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Higher Biology

Higher Biology. Unit 1 DNA and the Genome. KEY AREA 3: Gene Expression. DNA and the Genome Learning Intentions. KEY AREA 3 – Gene Expression Gene Expression Overview Transcription Translation One Gene Many Proteins Polypeptides. 3a) Gene Expression Overview.

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Higher Biology

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  1. Higher Biology Unit 1 DNA and the Genome KEY AREA 3: Gene Expression

  2. DNA and the Genome Learning Intentions KEY AREA 3 – Gene Expression • Gene Expression Overview • Transcription • Translation • One Gene Many Proteins • Polypeptides

  3. 3a) Gene Expression Overview The genetic composition of a cell is called the cell genotype The cell genotype is determined by the sequence of DNA bases in its genes Only a fraction of the genes in a cell are expressed

  4. 3b) Gene Expression Overview Gene expression is controlled by the regulation of Transcription and Translation The order of bases on DNA determines the sequence of amino acids that are made The sequence of amino acids joined together in polypeptide chains determine the structure, shape, function of the protein produced

  5. 3c) RNA Structure & Function RNA is a single strand of RNA nucleotides RNA nucleotides contain a ribose sugar, a phosphate and a base RNA nucleotides contain the bases Adenine, Uracil, Cytosine, Guanine The complementary base-pairs are Adenine-Uracil and Cytosine-Guanine

  6. 3d) RNA Structure & Function Transcription and translation involve 3 types of RNA: mRNA (messenger RNA) carries a copy of a section of the DNA code for a specific protein from the nucleus to the ribosome rRNA (ribosomal RNA) and proteins form a ribosome tRNA (transfer RNA) carries a specific amino acid to the ribosome mRNA is linear and is transcribed from DNA in the nucleus It is translated into protein by ribosomes in the cytoplasm Each triplet of bases on the mRNA is called a codon and codes for a specific amino acid (see textbook p.38 table 2.6) A mRNA codon is complementary to the triplet of bases on the original DNA strand

  7. 3e) RNA Structure & Function tRNA is found in the cytoplasm tRNA is folded on itself due to hydrogen bonds forming between complementary bases tRNA has exposed triplets of bases called tRNA anticodons tRNA anticodons are complementary to a mRNA codon tRNA pick up specific amino acids (on its amino acid attachment site) in the cytoplasm and carry them to the ribosome

  8. 3f) RNA Structure & Function mRNA codons and tRNA anticodons translate the genetic code into the correct sequence of amino acids to make a protein

  9. 3g) Transcription Transcription is the copying of the DNA code for a specific protein into mRNA Transcription of DNA into primary RNA then processing into mature RNA transcripts occurs in the nucleus 1. A promoter region of DNA initiates transcription 2. RNA polymerase enzyme moves to the specific section of DNA and unwinds the DNA double helix from that point by breaking hydrogen bonds between bases 3. RNA nucleotides pair with complementary DNA base pairs (A-U, G-C) forming mRNA 4. RNA polymerase can only add nucleotides to the 3’ end of mRNA 5. RNA polymerase joins the nucleotides together to form a new sugar- phosphate backbone 6. The mRNA becomes separated from the DNA template, and is called the primary transcript of mRNA

  10. 3h) Transcription

  11. 3i) Transcription- RNA Splicing Not ALL nucleotides in a gene play a role in the coding for the amino acids sequence Introns are non-coding regions of genes Exons are coding regions of genes Introns are found between the Exons Introns are cut out and removed from the primary transcript Exons are spliced together (RNA splicing) to form mRNA with a continuous sequence exons (this is called the mature transcript of mRNA) this does not change the order of the exons The mature transcript of mRNA moves from the nucleus through the cytoplasm to a ribosome Transcription Animation (1:52)

  12. Splicing (1:37)

  13. 3j) Stages of Translation • mRNA codons AUG complementary to tRNA anticodon UAC codes for the amino acid methionine (met) AND acts as the START CODON • mRNA codons UAA, UAG & UGA do not code for amino acids, but they act as STOP CODONS • Translation begins at a start codon and ends at a stop codon • Mature mRNA binds to the ribosome • Each tRNA anticodon binds to a complementary codon on the mRNA lining up the amino acids (being carried by tRNA) in a specific order • Peptide bonds form between the amino acids to form a growing polypeptide chain • When the tRNA detaches from its amino acid, it then collects another

  14. 3j) Translation

  15. 3j) Translation

  16. 3j) Translation

  17. 3j) Translation

  18. 3j) Translation Overview

  19. 3k) One gene, many proteins One gene can create many proteins as a result of alternative RNA splicing Different mature mRNA molecules are produced from the same primary transcript This is dependent on which exons are retained during RNA splicing

  20. 3l) Final Protein Structure Amino acids are linked by peptide bonds to form polypeptides Polypeptide chains fold to form three dimensional shape of a protein The folding is caused by hydrogen bonds and other interactions between individual amino acids Proteins have a large variety of shapes which determines their functions A cell’s phenotype is its physical and chemical state A cell’s phenotype is determined by the proteins it produces along with environmental factors that can influence the cell Translation animation (2:04)

  21. 3m) Genes and Proteins All proteins contain Carbon, Hydrogen, Oxygen and Nitrogen (sometimes sulphur) Each protein is made from amino acids linked by peptide bonds to form polypeptide chains During protein synthesis, the sequence of DNA bases determines the sequence of amino acids The sequence of amino acids, determines the structure and function of the protein Hydrogen bonds form between specific amino acids in a polypeptide chain, causing the chain to become coiled or folded

  22. 3n) Protein structure During folding, different regions of the polypeptide chain can come into contact with one another. This allows interaction between amino acids in one or more chains, resulting in cross connections Proteins are held in a three dimensional shape by peptide bonds, hydrogen bonds, and interactions between amino acids Polypeptide chains can become:- - Arranged in long parallel strands (e.g. fibrous protein – keratin) - Folded into a spherical shape (e.g. globular protein – enzyme amylase - Folded into a spherical shape with a non-protein part added (e.g. haemoglobin)

  23. 3o) Functions of Proteins Proteins have a large variety of structures and shapes resulting in a wide range of functions. Examples include:- Enzymes Structural proteins Hormones Antibodies

  24. DNA and the Genome Questions KEY AREA 3 – Gene Expression • Testing Your Knowledge 1 P 32 Q 1-2 2. Testing Your Knowledge 2 P 37 Q1-4 3. Testing Your Knowledge 3 P 42 Q 1-4 except 4e and 4f 4. What you Should Know P 43 5. Problem Solving P 6-9 Q 1-8 except Q 5 * you must be able to use a chromatogram to calculate Rf values, and to use Rf values to identify a substance on a chromatogram from a table * you must be able to work out the codon sequence given the anti-codon sequence and vice versa * you must be able to use a codon chart to identify which codon / anti- codon corresponds to which amino acid 6. Quick Quiz

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