains that DNA is highly condensed and packaged through wrapping around histone proteins to form nucleosomes, which are further compacted by winding around scaffold proteins. This allows the long DNA molecules to fit within the nucleus. Key structures of chromosomes include the centromere and telomeres. The number and size of chromosomes varies between species and can identify organisms. Banding patterns along chromosomes allow them to be identified and mapped.

1. DNA ORGANIZATION IN
CHROMOSOME

2. Key vocabulary
 Nucleoid/ nucleosomeNucleoid/ nucleosome
 ChromatinChromatin
 Scaffold proteinScaffold protein
 Histone/ non histoneHistone/ non histone
 CentromereCentromere
 TelomereTelomere
 KaryotypingKaryotyping

3. Organization
 Highly dependent on the type of org.Highly dependent on the type of org.
 Prokaryotic vs Eukaryotic org.Prokaryotic vs Eukaryotic org.
 Different technique used to visualise.Different technique used to visualise.

4. Precise location
Such a compact space. Question arises on how key activities inSuch a compact space. Question arises on how key activities in
protein synthesis can take place within this limited space.protein synthesis can take place within this limited space.

5. Closer view..

6. Chromatin
Chromosome discovered by W. Waldeyer.
Euchromatin –Fibers less packed, disperse–Fibers less packed, disperse
appearance occupying most of the nuclearappearance occupying most of the nuclear
region.region.
Heterochromatin- More dense area, found atMore dense area, found at
centromeres.centromeres.

7. Chromosome number.
Diff. org = diff. no.
 Man 23 pairs =Total 46.
 22 pairs of autosomes
 2 sex chromosomes.
 Cht. size shape + pattern,
 Numbered in order of size.
Different cell diff number eg.
Liver cells 92.

8.  Varies among species.Varies among species.
 Unrelated to the size or biological complexityUnrelated to the size or biological complexity
of an org.of an org.
 An asian deer = 3.An asian deer = 3.
 Diploid – 2 of the chromosome in a set.Diploid – 2 of the chromosome in a set.
 Tetraploid – 4 of each chr.Tetraploid – 4 of each chr.
 Octaploid – 8 of each chr.Octaploid – 8 of each chr.

9. G-bands
 Certain Tx/ staining techniques (Eg. Giemsa)Certain Tx/ staining techniques (Eg. Giemsa)
will allow chromosomes to have striations.will allow chromosomes to have striations.
 Large structures containing approx 10Large structures containing approx 1077
bp DNAbp DNA
 chromosomes can be id by cht. bandingchromosomes can be id by cht. banding
pattern- Used for karyotyping –pattern- Used for karyotyping –
 Translocations can be id. by comparing to theTranslocations can be id. by comparing to the
original diploid set.original diploid set.

10. Homologous pairs..Homologous pairs..

11. Homologous contd..
 Notice that the size,
order of bands, and
shape is the same for
both chromosomes.
 Carry the same genes
in the same order.

12. Human chromosomes..

13. Human Karyotype
Sex
chromosomes

14. Chromosomes and genes..
 The dark lines
represent bands.
 Each chromosome,
bears a particular set
of genes, these genes
are arranged in a
specific order.

15. Typical metaphase chromosome
i.i. Contains a DNA replication origin
 ii. A centromere to attach the DNA to the mitotic
spindle.
 iii. A telomere located at the end.
 DNA needs to be condensed.
 Chromosomes with AT/ GC base pair specific dyes. When
stained.
 Mitotic chromosomes have a banded structure
. ? Methaphase and not other stages?

16. Basic units of a chromosome
 i. i. DNA (2.2m = Massive folding + coiling)
 ii. Proteins (Histones, scaffold p, polymerase)
 iii.Small amounts of RNA.

17.  Complex between histones + DNA = chromatin.
 Nucleosome = basic structure of chromatin (beaded appearance)
 Scaffold protein = non-histone p. Nucleosome coils aound it.
 Polymerases = enzymes involved with
a)transcription of the gen. information during protein synthesis
b)replication of the DNA prior to the division of chromosomes.

18. Nucleosome..
 Contains 200 bp DNA.Contains 200 bp DNA.
 Subunit of chromatinSubunit of chromatin
composed of short DNAcomposed of short DNA
wrapped around histonewrapped around histone
 8 histone molecules =8 histone molecules =
octamer.octamer.
 Nucleosome fibre is tightlyNucleosome fibre is tightly
coiled and looped aroundcoiled and looped around
non-histone proteinsnon-histone proteins
 Nucleosomes are packedNucleosomes are packed
together = compact.together = compact.

19. Placement of genes
 Gene = A region of DNA Gene = A region of DNA
that that controls hereditary
info specifiying the
sequence of a particular
protein. .
 Carries biological info Carries biological info
that must be copied and that must be copied and
transmitted to its transmitted to its
progeny.progeny.
 Can be as short/long.Can be as short/long.
 2001: 30,00/40,000 2001: 30,00/40,000
genes.genes.

20.  Color BlindnessColor Blindness
 Muscular DystrophyMuscular Dystrophy
 Fragile X syndromeFragile X syndrome
 HemophiliaHemophilia