4A DNA, RNA, and protein synthesis

• how is DNA stored in eukaryotic cells?

  Linear DNA molecules that exist as chromosomes, they are wound round histones (proteins) and tightly coiled.
• what is a homologous pair?

  Two chromosomes of the same type, containing copies of the same genes laid out in the same order.
• how is DNA stored in prokaryotes?

  shorter and circular with no just ones. it supercoils and condenses.
• what is a gene?

  a sequence of DNA bases that codes for either a polypeptide or functional RNA.
• how many bases code for one amino acid?

  3.
• what is a codon?


  a three-nucleotide sequence that codes for an amino acid.
• what is a genome?

  the complete set of genes in an organism.
• what is a proteome?


  the full rage of proteins that the genome can produce.
• what are introns?

  non coding regions of DNA.
• why are introns removed in eukaryotic protein synthesis?

  so they don't affect the order of amino acids.
• what are exons?


  coding regions of DNA.
• What are non coding multiple repeats?

  regions of repeating units in DNA that dont code for amino acids.
• what are alleles?

  different versions of the same gene.
• what do alleles code for?

  slightly different versions of the same polypeptide.
• what is the purpose of protein synthesis?


  to produce new proteins.
• what are the two stages of protein synthesis?

  transcription and translation.
• what happens during transcription ( brief)?

  DNA is copied into MRNA.
• what happens during translation ( brief ) ?

  MRNA joins to a ribosome and the code is used to make a new protein.
• what are the two types of RNA?

  mRNA and tRNA.
• when is mRNA made?

  during transcription.
• what does mRNA do?

  carries the genetic code from DNA to ribosomes.
• what is the structure of mRNA?

  single polynucleotide strand. (contains uracil rather than thymine)
• what does tRNA do?

  carries amino acids needed to make proteins to ribosomes.
• what is the structure of tRNA?

  • single polynucleotide strand that's folded into a clover shape. held together by hydrogen bonds.• specific sequence of 3 bases at one end called anticodon. • amino acid binding site at the other end.
• what is pre-mRNA?


  the copy of introns and exons (genetic code) in eukaryotes.
• where is mRNA edited?

  in the nucleus.
• why does prokaryotic DNA not need to be spliced before mRNA is created?

  there are no introns in prokaryotic DNA.
• what is the genetic code?

  sequence of codons (base triplets) in mRNA that code for specific amino acids.
• name three characteristics of the genetic code.

  • non overlapping.• degenerate.• universal.
• what does the fact that the genetic code is universal mean?

  the same specific base triplets code for the same amino acids in all living things.
• How many combinations of codons /triplets are there?

  64.
• what does the fact that the genetic code is degenerate mean?

  that there are more possible combinations of triplets than amino acids, meaning some amino acids can be coded by multiple codons.
• do base triplets share their bases?

  no, they are non-overlapping.
• what role does ATP play in translation?

  ATP provides the energy needed for the bond between an amino acid and a tRNA molecule to form, allowing the tRNA to carry the amino acid to the ribosome.
• what are DNA molecules wound around in eukaryotes?

  histone proteins.
• what other types of DNA is similar to prokaryotic DNA?

  mitochondria and chloroplasts.
• which part of DNA carries the genetic information?

  the genes.
• what forms the primary structure of a protein?

  the sequence of amino acids.
• if a gene doesn't code for a polypeptide, what does it code for?

  a functional RNA.
• what is functional RNA?

  RNA molecules other than mRNA that perform specific tasks e.g. tRNA and rRNA.