DNA replication

DNA serves as the primary source of genetic information in all cells containing it, dictating cellular functions through the processes of transcription and translation.
Although not all cells utilize DNA affectively, every cell with DNA relies on it for protein synthesis.

The transcription begins with DNA, producing a preRNA transcript which undergoes splicing to remove introns and join together exons, resulting in a mature mRNA transcript.
This mature mRNA is then transported out of the nucleus into the cytoplasm for translation.
In the cytoplasm, the first codon (AUG) is recognized by a ribosome which then facilitates the binding with the corresponding tRNA carrying the methionine amino acid.

The ribosome reads mRNA in the cytoplasm, matching tRNAs with corresponding codons: initiates with AUG and continues sequentially.
Each bound tRNA carries an amino acid. The ribosome catalyzes the formation of peptide bonds between incoming amino acids, elongating the forming polypeptide chain.
The process continues until a stop codon is encountered, after which the ribosome disassembles, and the newly formed polypeptide is released.

The mRNA molecule has a transient existence; it is rapidly degraded after translation to avoid excess accumulation of transcripts.
This mechanism maintains efficient protein production while safeguarding the integrity of the DNA, which remains inside the nucleus.

DNA encodes the instructions for making proteins, critical for cellular function.
The integrity of DNA is of utmost importance, as damage or mutations can lead to improper protein synthesis, potentially resulting in diseases such as cancer.

Proteins are made of amino acids, encoded by nucleotide sequences in DNA. The correct primary sequence is crucial for proper protein folding and function.
Enzymatic processes rely on protein structure, which is determined by DNA coding.

Mutations in DNA can result in changes to amino acid sequences which affect secondary and tertiary structures of proteins, leading to malfunction and disease.
Understanding the consequences of mutations provides insights into genetic diseases and the development of therapies.

Human cells can express thousands of distinct proteins, coding from numerous segments of the genome.
Each protein serves unique functions, contributing to the organism's overall health and biological processes.

DNA replication occurs during the S phase of the cell cycle, where the entire genome is duplicated before cell division.
It involves several enzymes:
- Helicase: Unzips the DNA strands by breaking hydrogen bonds.
- Primase: Synthesizes RNA primers to initiate replication.
- DNA Polymerase: Synthesizes new DNA strands by adding nucleotides. It can also proofread for accuracy.
- Single-stranded binding proteins: Stabilize the open DNA strands to prevent them from rejoining.
- Topoisomerase: Relieves torsional stress during unwinding.
- DNA Ligase: Joins Okazaki fragments on the lagging strand, completing DNA synthesis.

DNA replication is semiconservative: each of the new DNA molecules contains one old strand and one newly synthesized strand.
This property ensures genetic continuity and fidelity during cell division, contributing to the stability of the genetic code.

Each cell has the capability to replicate its entire genetic code to produce new cells while utilizing transcription and translation for ongoing protein synthesis.
Assessing the processes governing DNA function is crucial for understanding cellular operations and addressing genetic diseases.