Genes & Chromosomes

Chromosomes

• structural unit of genetic material.

• In the nucleus(eukaryotes).• Rod shaped, 2chromatids,

centromere(cadherin).• Each chromatid is a single,

linear double-strand DNA molecule and associated proteins.(+small amount RNA).

• p arm(long one), q arm(short).

• consists of coding and non-coding sequence.

Chromosomes:

• bears a particular set of genes.

• Different organism = different # of CRMS*.

• Half the number of CRMS is inherited from the mother (maternal CRMS) and the other half from the father(paternal CRMS).

• Homologous CRMS are the same size and shape.

CRMS*: Chromosomes.

• Two types of CRMS : autosomal(22 pair) + sex(XX) or(XY).

• CRMS # 1= biggest CRMS.

• CRMS # 21= smallest one.

Chromosomes:

• CRMS are visible during cell division. In between cell division they appear thread like “Chromatin”.

• Two types of chromatins: heterochromatinhighly condensed inactive

DNA

Euchromatinmildly condensed active

DNA that contains the expressed genes

Functions of Chromosomes

• unique structure of CRMS keeps the DNA in a tightly wrapped position.

• control all the activities of a living cell.• essential for the process of cell division and

are responsible for the replication, division and creation of daughter cells.

• Chromosome functions include holding genes, the units of heredity.

Genes• The physical and functional unit of heredity.• The human genome contains at least

26,000 genes.• A locus on CRMS constituted of DNA

nucleotide sequence that code for certain characteristics.

• Version of the genes called alleles; their loci are the same on the homologous chromosome pairs.

Genes• In molecular terms, it is the entire DNA

sequence including exons, introns, and noncoding transcription- control regions- necessary for production of functional protein or RNA.

• Genes = regulatory region and transcriptional region.

• •Exons encode a peptide or functional RNA.• •Introns will be removed after transcription.

Functions of Genes

1. Carrier of traits from one generation of organism to the next generation of organism.2. Serve as template for copies of itself.3. Genes are expressed, mRNA is transcribed from the gene (template), the mRNA serves as a template during translation for peptide (protein) synthesis.

Chromosomal DNA in coiled hierarchy

• The length of the 46 DNA molecules in a single human cell is about two meters. Can’t fit in the nucleus without condensation.

• Condensation requires intervention of two classes of proteins : histone proteins(H1, H2A, H 2B, H3 and H4) and non-histone proteins.

• 1st level of condensation: nucleosome• bead on a string (11nm)= 2 nm DNA(146

bp*) + octamer of histones

• 2nd level: 30 nm fiber or solenoid.coiling of beads in a helical structure.(+H1)• 3rd level: loops, scaffolds and domains.

DNA condensation.mpg

Thank

you

Done by: Shahira M Chahrour.

To: Prof Dr. Mohamad Khalid.