From Gene to ProteinFrom Gene to Protein

Transcription & Transcription & TranslationTranslation

AN OVERVIEWAN OVERVIEW

Mobility ProblemMobility Problem

• DNA cannot leave the nucleus.DNA cannot leave the nucleus.• Proteins are made in the cytosolProteins are made in the cytosol• How to connect the 2?How to connect the 2?

TranscriptionTranscription

• RNA can leave the nucleus.RNA can leave the nucleus.• Similar structure to DNA, exceptSimilar structure to DNA, except

– Only one-strandedOnly one-stranded– Does not have Thymine (T). Has Uracil Does not have Thymine (T). Has Uracil

(U) instead.(U) instead.– Ribose for its sugar instead of Ribose for its sugar instead of

deoxyribose.deoxyribose.

mRNA (messenger RNA) is transcribed mRNA (messenger RNA) is transcribed according to instructions of the coding strand according to instructions of the coding strand

of DNA.of DNA.

mRNA can then carry the message of the mRNA can then carry the message of the DNA to the ribosome in the cytosol! DNA to the ribosome in the cytosol!

Language ProblemLanguage Problem

• Language of DNA- 4 bases, A, T, G, Language of DNA- 4 bases, A, T, G, & C& C

• Language of Proteins- 20 amino Language of Proteins- 20 amino acids.acids.

• How to translate?How to translate?

TranslationTranslation

• Synthesis of a polypeptide, under Synthesis of a polypeptide, under the direction of the translatorthe direction of the translatorRNARNA

• Occurs in cytosol, at the ribosome.Occurs in cytosol, at the ribosome.

Every 3 nucleotides code for the Every 3 nucleotides code for the production of a specific amino acid.production of a specific amino acid.

TranscriptionTranscription

A Closer LookA Closer Look

1.1. RNA polymerase separates 2 RNA polymerase separates 2 strands of DNAstrands of DNA

a)a) It then hooks RNA nucleotides It then hooks RNA nucleotides together as they match to DNA together as they match to DNA template.template.

b)b) 5’5’3’3’

2. Polymerase attaches to sequence 2. Polymerase attaches to sequence of DNA called of DNA called promoter.promoter.

3. Sequence that signals end of 3. Sequence that signals end of transcription is called transcription is called terminatorterminator..

Which strand of DNA to Which strand of DNA to transcribe?transcribe?

Modifying RNAModifying RNA

• Both ends of the RNA sequence are Both ends of the RNA sequence are altered.altered.– 5’ end is capped with a modified 5’ end is capped with a modified

GuanineGuanine– 3’ end is capped with a 3’ end is capped with a poly-Apoly-A tail. tail.

More ModificationMore Modification

• RNA splicingRNA splicing– Initial RNA sequence is approximately Initial RNA sequence is approximately

8,000 nucleotides8,000 nucleotides– Generally, only approx. 1,200 are Generally, only approx. 1,200 are

needed, though.needed, though.– Noncoding areas are found in between Noncoding areas are found in between

coding areascoding areas

IntronsIntrons

- - Noncoding regionNoncoding region

ExonsExons

- - Coding region of Coding region of nucleic acidnucleic acid

How are introns found & How are introns found & cut out?cut out?

• snsnRNPs (“snurps”) recognize the RNPs (“snurps”) recognize the end of an intronend of an intron

• They then form a They then form a spliceosomespliceosome with with other proteins and cut out that other proteins and cut out that intronintron

TranslationTranslation

A closer lookA closer look

What’s a triplet code?What’s a triplet code?

• Flow of information from gene Flow of information from gene (DNA) to protein is a triplet code(DNA) to protein is a triplet code

• Every 3 nucleotides will code for Every 3 nucleotides will code for the production of a specific amino the production of a specific amino acid.acid.

• mRNA base triplets are called mRNA base triplets are called codonscodons..

The purpose of tRNA.The purpose of tRNA.

• Interpreter of the mRNA codons is Interpreter of the mRNA codons is tRNA (transfer RNA)tRNA (transfer RNA)

• Each tRNA molecule has a section Each tRNA molecule has a section called the called the anticodonanticodon..

• tRNA grabs a specific amino acid & tRNA grabs a specific amino acid & brings it to the ribosomebrings it to the ribosome

How do mRNA & tRNA work How do mRNA & tRNA work together to get the correct together to get the correct

amino acid?amino acid?

• Anticodon of tRNA meets with the Anticodon of tRNA meets with the codon of mRNA at the ribosome.codon of mRNA at the ribosome.– Ex- mRNA codon UUUEx- mRNA codon UUU

- tRNA anticodon- AAA- tRNA anticodon- AAA

- tRNA will have phenylalanine to add - tRNA will have phenylalanine to add to the polypeptideto the polypeptide

• FirstFirst• Study ribosomes, Study ribosomes,

p. 316.p. 316.

• SecondSecond• Study Building a Study Building a

Polypeptide, p. Polypeptide, p. 317-318317-318