LS13translation

LS13translation - Translation -how are proteins made? The...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
Translation -how are proteins made? The genetic code What is genetic code? How did we know it? The role of tRNA and ARS How is the genetic codes decoded in the cell? The ribosome machinery How are proteins synthesized? The translation process Translation initiation Translation elongation Translation termination
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Genetic code -According to the central dogma, the genetic information of a gene is first transcribed as the nucleotide sequence of a RNA, and then translated into the amino acid sequence of a protein -The rules by which the nucleotide sequence of a gene is translated into the amino acid sequence of a protein are the genetic code . - the nucleotide sequence representing individual amino acid is called codon (located in mRNA), sequence complementary to codon is called anticodon (located in tRNA). -Genetic code is used universally in all organisms.
Background image of page 2
Genetic codes and reading frame 1. Genetic codes are triplets. Each 3-letter code ( codon ) specifies one of the 20 amino acids, or one of the three stop signal of translation. Codons are non-overlapping and there are no gaps between codons in mRNA. 2. A “open reading frame” ( ORF ) is the nucleotide sequence between a start codon and a stop codon. Codons in mRNA are read 5’ --> 3’.Depending on where to start, any nucleotide sequence can be read as three different “reading frames”.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Breaking the Genetic Code: mRNA -> Protein Translating 4 bases into 20 amino acids Read 1 base at a time = 4 (4 1 ) amino acids coded Read 2 bases at a time = 16 (4 2 ) amino acids coded Read 3 bases at a time = 64 (4 3 ) amino acids coded Genetic studies established a 3 base code (Crick & Brenner) Biochemical studies assigned triplet codons to different amino acids -translation of synthetic homopolymer RNAs (e.g. PolyU = PhePhePhe) (Nirenberg & Matthaei) -triplet/ribosome binding assays (e.g. AUG = Met) (Nirenberg & Leder) -translation of synthetic RNAs with defined mixed base sequences (Khorana)
Background image of page 4
Features of genetic code 1. Genetic code is not overlapping 2. Genetic code is continuous, there is no comma (or gap) in the reading frame 3. Genetic code is always triplet (3-letter) 4. There are a total of 61 amino acid-encoding codons but only 20 amino acids, so the genetic codes must be degenerate , which means that more than one codon can code for one amino acid
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Most codes are degenerated The codes for Arg, Leu, and Ser are most degenerated, each have 6 codons. Met, and Trp, each has only one codon, are least degenerated. The stop signal has three codons.
Background image of page 6
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The universal codon is used by all organisms, suggesting life evolved only once on earth. But some nuclear or organellar genomes may have one or a few unusual codons, mostly converting a stop codon to encode an amino acid. These are most likely later modifications during evolution.
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 34

LS13translation - Translation -how are proteins made? The...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online