DNA, GENE AND PROTEIN SYNTHESIS

• WHERE IS GENETIC MATERIAL STORED IN A CELL?

  chromosomes in the nucleus
• WHAT DOES EACH GENE CODE FOR?

  a sequence of amino acids to make a protein
• DURING PROTEIN SYNTHESIS WHAT MOVES FROM THE DNA TO THE RIBOSOME?

  mRNA
• STRUCTURE OF DNA

  double helix
• MUTATIONS IN DNA CAN CAUSE:

  change the shape and function of proteins
• 3 POSITIVES KNOWING THE GENOME:

  • search for genes linked to diseases
  • understand and treat inherited disorders
  • tracing migration patterns
• COMPLEMENTARY BASE PAIRS: when bases pair up with each other in a consistent way
• POLYPEPTIDE: chains of amino acids. Proteins are made up of one or more polypeptide molecules. The amino acids are covalently linked by peptide bonds.
• GENE: a section of DNA that contains the coded information for making polypeptides and functional RNA.
• A Gene is a base sequence of DNA that codes for:

  • The amino acid sequence in a polypeptide
  • the sequence of amino acids in a polypeptide forms the primary structure of a protein
  • The order of bases in a gene determines the order of amino acids in a particular polypeptide
  • the sequence if amino acids coded for by DNA is the primary structure of a protein. It’s this primary structure that gives rise to the tertiary structure and hence the shape of the protein. So DNA codes indirectly for the shape of proteins, including enzymes.
• There are only 20 different amino acids which occur in proteins
• Each amino acid is coded for by a sequence of 3 bases called a triplet
• 3 bases of DNA = a triplet code
• GENETIC CODE: the sequence of base triplets (codons) in mRNA which code for specific amino acids
• Each base triplet is read in sequence, separate from the triplet before and after it
• There are a possible 64 codons for just 20 amino acids (degenerate code)
• RULES FOR THE GENETIC CODE:

  • 4 bases exist
  • 20 different amino acids must be coded for.
  • therefore couldn’t 1:1 - that is it couldn’t be 1 codon (triplet bases) coding for just a single amino acid
• GENETIC CODE IS DEGENERATE: means most amino acids are coded for by more than one triplet
• GENETIC CODE IS NON-OVERLAPPING: means each base is only read once
• GENETIC CODE IS UNIVERSAL: means each triplet codes for the same amino acid in all organisms on earth
• (feature of genetic code) the start of a dna sequence that codes for a polypeptide is always the same triplet. This triplet codes for the amino acid methionine (AUG). It methionine doesn’t form part of the final polypeptide, it’s removed.
• (Feature of genetic code) 3 triplets don’t code for any amino acids. These 3 triplets are ’stop codes’, they mark the end of a polypeptide chain.
• RNA (RIBONUCLEIC ACID)

  • is a polymer
  • made of repeating mononucleotide subunits
  • it forms a single strand
  • each nucleotide is made up of:
  • -the pentose sugar ribsoe
  • -one organic base - A,G,C,U
  • -a phosphate group
• EXON: coding sequences in DNA that code for amino acids
• INTRON: non-coding sequences in DNA (junk DNA)
• Most DNA in eukaryotic cells doesn’t code for polypeptides, but for functional RNA.
• Genes that don’t code for polypeptides contain sections that don’t code for amino acids - called introns
• Parts of a gene that code for amino acids = exons
• Introns are removed during protein synthesis so they don’t affect The amino acid order
• Prokaryotic dna doesn’t have introns
• Eukaryotic dna also contains regions of multiple repeats
• Outside genes which are called non coding repeats
• Linear DNA molecules exist as chromosomes which are threadlike and made up of one long molecule of DNA
• The dna molecule is very long and is wound up so it can fit the nucleus
• The dna molecule is wound around proteins called histones
• Histone proteins help to support the dna
• The dna and histones are then coiled up tightly to make a compact chromosome
• Each thread of a chromosome is called a chromatid and joined by a centromere
• Each Gene occupies a specific position (locus) along the DNA molecule
• HOMOLOGOUS CHROMOSOMES: pairs of matching chromosomes