genes

• How is a gene ?

  A short section of DNA coding for polypeptides
• What does a gene code for in A-level biology?

  Polypeptide and functional RNA
• What is the primary structure of a protein?

  Polypeptide chain
• What is the role of the Golgi apparatus in protein processing?

  Processes polypeptide chains into functional proteins
• What is the definition of locus?

  Location of a gene on a chromosome
• How do humans differ genetically despite having the same genes?

  Different versions of the same genes (alleles)
• What is an allele?

  A different form of the same gene
• How do alleles affect traits in plants?

  Different alleles result in different traits
• How many pairs of chromosomes do humans have?

  23 pairs
• What is a homologous pair of chromosomes?

  Two chromosomes with the same genes
• How do homologous pairs arise in humans?

  From the combination of sperm and egg DNA
• What is a human karyotype?

  An image of all chromosomes organized in pairs
• What do the dark and light bands on chromosomes indicate?

  Same genes in the same positions
• What determines biological sex in humans?

  The 23rd pair of chromosomes
• How is DNA stored in eukaryotic cells?

  In chromosomes within the nucleus
• What shape are eukaryotic chromosomes?

  Linear
• What prevents DNA from tangling in eukaryotic cells?

  Histone proteins help coil DNA
• What is a nucleosome?

  DNA wrapped around histone proteins
• How does prokaryotic DNA differ from eukaryotic DNA?

  Prokaryotic DNA is circular and shorter
• Where is prokaryotic DNA located?

  Free in the cytoplasm
• What type of DNA do mitochondria and chloroplasts contain?

  DNA similar to prokaryotic DNA
• What is the approximate length of DNA in a human muscle cell?

  1. 3 meters
• How do you calculate the mean length of DNA in each chromosome?

  Divide total length by number of chromosomes
• What is the length of DNA in a human brain cell?

  1. 3 meters
• How do you convert meters to millimeters?

  Multiply by 1000
• How do you calculate base pairs per chromosome?

  Divide total base pairs by number of chromosomes
• What is the approximate number of base pairs in the human genome?

  3 billion
• What are the key differences between eukaryotic and prokaryotic DNA?

  • Eukaryotic DNA is linear and longer
  • Prokaryotic DNA is circular and shorter
  • Eukaryotic DNA is histone-bound
  • Prokaryotic DNA is not histone-bound
• What are the main points about DNA in mitochondria and chloroplasts?

  • DNA is similar to prokaryotic DNA
  • It is circular and shorter
  • Not histone-bound
  • Codes for essential enzymes
• What is the process of DNA compaction in eukaryotic cells?

  1. DNA wraps around histone proteins
  2. Forms nucleosomes
  3. Nucleosomes coil to form chromosomes
  4. Allows DNA to fit in the nucleus
• What are the definitions of gene and allele?

  • Gene: A section of DNA coding for polypeptides
  • Allele: A different form of the same gene
• What is the significance of homologous pairs of chromosomes?

  • They have the same genes
  • They may have different alleles
  • Formed from sperm and egg during fertilization
• What is a karyotype and its significance?

  • An organized image of chromosomes
  • Shows homologous pairs
  • Useful for identifying genetic disorders
• What are the functions of histone proteins?

  • Assist in tightly coiling DNA
  • Prevent DNA tangling
  • Help form nucleosomes
• What are the three key features of the genetic code?

  Degenerate, universal, and non-overlapping
• What is a start codon?

  Three bases at the start of a gene
• What does the start codon code for?

  Amino acid methionine
• What is the function of a stop codon?

  It signals the end of translation
• How many stop codons are there?

  Three
• What happens when the ribosome reaches a stop codon?

  The ribosome detaches and translation stops