DNA Packaging

Nucleosome - histones

Definition: The basic structural unit of DNA packaging.

Components: Consists of a segment of DNA wrapped around a core of histone proteins.

Histones: Small, positively charged proteins that help organize and condense DNA into a compact structure.

Function: Nucleosomes help regulate gene expression and DNA replication by controlling access to genetic information.

Chromatin

Components: Consists of DNA wrapped around histone proteins, forming nucleosomes, along with non-histone proteins.

Function: Chromatin helps organize DNA within the nucleus, regulates gene expression, and ensures DNA replication and repair.

Chromosome

Structure: Each chromosome consists of a single DNA molecule wrapped around histone proteins, organized into chromatin, and condensed into a distinct, visible structure during cell division.

Function: Chromosomes ensure the accurate transmission of genetic information during cell division and contribute to the regulation of gene expression.

Types of chromosomes

Types:

Somatic Chromosomes: Non-sex chromosomes that make up the majority of an organism's genome. (2 or 1 pair)

Sex Chromosomes: Determine the sex of an individual (e.g., X and Y chromosomes in humans). (44 or 22 pair)

How many chromosomes do humans have?

46 or 23 pairs

Centromere

Definition: The region of a chromosome where the two sister chromatids are joined together.

Types of centromere placements

• Metacentric

• Submetacentric

• Acrocentric

• Telocentric

Metacentric

• Definition: Centromere is located near the center of the chromosome, resulting in arms of approximately equal length.

• Appearance: Chromosome appears X-shaped with central centromere.

Submetacentric

Definition: Centromere is slightly off-center, creating one arm that is longer than the other.

Appearance: Chromosome has a slight asymmetry with a noticeable difference in arm length.

Acrocentric

Definition: Centromere is positioned very close to one end of the chromosome, creating one very short arm and one long arm.

Appearance: Chromosome appears almost "L" shaped with a long arm and a very short arm.

Telocentric

Definition: Centromere is located at the very end of the chromosome, resulting in a chromosome with only one arm.

Appearance: Chromosome has a single, long arm, and no visible short arm.

Denaturization temperature

94-95 C

Long arm and short arm can also be called

• Long - P

• Short - Q