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Chapter 7.  DNA contains all of our hereditary information  Genes are located in our DNA  ~25,000 genes in our DNA (46 chromosomes)  Each Gene codes.

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Presentation on theme: "Chapter 7.  DNA contains all of our hereditary information  Genes are located in our DNA  ~25,000 genes in our DNA (46 chromosomes)  Each Gene codes."— Presentation transcript:

1 Chapter 7

2  DNA contains all of our hereditary information  Genes are located in our DNA  ~25,000 genes in our DNA (46 chromosomes)  Each Gene codes for a specific polypeptide

3  Central Dogma  Francis Crick (1956)

4  Transcription  DNA to RNA  Translation  Assembly of amino acids into polypeptide  Using RNA DNA molecule Gene 1 Gene 2 Gene 3 DNA strand TRANSCRIPTION RNA Polypeptide TRANSLATION Codon Amino acid

5  RNA transcription  Initiation, Elongation, Termination  TATA box  Introns, Exons  mRNA, tRNA, rRNA  Translation  Ribosome  Codon  Amino Acids  Polypeptide

6 DNARNA Double strandedSingle stranded Adenine pairs with ThymineAdenine pairs with Uracil Guanine pairs with Cytosine Deoxyribose sugarRibose sugar

7  Protein is made of amino acid sequences  20 amino acids  How does DNA code for amino acid?

8  Codon  Three letter code  5’ to 3’ order  Start codon  Stop codon  AA are represented by more than one codon  61 codons that specify AA

9  Abbreviated  Three letters

10  DNA to RNA  Occurs in nucleus  Three process  Initiation  Elongation  Termination RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation Elongation Termination Growing RNA RNA polymerase Completed RNA

11  RNA polymerase binds to DNA  Binds at promoter region  TATA box  RNA polymerase unwinds DNA  Transcription unit  Part of gene that is transcribed

12  Transcription factors bind to specific regions of promoter  Provide a substrate for RNA polymerase to bind beginning transcription  Forms transcription initiation complex

13  RNA molecule is built  RNA polymerase  Primer not needed  5’ to 3’  3’ to 5’ DNA is template strand  Coding strand  DNA strand that is not copied  Produces mRNA  Messenger RNA  DNA double helix reforms

14  RNA polymerase recognizes a termination sequence – AAAAAAA  Nuclear proteins bind to string of UUUUUU on RNA  mRNA molecule releases from template strand

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16  Pre-mRNA undergoes modifications before it leaves the nucleus  Poly(A) tail  Poly-A polymerase  Protects from RNA digesting enzymes in cytosol  5’ cap  7 G’s  Initial attachment site for mRNA’s to ribosomes  Removal of introns

17  DNA comprised of  Exons – sequence of DNA or RNA that codes for a gene  Introns – non-coding sequence of DNA or RNA  Spliceosome  Enzyme that removes introns from mRNA

18  Spliceosome contains a handful of small ribonucleoproteins  snRNP’s (snurps)  snRNP’s bind to specific regions on introns

19  Increases number and variety of proteins encoded by a single gene  ~25,000 genes produce ~100,000 proteins

20  mRNA to protein  Ribosomes read codons  tRNA assists ribosome to assemble amino acids into polypeptide chain  Takes place in cytoplasm

21  Contains  triplet anticodon  amino acid attachment site  Are there 61 tRNA’s to read 61 codons?

22  First two nucleotides of codon for a specific AA is always precise  Flexibility with third nucleotide  Aminoacylation – process of adding an AA to a tRNA  Forming aminoacyl-tRNA molecule  Catalyzed by 20 different aminoacyl-tRNA synthetase enzymes

23  Translate mRNA chains into amino acids  Made up of two different sized parts  Ribosomal subunits (rRNA)  Ribosomes bring together mRNA with aminoacyl-tRNAs  Three sites  A site - aminoacyl  P site – peptidyl  E site - exit

24 1Codon recognition Amino acid Anticodon A site P site Polypeptide 2 Peptide bond formation 3 Translocation New peptide bond mRNA movement mRNA Stop codon  Three stages  Initiation  Elongation  Termination

25  Ribosomal subunits associate with mRNA  Met-tRNA (methionine)  Forms complex with ribosomal subunits  Complex binds to 5’cap and scans for start codon (AUG) – known as scanning  Large ribosomal subunit binds to complete ribosome  Met-tRNA is in P-site  Reading frame is established to correctly read codons

26  Amino acids are added to grow a polypeptide chain  A, P, and E sites operate  4 Steps

27  A site arrives at a stop codon on mRNA  UAA, UAG, UGA  Protein release factor binds to A site releasing polypeptide chain  Ribosomal subunits, tRNA release and detach from mRNA

28 b a Red object = ? What molecules are present in this photo?

29  Throughout cell  Single type of RNA polymerase transcribes all types of genes  No introns  mRNA ready to be translated into protein  mRNA is translated by ribosomes in the cytosol as it is being transcribed

30  What is a gene?  Where is it located?  What is the main function of a gene?  Do we need our genes “on” all the time?  How do we turn genes “on” or “off”?

