Cellular DNA Structure

Organization of DNA in Eukaryotic and Prokaryotic Cells

• In prokaryotes (e.g., bacteria), DNA is typically circular with no free ends, relatively short, and not bound to histones.
• In eukaryotes (e.g., humans), DNA is linear with two ends, longer, and tightly wrapped around histone proteins.

Structure of Chromosomes

• In eukaryotes, DNA is wrapped around histones, forming complex structures called chromosomes.
• Chromosomes are not found in prokaryotes since their DNA is not bound to histones.

Chromatin and Chromatids

• Before cell division, chromosomes are copied, and the two copies remain attached at the centromere.
• The two DNA molecules are called chromatids.
• At this stage, the whole structure is referred to as a chromosome.

Homologous Chromosomes

• In human cells, there are 46 chromosomes, with 23 coming from each parent.
• Homologous chromosome pairs have the same genes, but may have different alleles (versions) of those genes.
• The position of a gene on a chromosome is called the locus for that gene.

Genes and Alleles

• A gene is a section of DNA that encodes the amino acid sequence of a polypeptide.
• Random mutations can cause genes to occur in different versions, known as alleles.
• The blood group gene has three main alleles: A, B, and O.

Organization of DNA in Eukaryotic and Prokaryotic Cells

• Prokaryotic DNA is typically circular, relatively short, and not bound to histones.
• Eukaryotic DNA is linear, longer, and tightly wrapped around histone proteins.

Structure of Chromosomes

• In eukaryotes, DNA wraps around histones, forming complex structures called chromosomes.
• Chromosomes are absent in prokaryotes since their DNA is not bound to histones.

Chromatin and Chromatids

• Before cell division, chromosomes are copied, and the two copies remain attached at the centromere, forming chromatids.
• The entire structure, including the two chromatids, is referred to as a chromosome.

Homologous Chromosomes

• Human cells contain 46 chromosomes, with 23 coming from each parent.
• Homologous chromosome pairs have the same genes, but may have different alleles (versions) of those genes.
• The location of a gene on a chromosome is called the locus for that gene.

Genes and Alleles

• A gene is a section of DNA that encodes the amino acid sequence of a polypeptide.
• Random mutations can cause genes to occur in different versions, known as alleles.
• The blood group gene has three main alleles: A, B, and O.

This quiz covers the organization of DNA in eukaryotic and prokaryotic cells, including the structure of chromosomes. Learn about the differences between prokaryotes and eukaryotes in terms of their DNA.