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3.5 DNA is used to make proteins Transcription and Translation.

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Presentation on theme: "3.5 DNA is used to make proteins Transcription and Translation."— Presentation transcript:

1 3.5 DNA is used to make proteins Transcription and Translation

2 Compare the structure of RNA and DNA. Phosp hate Nitrogen Base Ribose 5Carbon sugar H H Phosp hate Nitrogen Base Deoxy- Ribose 5Carbon sugar OH H Ribose Nucleic Acid Deoxy - Ribose Nucleic Acid Look! No Oxygen!

3 There are 4 nitrogen bases in DNA: Adenine Thymine Guanine Cytosine There are 4 nitrogen bases in RNA: Adenine Uracil Guanine Cytosine But Uracil Replaces Thymine

4 mRNA – a single stranded ribbon rRNA – a globular knot that makes ribosomes tRNA – a club shaped amino acid carrier There is 1 type of DNA. It is double stranded and helical. There are 3 types of RNA:

5 DeoxyriboNucleicAcidRiboNucleicAcid Joblong-term storage and transmission of genetic information transfer the genetic code needed for the creation of proteins from the nucleus to the ribosome. This process prevents the DNA from having to leave the nucleus, StructureLong double- stranded molecule. Helix. Shorter single-stranded molecule. 3 main forms: mRNA – ribbon tRNA – club shaped rRNA - globular PairingA-T(Adenine-Thymine), G-C(Guanine-Cytosine) A-U(Adenine-Uracil), G-C(Guanine-Cytosine) StabilityDeoxyribose sugar in DNA is less reactive because of C-H bonds. Stable in alkaline conditions. DNA can be damaged by exposure to Ultra-violet rays. Ribose sugar is more reactive because of C-OH (hydroxyl) bonds. Not stable in alkaline conditions. RNA is more resistant to damage by Ultra-violet rays. How often made Copies only made during S phase in preparation for cell division. RNA strands are continually made, broken down and reused. WhereFound only in the nucleusFound in the nucleus and cytoplasm

6 Proteins Proteins are made up of long chains of amino acids. The sequence of amino acids is very important as it gives the protein its shape and therefore its function. ….is not the same as…. ……even if the amino acids are exactly the same! So when proteins are made the right sequence is important.

7 How do these ideas all come together to make proteins? Watson and Crick said: DNA makes RNA RNA makes protein Transcription Translation

8

9 Overview of Transcription and translation Transcription – Occurs in the nucleus. Is very similar to DNA replication except that RNA single strand is made using only one of the DNA strands; The DNA strand ‘re-helixes’ afterwards; U – T substitution. This RNA is then used in Translation. Translation – Occurs in the cytoplasm. Uses the RNA made in transcription in the 3 forms tRNA, rRNA and mRNA. The code on the mRNA is used to get the sequence of amino acids in a protein correct, tRNA carries the amino acids in, Ribosomal RNA joins the amino acids together. Image from: Terese Winslow; National Institutes of Health; nfo/scireport/images/figurea6.jpg

10 This model illustrate the process of transcription that takes place in the nucleus. The DNA base sequence of the gene is copied into messenger RNA (mRNA) The helix is unwound at the position of the gene by RNA polymerase RNA nucleotides are found in the nucleus space. One of the polynucleotide chains act as a template for mRNA Free nucleotides base pair with DNA nucleotides The bonds between mRNA nucleotides are formed by RNA polymerase mRNA is a single polynucleotide chain but the base thymine is replaced by Uracil. The DNA helix reforms After the mRNA is complete the molecule detach's from the DNA and leaves the nucleus for the cytoplasm ribosomes. Transcription

11 The RNA gets modified into: Messenger RNA (mRNA) – a ribbon of information carried as a sequence of RNA nucleotides. A U G C C U G U G G G C U A A The sequence of nucleotide ‘letters’ make up 3 letter ‘words’ or Codons. Each codon ‘codes for’ one amino acid. [ ][ ][ ][ ][ ]

12 Transfer RNA (tRNA) – The ribbon bends so that some of the nucleotides on the strand are able to form H bonds with other nucleotides later on the strand. This bit of the tRNA can join to an amino acid. This bit of the tRNA will allow the tRNA to join to mRNA during translation. It is called the anti codon. G A A

13 There are 20 different amino acids. There are 64 different anti-codons on the tRNA. Each type of amino acid can be carried by several different tRNAs, but one type of tRNA can only carry one type of amino acid C A GC A UC A AA U U STOP C C G C A C G G A U A C

14 Ribosomal RNA – the ‘protein factories’ are also made up of RNA! We normally draw them like this: Large sub-unit Where the mRNA goes Small sub unit

15 Look at this animation now. It puts the bits together….. online.com/objects/ViewObject.aspx?ID=AP online.com/objects/ViewObject.aspx?ID=AP130 2 The next slide shows an animation (of sorts) of a bit more detail for Translation.

16 A U G C C U G U G G G C U A A [ ][ ][ ][ ][ ] U A C G G A C A C C C G A U U STOP This is a strand of mRNA made by TRANSCRIPTION. Notice the TRIPLET CODONS. The small sub-unit of a Ribosome connects to the mRNA An initiator amino acid attaches to the first Triplet Codon with complementary base pairing. This allows the large ribosome subunit to attach to the mRNA. The empty site in the large sub-unit is filled by a tRNA with the right anti-codon carrying another amino acid. A Peptide bond forms between the amino acids. At the same time the tRNA detaches and leaves. The small Ribosome subunit moves along to the next codon. The large ribosome subunit follows creating a new space for the next tRNA and amino acid. The next tRNA carrying an animo acid comes in and fills the new empty space in the ribosome. Again the peptide bond forms and the tRNA leaves This process continues……. …………. …………….. ……. …..until a tRNA carrying a ‘STOP’ anti-codon attaches..this causes the tRNA to detach and the ribosome to fall apart and leaves the protein finished. The process can start again with a new ribosome.

17 Animations Here are 2 detailed animations of transcription and translation that explain the processes up to higher level syllabus understanding ; see if you can understand them…. tml tml ml ml

18 Discuss the relationship between one gene and one polypeptide. Discuss means to Give an account including, where possible, a range of arguments for and against the relative importance of various factors, or comparisons of alternative hypotheses. Theory: One gene is transcribed and translated to produce one polypeptide. Some proteins are composed of a number of polypeptides and in this theory each polypeptide has its own gene. e.g. haemoglobin is composed of 4 polypeptides (2 of each type) and there is a gene for each type of polypeptide. This theory, like so many in biology has exceptions. e.g. 1) Some genes code for types of RNA which do not produce polypeptides. 2) Some genes control the expression of other genes.

19 You should now be able to: Compare the structure of RNA and DNA. Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase. Describe the genetic code in terms of codons composed of triplets of bases. Explain the process of translation, leading to polypeptide formation. Discuss the relationship between one gene and one polypeptide.


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