Genes chromosomes and the genetic code

• What is a Gene?


  A base sequence of DNA on a chromosome that codes for the amino acid sequence of a polypeptide and functional RNA.
• What is a Chromosome?

  Thread-like structures made out of histones(proteins) and DNA
• What is DNA?

  deoxyribose acid-what genes and chromosomes are made out of.
• What is an Amino acid?


  The building blocks of proteins.
• What is a Triplet?


  3 bases that code for an amino acid. (DNA)
• What are the features of Eukaryotes?


  -DNA inside the nucleus

  -DNA associated with proteins(histones)

  -DNA in chromosomes

  -DNA is longer than in prokaryotes
• What are the features of Prokaryotes?

  • DNA in a single loop in the cytoplasm,
  • DNA in circular plasmids
  • Not associated with proteins
  • Not in chromosomes
• DNA coils itself to form loops, this forms the chromosome.

  DNA combines with histones(proteins) to form DNA-histone complexes to help it coil.

  Histones and coiling help DNA to be condensed into a single chromosome.

  Each chromosome is a single DNA molecule.
• Chromatids are 2 identical threads held together by a centromere.
• Genes occur at different loci (locations) along the DNA molecule-each gene is at a specific locus.
• • Humans have 23 pairs of chromosomes (23 maternal and 23 paternal)
  • Pairs of chromosomes are known as homologous chromosomes
• What are Homologous chromosomes?


  Chromosomes with the same genes but different alleles.
• What is the diploid number of chromosomes?


  46 chromosomes
• What is an allele?


  An alternative version of a gene.

  • You have 2 alleles for each characteristic (homozygous and heterozygous)
• What is homozygous?


  Two of the same alleles.
• What is Hetrozygous?


  Two different alleles.
• What is a Mutation?

  A change in the base sequence of a gene.
• How does a mutation lead to to a non-functional protein?


  1. A mutation causes a change in the base sequence of a gene
  2. This changes the sequence of amino acids
  3. A different amino acid sequence leads to a formation of a different polypeptide
  4. so a different maybe non-functional protein
• What are the 5 Features of the genetic code?


  Triplets, A degenerate code, A Non-overlapping code, A universal code and most DNA is Non-coding.
• What are triplets? (features of a genetic code)


  A Triplet is always read in 1 direction along the DNA strand.

  The start of a DNA sequence always starts with the same triplet.

  Stop codons mark the end of a polypeptide chain.
• What is degenerate code? (features of a genetic code)


  Most amino acids are coded for by more than one triplet.
• What is A universal code?(features of a genetic code)


  With a few exceptions, each triplet codes for the same amino acid in all organisms (this is indirect evidence for evolution)
• What is Most DNA is non-coding?


  Between genes there are non-coding sequences made up of multiple repeats of base sequences,