DNA, genes and chromosomes

• Features of eukaryotic DNA

  Linear and long DNA molecules

  Associated with histones

  DNA and histones are coiled up tightly to form chromosomes
• Features of eukaryotic mitochondria and chloroplasts

  Short and circular DNA molecules

  Not associated with histones
• Features of prokaryotic DNA

  Short and circular DNA molecules

  Not associated with histones
• Do prokaryotes carry DNA as chromosomes?

  Yes

  Condensed in the nucleus by supercoiling
• Gene

  A sequence of DNA bases that codes for a specific sequence of amino acids to make a polypeptide or functional RNA
• Primary structure of a protein

  The sequence of amino acids in a polypeptide
• Triplet

  A sequence of three DNA bases
• Locus

  A fixed position of a gene on a DNA molecule/chromosome
• Features of the genetic code

  Universal

  Non-overlapping

  Degenerate
• Non-overlapping

  Each triplet is only read once
• Degenerate


  More than one triplet codes for the same amino acid
• Universal


  Each base sequence codes for the same amino acid in all species
• Functional RNA

  A molecule, other than mRNA which performs special tasks during protein synthesis (e.g: tRNA and rRNA)
• Exons

  Coding portions of DNA or RNA that code for amino acid sequences
• Introns

  Non-coding sections of DNA which do not code for amino acids
• How are introns removed?

  Using splicing during protein synthesis
• Which type of DNA contains introns?

  Only eukaryotic DNA
• Non-coding repeats

  DNA sequences that repeat over and over that don't code for amino acids
• Alleles

  Different versions of the same gene
• How is DNA stored in eukaryotic cells?

  Chromosomes
• How many pairs of chromosomes do humans have

  23 pairs - 46 in total
• What are the 3 components of nucleotides?

  Pentose sugar, phosphate group and an organic base
• Describe the structure of DNA

  Deoxyribose sugar, phosphate group and an organic base

  ACGT

  Double-stranded

  Hydrogen bonds between bases
• Describe the role of DNA

  Carries genetic info.

  Determines our inherited characteristics
• Describe the structure of RNA

  Ribose sugar. phosphate group and an organic base

  AGCU

  Single stranded
• Describe the role of RNA

  Transfers genetic info. from DNA to ribosomes for protein synthesis
• Purine bases

  Adenine and guanine

  Double ring
• Pyrimidine bases

  Cytosine

  Thymine

  Uracil

  Single ring
• How is DNA in eukaryotic cells different from in prokaryotic cells

  Eukaryotic - found in nucleus

  long and linear

  associated with histones

  Prokaryotic + mitochondria and chloroplast - short and circular

  not associated with histones
• Genetic code

  The order of bases on DNA

  Consists of codons
• Codon

  Triplets of bases that code for a particular amino acid
• Where are introns found

  Between introns

  Within genes