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Genes and Protein Synthesis

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Presentation on theme: "Genes and Protein Synthesis"— Presentation transcript:

1 Genes and Protein Synthesis
Chapter 7 Genes and Protein Synthesis

2 One Gene-One Polypeptide Hypothesis
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 Main Idea Central Dogma Francis Crick (1956)

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

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

6 Adenine pairs with Thymine Adenine pairs with Uracil
DNA RNA Double stranded Single stranded Adenine pairs with Thymine Adenine pairs with Uracil Guanine pairs with Cytosine Deoxyribose sugar Ribose sugar

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

8 Genetic COde Codon AA are represented by more than one 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 Amino acids Abbreviated Three letters

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

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

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

13 Elongation RNA molecule is built Primer not needed 5’ to 3’
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 Termination RNA polymerase recognizes a termination sequence – AAAAAAA
Nuclear proteins bind to string of UUUUUU on RNA mRNA molecule releases from template strand


16 Post-transcriptional modifications
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 Splicing the pre-MRNa DNA comprised of Spliceosome
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 Splicing Process Spliceosome contains a handful of small ribonucleoproteins snRNP’s (snurps) snRNP’s bind to specific regions on introns

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

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

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

22 TRNa: Wobble Hypothesis
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 Ribosomes 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 Translation process Three stages Initiation Elongation Termination
Amino acid Translation process Polypeptide A site P site Anticodon mRNA Three stages Initiation Elongation Termination 1 Codon recognition mRNA movement Stop codon New peptide bond 2 Peptide bond formation 3 Translocation

25 Initiation Reading frame is established to correctly read codons
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 Elongation Amino acids are added to grow a polypeptide chain
A, P, and E sites operate 4 Steps

27 Termination 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 polysome a b What molecules are present in this photo? Red object = ?

29 Prokaryotic RNA transcription/Translation
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 Review 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 Regulating Gene expression
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 Transcriptional regulation
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 Transcriptional regulation
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

34 Agouti mice

35 Post transcriptional regulation
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 Translational regulation
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 Post-translational regulation
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 Prokaryotic Regulation
lacOperon Regulates the production of lactose metabolizing proteins

39 Prokaryotic Regulation
trpOperon Regulates the expression of tryptophan enzymes

40 Cancer 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

41 cancer

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

43 Small-scale mutations
Four groups Missense, nonsense, silent, frameshift Lactose, sickle cell anemia SNPs – single nucleotide polymorphisms Caused by point mutations

44 Missense mutation 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 Nonsense mutation Change in single base pair or group of base pairs
Results in premature stop codon Protein will not be able to function

46 Silent mutation 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 Frameshift mutation 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 Large-scale mutations
Multiple nucleotides, entire genes, whole regions of chromosomes

49 Large-scale mutations
Amplification – gene duplication Entire genes are copied to multiple regions of chromosomes

50 Large-scale mutations
Large-scale deletions Entire coding regions of DNA are removed Muscular Dystrophy

51 Large-scale mutations
Chromosomal translocation Entire genes or groups of genes are moved from one chromosome to another Enhance, disrupt expression of gene

52 Large-scale mutations
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 Large-scale mutations
Trinucleotide repeat expansion Increases number of repeats in genetic code CAG CAG CAG CAG CAG CAG CAG CAG Huntingtons disease

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

55 Chemical Mutagens 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 Radiation - Low energy UV B rays Non-homologous end joining
Bonds form between adjacent nucleotides along DNA strand Form kinks in backbone Skin cancer

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

58 Mutation in prokaryotes
DNA is mostly coding sequences Mutation is harmful – superbugs

59 Genomes and Gene organization
Human Body 22 autosomal chromosomes 1 pair of each sex chromosome (XX, YY)

60 Genomes and Gene organization
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 Viruses Not alive but can replicate themselves Contain DNA or RNA
Capsid – protein coat Envelope – cell membrane

62 Virus 4000 species of virus have been classified

63 replication DNA RNA (retrovirus) Transcription and translation
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


65 Virus as Vectors Transduction
Using a virus vector to insert DNA into a cell or bacterium

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