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Genetic Code , tRNA and rRNA. YILDIRIM BEYAZIT UNIVERSITY FACULTY OF MEDICINE THE DEPARTMENT OF MEDICAL BIOLOGY ASST. PROF. DR. ENDER ŞİMŞEK. The Genetic Code. Correspondence between the sequence of bases in a codon and the amino acid residue it specifies . The Genetic Code.

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slide1

GeneticCode, tRNAandrRNA

YILDIRIM BEYAZIT UNIVERSITY FACULTY OF MEDICINE

THE DEPARTMENT OF MEDICAL BIOLOGY

ASST. PROF. DR. ENDER ŞİMŞEK

slide2

The Genetic Code

  • Correspondence between the sequence of bases in a codon and the amino acid residue it specifies.
slide3

The Genetic Code

  • Correspondence between the sequence of bases in a codon and the amino acid residue it specifies.
  • 4 possible bases (U, C, A, and G) can occupy three positions of codon, therefore 43 = 64 possible codons.
slide4

The Genetic Code

  • Correspondence between the sequence of bases in a codon and the amino acid residue it specifies.
  • 4 possible bases (U, C, A, and G) can occupy three positions of codon, therefore 43 = 64 possible codons.
  • 61 codons specify amino acids, and 3 codons (UAA, UAG, and UGA)are stop codons (cause ribosome to end polypeptide synthesis and release the transcript).
properties of the genetic code
Properties of the Genetic Code
  • The genetic code is composed of nucleotide triplets.
properties of the genetic code1
Properties of the Genetic Code
  • The genetic code is composed of nucleotide triplets.
  • The genetic code is non-overlapping.
properties of the genetic code2
Properties of the Genetic Code
  • The genetic code is composed of nucleotide triplets.
  • The genetic code is non-overlapping.
  • The genetic code is comma-free.
properties of the genetic code3
Properties of the Genetic Code
  • The genetic code is composed of nucleotide triplets.
  • The genetic code is non-overlapping.
  • The genetic code is comma-free.
  • The genetic code is degenerate.
properties of the genetic code4
Properties of the Genetic Code
  • The genetic code is composed of nucleotide triplets.
  • The genetic code is non-overlapping.
  • The genetic code is comma-free.
  • The genetic code is degenerate.
  • The genetic code is ordered. (5’ to 3’)
properties of the genetic code5
Properties of the Genetic Code
  • The genetic code is composed of nucleotide triplets.
  • The genetic code is non-overlapping.
  • The genetic code is comma-free.
  • The genetic code is degenerate.
  • The genetic code is ordered. (5’ to 3’)
  • The genetic code contains start and stop codons.
properties of the genetic code6
Properties of the Genetic Code
  • The genetic code is composed of nucleotide triplets.
  • The genetic code is non-overlapping.
  • The genetic code is comma-free.
  • The genetic code is degenerate.
  • The genetic code is ordered. (5’ to 3’)
  • The genetic code contains start and stop codons.
  • The genetic code is nearly universal.
slide12
Initiation and termination Codons
  • Initiation codon: AUG
  • Termination codons: UAA, UAG, UGA
key points
Key Points
  • Each of the 20 amino acids in proteins is specified by one or more nucleotide triplets in mRNA. (20 amino acids refers to what is attached to the tRNAs!)
key points1
Key Points
  • Each of the 20 amino acids in proteins is specified by one or more nucleotide triplets in mRNA. (20 amino acids refers to what is attached to the tRNAs!)
  • Of the 64 possible triplets 61 specify amino acids and 3 signal chain termination. (have no tRNAs!)
key points2
Key Points
  • The code is non-overlapping, with each nucleotide part of a single codon, degenerate, with most amino acids specified by two to four codons, and ordered, with similar amino acids specified by related codons.
key points3
Key Points
  • The code is non-overlapping, with each nucleotide part of a single codon, degenerate, with most amino acids specified by two to four codons, and ordered, with similar amino acids specified by related codons.
  • The genetic code is nearly universal; with minor exceptions, the 64 triplets have the same meaning in all organisms.
key points4
Key Points
  • All but two amino acids (Met, Trp) are specified by more than one codon.
  • Three (Leu, Ser, Arg) are specified by six codons.
key points5
Key Points
  • All but two amino acids (Met, Trp) are specified by more than one codon.
  • Three (Leu, Ser, Arg) are specified by six codons.
  • Synonyms-multiple codons can code the same amino acid.
  • tRNA may recognize up to 3 synonymous codons because the 5’ base of a codon and 3’ base of the anticodon can interact in ways other than via Watson-Crick base pairs.
key points6
Key Points
  • All but two amino acids (Met, Trp) are specified by more than one codon.
  • Three (Leu, Ser, Arg) are specified by six codons.
  • Synonyms-multiple codons can code the same amino acid.
  • tRNA may recognize up to 3 synonymous codons because the 5’ base of a codon and 3’ base of the anticodon can interact in ways other than via Watson-Crick base pairs.
  • Translation is initiated at the AUG codon (Met) but this tRNA differs from the tRNA for internal amino acid the Met codon.
to synthesize protein
Tosynthesize protein:
  • mRNA
  • Ribosomes
  • tRNA’s
  • Amino acids
  • Enzymes
ribosomes rrna s
Ribosomes & rRNA’s

S: Svedberg unit

S: Svedberg unit

transfer rnas trnas
Transfer RNAs (tRNAs)
  • tRNAs are adapters between amino acids and the codons in mRNA molecules.
  • The anticodon of the tRNA base pairs with the codon of mRNA.
  • The amino acid is covalently attached to the 3’ end of the tRNA.
specificity of trnas
Specificity of tRNAs
  • tRNA molecules must have the correct anticodon sequence.
  • tRNA molecules must be recognized by the correct aminoacyl-tRNAsynthetase.
  • tRNA molecules must bind to the appropriate sites on the ribosomes.