topic 4

• What do DNA coils around to form chromosomes?

  Proteins called histones
• What is a gene?

  A sequence of DNA bases coding for protein
• What does locus refer to in genetics?

  Position on a chromosome for an allele
• What is a triplet in genetics?

  A series of 3 bases coding for one amino acid
• What is an exon?

  A section of DNA that codes for an amino acid
• What is an intron?

  A section of DNA that doesn’t code for amino acids
• What is the role of the centromere?

  Minimizes mutation and starts protein synthesis
• What are sister chromatids?

  Identical copies of a chromosome
• How is DNA organized in eukaryotic cells?

  Held on linear chromosomes in the nucleus
• How is DNA organized in prokaryotic cells?

  Held on circular plasmids in the cytoplasm
• What is DNA classified as?

  A polymer of repeating nucleotides
• What are the two main stages of protein synthesis?

  1. Transcription: DNA is copied into mRNA
  2. Translation: mRNA is used to synthesize proteins
• What is mRNA made during?

  Transcription
• What is the function of mRNA?

  Carries genetic code from DNA to ribosome
• What is the structure of mRNA?

  Single polynucleotide strand
• What is a codon?

  A sequence of 3 bases in mRNA
• What happens during mRNA transcription?

  DNA is unzipped and RNA nucleotides are joined
• What is the role of RNA polymerase?

  Joins RNA nucleotides to form pre-mRNA
• What is pre-mRNA splicing?


  Removing introns to form mRNA
• What is the shape of tRNA?

  Clover-shaped
• What is found at one end of tRNA?

  Anticodon
• What is found at the opposite end of tRNA?

  Amino acid binding site
• What are the steps of translation?

  1. Ribosome attaches to mRNA at initiation codon
  2. tRNA binds to mRNA codon via anticodon
  3. Peptide bond forms between amino acids
  4. Ribosome moves along mRNA, elongating polypeptide chain
• What are the differences between DNA, mRNA, and tRNA?

  • DNA: double-helix, deoxyribose, A,T,C,G
  • mRNA: single-stranded, ribose, A,U,C,G
  • tRNA: clover-shaped, ribose, A,U,C,G, has amino acid binding site
• What is a mutation?

  A change in base sequence of amino acids
• What are the ways mutations can occur?

  Insertion, deletion, substitution, inversion, duplication, translocation
• What is a chromosomal mutation?

  A mutation affecting the structure of chromosomes
• What is non-disjunction?

  Loss or gain of an entire chromosome
• What is an example of a condition caused by non-disjunction?

  Down's syndrome
• What are mutagens?

  Factors that cause mutations
• What are spontaneous mutations?

  Mutations occurring without external influence
• What is meiosis?

  Process producing haploid gametes
• What happens during meiosis 1?

  Homologous chromosomes pair and cross over
• What happens during meiosis 2?

  Sister chromatids separate into different daughter cells
• What is independent segregation?

  Random distribution of homologous chromosomes
• What are the ways genetic variation occurs?

  Independent segregation, recombination, random fertilization
• What is the formula for combinations in meiosis?

  $2^n$
• What is a bottleneck effect?

  Population reduction decreasing allele diversity
• What is natural selection?

  Advantageous mutations help species survive
• What is stabilizing selection?

  Individuals in the middle range survive better