Understanding DNA, Gene Expression, and Cell Division

The Building Blocks of Life: DNA and Nucleic Acids

DNA (Deoxyribonucleic Acid) is the main component of genetic material in most organisms. Together with RNA (Ribonucleic Acid), it forms the genetic material for some viruses. Both DNA and RNA belong to a group of molecules called nucleic acids.

Nucleotides: The Basic Units

Nucleotides are the smaller molecules that, when linked together in a repeating pattern, form the structure of nucleic acids like DNA.

The Structure of DNA

DNA has a super-compact, coiled form that allows it to fit inside cells. This coiled structure is organized into bodies called chromosomes.

Location of DNA in Cells

• Prokaryotes: The DNA is located in the cytoplasm.
• Eukaryotes: The DNA is found within the cell nucleus.

The Core Functions of DNA

DNA is the biomolecule that contains hereditary information, which is transmitted from one generation to the next. It also holds the instructions for producing proteins. This process involves RNA, which extracts the information from the DNA in the nucleus and carries it to the ribosomes for protein synthesis.

Key Genetic Terminology

• Gene: A specific segment of DNA that contains the information for a particular trait or protein.
• Genotype: The complete set of genes an organism inherits.
• Phenotype: The set of observable characteristics or traits of an organism, resulting from the interaction of its genotype with the environment.
• Genome: The complete set of genes for a species.
• Germline: The sequence of germ cells (e.g., male and female gametes) that have genetic material that may be passed to a descendant.

DNA Replication and Cell Division

The Process of DNA Replication

Before a cell divides, it must duplicate its entire chromosome content through a process called DNA replication. This ensures that each new daughter cell receives a complete set of chromosomes. After duplication, two identical copies of the DNA exist.

When Does Replication Occur?

DNA replication happens just before mitosis (cell division).

Importance of Accuracy

If this process is not carried out correctly, mutations can occur.

Semiconservative Replication

Replication is described as semiconservative because each new DNA molecule consists of one original strand and one newly synthesized strand, thus retaining half of the original information.

Mitosis and Meiosis

Mitosis is the process of cell division where genetic information is transmitted to create two identical daughter cells. Meiosis is a different type of cell division that produces gametes (sperm and egg cells) for sexual reproduction.

Diploid and Haploid Cells

These terms refer to the number of chromosome sets in a cell. Diploid cells have two sets of chromosomes, while haploid cells have only one set.

From Genes to Proteins: Expression

Proteins are responsible for the expression of the genetic information that is transmitted between generations.

Transcription: DNA to RNA

Transcription is the first step in gene expression. In this process, the information contained in a DNA sequence is transferred to an intermediary molecule, messenger RNA (mRNA). A segment of the DNA is essentially copied into an RNA sequence.

Translation: RNA to Protein

Translation is the second major step in protein synthesis. The mRNA sequence is decoded to produce a polypeptide—a chain of amino acids that will fold to become a functional protein. Translation must always follow transcription and occurs in four main phases:

1. Activation
2. Initiation
3. Elongation
4. Termination

Pioneers in DNA Discovery

Rosalind Franklin

Rosalind Franklin was a scientist whose X-ray diffraction photographs were crucial in revealing the double-helical structure of DNA.