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DNA
Transcription Translation
TraitRNA Protein
RNA processing
The ““““Central Dogma””””
What’’’’s Next?
←←←← Contents Transcription and Translation
←←←← Contents Transcription and Translation
Transcription
• DNA code is COPIED asmRNA
– mRNA is the transcript
• Why?
• Location: Nucleus
• Promoter signals where to start
• RNA polymerase binds to
promoter
– Unwinds DNA
– Builds pre-mRNA strand using
DNA as a template strand
Another View of Transcription
The enzyme RNA polymerase opens the DNA strands and
synthesizes an RNA complementary to only one of the DNA strands.
RNA polymerase acts here
Transcription
The decision to transcribe a gene is the most important step in the
control of gene expression. Transcription starts and stops at distinct
sites at the ends of a gene.
DNA mRNA
G--------C
C--------G
A--------U
T--------A
Practice
• DNA: ACGCGCGCGATAATG
• mRNA: UGCGCGCGCUAUUAC
• mRNA processing
– Cut out introns -Junk
– Keep exons- (mRNA that codes)
– Add cap(ribosome recognition) and poly-Atail protection
• Finished mRNA leaves
nucleus & goes to a
ribosome
Alternative Splicing – More Bang for the Buck
• Process where exons of mRNA are reconnected in
multiple ways. Why is this important?
• 23,000 genes
• 100,000 proteins
• How is this possible?!!!!
• SUBWAY analogy
DNA
Transcription Translation
TraitRNA Protein
RNA processing
The ““““Central Dogma””””
Continued….
←←←← Contents Transcription and Translation
←←←← Contents Transcription and Translation
Translation
• Process of makingprotein using themRNA ““““recipe””””
– ““““Translating thecode””””
– 1 gene makes 1polypeptide chain(baby protein)
– Pg. 339
• Location: ribosome
• 3 Sites on ribosome: A, P, E
• Starts w/ a start codon (AUG) on mRNA
• tRNA w/ complimentary anticodon (UAC)
binds to mRNA codon (AUG)
• Each tRNA carries 1 amino acid
• tRNA moves to P site & gives up amino acid to build apolypeptide chain while a new tRNA enters ribosome
– Peptide bonds hold amino acids together (20amino acids)
• E site is where ““““empty”””” tRNA exits
• Stop codon
– Release factor adds
water molecule which
ends translation
Another View of Translation
Many antibiotics
block steps in
translation within
bacterial cells.
Practice
• mRNA: AUGUCAUUUCCA
• tRNA: UACAGUAAAGGU
• Amino acid sequence:
– MET, SER, PHE, PRO
– 64 codons for 20 amino acids
• Using a codon wheel
mRNA tRNA
G--------C
C--------G
A--------U
U--------A
DNA
Deoxyribonucleic Acid
Video- Biologix DNASummary of DNA &Central Dogma 27 min
Mutations?
• Parasitic twins or Siamese twins
– Not a mutation
Mutations
• Change in DNA
• 4 types of effects
• None
• New protein
• Less protein (shorter)
• No protein
Point Mutation
• Most common
• Insert, delete, or change ONE base
• Ex: albinism, Taysach’’’’s Disease, Sickle Cell Anemia– Taysachs- Fat builds up in brain- cant break down
Types of Point Mutations
• Missense
– Affects 1 amino acid
• Nonsense
– Stops early
• Frameshift
– Insertion or deletion
– Shifts sequence
– Affects MANY amino
acids
• Silent
– Codes for same AA
• Practice Worksheet