Central Dogma of Biology Information flows from DNA RNA Proteins Think of it as exchanging money in a different country proteins cannot be built directly from DNA Three main processes involved ID: 262961
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TranscriptionSlide2
“Central Dogma” of Biology
Information flows from
DNA
RNA ProteinsThree main processes involved:Replication (copies DNA)Transcription: DNA RNATranslation: RNA ProteinSlide3
RNA vs. DNA
3 main differences:
Sugar is called
ribose (DNA has deoxyribose)Uracil (U) instead of thyminepairs with adenine (A)Single-strandedSlide4
RNA Molecules
3 major types
Messenger RNA (
mRNA): codes for proteinsRibosomal RNA (rRNA): part of the ribosomeTransfer RNA (tRNA): helps read the mRNA code to build proteins during the process of translationSlide5Slide6Slide7
What is Transcription?
Transcription
is a process that uses a portion of DNA to make a complementary RNA strand
Similar to replicationJust one gene at a time is transcribed, not the whole DNA moleculestarts at promoter DNA (TAC box)Ends at terminator DNA (stop)When complete, mRNA molecule is released and leaves nucleus to bring genetic code to the ribosomesSlide8
Initiation
RNA polymerase finds the beginning of a gene (promoter region)
Part of the DNA unwindsSlide9
Elongation
RNA polymerase uses the DNA strand as a pattern to build a complementary RNA strand
C pairs with G
A pairs with URNA strand hangs off the DNA strand, and DNA helix zips back togetherSlide10
Termination
After the whole gene has been transcribed, the RNA strand detaches completely from the DNA.Slide11
mRNA Processing
After the DNA is transcribed into RNA, editing must be done to make the RNA functional
Introns
(non-functional segments of DNA) are snipped out of the chain by enzyme splicesome“Useful” segments that code for proteins (called exons) are left behind and joined back together by the enzyme ligaseA guanine triphosphate cap is added to the 5’ end and a poly A tail to the 3’ endThe newly processed mRNA can then leave the nucleusSlide12Slide13Slide14Slide15
Replication vs. Transcription
Where does the process take place?
Enzymes involved
Step 1
Step 2
Step 3
Replication
TranscriptionSlide16
Replication vs. Transcription
Where does the process take place?
Enzymes involved
Step 1
Step 2
Step 3
Replication
Nucleus
Transcription
NucleusSlide17
Replication vs. Transcription
Where does the process take place?
Enzymes involved
Step 1
Step 2
Step 3
Replication
Nucleus
DNA helicase,
DNA polymerase
Transcription
Nucleus
RNA polymeraseSlide18
Replication vs. Transcription
Where does the process take place?
Enzymes involved
Step 1
Step 2
Step 3
Replication
Nucleus
DNA helicase,
DNA polymerase
DNA strand
is unzipped
Transcription
Nucleus
RNA polymerase
DNA strand is unzipped (initiation)Slide19
Replication vs. Transcription
Where does the process take place?
Enzymes involved
Step 1
Step 2
Step 3
Replication
Nucleus
DNA helicase,
DNA polymerase
DNA strand
is unzipped
Complementary bases attached; whole DNA strand
Transcription
Nucleus
RNA polymerase
DNA strand is unzipped (initiation)
Complementary RNA bases attached; only one gene (elongation)Slide20
Replication vs. Transcription
Where does the process take place?
Enzymes involved
Step 1
Step 2
Step 3
Replication
Nucleus
DNA helicase,
DNA polymerase
DNA strand
is unzipped
Complementary bases attached; whole DNA strand
Two identical DNA molecules
Transcription
Nucleus
RNA polymerase
DNA strand is unzipped (initiation)
Complementary RNA bases attached; only one gene (elongation)
mRNA
strand floating free from DNA (termination)Slide21
Transcription Practice
Write the following DNA sequence: GTTCACTAG
Write the complementary DNA strand.
Circle one DNA strand. Simulate transcription by writing its complementary RNA sequence.Does the RNA strand more closely resemble the DNA strand from which it was transcribed or the complementary strand that wasn’t used? Why?What is the main enzyme involved in transcription? What is its function?List 3 types of RNA and briefly describe each one.