3.5 transcription & translation

  • 797 views
Uploaded on

 

More in: Technology
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Be the first to comment
    Be the first to like this
No Downloads

Views

Total Views
797
On Slideshare
0
From Embeds
0
Number of Embeds
2

Actions

Shares
Downloads
37
Comments
0
Likes
0

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide

Transcript

  • 1. 3.5 Transcription & Translation Topic 3 The Chemistry of Life
  • 2. 3.5.1 Compare the structure of RNA and DNA. Limit this to the names of sugars, bases and the number of strands. 3.5.2 Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase TRANSCRIPTION
  • 3. 3.5.3 Describe the genetic code in terms of codons composed of triplets of bases. 3.5.4 Explain the process of translation, leading to polypeptide formation. (Include the roles of messenger RNA (mRNA), transfer RNA (tRNA), codons, anticodons, ribosomes and amino acids). 3.5.5 Discuss the relationship between one gene and one polypeptide. (Originally, it was assumed that one gene would invariably code for one polypeptide, but many exceptions have been discovered). TRANSLATION
  • 4. DNA & RNA There are TWO types of Nucleic acids: – DNA – RNA Both DNA and RNA consist of chains of nucleotides, each composed of a sugar, a base and a phosphate. However, there are THREE differences between DNA and RNA: Feature DNA RNA No. of Strands Two Strands One Strand Sugar Deoxyribose Ribose Bases A-T, C-G A-U, C-G U = Uracil
  • 5. The Genetic Code The functional unit of information on the chromosome is the gene A gene consists of a unique sequence of bases that code for a polypeptide or an RNA molecule. For the DNA molecule to influence the activities of a cell, it has to first be translated into proteins. One gene codes for a polypeptide or an RNA molecule. So how can 4 bases be translated into a sequence of amino acids when there are 20 possible amino acids to code for?
  • 6. The Triplet Code If each base coded for one amino acid only 4 amino acids could be sequenced. If we had pairs of bases coding for amino acids, how many combinations would then be possible? – 16 still not enough The answer is to use 3 bases to code for each amino acid. – With three bases 64 combinations are possible. – More than enough for the 20 amino acids and start and stop signals. This is called the Triplet Code.
  • 7. The Triplet Code Experiments have verified that the genetic code is made up of base triplets. These base triplets are called codons (on mRNA). Each triplet codes for an amino acid. Out of the 64 possible codons: – 61 code for amino acids. – 3 are stop codons (they do not code for an amino acid). The genetic code is degenerate. This means that it is possible for two or more codons to code for the same amino acid. The genetic code is universal. This means that all living organisms use the same code. Viruses also use this code.
  • 8. The Triplet Code Ref: Biology Key Ideas
  • 9. Protein Synthesis The central dogma of molecular genetics is that the flow of information for organisms is unidirectional. – It only flows in one direction (some viruses can reverse this). DNA  RNA  Protein There are two main processes involved in Protein Synthesis: – Transcription. • Where a molecule of mRNA is formed from the DNA template strand. – Translation • Where the mRNA sequence is converted into a polypeptide chain.
  • 10. Transcription DNA  RNA. Basically it is a process in which the message written in DNA code is transcribed into a working copy of mRNA (messenger RNA). The process is: – The RNA polymerase enzymes separate the two strands of DNA. – One strand of the DNA is used as a template for mRNA synthesis. – RNA polymerase forms the mRNA molecule using Uracil instead of Thymine. – When the mRNA molecule is complete, it breaks away from the DNA and travels through the nuclear pores into the cytoplasm. – The DNA strands rejoin.
  • 11. Transcription Ref Biology for the IB Diploma, Allott
  • 12. Transcription In Transcription, complementary base pairing occurs as in DNA replication, except that uracil replaces thymine: – ie. Cytosine – guanine – Adenine – uracil DNA base sequence: T A G G C T T G A T C G mRNA base sequence: A U C C G A A C U A G C
  • 13. Translation RNA  Protein Basically it is a process in which a polypeptide chain is built from a codon sequence on the mRNA molecule. The process is: – The mRNA molecule attaches to a Ribosome. – tRNA molecules bring specific amino acids to the ribosome according to the codon on the mRNA. – There is a different tRNA molecule for each of the 61 codons. – Each tRNA molecule is about 80 nucleotides long and is folded into a clover shape. – At one end there is an exposed triplet of bases called an anticodon and at the other a specific amino acid. – The anticodon on the tRNA matches the codon on the mRNA.
  • 14. Translation The ribosomes provide the platform where the tRNA-amino acid and mRNA are brought together. As the amino acids are bought alongside one another they are joined together by enzymes to form a polypeptide. Translation begins with a signal code, the start codon AUG. – AUG codes for the amino acid Methionine. The ribosome moves along the mRNA strand one codon at a time. As the tRNA molecule deposits its amino acid, it is released back to the cytoplasm to link with another amino acid. When a stop codon is reached, translation ceases and the polypeptide chain is completed and released from the ribosome. The polypeptide folds into its final protein shape. If the protein is more than one polypeptide, the chains link and form their tertiary structure.
  • 15. Ref Biology for the IB Diploma, Allott
  • 16. One Gene - One Polypeptide 1.DNA codes for a specific sequence of polypeptides. 2. The DNA code for one polypeptide is a gene. 3. DNA is transcribed into mRNA. 4. mRNA is translated into a polypeptide. 5. Originally it was thought that one gene always codes for one polypeptide. 6. Some genes do not code for a polypeptide. 7. Some genes code for tRNA and rRNA. 8. Some sections of DNA code for regulators which are not polypeptides. 9. Antibody production does not follow the transcription and translation pattern. 10. Change in gene due to mutation will affect the primary structure of the polypeptide.
  • 17. 3.5.1 Compare the structure of RNA and DNA. Limit this to the names of sugars, bases and the number of strands. 3.5.2 Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase TRANSCRIPTION, IBO guide:
  • 18. 3.5.3 Describe the genetic code in terms of codons composed of triplets of bases. 3.5.4 Explain the process of translation, leading to polypeptide formation. (Include the roles of messenger RNA (mRNA), transfer RNA (tRNA), codons, anticodons, ribosomes and amino acids). 3.5.5 Discuss the relationship between one gene and one polypeptide. (Originally, it was assumed that one gene would invariably code for one polypeptide, but many exceptions have been discovered). TRANSLATION, IBO guide: