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FROM DNA TO PROTEINSwww.psmag.com
PART 3
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GENERAL PATHWAY PROKARYOTES vs EUKARYOTES
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Prokaryotes vs EukaryotesProkaryote Eukaryote
Site of DNA Replication Protoplasm Nucleus
Site of Transcription Protoplasm Nucleus
Site of RNA Splicing Rare Nucleus
Site of Translation Protoplasm Cytoplasm
Site of Recombination Protoplasm Nucleus
GENERAL STEPS IN DNA REPLICATION
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DNA REPLICATIONSEMI-CONSERVATIVE
STEPSUnwinding & Strand Separation
Helicase will unwind the parental strands breaks the H-bonds between bases
SSBP (Single-stranded DNA-binding proteins)
attaches to separated strands and keep them from annealing back
STEPS
STEPSUnwinding & Strand Separation
Topoisomerase breaks and rejoins the DNA double helix to relieve twisting forced by the opening of the helix (supercoils) mol-biol4masters.masters.grkraj.org
STEPSPriming
Primase catalyzes synthesis of RNA primers RNA primers attach to specific site of DNA strand (ORI region)
Synthesis of New Strands Leading strand (Continuous): DNA polymerase III catalyzes synthesis of new DNA strands at 5’ to 3’ direction (as single polymer) and extends the leading strand
STEPS
STEPSSynthesis of New Strands
Lagging strand (Discontinuous): DNA polymerase III extends the Okazaki fragments DNA polymerase I removes RNA primers and replaces it with DNA
Sealing the nick DNA Ligase forms covalent bonds from 3’ to 5’ direction to join the Okazaki fragments into a continuous strand
STEPS
DNA REPLICATION: Prokaryotespulpbits.com
DNA REPLICATION: Eukaryotes
For VIDEOS: https://www.youtube.com/watch?v=27TxKoFU2Nw
TELOMERASE AND GENE EROSION
TELOMERES: ends of the DNA each chromosome is one continuous double stranded length of DNA with 2 telomeres
The 3’ to 5’ parent strand is copied no trouble as the leading strand BUT the lagging strand (parent 5’ to 3’) has small primers made every so often and filled in NOTE: no template at the end to bind to so when the primers are removed there is an overhang and exposes the DNA to digestion which would eventually eat into the genes at the end (gene erosion)
TELOMERASE AND GENE EROSION
TELOMERASE AND GENE EROSION
QUESTIONS????
REVERSE TRANSCRIPTION
REVERSE TRANSCRIPTION
OVERVIEW OF TRANSCRIPTION & TRANSLATION
TRANSCRIPTIONProcess of copying DNA to RNA
NOTE: only one strand of DNA, the template strand, is used to make mRNA
Does not need a primer to start and can involve multiple RNA polymerases Divided into 3 stages
Initiation Elongation Termination
For VIDEOS: https://www.youtube.com/watch?
v=WsofH466lqk
STEPS IN TRANSCRIPTION
STEPS IN TRANSCRIPTION
RNA POLYMERASERNA polymerase only transcribes one strand of the parental DNA molecule (the template strand) in the 3' to 5' direction
RNA polymerase will never add a T, instead it will add a U
Transcription ceases when RNA polymerase encounters special DNA sequences termed terminators that stop the process of transcription
RECALL…
INTRONS AND EXONSIntrons
sequences in the DNA that are NOT used to make mRNA or to make a protein
they are NOT transcribed
Exons
sequences in the DNA that are expressed or used to make mRNA and ultimately are used to make a protein
POST-TRANSCRIPTIONAL MODIFICATION IN EUKARYOTES
RNA SPLICING
REMOVAL OF INTRONS
5’ METHYLATED CAP AND POLYADENYLATION
PREVENTS DEGRADATION DURING TRANSIT FROM NUCLEUS TO CYTOPLASM
FINAL PRODUCT AFTER TRANSCRIPTION
TRANSLATION CAN BEGIN…www.can-con.ca
CONTROL DURING TRANSCRIPTION
PROKARYOTES
regulating genetic expression in nearby genes (e.g. LAC OPERON)
EUKARYOTES
involves the organization of chromatin and specific transcription factors which function by either changing the rate of transcription or altering the accessibility of chromatin to transcriptional machinery
the LAC OPERON
TRANSLATION: FROM VAGUE DNA CODES TO
MEANINGFUL TRAITS
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IN SUMMARY…
EXAMPLE…DNA 5’-ATG GTT CGG TAG-3’ !
Replicating this strand.. 5’-CTA CCG AAC CAT-3’
mRNA transcript to undergo translation 5’-AUG GUU CGG UAG-3’
peptide from mRNA after translation Met-Val-Arg-STOP
THE GENETIC CODE
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http://www.genome.jp/kegg/catalog/codes1.html
NUCLEOTIDE CODES
A
Adenine
G Guanine
C Cytosine
T Thymine
U Uracil
R Purine (A or G)
Y Pyrimidine (C or T)
N Any nucleotide
W Weak (A or T)
S Strong (G or C)
M Amino (A or C)
K Keto (G or T)
B Not A (G or C or T)
H Not G (A or C or T)
D Not C (A or G or T)
V Not T (A or G or C)
AMINO ACID CODES
Ala A Alanine
Arg R Arginine
Asn N Asparagine
Asp D Aspartic acid
Cys C Cysteine
Gln Q Glutamine
Glu E Glutamic acid
Gly G Glycine
His H Histidine
Ile I Isoleucine
Leu L Leucine
AMINO ACID CODES
Lys K Lysine
Met M Methionine
Phe F Phenylalanine
Pro P Proline
Ser S Serine
Thr T Threonine
Trp W Tryptophan
Tyr Y Tyrosine
Val V Valine
Asx B Asn or Asp
Glx Z Gln or Glu
Xle J Leu or Ile
Sec U Selenocysteine (UGA)
Pyl O Pyrrolysine (UAG)
Unk X Unknown
DNA SEQUENCE
PROTEIN SEQUENCE
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LET’S TRY…
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Met M Methionine
His H HistidineGly G GlycineAsn N Asparagine
Leu L Leucine
AMINO ACID SEQUENCE IS…
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Met M Methionine
His H HistidineGly G GlycineAsn N Asparagine
Leu L Leucine
MHGNL met-his-gly-asn-leu
NUCLEOTIDE SEQUENCE IS…
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from the sequence… (AUA or AUG)-(CAU or CAC)-(GGU or GGC or GGA or GGG)-(AAU or AAC)-(CUU or CUC or CUA or CUG) !EXAMPLE: nucleotide sequence may be AUA-CAU-GGU-AAU-CUU !EXAMPLE: amino acid sequence is MHGNL or met-his-gly-asn-leu
LET’S HAVE A GROUPIE…
FORM YOUR GROUPSYou will be given set of questions and can discuss by group for the FINAL answer
The score of the group will be the score of each individual for today’s QUIZ
Submission is TOMORROW, 12noon, DB (Look for ate Malou)
READY???
QUESTIONSIn order to properly construct a protein, which process must occur first: transcription or translation? Why?
LAC operon: Under what conditions is the operator activated? Under what conditions is it inactivated?
Assume that the following sequence of bases represents a segment of DNA that is to undergo transcription. Determine the corresponding sequence of bases in the resulting RNA molecule.
3’-TAC GGC ATT GCA CAT TTT AGG GGC AAT ATT-5’
The following mRNA segment represents three codons. In each case determine what the anticodon would be on the appropriate tRNA.
AAA CGA AAU
SEE YOU ON MONDAY FOR YOUR EXAM 1
