DNA Replication and Structure
DNA replication is a crucial process in cell division and inheritance. The structure of DNA consists of nucleotides with purines adenineandguanine and pyrimidines thymineandcytosine connected by phosphate groups and pentose sugars. The DNA replication process step by step involves several key enzymes and follows a semi-conservative model.
Vocabulary: Purines are nucleotides with two carbon rings, while pyrimidines have one carbon ring.
The steps of DNA replication in order are as follows:
- DNA helicase unzips the double helix by breaking hydrogen bonds.
- Free nucleotides enter the replication fork.
- DNA polymerase adds bases to the growing strands after a primer is laid down.
- DNA ligase forms new hydrogen bonds to complete the process.
Highlight: The semi-conservative replication model ensures that each new DNA molecule contains one original strand and one newly synthesized strand.
The replication process differs slightly between the leading strand 5′to3′direction and the lagging strand 3′to5′direction, with the lagging strand requiring additional steps to form Okazaki fragments.
Definition: Complementary base pairing is the rule that governs DNA replication, where A pairs with T and G pairs with C.
Protein Synthesis
Protein synthesis is a two-step process involving transcription and translation. This process is essential for creating the proteins necessary for cellular function.
Highlight: Why is protein synthesis important? It allows cells to produce the proteins needed for structure, function, and regulation of the body's tissues and organs.
Transcription:
- The DNA molecule opens up as hydrogen bonds break.
- Free RNA bases attach to the antisense strand of DNA.
- mRNA is formed through complementary base pairing.
- The process continues until a stop codon is reached.
- The DNA zips back up behind the transcription bubble.
Translation:
- mRNA travels to a ribosome for processing.
- tRNA brings amino acids to the ribosome.
- Anticodons on tRNA link to codons on mRNA.
- Amino acids are joined to form a growing polypeptide chain.
- The process continues until a stop codon is reached, forming a complete protein.
Example: The genetic code determines which amino acids are added to the growing protein chain. For instance, the codon AUG codes for the amino acid methionine and also serves as the start codon.