31  Proteins are not required by all cells at all times  Regulated  Eukaryotes – 4 ways  Transcriptional (as mRNA is being synthesized)  Post-transcriptional (as mRNA is being processed)  Translational (as proteins are made)  Post-translational (after protein has been made)  Prokaryotes  lacOperon  trpOperon

32  Most common  DNA wrapped around histones keep gene promoters inactive  Activator molecule is used (2 ways)  Signals a protein remodelling complex which loosen the histones exposing promoter  Signals an enzyme that adds an acetyl group to histones exposing promoter region

33  Methylation  Methyl groups are added to the cytosine bases in the promoter of a gene (transcription initiation complex)  Inhibits transcription – silencing  Genes are placed “on hold” until they are needed  E.g. hemoglobin

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35  Pre-mRNA processing  Alternative splicing  Rate of mRNA degradation  Masking proteins – translation does not occur  Embryonic development  Hormones - directly or indirectly affect rate  Casein – milk protein in mammary gland  When casein is needed, prolactin is produced extending lifespan of casein mRNA

36  Occurs during protein synthesis by a ribosome  Changes in length of poly(A) tail  Enzymes add or delete adenines  Increases or decreases time required to translate mRNA into protein  Environmental cues

37  Processing  Removes sections of protein to make it active  Cell regulates this process (hormones)  Chemical modification  Chemical groups are added or deleted  Puts the protein “on hold”  Degradation  Proteins tagged with ubiquitin are degraded  Amino acids are recycled for protein synthesis

38  lacOperon  Regulates the production of lactose metabolizing proteins

39  trpOperon  Regulates the expression of tryptophan enzymes

40  Lack regulatory mechanisms  Mutations in genetic code (mutagens)  Probability increases over lifetime  Radiation, smoking, chemicals  Mutations are passed on to daughter cells  Can lead to a mass of undifferentiated cells (tumor)  Benign and malignant  Oncogenes  Mutated genes that once served to stimulate cell growth  Cause undifferentiated cell division

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42  Positive and negative  Natural selection – evolution  Cancer –death  Small-Scale – single base pair  Point mutations  Substitution, insertion/deletion, inversion  Large-Scale – multiple base pairs

43  Four groups  Missense, nonsense, silent, frameshift  Lactose, sickle cell anemia  SNPs – single nucleotide polymorphisms  Caused by point mutations

44  Change of a single base pair or group of base pairs  Results in the code for a different amino acid  Protein will have different sequence and structure and may be non-functional or function differently

45  Change in single base pair or group of base pairs  Results in premature stop codon  Protein will not be able to function

46  Change in one or more base pairs  Does not affect functioning of a gene  Mutated DNA sequence codes for same amino acid  Protein is not altered

47  One or more nucleotides are inserted/deleted from a DNA sequence  Reading frame of codons shifts resulting in multiple missense and/or nonsense effects  Any deletion or insertion of base pairs in multiples of 3 does not cause frameshift

48  Multiple nucleotides, entire genes, whole regions of chromosomes

49  Amplification – gene duplication  Entire genes are copied to multiple regions of chromosomes

50  Large-scale deletions  Entire coding regions of DNA are removed  Muscular Dystrophy

51  Chromosomal translocation  Entire genes or groups of genes are moved from one chromosome to another  Enhance, disrupt expression of gene

52  Inversion  Portion of a DNA molecule reverses its direction in the genome  No direct result but reversal could occur in the middle of a coding sequence compromising the gene

53  Trinucleotide repeat expansion  Increases number of repeats in genetic code  CAG CAG CAG CAG CAG CAG CAG CAG  Huntingtons disease

54  Spontaneous mutations  Inaccurate DNA replication  Induced mutations  Caused by environmental agent – mutagen  Directly alter DNA – entering cell nucleus  Chemicals, radiation

55  Modify individual nucleotides  Nucleotides resemble other base pairs  Confuses replication machinery – inaccurate copying  Nitrous acid  Mimicking DNA nucleotides  Ethidium bromide – insert itself into DNA

56  UV B rays  Non-homologous end joining  Bonds form between adjacent nucleotides along DNA strand  Form kinks in backbone  Skin cancer

57  Ionizing radiation – x-ray, gamma rays  Strip molecules of electrons  Break bonds within DNA  Delete portions of chromosomes  Development of tumors

58  DNA is mostly coding sequences  Mutation is harmful – superbugs

59  Human Body  22 autosomal chromosomes  1 pair of each sex chromosome (XX, YY)

60  Components  VNTR’s– variable number tandem repeats (microsatellites)  Sequences of long repeating base pairs  TAGTAGTAGTAGTAG  LINEs – long interspersed nuclear elements  SINEs – short interspersed nuclear elements  Transposons – small sequences of DNA that move about the genome and insert themselves into different chromosomes  Pseudogene – code is similar to gene but is unable to code for protein

61  Not alive but can replicate themselves  Contain  DNA or RNA  Capsid – protein coat  Envelope – cell membrane

62  4000 species of virus have been classified

63  DNA  Transcription and translation  RNA (retrovirus)  Uses reverse transcriptase – enzyme  Uses cells parts to make a single strand of DNA and then makes a complementary strand from that copy  Integrase – incorporates into our genetic code

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65  Transduction  Using a virus vector to insert DNA into a cell or bacterium


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