DNA ORGANIZATION IN CHROMOSOME

Key vocabulary

Nucleoid/ nucleosomeNucleoid/ nucleosome Chromatin Chromatin Scaffold proteinScaffold protein Histone/ non histoneHistone/ non histone CentromereCentromere TelomereTelomere KaryotypingKaryotyping

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.

Precise location

 

Such a compact space. Question arises on how key activities in Such 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.

Closer view..

Chromatin

Chromosome discovered by W. Waldeyer.Euchromatin –Fibers less packed, disperse –Fibers less packed, disperse

appearance occupying most of the nuclear appearance occupying most of the nuclear region.region.

Heterochromatin- More dense area, found at More dense area, found at centromeres.centromeres.

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.

Varies among species.Varies among species. Unrelated to the size or biological complexity Unrelated 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.

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 107 7 bp bp DNADNA

chromosomes can be id by cht. banding chromosomes can be id by cht. banding pattern- Used for karyotyping – pattern- Used for karyotyping –

Translocations can be id. by comparing to the Translocations can be id. by comparing to the original diploid set.original diploid set.

Homologous pairs..Homologous pairs..

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.

Human chromosomes..

Human Karyotype

Sex chromosomes

Chromosomes and genes..

The dark lines represent bands.

Each chromosome, bears a particular set of genes, these genes are arranged in a specific order.

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?

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

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.

Nucleosome.. Contains 200 bp DNA.Contains 200 bp DNA. Subunit of chromatin Subunit of chromatin

composed of short DNA composed of short DNA wrapped around histonewrapped around histone

8 histone molecules = 8 histone molecules = octamer.octamer.

Nucleosome fibre is tightly Nucleosome fibre is tightly coiled and looped around coiled and looped around non-histone proteinsnon-histone proteins

Nucleosomes are packed Nucleosomes are packed together = compact.together = compact.

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.

Color BlindnessColor Blindness Muscular DystrophyMuscular Dystrophy Fragile X syndromeFragile X syndrome HemophiliaHemophilia