Download Activating Strategy AP Lesson #51 What is the code? What is

Activating Strategy
• Think – Pair - Share
– Explain why RNA splicing in eukaryotic cells is
similar to editing a video.
What is the code?
• Code for ALL life!
– strongest support for a
common origin for all
life
• Code is redundant
– several codons for
each amino acid
– 3rd base “wobble”
• Start codon
intron = noncoding (inbetween) sequence
eukaryotic DNA
– AUG
– methionine
• Stop codons
exon = coding (expressed) sequence
– UGA, UAA, UAG
What is needed to read the code?
AP Lesson #51
EQ: How is the message from mature
mRNA translated into the proteins?
• tRNA (transfer RNA)
– Carries amino acids
– Translates mRNA (reads)
• Ribosomes
– Facilitate coupling of
tRNA anticodon to
mRNA codon
E P A
How does a cell know what mRNA means?
How are the codons matched to amino acids?
• tRNA has a “Clover leaf” structure
– anticodon on “clover leaf” end
• Complementary to mRNA codon
DNA
TACGCACATTTACGTACGCGG
Transcription
codon
mRNA
AUGCGUGUAAAUGCAUGCGCC
Translation
protein
?
Met Arg Val Asn Ala Cys Ala
– amino acid attached on 3′ end
How does tRNA get its Amino Acids?
What is next for the polypeptide?
• Aminoacyl tRNA synthetase
– enzyme which bonds amino acid to tRNA
– bond requires energy = ATP → AMP
• bond is unstable
• so it can release amino acid at ribosome easily
Trp C=O
■
■
■
■
– Sequence of amino acids that are
recognized by Signal-Recognition Particle
– SRP delivers the growing polypeptide to
where it will be used by the cell
■
secretion
nucleus
mitochondria
chloroplasts
cell membrane
cytoplasm
O
activating
enzyme
tRNATrp
tryptophan attached
to tRNATrp
AC C
UGG
=O
C
H2O
O
anticodon
■
Trp
Trp C=O
OH
OH
Destinations:
• Interactions among amino acids give
the protein its 2nd & 3rd structure and
can be modified (ex. carb chains)
• Signal Peptides
mRNA
tRNATrp binds to UGG
condon of mRNA
What are ribosomes?
Summarizing Strategy
• Ribosomal RNA (rRNA) &
proteins
• Complete this graphic organizer
Definition
– 2 subunits (large & small)
Characteristics
• A site (aminoacyl-tRNA site)
– holds tRNA carrying next amino
acid to be added to chain
• P site (peptidyl-tRNA site)
Translation
Examples
– holds tRNA carrying growing
polypeptide chain
Non-Examples
• E site (exit site)
– empty tRNA leaves ribosome
from exit site
E P A
So how does the ribosome
build a protein?
Assessment
• DNA to Protein Essay
• Can you tell the story?
• Initiation
– brings together mRNA, ribosome subunits,
initiator tRNA (Met), read from 5’ 3’
– In an detailed essay, describe the complete process
in the figure below
– While explaining, be sure to use correct vocabulary
and definitions.
– Take me through the process the picture shows
• Elongation
– tRNA brings amino acids based on codon
sequence, amino acids form peptide bonds
– requires energy from GTP
• Termination
3 2 1
– Reach a stop codon, polypeptide is released
Leu
Val
Met
Met
Met
Met Leu
release
factor
Ser
Ala
Leu
Leu
A
C
tRNA
G
U A C U G AA U
5'
C
mRNA A U G
3'
E P A
5'
UA C G AC
AU G CU GAA U
5'
3'
U A C GA C
AU G C UG AAU
5'
3'
U AC G A C AA U
AU G C U G
3'
A CC
U GG U A A
• Essay is Due on Thursday
– 20 point quiz grade
Trp
3'