Molecular Structure of DNA

Structure

• DNA (Deoxyribonucleic acid) is a double-stranded helix composed of:
  • Two complementary strands of nucleotides
  • Sugar molecules (deoxyribose) and phosphate groups
  • Nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T)
• The sugar and phosphate molecules make up the backbone of the DNA, while the nitrogenous bases project inward from the backbone and pair with each other in a complementary manner:
  • A pairs with T (two hydrogen bonds)
  • G pairs with C (three hydrogen bonds)

Replication

• DNA replication is the process of creating an exact copy of a DNA molecule
• It occurs during cell division and is initiated by an enzyme called helicase
• The process involves:
  1. Unwinding of the double helix
  2. Binding of primers to the template strands
  3. Synthesis of new DNA strands by DNA polymerase
  4. Proofreading and editing to correct errors
• The resulting DNA molecule is identical to the original, with each new strand containing one old strand (template) and one new strand synthesized during replication

Genetic Code

• The genetic code is the set of rules that dictates how the sequence of nitrogenous bases in DNA is translated into a sequence of amino acids in proteins
• The code is based on triplets of nucleotides called codons
• There are 64 possible codons, but only 20 amino acids are commonly used in proteins
• The genetic code is degenerate, meaning that more than one codon can code for the same amino acid
• The code is also universal, meaning that it is the same for all living organisms

Mutations

• A mutation is a change in the DNA sequence of an organism
• Types of mutations:
  • Point mutations: a change in a single nucleotide
  • Frameshift mutations: an insertion or deletion of one or more nucleotides, leading to a change in the reading frame of the genetic code
  • Chromosomal mutations: changes in the number or structure of chromosomes
• Mutations can occur spontaneously or be induced by environmental factors such as radiation or chemicals
• Mutations can have significant effects on the function and structure of proteins, leading to changes in the phenotype of an organism

Gene Expression

• Gene expression is the process by which the information in a gene's DNA is converted into a functional product, such as a protein
• The central dogma outlines the flow of genetic information:
  1. Transcription: DNA is transcribed into RNA
  2. Translation: RNA is translated into protein
• Gene expression is regulated by a variety of mechanisms, including:
  • Transcriptional regulation: controlling the transcription of DNA into RNA
  • Post-transcriptional regulation: controlling the processing and translation of RNA into protein
  • Epigenetic regulation: controlling gene expression through modifications to DNA or histone proteins

DNA Structure

• DNA is a double-stranded helix composed of two complementary strands of nucleotides, sugar molecules (deoxyribose), and phosphate groups
• Nitrogenous bases include adenine (A), guanine (G), cytosine (C), and thymine (T)
• Sugar and phosphate molecules make up the backbone of the DNA, while nitrogenous bases project inward and pair with each other in a complementary manner
• Adenine (A) pairs with thymine (T) using two hydrogen bonds, and guanine (G) pairs with cytosine (C) using three hydrogen bonds

DNA Replication

• DNA replication is the process of creating an exact copy of a DNA molecule, occurring during cell division
• Helicase initiates the process, which involves unwinding the double helix, binding of primers, and synthesis of new DNA strands by DNA polymerase
• Proofreading and editing ensure that errors are corrected during the replication process
• The resulting DNA molecule is identical to the original, with each new strand containing one old strand (template) and one new strand synthesized during replication

Genetic Code

• The genetic code is the set of rules that dictates how the sequence of nitrogenous bases in DNA is translated into a sequence of amino acids in proteins
• The code is based on triplets of nucleotides called codons, with 64 possible codons and 20 commonly used amino acids
• The genetic code is degenerate, meaning that more than one codon can code for the same amino acid
• The code is universal, meaning that it is the same for all living organisms

Mutations

• A mutation is a change in the DNA sequence of an organism, which can occur spontaneously or be induced by environmental factors
• Types of mutations include point mutations, frameshift mutations, and chromosomal mutations
• Mutations can have significant effects on the function and structure of proteins, leading to changes in the phenotype of an organism

Gene Expression

• Gene expression is the process by which the information in a gene's DNA is converted into a functional product, such as a protein
• The central dogma outlines the flow of genetic information: transcription (DNA to RNA), and translation (RNA to protein)
• Gene expression is regulated by transcriptional regulation, post-transcriptional regulation, and epigenetic regulation