Transcript Ch. 11.4 & 11.5: Transcription & Translation Objectives

Ch. 11.4 & 11.5: Transcription & Translation
Objectives:
•
•
•
•
•
•
Explain one-gene-one polypeptide
hypothesis.
Describe the process of transcription.
Explain how RNA is edited.
Describe how RNA is translated into a
protein.
Describe how amino acids are coded.
Summarize protein synthesis.
Vocab.:
Transcription, RNA (ribonucleic acid), mRNA, RNA polymerase, intron, extron,
RNA splicing
Translation, tRNA, codon, anticodon, Codon, rRNA
One Gene, One Polypeptide
Genotype: sequence of nucleotides bases in DNA.
Phenotype: Organism traits; based on proteins & protein fxns
Beadle & Tatum:
Research leads to “One gene, one enzyme”
•Expose bread mold to
X-rays (Mutation =
Damaged DNA).
•Essential
enzyme/amino acid
cannot be made from
damaged DNA.
“one enzyme” - not accurate. 1 gene = 1 polypeptide (part of 1 enzyme/protein)
•Mutated mold won’t
grow on “minimal”
medium that lacks
enzyme/amino acid it
can’t make.
Beadle & Tatum Experiment: 9:57 min http://www.youtube.com/watch?v=vP_h08cT5jw
RNA carries DNA instructions to Ribos.
Ribosomes make PROTEINS.
RNA: Ribonucleic Acid
Single strand nucleotide
1. 5-C Sugar: Ribose
2. Phosphate
3. Nitrogen base
(A, U, G, C)
U = Uracil; Replaces T
A binds to U; G binds to C
Transcription: DNA --> mRNA
•
•
•
DNA cannot leave
nucleus.
DNA nucleotide sequence
is converted into mRNA
(messenger RNA).
mRNA leaves nucleus -->
directs protein synthesis
@ ribo. in cytoplasm.
http://www.youtube.com/watch?v=983lhh20rGY&feature=related
http://www.youtube.com/watch?v=41_Ne5mS2ls
Transcription: RNA Polymerase
• Enzyme that links
RNA nucleotides
together (like
DNA polymerase)
• Transcribes
specific segments
of DNA.
RNA SPLICING: Editing mRNA
1. INTRONS
removed/spliced
•
non-coding
sequences (junk)
•
Do not code for
amino acids
2. EXONS:
•
Coding sequences
•
Translate into amino
acids (expressed)
Splicing: In eukaryotes mRNA
is modified before it leaves
nucleus.
Modifying
mRNA
Translation: mRNA --> proteins
• Based on CODON “language”
• 3-bases translate into a CODE for specific amino
acids.
• Amino acids build polypeptides.
Nucleic acids -->
Proteins
TRANSLATION
Each codon codes
for 1 amino acid.
Start codons:
AUG (start
translating)
Stop codons:
UAA, UAG, UGA
Same codes for
almost ALL
organisms!
Translation
Required
• ATP
• mRNA
• Ribosomes
• tRNA
tRNA: Transfer RNA
• Translates codon of mRNA into amino acids.
• “Fetches” correct amino acid
• Attatches to correct codon.
• Has “anti-codon” complement to attatch to codon.
Translation: rRNA (Ribosome)
rRNA: ribosome
(organelle)
• 2 subunits snap
together.
• mRNA and tRNA join
each other in
RIBOSOME.
2 tRNA binding sites where translation happens:
P site: Growing polypeptide chain.
A site: new amino acid binds
Translation:
Elongation
Polypeptide chain grows.
• Translation begins (AUG) codon
• Amino acids are added by tRNA
(based on mRNA codons).
• Translation ends (UAA, UAG, UGA);
stop codon.
• Polypeptide released (Goes to E.R. and
Golgi for modification)
Translation Summary