lec 2

• DNA


  Deoxyribonucleic acid, carries genetic information in all living organisms and viruses, involved in reproduction, functioning, growth, and development

  
• DNA


  • Long polymer composed of deoxyribonucleotides
  • In both prokaryotic and eukaryotic organisms, double-stranded DNA serves as the primary genetic material

  
• DNA chemistry studies trace back to

  1868
• It was understood that DNA comprises nucleotides


  1940s
• J.D. Watson and F.H. Crick proposed the DNA structure


  1953
• Nucleotide


  Comprises an organic base, a five-carbon sugar, and a phosphate group

  
• DNA usually exists as a double-stranded (ds) molecule - two strands wind around each other, forming a double helix
• Certain viruses have single-stranded (ss) DNA

  
• Genetic material


  Has two primary functions: encodes information required for protein production, undergoes replication with high accuracy to transfer encoded information to new cells

  
• After one round of replication, two daughter molecules are generated, each retaining the same sequence of nucleotide pairs as the original DNA molecule
• Central Dogma


  A theory stating that genetic information flows only in one direction, from DNA, to RNA, to protein, or RNA directly to protein

  
• Genetic Code


  Instructions contained in a gene that direct a cell on how to produce a specific protein

  
• Genetic Code


  • Each gene's code utilizes four DNA nucleotide bases: adenine (A), cytosine (C), guanine (G), and thymine (T)
  • These bases form three-letter "codons" within the gene sequence
  • Codons specify the amino acid required at each position within the protein

  
• Gene-to-protein journey


  1. Transcription

  2. Translation

  
• Transcription


  DNA information transcribed to RNA in the nucleus

  
• Translation


  Occurs in the cytoplasm, mRNA interacts with ribosome, which reads mRNA sequence, Transfer RNA (tRNA) assembles proteins by adding one amino acid at a time, Protein assembly continues until ribosome encounters a "stop" codon, signaling the end of protein synthesis

  
• Proteins


  • Consist of one or more long, folded chains of amino acids, known as polypeptides
  • The sequence of amino acids in polypeptides is determined by the DNA sequence of the protein-encoding gene

  
• Functions of proteins


  • Structural component
  • Transport/storage
  • Enzyme
  • Antibodies
  • Messenger
• Each gene provides instructions for a functional product, that is, a molecule needed to perform a job in the cell
• In many cases, the functional product of a gene is a protein
• The cell builds proteins using instructions found in genes

  
• The order of nucleotides in a gene determines the order of amino acids in one or more proteins
• Genes that specify proteins are called protein-coding genes
• An organism has many different genes, and so can produce many different proteins
• These proteins have functions that affect the organism's traits
• Osmosis


  The passage of water from a region where its concentration is high, through a semi-permeable membrane, into a region where its concentration is lower
• Vesicular transport


  Can be classified as endocytosis (pinocytosis, phagocytosis, receptor-mediated endocytosis) and exocytosis (fusion of membrane-bound vesicles with the plasma membrane, allowing their contents to be released into the extracellular space)