DNA & Protein Synthesis

• Chromatin is a complex of nucleic acids (DNA/RNA) and proteins (histones), which condenses to form a chromosome during cell division.
• A gene is a sequence of DNA bases that codes for either a polypeptide or functional RNA (m/t/r).
• One nucleosome is a core of eight histone proteins.
• Coding DNA codes for a polypeptide chain.
• A single nucleosome consists of about 150 base pairs of DNA sequence wrapped around a core of histone proteins.
• A chromosome is a thread-like structure made up of a single molecule of DNA and proteins (histones).
• A chromatid is one of two identical halves of a replicated chromosome.
• A centromere is the constricted region of linear chromosomes. It serves as an attachment site for the two halves of each replicated chromosome (the sister chromatids).
• Homologous chromosomes are an identical chromosome pair.
• A locus is the position of a gene on a chromosome (plural loci).
• Alleles are different versions of a gene.
• The genome is the complete set of genes in a cell.
• The proteome is the full range of proteins that the cell is able to produce from the genome.
• Non coding DNA introns are sections of genes that don't code for polypeptides.
• Non-coding DNA is only found in eukaryotic DNA.
• Exons are parts of a gene that code for polypeptides.
• Introns in eukaryotes are removed during protein synthesis.
• Multiple repeats are DNA sequences that repeat over and over. These areas don't code for amino acids either, so they're called non-coding multiple repeats.
• A karyotype is an image of the homologous chromosomes inside a cell.
• The proteome is the complete set of proteins that can be expressed by a cell or organism.
• DNA has the largest nucleotide structure.

  mRNA has a smaller nucleotide structure than DNA.

  tRNA has the smallest nucleotide structure.
• The pentose sugar in DNA is deoxyribose.

  The pentose sugar in mRNA and tRNA is ribose.
• The pyrimidine bases in DNA are cytosine and thymine.

  The pyrimidine bases in m and tRNA are cytosine and uracil.
• The purine bases in DNA, mRNA and tRNA are adenine and guanine.
• DNA consists of 2 polynucleotide strands.

  mRNA and tRNA have 1 polynucleotide strand.
• DNA has millions of nucleotides in its chains.

  mRNA has thousands of nucleotides in its chain.

  tRNA has 75 nucleotides in its chain.
• DNA has hydrogen bonding between complementary base pairs.

  mRNA has no hydrogen bonding between base pairs as it is an unfolded single strand.

  tRNA only has hydrogen bonding between complementary base pairs in some parts of the molecule (four-leaf clover shape).
• DNA is found in the nucleus.

  mRNA and tRNA are made in the nucleus but are found in the cytoplasm.
• Transcription is the elimination of the introns and the splicing of the exons to form an mRNA strand.
• All genes begin with the start codon TAC (AUG in RNA) which codes for the amino acid Methionine.
• There are four bases in DNA (ATCG) and therefore 3 bases are needed to make enough combinations to code for at least 20 amino acids.

  4¹ = 1 base = 4(x1) = 4 amino acids in total

  4² = 2 bases = 4x4 = 16 amino acids in total

  4³ = 3 bases = 4x4x4 = 64 amino acids in total
• 𝙏𝙃𝙀 𝘿𝙄𝙎𝘾𝙊𝙑𝙀𝙍𝙔 𝙊𝙁 𝙏𝙃𝙀 𝙏𝙍𝙄𝙋𝙇𝙀𝙏 𝘾𝙊𝘿𝙀:

  Crick, Barnett, Brenner and Watts-Tobin (1961) introduced a single frameshift mutation into a viral protein in E.coli bacteria. This rendered the protein ineffective. The researchers then introduced additional frameshift mutations in the hope that doing so would restore the correct reading frame (AKA functional protein).

  They noted that the introduction of three separate frameshift mutations (each adding one base) to the same DNA was able to put the code back on track when placed close together.
• 𝘿𝙉𝘼 𝙏𝙍𝙄𝙋𝙇𝙀𝙏 𝘾𝙊𝘿𝙀:

  • a gene is a sequence of nucleotide bases in a DNA molecule that codes for the production of a specific amino acid sequence, which in turn makes up a polypeptide.
  • the DNA nucleotide base code found within a gene is a 3-letter (triplet) code.
  • each sequence of 3 bases (one codon) codes for one amino acid.
  • some triplets code for start and stop signals, ensuring the cell reads the DNA correctly to produce the correct sequences of amino acids.
  • 4 bases = 64 triplets
• Why is the genetic code 𝗱𝗲𝗴𝗲𝗻𝗲𝗿𝗮𝘁𝗲?

  Different codons specify (code for) the same amino acids.
• Why is the genetic code 𝗻𝗼𝗻-𝗼𝘃𝗲𝗿𝗹𝗮𝗽𝗽𝗶𝗻𝗴?

  Successive triplets are read in order.

  This prevents point mutations from affecting proteins.
• Why is the genetic code 𝘂𝗻𝗶𝘃𝗲𝗿𝘀𝗮𝗹?

  Each triplet code sequence codes for the same amino acid in all species.

  This is direct evidence for evolution and allows for genetic engineering.
• What are 𝘀𝘆𝗻𝗼𝗻𝘆𝗺𝗼𝘂𝘀 𝗰𝗼𝗱𝗼𝗻𝘀?

  Different codons that encode the same amino acid.
• What is 𝗰𝗼𝗱𝗼𝗻 𝗯𝗶𝗮𝘀?

  "𝘛𝘩𝘦 𝘱𝘳𝘦𝘧𝘦𝘳𝘦𝘯𝘵𝘪𝘢𝘭 𝘶𝘴𝘦 𝘰𝘧 𝘤𝘦𝘳𝘵𝘢𝘪𝘯 𝘤𝘰𝘥𝘰𝘯𝘴 𝘧𝘰𝘳 𝘵𝘳𝘢𝘯𝘴𝘭𝘢𝘵𝘪𝘰𝘯."

  Certain synonymous codons are used more frequently than others even though they code for the same amino acid.
• What is the 𝗰𝗼𝗱𝗶𝗻𝗴 𝘀𝘁𝗿𝗮𝗻𝗱?

  The strand of DNA which codes for the gene of interest and has the same sequence as the new RNA molecule.
• What is the 𝗻𝗼𝗻-𝗰𝗼𝗱𝗶𝗻𝗴 𝘀𝘁𝗿𝗮𝗻𝗱?

  The DNA strand that serves as a template for transcription at any given time.

  This is possible because it contains anticodons.