Introduction to DNA and Genetics

DNA and Chromosomes

• DNA is composed of four nucleotide building blocks: adenine (A), cytosine (C), guanine (G), and thymine (T).
• Nucleotides are linked together into polynucleotide chains forming a sugar-phosphate backbone
• DNA strands are held together by hydrogen bonds between complementary base pairs (A with T, C with G).
• DNA is organized in structures called chromosomes.
• DNA replication is the process by which DNA is copied. The original DNA molecule serves as a template for creating a new double helix.

The Central Dogma of Biology

• The central dogma is a fundamental concept in molecular biology. It describes the flow of genetic information.
• DNA -> RNA -> Protein. The genetic information encoded in DNA is transcribed to RNA, then translated into protein.

Genetics Introduction

• DNA encodes information in a unique sequence of nucleotides in a double helix.
• DNA replication involves the use of one strand as a template to generate complementary strand.
• DNA's information is transcribed into RNA.
• RNA translates the coded messages into proteins.

The Structure of DNA

• DNA consists of two polynucleotide chains that are anti-parallel.
• The repeating units of DNA include sugars, phosphates, and nitrogenous bases.
• The double-helix configuration is stabilized by hydrogen bonds between the bases.

DNA Replication

• DNA replication uses the existing DNA strand as a template to create a new complementary strand.
• DNA polymerase is the key enzyme responsible for DNA replication. It adds nucleotides to the growing strand.
• RNA primers are needed as starting points for DNA replication on the lagging strand.
• Okazaki fragments are formed on the lagging strand since replication is discontinuous.
• DNA ligase joins these fragments to a single continuous strand.

DNA Synthesis Begins at Replication Origins

• DNA replication begins at specific sites called replication origins.
• Helicase unwinds the DNA double helix.
• Replication forks are the sites where the DNA unwinds to create single strands.
• Single-stranded DNA binding proteins stabilize the DNA strands preventing them from re-annealing.
• Initiator proteins are responsible for opening the replication forks.
• DNA polymerase replicates the DNA strands.

DNA Synthesis Enzymes

• Helicase unwinds the DNA double helix separating the two strands.
• DNA polymerase III adds nucleotides to the growing strands.
• Ligase joins the DNA fragments together, especially the okazaki fragments.

A summary of DNA Replication

• Helicases unwind the DNA double helix.
• Single-strand binding proteins stabilize the DNA strands.
• Primase synthesizes RNA primers on the lagging strand to start DNA synthesis.
• DNA polymerase synthesizes new DNA strands based on the template strand.
• Okazaki fragments are formed on the lagging strand, and DNA ligase joins these fragments to form a continuous strand.

Transcription

• RNA polymerase is the enzyme responsible for copying DNA into RNA.
• Transcription produces a complementary RNA strand from a DNA template strand.
• The non-template strand, sometimes called the coding strand, has a sequence equivalent to the RNA produced.

Translation

• The genetic code is the set of rules for translating RNA sequence into an amino acid sequence for protein production.
• In this process codons ( mRNA sequences of three nucleotides) are translated into specific amino acids.

Eukaryotes handle their RNA transcripts differently

• Eukaryotic RNA transcripts undergo processing.
• mRNA transcripts undergo splicing to remove introns, cap addition and tail addition before translation in the cytoplasm.

Code, Codon, and anti codon

• A codon is a sequence of three nucleotides in mRNA that codes for a particular amino acid.
• An anticodon is a sequence of three nucleotides in tRNA that is complementary to a codon.
• tRNA carries the corresponding amino acid to the ribosome to build the polypeptide chain of the protein.