4.1 Nucleic Acids

• Give some similarities and differences of a homologous pair of chromosomes.

  They're the same size with the same genes but the version of the allele within the gene could be different.
• What is an intron?

  These are the sections within a gene that do not code for amino acids.
• What is an exon?

  These are the sections within a gene that code for amino acids.
• What does a gene do?

  A gene codes for one polypeptide
• Do prokaryotes or eukaryotes have introns?

  Only eukaryotes do
• What can genes be divided into?

  Triplets
• How long are triplets?

  3 bases long
• What does every condon carry?

  The specific 3 letter sequence for a single amino acid.
• What is a genome?

  The full set of genes possessed by an organism
• What is a proteome?

  The entire set of proteins expressed by the genes in a genome.
• A protein has 4 amino acids, so the minimum number of bases that could code for this protein is 12. Why may the true number of bases be more than this?

  Due to the presence of introns and multiple repeats that do not code for anything and so more bases may be needed.
• Give three features of genetic code

  Degenerate, non-overlapping and universal.
• A feature of genetic coding is that it's degenerate. What does this mean?

  Most of the amino acids have more than 1 triplet coding for them.
• A feature of genetic coding is that it's non-overlapping. What does this mean?

  Each base is part of only 1 triplet so it is read only once in one direction.
• A feature of genetic coding is that it's universal. What does this mean?

  The same triplets are present for the same amino acids in all living organisms.
• What's the relationship between DNA, RNA and proteins? [4]

  DNA carries genetic code but can't leave the nucleus and proteins are made at ribosomes on the rough ER. So mRNA copies the DNA code and sends it to the ribosomes. tRNA is found in the cytoplasm and delivers amino acids to the ribosome.
• Describe the structure of mRNA. [5]

  ○ It's a polymer of RNA nucleotides.

  ○ Ribose is the sugar.

  ○ The bases are; adenine, cytosine, guanine and uracil.

  ○ It's a complementary copy of a gene.

  ○ The number of nucleotides depends on the length of the gene.

  ○ Phosphodiester bonds form a sugar phosphate backbone.

  ○ The molecule is linear.

  ○ Its shape is a single helix.

  ○ It has no base pairs so has no hydrogen bonds.
• Describe the structure of tRNA. [5]

  ○ Clover leaf shaped.

  ○ There are some areas of base pairing and so some hydrogen bonds are present.

  ○ The anticodons present on tRNA matchup with codons present on mRNA.

  ○ Each amino acids attachment site carries one specific amino acid.

  ○ It's about 75 nucleotides long.
• Describe the shape of DNA. [2]

  It's linear and double helixed.
• Is DNA a strong molecule? Why?

  Yes, it has many hydrogen bonds to provide strength.
• Why is mRNA weaker than tRNA?

  mRNA has no hydrogen bonds compared to tRNA which has some to provide strength.
• Which has an amino acid binding site; DNA, mRNA or tRNA?

  tRNA
• Eukaryotes contain regions of multiple repeats. What are these regions?

  These are DNA sequences that repeat over and over (E.g. CCTTCCTTCCTT). These areas do not code for amino acids and are called non-coding repeats.