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Transcription and Translation
RNA: Composition and Shape
• Composition:– Ribose (a sugar)– Phosphate group--N-base: Adenine(A),
Uracil(U), Cytosine (C), and Guanine (G)
• Shape: single-stranded
RNA: Types• mRNA – messenger RNA carries info from DNA
in the nucleus to the cytoplasm.• tRNA- transfer RNA takes info from the mRNA
and binds to amino acids.• rRNA- ribosomal RNA exists where proteins are
made.
• DNA codes for DNA = REPLICATION
• DNA codes for RNA = TRANSCRIPTION
• RNA codes for protein = TRANSLATION
How do we know what to transcribe?• Promoter– Characteristic region of DNA that signals the start of a
gene. – A sequence of letters that signals “gene ahead!”– Start and stop codons ( 3 consecutive nucleotides that
specify a single amino acid)
Transcription - Step One:RNA
Polymerase unwinds and unzips the DNA double helix.
Transcription: Step Two:RNA polymerase adds on
free-floating nucleotidesA, G, C, U
What does each bind with?
Stops at STOP codonReleases RNA polymerasereleases mRNA mRNA
RNA Editing
While still in the nucleus:
a. INTRONS are cut out, and
b. EXONS are spliced together
c. before the RNA sequence is sent to the cytoplasm for translation
http://www.youtube.com/watch?v=ztPkv7wc3yU
• Transcription animation
Translation• The mRNA leaves the nucleus cytoplasm• Message is read at the ribosome• 1 Codon (3 letter message) is translated into 1
amino acid• tRNA molecule has one end (anticodon) that
matches the mRNA . Each anticodon specifies an amino acid.
• The amino acids are bonded together as peptide chains…which fold into proteins
The Genetic Code:3 letters = 1 codon 1 amino acid
http://www.youtube.com/watch?v=PEDQoQuIhkg
• Animation of translation
Practice with this sequence• DNA: TCGATGTTCCGCCGTACGTCGTAACCG
AGCTACAAGGCGGCATGCAGCATTGGC Use the bottom strand as the complement to the mRNA.
What’s that mean? Hint: Look for where it starts. How do you know?Once you’ve found the “reading frame”, write in tripletsmRNA Use your genetic code wheel to write the amino acid
sequence. How will you know when to stop?
Try again without helpDNA: CCGTCATGTTCGCGCTACAAATGAAATGA
GGCAGTACAAGCGCGATGTTTACTTTACT
mRNA:
Polypeptide: