Unit 4

• What are the key similarities between eukaryotic and prokaryotic DNA?

  • Both are made up of DNA nucleotides
  • Both contain deoxyribose, a phosphate group, and a nitrogenous base
  • Nucleotides are joined by phosphodiester bonds
• What are the key differences between eukaryotic and prokaryotic DNA?

  • Eukaryotic DNA is longer and linear; prokaryotic DNA is circular
  • Eukaryotic DNA is associated with histones; prokaryotic DNA is not
• What is the structure of eukaryotic DNA in the nucleus?

  It is tightly coiled into chromosomes
• What is the function of the DNA in mitochondria and chloroplasts?

  To transcribe and translate enzymes needed for photosynthesis and respiration
• What is a gene?

  • A sequence of DNA
  • Codes for the amino acid sequence of a polypeptide
  • Codes for functional RNA, such as mRNA
• What does the term 'locus' refer to in genetics?

  The exact position of a gene on a chromosome
• What are the three features of the genetic code?

  1. Degenerate code
  2. Universal
  3. Non-overlapping
• Why is the genetic code described as degenerate?

  Because multiple triplets can code for the same amino acid
• What is a codon?

  A sequence of three bases on mRNA that codes for a specific amino acid
• What is the role of introns in DNA?

  They are sequences that do not code for polypeptides
• What is a start codon?

  A codon that initiates translation
• What is a stop codon?

  A codon that signals the end of translation
• What is the difference between a genome and a proteome?

  • Genome: Complete set of genes in a cell
  • Proteome: Full range of proteins that a cell can produce
• How does the genome differ between species?

  It varies in the number of DNA base pairs
• How many DNA base pairs do humans have?

  Approximately 3 billion base pairs
• What is the role of mRNA in protein synthesis?

  • It is a copy of one gene
  • It is single-stranded
  • It is made during transcription
  • It carries the code for amino acids to the ribosome
• What does tRNA stand for?

  Transfer RNA
• What is the function of tRNA?

  To bring specific amino acids to the ribosome during translation
• What shape does tRNA have?

  Cloverleaf shape
• What are the two main stages of protein synthesis?

  1. Transcription
  2. Translation
• What happens during transcription?

  • DNA unwinds to expose bases
  • One strand acts as a template
  • RNA nucleotides align opposite complementary DNA bases
  • RNA polymerase joins RNA nucleotides to form mRNA
  • mRNA is modified and leaves the nucleus
• What is splicing in eukaryotes?

  The process of removing introns from pre-mRNA
• What occurs during translation?

  • mRNA binds to a ribosome
  • tRNA molecules align with complementary codons
  • Amino acids are joined by peptide bonds
  • The process continues until a stop codon is reached
• What is a gene mutation?


  A change in the base sequence of DNA
• What can increase the likelihood of gene mutations?

  Exposure to mutagenic agents
• What is non-disjunction?

  Failure of chromosomes to separate properly during meiosis
• What are the two forms of chromosome mutations?

  1. Polyploidy: Change in the whole set of chromosomes
  2. Aneuploidy: Change in the number of individual chromosomes
• What genetic condition is associated with non-disjunction of chromosome 21?

  Down syndrome
• How does non-disjunction lead to Down syndrome?

  It results in three copies of chromosome 21 instead of two
• What are the effects of gene mutations?

  • May have no impact if the new codon codes for the same amino acid
  • Can lead to changes in the amino acid sequence
  • May result in genetic disorders
• What is the significance of the genetic code being universal?

  • Same triplet codes for the same amino acid in all organisms
  • Indicates a common evolutionary origin
• What is the significance of the genetic code being non-overlapping?

  • Each base is part of only one codon
  • Minimizes the impact of mutations
• How does non-disjunction lead to Down syndrome?

  Non-disjunction on chromosome 21 results in three copies of that chromosome instead of two.
• What happens during non-disjunction in meiosis I?

  In meiosis I, spindle fibers may attach to one homologous pair, pulling both to one cell, resulting in a gamete with an extra chromosome.
• What is the result of non-disjunction in meiosis II?

  Non-disjunction in meiosis II results in one gamete with an extra chromosome and another gamete missing that chromosome.
• What is the term for a gamete with one extra chromosome?

  A gamete with one extra chromosome is described as $n +$$1$.
• What is the term for a gamete missing one chromosome?

  A gamete missing one chromosome is described as $n - 1$.
• How does trisomy occur?

  Trisomy occurs when a haploid gamete with an extra chromosome fuses with a normal haploid gamete, resulting in three copies of a chromosome.
• What is the role of meiosis in genetic variation?

  Meiosis introduces genetic variation through independent segregation and crossing over of homologous chromosomes.
• What are the two mechanisms through which meiosis introduces variation?

  • Independent segregation of homologous chromosomes
  • Crossing over between homologous chromosomes